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DISPOSES AND PESTS 
OP 1 THE RUBBER TREE 



MACMILLAN AND CO., LIMITED 

LONDON BOMBAY CALCUTTA MADRAS 
MELBOURNE 

THE MACMILLAN COMPANY 

NEW YORK BOSTON CHICAGO 
DALLAS ATLANTA SAN FRANCISCO 

THE MACMILLAN COMPANY 
OF CANADA, LIMITED 

TORONTO 



DISTRIBUTION Of OlDIUM 

IN 



1933 



CHINA 



5EA 




SUMATRA 



SINGAPORE 



DISEASES AND PESTS 

OF 

THE RUBBER TREE 



BY 

ARNOLD 

A.B.C.Sc., D.I.C. 

LATE HEAD OF THE PATHOLOGICAL DIVISION, RUBBER 

RESEARCH INSTITUTE OF MALAYA, AND FORMERLY 

GOVERNMENT MYCOLOGIST, DEPARTMENT OF 

AGRICULTURE, S.S. AND F.M.S. 



MACMILLAN AND CO., LIMITED 

ST. MARTIN'S STREET, LONDON 

1936 



COPYRIGHT 



PRINTED IN GREAT BRITAIN 
BY R. & R. CLARK, LIMITED, HDINBT7RGH 



PREFACE 

THE results obtained since 1931 at the Pathological Division, Rubber 
Research Institute, Malaya, and elsewhere have proved of such out- 
standing importance that a permanent record becomes very desir- 
able. The Institute has passed through more than one critical period 
in recent years, but despite the fact that administrative troubles 
caused considerable concern ^chiring the period 1931-34, credit is due 
to those members of the staff who maintained the closest interest in 
the scientific problems on which they were engaged. In the patho- 
logical division continuous progress was maintained. The same 
remarks can be applied to other divisions in the Institute, and in 
this particular instance, a tribute to the detached attitude by 
scientific workers towards administrative troubles, is well deserved. 

My acknowledgments are due to the many authors whose works 
have been consulted. Extensive use has been made of the two most 
important works written on the diseases of the rubber tre'e; -namely, 
The Diseases and Pests of the Rubber Tree (T. Fetch, 1921) and 
Diseases and Pests of Hevea brasiliensis (Dr. A. Steinmann, 1925). 
With reference to insect pests, I am indebted mainly to The Agri- 
cultural Zoology of the Malaya Archipelago, by Dr. K. W. Dammer- 
mann. Further, I have made considerable use of Diseases of Crop 
Plants in the Lesser Antilles, by W. Nowell, published by the West 
India Committee, and I have obtained valuable aid from Fungi and 
Disease in Plants, by Dr. E. J. Butler, F.R.S., 1918. Again, I have to 
mention my indebtedness to the evergreen Text Book of Botany, by 
Strasburger, in respect of Part II, and also to the work, by W. C. 
Stevens, entitled Plant Anatomy, 1924. Short extracts have also been 
taken from Fungus Diseases of Plants, by B. M. Duggar, 1909. No 
attempt has been made to make alterations in the written text of 
portions taken from other books if the extracts adequately meet the 
case. It is thought that much useless repetition has been saved by 
adopting this; procedure, while any improvement could scarcely be 
anticipated. Full references to other works consulted will be found in 
the text. 

It is not an easy matter to make full acknowledgment to all past 
and present colleagues who have willingly assisted me with the latest 
information in their respective lines of work. I am greatly indebted to 
Mr. R. P. N. Napper, for I have utilised his recent reports on root- 



viii DISEASES AND PESTS OF THE RUBBER TREE 

disease problems to the full. The same applies to the work of Mr. F. 
Beeley in connection with work on Oidium leaf-fall disease and also 
with reference to incidental problems such as the treatment of white- 
ant attacks, of mouldy -rot control, and in connection with the latter, 
in the preparation of a White List of proprietary compounds posses- 
sing fungi cidal properties, which have passed the required tests 
successfully. 

It is desirable at this stage to mention the work carried out by 
colleagues in the Department of Agriculture, Straits Settlements and 
Federated Malay States. To Mr. W. N. C. Belgrave, the present Chief 
Research Officer in the Department, full tribute must be paid for his 
unfailing help when abstruse aspects of disease problems required dis- 
cussion. His own personal contributions on disease problems in 
rubber plantations, such as the work on red root disease and on the 
various panel diseases, is well known. I am also indebted for aid and 
collaboration from Mr. F. W. South. The work of my successor to 
the post of Government Mycologist, Mr. A. Thompson, on the various 
"Phytophthoraceous" fungi found affecting rubber trees is worthy of 
mention, and his publication has proved to be of great use in leading 
to a correct presentation of this intricate subject. I wish also to 
record my indebtedness to Mr. G. H. Corbett, Government Ento- 
mologist, Department of Agriculture, S.S. & F.M.S., both for supply- 
ing information and for personal help in many entomological prob- 
lems which have appeared during my three years as head of the 
Pathological Division of the Rubber Research Institute. The Insti- 
tute has no specialist officer in entomology attached to the staff, and 
this branch has had therefore to be dealt with by the Pathological 
division as far as possible. Information on Psilopholis grandis was 
due almost entirely to Mr. Corbett, whose part-time services were 
obtained by arrangement with the Department of Agriculture. 
Mention must also be made of information provided by Mr. H. M. 
Pendlebury, Curator of Museums, Selangor, with reference to certain 
entomological work which has been dealt with over the last few years. 

It is with the greatest pleasure I place on record my appreciation 
of the help afforded by the Imperial Mycological Institute, Kew, not 
only from its Director, Dr. E. J. Butler, F.R.S., but also from every 
member of the staff. It is doubtful if one of the largest obstacles en- 
countered during the writing of the book would have been success- 
fully surmounted but for their ever-ready assistance, tendered over 
a fairly long period during which I was working there. The Imperial 
Mycological Institute should receive extended support from all 
quarters, for there cannot be the slightest doubt that the organisation 



PREFACE ix 

has made and occupies a unique place in its own particular sphere, 
and full financial support is merited. Mention must be made of the 
personal assistance given by Mr. S. F. Ashby, in connection with the 
organism commonly associated with the bark disease known as 
patch canker, and also for reading through the important section on 
panel diseases. I am grateful also to Dr. S. P. Wiltshire for the illus- 
trations, Figs. 31 and 58, and to Mr. E. W. Mason for information 
supplied during certain discussions on fungi associated with rubber 
disease problems. I must mention my indebtedness to Miss E. M. 
Wakefield, of the Kew Herbarium, for help in finding the authorities 
for many of the scientific names of the plants mentioned in the book. 

The illustrations should prove of the utmost value to any planter 
interested in rubber diseases. For the microphotographs, and a large 
number of the ordinary photographs, I am indebted entirely to Mr. 
H. Gunnery. It has been my personal feeling for many years that a 
great progressive step would be made if it could be impressed upon 
agricultural research workers that it would be of the greatest value 
if a closer touch could be maintained with the finer phases of micro- 
scopical work. Tropical research workers are more especially in mind. 
Mr. Gunnery was attached to my division for a period of twelve 
months, and I can confidently state that, owing to his activities, 
the research work of the division went forward very satisfactorily. 
All the intimate details, relating to the fungi associated with the 
various diseases of rubber trees, which could be dealt with during a 
short period were disclosed and new facts were obtained in every 
single instance. The features depicted in the illustrations of Sphaero- 
stilbe repens are sufficient proof of this statement. 

In connection with paintings and photographic illustrations, men- 
tion must be made of the effective work contributed by Mr. Lim 
Keng Chuan, artist at the Rubber Research Institute. 

Grateful acknowledgment is made also of help from numerous 
planters in Malaya who have supplied information in the past, and 
in many cases given considerable help in field experiments. It would 
be invidious to single out individuals for special mention, for helpers 
have been so numerous that it is only fair that thanks should be 
tendered to the general planting community. 

References to literature are given in chronological order, following 
the example set by the Annals of Applied Biology. No claim is put 
forward that an exhaustive list has been compiled, but an endeavour 
has been made to indicate the papers of major importance and also 
to direct attention to those of very early workers, which often escape 
notice since they are published in journals which have either changed 



x DISEASES AND PESTS OF THE RUBBER TREE 

their identity or ceased publication. These short notes often contain 
sapient remarks which, if viewed hypercritically, might be regarded 
as mere hazards in the absence of supporting work, but in spite of this 
they are worthy of recognition. 

A list of fungi recorded as occurring on rubber trees mainly in 
Malaya is included. 

It was originally intended to divide the book into four parts, but 
the advent of restriction necessitated a change. The subjects intended 
for inclusion in the proposed Part IV were (a) Forestry methods 
as applied to cultivation in rubber plantations, and (b) Future 
possibilities in respect of planting high-yielding strains of rubber 
trees derived through bud-grafting or seed selection. Now that re- 
striction of rubber is an accomplished fact, it is doubtful if it would 
be advisable to discussPpros and cons of the latter subject. After com- 
pletion of Part III, therefore, the only subject remaining to be dealt 
with was forestry methods, around which much controversy had 
raged since 1930. In this book the subject has been dealt with at some 
length, but the main endeavour has been to show that there never 
was any real reason why the controversial issues should have been 
raised i the advocates of forestry methods had not made very wide 
claims for which little or no supporting evidence could be advanced. 
Controlled natural covers, comprising a mixture of shade-loving 
plants, which are the only type of plant capable of normal develop- 
ment under mature rubber, are but slightly different, and serve 
the same purpose as the controlled, leguminous cover crops which 
are established everywhere as the common practice in young rubber 
plantations. It is most satisfactory to know that the rank and 
file of rubber planters now generally speak of controlled forestry 
methods, the word " controlled", as contrasted to unrestricted or un- 
controlled, being an addition which I myself insisted upon. The 
latest authoritative publication is entitled The Uses and Control of 
Natural Undergrowths, and the phrase "control of natural under- 
growths" at once rerhoves any objections which might have been 
raised in the past from a pathological point of view. 

Parts I, II and III may be read quite independently of one another. 
Part III, dealing with the subject of pests and diseases of the rubber 
tree, should prove of most interest to planters. In many cases 
minute details relating to the structure of fructifications and pro- 
duction of Spores have not been set out, for they are of little interest 
to planters, and investigators can obtain them from the publications 
cited. I hope that Parts I and II will receive due attention, for while 
the subject matter dealt with will present some intricacies to the lay- 



PREFACE xi 

man, every care has been taken to give the simplest and barest out- 
lines compatible with utility. The planter who makes a study of these 
elementary treatises will be in a position to appreciate the remaining 
portions in a practical manner. Parts t and II may well serve as the 
basis for the examinations conducted by the Incorporated Society 
of Planters. A correct even if elementary knowledge of the anatomy 
and physiology of both the parasite and host plant is necessary if a 
true understanding of the disease problems which are met with in 
rubber plantations in Malaya is to be obtained. 

A. S. 



CiOIN TENTS 



PAGE 

INTRODUCTION ......... 1 



PART I 

GENERAL REMARKS ON PLANT DISEASES, STRUCTURE, 
REPRODUCTION, AND PHYSIOLOGY OF FUNGI 

CHAPTER I 
GENERAL ......... 9 

CHAPTER II 
CAUSATION OF DISEASE, ETC. . . . . . .19 

CHAPTER III 
PHYSIOLOGY OF FUNGI ...... 



CHAPTER IV 

EXTERNAL FACTORS AND RUBBER TREE DISEASES . . .36 

PART II 
FORM AND FUNCTION 

CHAPTER V 
PLANT FORM ......... 55 

CHAPTER VI 

PLANT FUNCTIONS ...... .69 

xiii 



xiv DISEASES AND PESTS OF THE RUBBER TREE 

PART III 
DISEASES AND PESTS 

SECTION I 
ROOT DISEASES 

CHAPTER VII 

, IPAGE 
GENEBAL ......... 75 

CHAPTER VIII 

USTULINA ZONATA SPHAEROSTILBE BEPENS . . . .90 

CHAPTER IX 

FOMES LIGNOSUS GANODEBMA PSEUDOFERRETJM FOMES NOXIUS . 113 

CHAPTER X 
OTHER ROOT AFFECTEONS AND SOME PROBLEMS BELATING TO ROOT 

DISEASES ......... 175 

SECTION 2 
TAPPING PANEL AFFECTIONS 

CHAPTER XI 
MAJOB DISEASES ........ 208 

CHAPTER XII 
MAJOB DISEASES (contd.) ....... 238 

CHAPTER XIII 
MINOB PANEL AFFECTIONS ....... 256 

SECTION 3 
STEM DISEASES 

CHAPTER XIV 
MAJOB AND MINOB STEM DISEASES . . . . .266 



CONTENTS xv 

SECTION 4 

LEAF DISEASES 

CHAPTER XV 

PAGE 

MAJOR AND MINOR LEAF DISEASES ..... 294 

SECTION 5 
SCORCHING AND AFTER-EFFECTS, AND MISCELLANEOUS 

CHAPTER XVI 
SCORCHING AND AFTER-EFFECTS ...... 326 

CHAPTER XVII 
MISCELLANEOUS ........ 354 

S ECTION 6 
PESTS 

CHAPTER XVIII 
INSECT PESTS ........ 369 

CHAPTER XIX 

ANIMAL AND OTHER PESTS . . . . . . .414 

CHAPTER XX 
TREATMENT OF DISEASES ....... 427 

CHAPTER XXI 
FORESTRY METHODS OF CULTIVATION ..... 448 

APPENDIX: LIST OF FUNGI RECORDED ON RUBBER TREES IN MALAYA. 465 
GLOSSARY ......... 471 

INDEX .......... 473 



LIST OF COLOURED PLATKS 

^ , . (Ganoderma pseudoferreum 1 , 

PLATE I. Roots attacked by J J I To face page 1 1 2 

| Sphaerostilbe re pens J 

( Ganoderma jiseudoferreum \ 

PLATE II. Fructiiicatioiis of J J I 139 

^Jf^oy/iCd lignosus J 

PLATE 111. J3rowii bast. Mouldy rot . . . ,, ,, 229 

PLATE IV. Pink disi?uso . . . . . ,, 207 



INTRODUCTION 

AT the beginning of 1913, when I took up official duties as assistant 
mycologist in the Department of Agriculture, Federated Malay 
States, there were few phytopathological records available, and there 
were many outstanding problems which required immediate atten- 
tion. To-day the agricultural position in the rubber industry, in 
respect of pathological problems, is vastly improved. 

A short historical resume of the rubber industry as regards disease 
research in Malaya may prove of interest. At the outset, the one item 
worthy of note was the numerous changes which took place in the 
pathological workers appointed to the Department of Agriculture, in 
the first six years after the post of Government mycologist was in- 
stituted, in 1906. Carruthers, followed by Gallagher, and then Bancroft 
with Bateson as assistant mycologist, held office between 1906 and 
1914. Early in 1914, F. T. Brooks arrived from Cambridge to take up 
a temporary agreement which terminated at the end of the year. The 
appointment of this experienced pathologist marked a new era, and 
it seemed unfortunate that circumstances prevented the appointment 
being made permanent at the time. Malayan agriculture would have 
gained considerably if such a step had been taken. I had the difficult 
task of following the example set by him, being ultimately appointed 
Government mycologist in 1916. 

The research work carried out in the Department of Agriculture 
on diseases of rubber trees, up till 1926, is well known; in this year 
the proposed Rubber Research Institute of Malaya took concrete 
form and all the work on rubber tree diseases was transferred to the 
newly formed Institute. No detailed reference to the troublous times 
which the Institute passed through in the early years need be men- 
tioned; but in 1930 the suggestion was made that I should be seconded 
from Government service to take over the post of Head of the Patho- 
logical Division, which had been vacated by Dr. J. H. Weir. After 
long consideration, the offer was finally accepted, and duties were 
commenced in 1931. The disease records available at the time were 
not extensive, but the present disease position is undoubtedly satis- 
factory, a fact which is freely admitted by eminent outside authorities. 
It may be of interest to readers in Malaya to know that Dr. E. J. 
Butler, Director, Imperial Mycological Institute, stated in his presi- 
dential address to the British Mycological Society, 1926, that "no one 

1 B 



2 DISEASES AND PESTS OF THE RUBBER TREE 

can doubt, who knows the facts, that the rubber industry of Malaya 
has been saved not once but several times by the control measures 
devised by local mycologists against disease"; if this statement was 
applicable in years gone by, the records published in this work will 
provide convincing testimony that extraordinary progress has been 
made towards putting the industry in Malaya on the soundest possible 
basis, in so far that a safe guarantee can be given that large losses 
need not be anticipated from the plant diseases, now well known, 
if adequate safeguards are provided for their control. The dangers 
from outbreaks of new diseases must always be faced, but this con- 
tingency can be considered with equanimity if agricultural methods 
and procedure remain fairly stable. But changes in the rubber 
industry seem inevitable, and the introduction of bud-grafted 
material into planting practice may result, before many years are 
past, in very different disease problems arising for intensive in- 
vestigation. 

The foregoing is given prominence at this early stage to emphasise 
my firm opinion that there appears to be every justification for the 
claim that all expenditure on pathological work in Malaya has been 
repaid many times over. Unfortunately, the item cannot be shown 
as a concrete profit in the balance-sheet, and therefore there is diffi- 
culty in putting it forward as an item sufficiently impressive to 
attract immediate attention. The soulless science of economics 
naturally rules applied scientific work, and it appears that the only 
essential distinction between applied and pure research is that, in 
the former, profits must be clearly visible, while, in the latter, the 
completion of a line of research work is the primary consideration, 
and whether or not profitable issues may be the ultimate outcome 
does not affect the question. There is no doubt that the cynic was 
near the truth when he said, "Show me that a course is economical 
and expedient and I'll soon find you moral sanction for it", especially 
in the view of the unfortunate scientific officers who have fully proved 
their worth and who have had their posts abolished during recent 
depressed financial periods. Pathological research workers are often 
considered fortunate in possessing an argument which appeals when 
agricultural industries are undergoing profitable development. All 
men are keen to recognise the security offered by a satisfactory form 
of insurance, and active work on disease prevention is always en- 
couraged during prosperous periods; no difficulty is encountered even 
if high premiums have to be paid. But the position is reversed, often 
exceedingly rapidly, during depressed periods, and premiums are 
often allowed to lapse. Even the most capable scientific research 



INTRODUCTION 3 

workers may suffer, but this is one of the disabilities under which the 
worker engaged on applied research must labour. 

The quotation mentioned above appears in a book describing the 
work done by the scientific staff of the Anglo-Persian Oil Company. 
Moral sanction is possibly not required, or becomes of the smallest 
significance in business undertakings, when the question of profit 
and loss is to be decided. But it is certainly good ethics to instil and 
practice sound economics in plant pathological work, and all re- 
commendations for the control of plant diseases should be subjected 
to the acid test supplied by the query, "Will it prove a paying pro- 
position?" I believe that all plant pathologists who intend under- 
taking applied research in large agricultural combines should have 
a knowledge of business and financial details included in their training 
curriculum. Scientific workers, when engaged by business combines, 
are expected favourably to influence the future developments of the 
business by their work, and as a direct result, to maintain or increase 
the profits. It is suggested that a better understanding between the 
business directors and the scientific workers would be more rapidly 
established if the latter had passed through a course of training in 
business methods and organisation; the inclusion of such a course 
in a scientific officer's training might lead to their work being suitably 
appreciated from the commencement, and eventually it might be 
possible to include the scientist as an integral part in the business 
organisation. 

There is no special aim to be attached to this book, beyond record- 
ing the progress of pathological research in Malaya. It is hoped that 
the book will make a direct appeal to practical planters. The effort 
will be aided considerably by the programme inaugurated by the 
Incorporated Society of Planters, whose leaders realise keenly that 
a change is impending in the rubber industry which is likely to be 
fraught with far-reaching consequences. In the early days, a planta- 
tion could be successfully established only by the acquisition and 
maintenance of a settled labour force, and the planter who had a flair 
for controlling labour became the successful plantation manager. 
This still remains an important part of a planter's duties, but addi- 
tional attainments are now required, and these will become still more 
valuable in the not far distant future. Many changes have come about 
recently, and the successful planter of the future must possess a much 
closer knowledge of modern developments in planting and must, 
moreover, be able to control and put the concepts into practice. 
The Society has established, for its members, a series of courses along 
varied lines appertaining to rubber planting, and examinations are 



4 DISEASES AND PESTS OF THE RUBBER TREE 

held at intervals. This is a very definite forward move, and it is 
encouraging to think that the present volume on diseases and pests 
of the rubber tree will be more readily appreciated than might other- 
wise have been the case. 

A broad treatment has been adopted as far as possible, which 
makes for a discursive account and leads to more repetition than 
might be considered necessary. Possibly, these obvious repetitions 
will not find favour with those readers possessing an intimate 
knowledge of plant diseases. But in view of present-day working 
conditions, when the planter's daily routine duties are much more 
arduous than before the depression, they will seldom feel the urge 
towards long spells of studious reading. Intermittent periods of 
"dipping-in" will be the rule, and, under the circumstances, it seems 
not an undesirable feature to repeat the items of special interest to 
planters wherever the opportunity arises. The above is purely a 
personal view and I hope that planters will benefit from the method 
adopted. The portion dealing in a very elementary way with the subject 
of forms and functions of plants represents an endeavour to provide 
the practical planter with the essential fundamentals of the important 
vital activities of the host plant, and to emphasise the point that 
hi plant life there is a complete circulatory system, a fact which is 
not understood amongst planters in general. 

The needs of active investigators of rubber disease problems have 
been kept in mind, and provision for them has been made by indicat- 
ing the directions for future research on particular problems. In 
addition, an attempt has been made to compile and include as much 
as possible of all the reliable information which is available. 

A subject of considerable importance, requiring close consideration 
by phytopathological workers, is the confusion arising from the 
numerous misidentifications of the fungi responsible for even the 
commonest plant diseases. Little can be gained by constant disagree- 
ment over the correct systematic position and name of an organism 
causing a common plant disease, and it certainly leads to lack of 
confidence between planters and the pathological workers who are 
called upon for advice. The story of the name-changing in respect 
of the fungus causing white-root disease is given on page 76, and it 
does not reflect much credit upon the workers who have created the 
position as it now stands. There is still conjecture regarding the name 
Fames lignosus, as is shown by an article published in 1933, in which 
the author apparently accepts the name of Rigidoporus microporw, 
proposed by Van Overeem. To avoid confusing the planter, the pro- 
cedure followed in this book is, when there is the slightest doubt 



INTRODUCTION 5 

surrounding a newly proposed name, to utilise the old name which 
has been in common use. In fact, up to the recent publication of 
Corner's work on the fungi associated with the brown-root disease 
of tropical crops, there was much reason to doubt whether it was 
worth while, in connection with disease problems, taking the sys- 
tematic side of the work really seriously. The critical and close 
analytical work of Corner represents an effort which will set a satis- 
factory standard for the future, and there is no doubt that the 
information given in his article is of the greatest importance towards 
a correct understanding of the widespread problem presented by 
brown -root disease. 

An attempt has been made to show that an ideal condition is 
created, in the tropics at least, for research workers on plant diseases, 
when critical systematic work of the type of Corner's is combined 
with full researches into the structure of parasite and host plant and 
the interactions between them. In respect of the latter, climatic and 
soil factors exert a very large, if not entirely dominating influence. 
The routine outlined would form a basis for a detailed but extremely 
large and varied programme, and it is only very occasionally that 
opportunities arise for dealing completely with all the items, or even 
with all the major ones requiring immediate attention. Research 
work on disease problems in the tropics, and perhaps in other parts 
of the world, is governed entirely by the opportunities which present 
themselves during any particular period. The root disease caused by 
Fomcs Ugnosu-s was always prominent from the earliest days, and an 
intensive research would undoubtedly have provided interesting 
information if time and attention could have been found to devote 
to the subject. But while this was fully recognised, the problem did 
not prove to be an outstanding one in the period around 191015, 
and various new problems came up for immediate elucidation. For 
example, the cause of discolorations in white crepe and sheet rubber, 
followed by the necessary careful enquiries into the rapid spread of 
pink disease in various parts of the country, had to be dealt with 
quickly. The root disease caused by Ustulina zonata was then re- 
corded during the time Brooks held office as Government mycologist 
and was investigated by him. A little later, the root disease caused 
by Ganoderma pseudoferreum was first recognised by Belgrave as an 
affection distinct from the one caused by U. zonata. About the same 
time, circa 1916, the panel diseases known as black stripe and mouldy 
rot first made their definite appearance in Malaya, and the problems 
presented by these diseases required sustained work; following on 
these there was a sudden and widespread outbreak of brown bast, 



6 DISEASES AND PESTS OF THE RUBBER TREE 

which affection created a considerable scare. All these developments 
occurred during the period 1913-18. From 1917 to 1920 I was away 
from Malaya engaged on war service. 

After 1920, a second period was entered upon, and the investiga- 
tions on brown bast occupied practically the whole time over a 
four-year period, though it was possible to undertake preliminary 
observations on root disease problems, and the results obtained were 
of such interest that it was obvious this problem still required further, 
careful investigation. With the inauguration of the Rubber Research 
Institute of Malaya, research work on rubber diseases passed into 
other hands; but the root disease problems in rubber plantations still 
remained for solution when I joined the Pathological Division in 1931. 
The opportunity for dealing directly with the root disease problem 
had obviously arrived and no time was lost in drawing up a suggestive, 
provisional, research programme, which was placed in the capable 
hands of Mr. R. P. N. Napper, who had recently joined the staff of 
the Institute as a junior pathologist. Thus it had taken nearly twenty 
years for an opportunity to materialise of undertaking research on 
root disease problems in Malaya. Similar experiences could be related 
as being encountered in other tropical countries, but this is cited as 
indicating that, in tropical work, the choice of a line of research is 
entirely dependent on opportunity; if good opportunities present 
themselves and full advantage is taken of them, most researches can 
be expected to produce profitable results. 

An important point now arises for consideration. There will be 
little opposition to the view that in order to obtain a completely 
satisfactory picture of any plant disease problem neither the in- 
vestigations on the fungus, nor on the host plant, nor on the external 
factors influencing them, can be neglected. The side which shows up 
most prominently at the commencement would naturally receive the 
earliest consideration. It is obvious that, in the problem of brown- 
root disease, the identification of the causal fungus was of primary 
importance, and now this is settled there should be few further com- 
plications. In a so-called physiological disease, such as is presented 
by brown bast, the host plant requires the greater consideration, 
but in both cases outside factors are of such a degree of importance 
that they must also receive attention. These two cases might be said 
to be exceptional. The influence of external factors appears pre- 
eminent in all disease problems which have been encountered in 
Malayan rubber plantations, and, once satisfactory evidence has been 
obtained as to the causative agent of the disease, should therefore 
claim priority of attention. If we instance Oidium leaf -fall as an 



INTRODUCTION 7 

example, it is obvious, from a practical point of view, that in the 
early stages of the investigation a long period should not be spent 
enquiring into the intimate details attached to the difficulties of 
isolating the fungus in the laboratory and cultivating it artificially. 
After the initial investigations have been made, it is obvious that 
atmospheric factors are of the greatest significance since they pro- 
foundly influence outbreaks of this disease. It is not then difficult 
to appreciate that, as only limited opportunities generally exist for 
exhaustive research, the investigations into atmospheric factors should 
claim early consideration, if control methods are to be arrived at ex- 
peditiously. This point has been kept well in mind in the work carried 
out on Oidium leaf-fall by Mr. F. Beeley; laboratory details on the 
isolation of the fungus, growth in culture, artificial inoculations, etc., 
will undoubtedly follow later when the full control routine has been 
satisfactorily established. A similar routine has been followed by 
Napper in his root disease researches; it is the picture as presented 
in the field which is of paramount importance, and once a satisfactory 
scheme of control is established, other more intimate details respect- 
ing the causal fungus and host plant can be dealt with. 

A specific statement is made above that one aspect of a disease 
investigation should not be neglected at the expense of another. In 
the past, it seems that full importance has not been attached to the 
question of external factors and influences; in fact it can be truthfully 
said that the study of this side has often been sadly neglected. This 
statement is naturally more applicable in cultivations of permanent 
and semi -permanent trees than in annual cultivations, as will be 
fully appreciated when rubber tree diseases are dealt with in detail. 

It is suggested that, once the causal fungus has been identified 
satisfactorily, the detailed study of host parasite relationships can 
be considered of secondary importance, as compared with the in- 
tensive investigation of external factors likely to be concerned in 
initiating and influencing the spread of the disease. This brings up 
the debatable question of the compilation of lists of fungi associated 
with the host plant and whether these should be considered a matter 
of primary importance, since, in the tropics at least, phytopatho- 
logical workers are only too few in number to cope with the numerous 
problems awaiting investigation. Lists of fungi undoubtedly serve 
a useful purpose, but it can hardly be doubted that exaggerated 
importance has been attached to this line, in so far as it has probably 
led to the neglect of the all-important investigations on the effects 
of climatic, soil or other outside factors on olisease problems. The 
latter branch of study seems of such great importance to the writer 



8 DISEASES AND PESTS OF THE RUBBER TREE 

that a further suggestion might be made, viz. that all pathological 
workers should receive, during their course of training, a grounding 
in the use of meteorological instruments. These could then be 
adequately utilised in researches on plant diseases affecting permanent 
or semi -permanent cultivations. Information along these lines should 
be sought for from the inception of the research, more especially on 
the subject of diseases of aerial portions of plants. This suggestion 
is much more to the point at the present date than it would have 
been several years ago, for the improvements in self-recording in- 
struments render the routine simple, and with movable sets, which 
can easily be transferred from one district to another, much of 
the unreliable information commonly obtained hitherto would be 
avoided. The above remarks are offered in the hope that the influence 
of the various factors operating outside host and parasite will receive 
full recognition in future researches on plant diseases. 



PART I 

GENERAL REMARKS ON PLANT DISEASES, 

STRUCTURE, REPRODUCTION, AND 

PHYSIOLOGY OF FUNGI 

CHAPTER I 

GENERAL 

Losses from Plant Diseases, etc. Mycologist versus Plant Pathologist Modern View 
of Plant Pathology with reference to Rubber Tree Diseases in Malaya New 
Work carried through, 1931-34. 

THE study of fungoid and bacterial diseases in their true relation to 
extensive cultivations is of comparatively recent date, and it is only 
during the last few decades that the losses suffered by cultivators 
have been realised and approximately estimated. Generally, it is 
freely admitted that cultivators suffer heavy financial loss owing to 
the ravages of plant diseases, but in spite of the extraordinary 
advances made by scientific workers in protecting cultivators from 
plague and pestilence, there is still no absolute security against loss. 
This is clearly evident from the daily reports of enormous damage 
to grain crops owing to abnormal drought conditions during 1934. 
The ruin of the coffee plantation industry in Ceylon many years ago, 
as a result of the outbreak of the coffee-leaf disease, caused by the 
fungus Hemileia va-statrix, is well remembered by tropical cultivators 
in the East. In connection with the cultivation of rubber plantations, 
the activities of the fungus causing the South American leaf disease 
have frustrated all the efforts to establish its successful cultivation 
in British Guiana and Surinam, and there seems little hope of the 
rubber industry ever becoming permanently established in these 
countries. In Malaya at the present time, most estates possessing 
large areas of old rubber between fifteen and thirty years of age fully 
appreciate that an enormous number of trees may figure in the 
casualty lists, the chief agent of destruction being the fungus Gano- 
derma pseudoferreum, a parasite which affects the root systems and 
spreads by root-contact. There seems little reason to doubt the state- 
ment that this disease will prove the "limiting factor" which will 
prevent the economic development of old rubber areas in Malaya. 

9 



10 DISEASES AND PESTS OF THE RUBBER TREE PART i 

This is all the more regrettable as the losses accruing from this cause 
are largely preventable. There is not the slightest doubt that old areas 
of rubber trees of the age indicated, which have escaped serious 
disease attacks, will retain satisfactory yielding capacities and con- 
tinue to be classed as economic units, even if in the future high- 
yielding, bud-grafted areas are developed on a large scale. This state- 
ment is perhaps of greater significance now that restriction of rubber 
exports is an accomplished fact, for one result of this policy will 
certainly be to retard any scheme designed to increase the yielding 
powers of rubber areas. 

It has been pointed out above that it is only relatively recently 
that the study of plant diseases has been intensively taken up. This 
movement was probably stimulated by the recognition, tardy though 
it was, of the extensive losses caused to cultivators by plant diseases. 
Since those caused by fungi were most conveniently and, perhaps, 
the most easily studied, the expert on fungi, i.e. the mycologist, was 
the first class of investigator to be closely engaged in the study of 
plant diseases and of measures for their control. But it became 
increasingly evident that the pure mycologist could not be fully 
equipped to carry forward all enquiries into phytopathological 
problems. The position might have been much worse but for the fact 
that a student of fungi must have a good groundwork of training in 
general botany. All professional mycologists had, from their training, 
the capacity to obtain a knowledge of the general morphology 'of 
the higher plants and so could appreciate the possible reactions 
of the host plant towards fungal invasion, though their knowledge 
along these lines would, of necessity, be somewhat limited. The 
next development in phytopathological research was the full recog- 
nition of the importance of the reactions of the host plant, and this 
line of investigation then became the particular study of the patho- 
logist. 

Many writers have dealt at length with the presumed antagonistic 
positions of the mycologist and the plant pathologist. They have 
considered that the older conception of mycology has overpowered 
to some extent the newer science of plant pathology and that the 
claims of the latter have been dwarfed and obscured, on account of 
the unfortunate English usage of the terms mycology and mycologist. 
The great plant phylum of Fungi happens to form a common basis 
for the two studies. There are tens of thousands of fungi for the myco- 
logist to study, but a comparatively small number only are active 
agents in causing plant diseases. In addition to fungi there are 
numbers of otjier agents causing plant diseases, and to these the plant 



CHAP, i GENERAL 11 

pathologist must give full consideration, i.e. virus diseases; physio- 
logical diseases such as brown bast; bacterial diseases; phanerogamic 
plants causing maladies of different plant species. The mycologist 
engaged solely in the study of fungi would seldom venture into the 
realms indicated. While the fungi form a common basis for study, 
the approaches thereto are usually very different and set far apart. 
It seems to the writer that there should be no real antagonism be- 
tween mycology and pathology with its wider scope, for close contacts 
with nearly related sciences should necessarily be maintained if a 
complete understanding of a subject is to be arrived at. The patho- 
logist studies the nature of disease, whether of fungous origin or 
otherwise; the prevention and cure of disease; the economic losses 
caused by disease of whatever origin. Mycology, on the other hand, 
studies the structure and development of fungi with a view to under- 
standing their activities as a component part of the great plant world. 
Further, as the main plank in the platform of the plant pathologist 
(viz. reaction of host and parasite with special reference to external 
environmental conditions) is of little or no concern to the mycologist, 
there should, once the true position becomes clear, be no indication 
of the "fissiparous tendency" stage. There can be but little doubt that 
plant pathology has now won full autonomy as an independent 
science, but if the best results are desired, it should not be divorced 
from associated studies. 

The influence of external factors, such as those of atmosphere and 
soil, are emphasised in the paragraphs immediately following, and in 
all references to the control of the important diseases, special atten- 
tion has been directed to the economic side. In these wide fields the 
mycologist qua mycologist is an utter stranger, and why the old 
conception of mycology should ever have come to dominate plant 
pathology is indeed surprising. It cannot be said that this domination 
is so apparent at the present day as it was in the past, and when the 
great influence of climatic and soil differences and changes on plant 
diseases becomes more generally appreciated, there will be no more 
wordy warfare on this subject. 

By keeping the modern viewpoint of plant pathology in due 
prominence, the writer hopes to make it abundantly clear that a 
successful attempt has been made to elucidate many of the more 
important plant-disease problems in the rubber plantations of Malaya. 
In taking a wider and more general concept of root diseases, it has 
been found possible to define a new policy which will have far-reach- 
ing effects in future plantings of rubber. With respect to the various 
species of Fames causing root diseases, the idea that F. lignosus, 



12 DISEASES ANJ> PESTS OF THE RUBBER TREE PART i 

Ganoderma pseudoferreum and F. noxius were each the cause of a 
particular disease Which had no intimate relationships with one 
another, has been discarded, and a new idea is promulgated to the 
effect that these important root diseases would be found to have a 
strong family relationship physiologically, and that the many prac- 
tical problems to which they give rise in the field are but merely 
variants of a single general problem. Preliminary studies on red-root 
and brown-root diseases, in 1925, indicated the probable importance 
of the physiological concept, but the opportunity for full proof did 
not arise until the last three years, and Napper has now proved the 
matter up to the hilt. 

Pioneer rubber planting commenced in the middle eastern countries 
around 1906, and the flood-tide actually started about the boom 
period of 1910. There is a tremendous acreage of rubber over twenty 
years of age in existence; much of this approaches thirty years of 
age, and a small proportion is even over this figure. It is only just 
beginning to be adequately realised that a large proportion of 
the old rubber areas in Malaya, carrying trees over twenty years 
of age, are seriously affected by a root disease which is causing 
a tremendous amount of damage. Attention was directed to the 
potential dangers facing Malayan rubber plantations in 1925, when 
the root systems of some 1400 trees, fourteen years old (which 
did not appear more seriously affected by root disease than other 
trees of similar age), were opened up in an experimental area. 
The results were most unexpected. The percentage number of 
diseased trees totalled 56. The diseased trees could be divided into 
two classes: 

(I) Trees affected with a parasitic fungus in the lateral roots, i.e. the 
fungus had not progressed sufficiently up the side roots to infect the 
main stem. 

(II) Trees showing the fungus making active progress in the main 
stem, having gained access to this region through diseased lateral 
roots. 

The total number of diseased trees was approximately equally 
divided between the two classes. All the trees in class (I), i.e. those 
slightly affected in the lateral root system, could have been saved by 
the simple excision of the diseased roots, followed by complete 
extraction of the diseased portions from the soil. The diseased trees 
falling in class (II) had to be completely removed. 

The actual demonstration of the position outlined above showed 
quite clearly that if such proved to be of general occurrence through- 
out Malaya, there was good reason for issuing a warning that grave 



CHAP, i GENERAL 13 

dangers existed of large tree-losses in the future, more especially if 
the facts were ignored and control measures were neglected. It 
appeared that little notice was taken of the warning. The industry 
was flourishing at the time, and most responsible planters showed 
the not unusual attitude of considering the report interesting, but on 
the alarmist side. The intrepid manager, who was really responsible 
for exposing the true facts of the case against the writer's original 
opinion, deserves high commendation for his prescience in respect of 
the true position. As a result of the neglect of this warning, Malayan 
plantations are now faced with a situation such that large areas of 
old rubber, which should be capable of yielding exceedingly well at 
the present date, will have to be replanted if they are to be brought 
back into the lists as economic units. 

The statement that old trees which have remained unaffected by 
root disease should give very satisfactory yields can be supported, for 
there are old rubber areas, carrying trees twenty-five years of age, 
which still show excellent yielding capacity. These old areas, which 
are in good order to-day, have been specially guarded against root 
diseases, and their percentage infection at the present date can be 
considered negligible. But the great majority of estates with rubber 
trees over twenty years of age cannot report this happy state of 
affairs. It was becoming increasingly evident, from the number of 
estates actively engaged in replanting portions of their old areas 
when the writer left Malaya, in February 1934, that the position is 
being frankly faced, and that appropriate steps are being taken to 
rectify the position. 

Taking these facts into consideration, it is necessary to emphasise 
once again the need for continuous, comprehensive research on plant 
diseases, particularly in a country such as Malaya, where true pro- 
sperity lies in agriculture. In normal times the need is admitted, but 
ready approval to provide for research is not met with during 
depressed financial periods, more especially in those agricultural 
industries in which speculation is a prominent feature. During slump 
periods the scientific needs of agricultural industries are usually sadly 
neglected, and one of the first efforts to reduce expenditure is the 
modification or even complete neglect of the measures to prevent 
losses from preventable diseases. Even during normal periods, the 
speculator and producer, who often join forces and claim to "pay the 
piper", realise but little that the tree of science does not readily yield 
its fruits and that long and arduous toil is usually necessary before a 
good crop can be secured. Scientific investigators can seldom respond 
to the "quick result" tune which is so often called for, or at least the 



14 DISEASES AND PESTS OF THE RUBBER TREE PAKT i 

results which do accrue quickly cannot, to any great extent, be 
relied upon. 

Continuous work over a prolonged period had prepared the way 
for a general plan of campaign in respect of rubber disease investiga- 
tions in Malaya, and the period from 1931 to 1934 proved a specially 
fruitful time. As the years have passed it has become recognised 
more and more that fungus diseases of rubber trees need observing 
from a new angle. Firstly, certain diseases have been shown to possess 
similar fundamentals, and when the question of control is being 
considered, diseases formerly classed as separate units must be 
grouped together so as to ensure full and economic control. Secondly, 
it is becoming more and more obvious that outside factors have the 
greatest significance in connection with rubber tree diseases. For 
instance, panel, stem and leaf diseases are largely influenced by 
meteorological factors; the root diseases which appear in a rubber 
plantation entirely depend on the vegetation previously existing on 
the area, while direct atmospheric effects from lightning damage, 
scorching by the sun's heat, etc., play an important part in causing 
damage in certain areas. 

Many references have been made already to the names of the fungi 
causing the more important diseases. It is now intended to direct 
attention to the more important matters which have come under 
special notice since 1931, and this provides a convenient opportunity 
to present in tabular form the various diseases dealt with, together 
with their common names, if any, and the names of the causal fungi. 
This will aid in preventing misunderstanding regarding the causes 
and common names of rubber tree diseases. 



ROOT DISEASES 
Common Name Names of Causal Fungi 

White-Root Disease . . Fomes lignosus, Klotzsch 

Red-Root Disease . . Oanoderma pseudqferreum 

(Wakef.), Van O. et St. 

Brown -Root Disease . . Fomes noxius. Corner 

Dry-Root Rot . . Ustulina zonata (Lev.), Sacc. 

Sometimes called Stinking Sphaerostilbe repens, B. & Br. 
Disease 



GENERAL 15 



TAPPING PANEL DISEASES 
Common Name Names of Causal Fungi 

Mouldy Rot . . . Ceratostomella fimbriaia 

(E. & H.), Elliot 
Black Stripe (commonest Phytophthora palmivora, Butl. 

cause in Malaya) 

Patch Canker (commonest Pythium complectens, Braun 
cause in Malaya) 

.... Marasmius sp., probably 

M. palmivorus, Sharpies 
Brown Bast . . . Physiological disease 



STEM DISEASES 
Common Name Names of Causal Fungi 

Pink Disease . . . Corticium salmonicolor, 

B. & Br. 

Stem Ustulina . . Ustulina zonata (Lev.), Sacc. 

Diplodia Die -back . . Diplodia sp. 

Thread Blight . . . Cyphella heveae, Mass. ? 

Horse Hair Blight . . Marasmius equicrinis, Mull. 

Mistletoes . . . Loranthus species 



LEAF DISEASES 
Common Name Names of Causal Fungi 

South American Leaf Disease Melanopsammopsis ulei 

(Henn), Stahel 

Phytophthora Leaf -fall . Phytophthora meadii, McRao 

Oidium Leaf-fall . . Oidium heveae, Stein. 

Mite Attack associated with . Qloeosporium alborubrum, 

Petch, and 

Gloeosporium heveae, Petch 
Bird's-eye Spot . . Helminthosporium heveae, 

Petch 

Shot-hole Leaf Disease . Several fungi are found asso- 

ciated with these symptoms 

Rim Blight . . . Ascochyta heveae, Petch 

Sphaerella heveae, Petch 
Guignardia heveae, Syd. 
Red Rust (more common on Cephaleuros my co idea, Karst. 

Tea) 
Sooty Moulds . . . Capnodiae spp. 



10 DISEASES AND PESTS OF THE RUBBER TREE PART i 

Taking the diseases in the order presented in the book, it will be 
seen that matters of importance have been under consideration since 
1931, and in most cases valuable additions to our knowledge have 
been made. On the subject of root diseases caused by the Fames type 
of fungi, our views have been completely reversed. The following 
short statements indicate very briefly the important features which 
have recently been dealt with in connection with the various diseases 
which affect rubber trees in Malaya. 

ROOT DISEASES 

Ustulina zonata. Nothing of importance to report. 

Sphaerostilbe repens. Noteworthy additions to the morphological 
structure of the fungus have been made (Figs. 10, 11 and 12). The 
fact that outbreaks of the disease are closely associated with the 
flooding of rubber areas is emphasised, and further cases are described. 

Fames lignosus. Factors which were formerly considered to 
influence the spread of this disease were: 

1. The independent travel of the mycelium through the soil. 

2. Spore infection of old jungle stumps, and as a result these 

became primary centres of infection. 

3. Trenching was recommended for control. 

The above are now considered of little importance in Malaya. It 
has been established that rubber trees are found diseased only under 
the following conditions: 

1 . When their roots come into direct contact with diseased jungle 

wood. This is supported by De Jong's recent work in Java. 

2. When infection has been brought about as a result of the 

natural increase in length of roots, so that they pass into 
soil areas containing diseased jungle timber. It is not 
brought about by the growth of the mycelium through 
the soil. 

If the above is correct, it is clear that the dangerous soil areas are 
disclosed by the increase in length of the roots. As a consequence 
trenching will be of little use in preventing spread. The essential item 
in control is the complete removal of infective material in the shape 
of infected timber and stumps derived from jungle trees. 

Oanoderma pseudoferreum. This disease was previously con- 
sidered to be one primarily associated with rubber trees ten years of 
age or over, and therefore entirely distinct from the disease caused by 
Fomes lignosu*. But it has been proved beyond doubt that the two 



CHAP, i GENERAL 17 

fungi start in exactly the same way. They attack trees in the jungle, 
and when this is felled, the soil areas carrying the diseased trees form 
the danger zones for the young rubber plants. The danger zones 
formed by the presence of O. pseudoferreum are not so conspicuous 
in the early years as those of F. lignosus. The latter fungus shows 
more vigorous growth and the losses due to it reach a peak about 
the fourth or fifth year, whereas O. pseudoferreum seldom becomes 
prominent before the tenth year. As both fungi spread from one tree 
to others by root-contact, control measures for one apply equally for 
the other, and disease zones, centres or knots of both fungi, consisting 
of buried jungle timber, must be removed as early as possible if 
successful control of these root diseases is to be established in new 
plantings. A combined system of control for both diseases removes all 
the doubts which have often been expressed in the past as to the 
economic outcome of measures advised for controlling the disease 
caused by F. lignosus alone. 

Fomes noxlus. Corner's work on the identification of the fungus 
causing brown-root disease of rubber trees and other tropical crops 
has already been mentioned. The facultative parasite responsible for 
the disease has been named by him Fomes noxius, and he shows that 
it has been confused with Fomes lamaemis, which, although closely 
related, is a harmless saprophyte. 

PANEL DISEASES 

Nothing new can be reported in respect of black-stripe or brown- 
bast diseases, though the description of the latter here provided is the 
first complete account to appear in book form in a British publication. 
The latter remark applies also to mouldy rot, a disease which has not 
hitherto been reported from any other rubber-growing countries 
except Java and Sumatra. The peculiar manner of its spread from 
one district to others, often separated by a distance totalling hundreds 
of miles, can only be explained by the spores being carried upon 
clothes or implements (such as tapping knives) during the migration 
of human beings. It has further been fully established that, when 
water vapour is present in too abundant quantities, mouldy rot is 
practically impossible to control by known methods. This finding is 
of the greatest importance when any proposal is made to establish, 
under mature rubber trees, a natural cover comprising a mixture of 
shade-loving plants. The natural result of this would be the accumula- 
tion of large amounts of water vapour, due to the transpiration of the 
cover plants, more especially if adequate ventilation is not provided. 

c 



18 DISEASES AND PESTS OF THE RUBBER TREE PART i 

New observations have also been made in Malaya on patch canker, 
and the most common agent in the country has been ascertained to 
be the fungus Pythium complectens, Braun. There has been some 
doubt about the actual causal fungus and authorities have previously 
considered that a species or strain of Phytophthora was the cause in 
other countries. The common association of patch canker, following 
on lightning damage, has moreover been fully established. 

A new record has been made of a minor panel disease and its origin, 
for the fructifications of the causal fungus have now been successfully 
developed. The fungus proved to be a species of Marasmius, probably 
M . palmivoms, Sharpies, which is commonly found on disintegrating 
coconut material. 



STEM, BRANCH AND LEAF DISEASES 

The only item of note under this heading is the work on Oidium 
heveae. The conditions favouring the development of the disease have 
been fully described and methods of control by means of sulphur 
dusting have been devised. 



INSECT PESTS 

Noteworthy items under this heading are those concerning the work 
on white ants and the white grub plague; the latter is the grub stage 
of Psilopholis grandis. The new record of Thosea sinensis on rubber 
is also worthy of note. 

DIRECT AGENCIES AFFECTING RUBBER TREES 

The investigation on lightning damage in rubber plantations in 
1933 is specially noteworthy. The records obtained show that this 
agency must be considered to be a major cause of damage, a fact 
which has not been recognised before. The writer has produced con- 
clusive proof that lightning is a primary agent in the initiation of 
coconut-palm affections in Malaya, and it is not at all improbable that 
evidence will be obtained in years to come that lightning plays an 
extensive part also in the tree affections seen above-ground in rubber 
plantations. 



CHAPTER II 
CAUSATION OF DISEASE, ETC. 

Causation of Plant Diseases Vegetative Structure of Fungi Reproductive 
Structures and Classification of Fungi. 

CAUSATION OF PLANT DISEASE 

WHEN considering affections of the rubber tree, the only distinction 
existing in the minds of planters is that lying between fungus diseases 
and insect pests. Such a distinction does not meet the situation when 
the real facts are given due prominence, i.e. that derangement of 
function, brought about by any cause, organic or inorganic, may 
result in a diseased or pathological condition. Leaving insect pests 
out of consideration for the time being, and confining remarks to 
the common diseases of rubber trees, various causes, other than 
fungi, can be distinguished, as under: 

(a) Affections caused by phanerogamic parasites, such as mistle- 
toes (Loranthus spp.), on rubber trees. 

(6) Affections caused directly by derangement of function, without 
an obvious organic cause, as in the case of brown bast of rubber trees; 
this affection is non-transferable by ordinary methods from diseased 
to healthy trees. 

(c) Affections which occur owing to unsuitable agricultural con- 
ditions. In many common affections of rubber trees the latter form 
the main predisposing factors towards disease. 

The groups of disease-causing agencies listed above indicate the 
wide range which exists outside the fungi, even in rubber plantations. 
Fungi, nevertheless, must be considered of primary importance in 
this crop. But there are, in addition to fungi, two important agencies 
causing diseases of cultivated plants, examples of which have not 
yet been reported from rubber estates. In world economy, the diseases 
caused by these agencies are of importance equal to, if not greater, 
than those caused by fungi, and are known as (1) Bacterial diseases 
and (2) Virus diseases. The latter class has attained great prominence 
in recent years, and work on the specific diseases comprised in the 
group is being most actively pursued at the present date. 

At this point it will probably be of assistance if the schedule of 
operations worked to during a disease investigation is indicated; in 

19 



20 DISEASES AND PESTS OF THE RUBBER TREE PART i 

particular, when the causal organism is being sought for. Organisms, 
such as bacteria and fungi, which can be identified by specific form 
and other characteristics, and which may be constantly associated 
with specific symptoms of a particular plant disease, must first be 
isolated from diseased portions, with a view to growing them entirely 
alone, unmixed with other organisms, on artificial culture media of 
suitable composition. It is by this means that "Pure Cultures" are 
established. Attempts are next made to inoculate healthy plants with 
small portions of the organism grown in pure culture. If the disease 
can be successfully transmitted to healthy plants by means of artificial 
inoculations, and the typical symptoms reproduced, the attempt 
should be made to re-isolate the organism from the plants inoculated. 
If the organism can be re -isolated and again successfully established 
in pure culture, and is found to be identical with the one originally 
isolated from diseased tissues, it is considered that the normal 
disease cycle has been completed. This is, moreover, regarded as satis- 
factory evidence that a particular organism is the cause of a disease 
distinguished by certain characteristic symptoms. The cycle of 
events is designated as Koch's cycle, because it was first formulated 
by the famous pathological investigator Koch, and is regarded by 
all pathological authorities as a first necessity when attempts are 
being made to establish the cause of any particular plant disease. 

No further remarks are necessary at this point on the diseases 
caused by the agencies mentioned under (a) and (b) above. Those 
caused by the agencies mentioned under (c) still require much atten- 
tion. Their investigation is by no means simple, for it is always a 
difficult matter strictly to evaluate the exact, or even the approximate, 
influence which any particular set of abnormal conditions exert 
towards setting up a pathological state. Unfavourable climatic or 
soil conditions, etc., often lead to a considerable reduction in vigour, 
and the final result is a much greater predisposition to attack from 
disease -causing organisms. No well suggests the term debility diseases 
for affections of this type. 

For comparative purposes, virus, bacterial and fungus diseases 
can be contrasted as regards their size as they appear under the micro- 
scope. Fungi are forms of plant life of relatively simple structure, but 
with a definite and distinctive one, often visible to the naked eye and 
easily visible under the microscope. The organisms comprised in the 
group of Bacteria are comparatively very minute in size, but they 
possess a definite structure which can be recognised under the higher 
powers of the microscope. The group contains forms which may be 
considered #s transition forms between the animal and plant kingdom. 



CHAP, ii CAUSATION OF DISEASE, ETC. 21 

With regard to virus diseases, no organism with a definite structure 
has ever been demonstrated with certainty, and if particles of definite 
structure are associated with these diseases they must be exceedingly 
minute, and ultramicroscopic in size, i.e. not visible under the micro- 
scope. That virus diseases are transferable from diseased to healthy 
plants is proved by obtaining plant juice extracts from diseased 
plants and inoculating small quantities of the extract into healthy 
plants. The spread of virus diseases is commonly found to be de- 
pendent on an insect vector. 

No well remarks that as no strict definition of disease can be given 
there is no fixed limit to a list of disease-causing agencies. But ex- 
cepting brown bast and the damage done directly by atmospheric 
agencies, there is no necessity to go beyond the subject of damage 
caused by fungi and insect and animal pests, when reviewing the 
affections of rubber trees. The section devoted to insect and animal 
pests is merely an attempt to compile as much reliable information 
as possible from the scattered literature on the subject, and to give, 
in addition, the information obtained over the last few years in 
Malaya. 

While the most important causes of plant diseases have been 
shortly referred to, no mention has been made of two other groups 
of organisms which cause plant diseases of some importance in other 
countries. These groups are known as (a) Actinomycetes, (b) Myxo- 
mycetes. The organisms included in the former show relationships to 
some of the filamentous bacteria and also to certain fungi, but they 
are probably most nearly related to the former. Diseases of potatoes, 
mangolds and beets have been recorded as caused by these organisms. 
The myxomycetes arc a group of organisms devoid of chlorophyll, 
having a preponderance of plant characters, but possessing some 
animal characters. The common finger-and-toe disease of turnips, 
and the corky scab of potatoes, are probably the best known diseases 
caused by organisms belonging to this group. 

VEGETATIVE STRUCTURE OF FUNGI 

Before commencing this section it will be advisable to state at once 
the fundamental distinction between fungi and all other groups of 
plants which are higher in the scale of organisation. All parts of fungi, 
both vegetative and reproductive, are devoid of chlorophyll, i.e the 
green colouring matter found in all the higher plants, and this results 
in a fundamental difference between the fungi and the higher plants 
in the matter of food synthesis. 



22 DISEASES AND PESTS OF THE RUBBER TREE PART i 

The vegetative portion of a fungus is known as the Mycelium and 
is usually quite simple in structure. It is commonly made up of a 
mass of intertwining filaments, microscopic in size. Each individual 
filament is spoken of as a Hypha, so that the mycelium is composed 
of a number of hyphae. The mycelium is usually found permeating the 
invaded substance from which are absorbed the nutrient materials 
required. The hyphae, in most groups of fungi, are divided into short 
cells by the formation of cross-walls, but in certain groups no cross- 
walls or only very few are formed, so that a hypha simulates a long, 
undivided tube, e.g. Pythium and Phytophthora. 

The technical terms used by Gaumann and Dodge in their recent 
text-book for the vegetative structures developed by fungi will be 
used here. In many cases the hyphae grow together in groups, inter- 
twine, adhere and form a thick tissue which is termed Plectenchyma. 
If the single hyphal elements are still recognisable as such, the tissues 
formed are termed prosoplectenchyma or prosenchyma; if the hyphae 
have lost their individuality so that they lie beside each other (in 
sections), with the cells appearing isodiametric and continuous, as in 
the parenchyma of higher plants, the tissues so formed are termed 
paraplectenchyma or pseudoplectenchyma. 

The hyphae may become concentrated and aggregated into thickish 
threads known as rhizomorphs, structures which may attain to a 
considerable degree of complexity. Rhizomorphs indicate a further 
step in the development of plectenchyma. They arise chiefly from 
parallel hyphae and often have a definite apical growth from an 
apical meristem, as in the root-tips of higher plants. Under suitable 
conditions, they may again spread out in sheets of mycelium. In the 
higher forms, a dark, thick, irregularly intertwined rind and a loose, 
white core are differentiated from parallel hyphae. They serve chiefly 
for transport of food in saprophytic fungi. Occasionally the conduct- 
ing function becomes less evident and they attain a more sclerotic 
character. In parasitic fungi, the conducting function of rhizomorphs 
must be considered definitely of a secondary nature as compared with 
their ability to withstand adverse conditions. 

In sclerotia the plectenchyma appears tuberiform, with a firmer 
pseudoparenchymatic rind and a looser prosenchymatic core. This 
structure serves to carry the organism over unfavourable conditions 
of growth and, with the return of normal conditions, it "germinates", 
developing into the usual mycelium or into a fructification. 

Gaumann and Dodge use the term plectenchyma as indicated 
above, in connection with tissue developed by fungi which form 
tuberiform sderotia. If such usage is valid, it seems equally so when 



CHAP, ji CAUSATION OF DISEASE, ETC. 23 

the term is applied descriptively to any aggregations of fungus tissue, 
whether in the typical form of rhizomorphs or as definite lines running 
through the woody tissues of diseased rubber trees, usually black or 
brown in colour. If this view is accepted, plectenchyma of different 
types is developed by all the fungi causing the major root diseases 
of rubber trees. The term external plectenchyma can be used con- 
veniently for the external rhizomorphs of Fomes lignosus and Gano- 
derma pseudoferreum, and the term internal plectenchyma could be 
applied to the black lines of fungus tissue which are always prominent 
in the roots of rubber trees affected by Ustulina zonatd. In the latter 
case, the internal plectenchymatic tissue has lost the typical rhizo- 
m orphic appearance, but in the case of Sphaerostilbe repens the 
internal plectenchymatic strands, of microscopical size, which grow 
through the diseased cortical tissues, retain the typical rhizomorphic 
appearance. In this connection it may be of interest to state that 
when Sphaerostilbe repens is grown in pure culture, the mycelium 
always forms small, rhizomorphic strands, which are clearly visible 
to the naked eye. Fig. 8 (d) will show that Ustulina zonata develops 
similar structures in pure culture. 

Fig. 10 illustrates the microscopical rhizomorphs of Sphaerostilbe 
repens running through the diseased cortical tissues of the root of a 
rubber tree. It shows the apical meristem from which growth in, 
length takes place and is reminiscent of Hartig's figure given in 
Gaumann and Dodge's book. Fig. 21 shows the internal plectenchyma 
formed by G. pseudoferreum in diseased rubber roots; this fungus also 
develops typical external rhizomorphs and rhizomorphic membranes. 

This subject will be again referred to after the root diseases of the 
rubber tree have been described. Nothing has so far been said regard- 
ing the utility of rhizomorphs in the causation and spread of plant 
diseases, and but little has been published in the literature on this 
subject. An extract from Butler's book will therefore prove a useful 
introduction: 

Such specialised strands are known as "rhizomorphs" and they may 
reach a considerable degree of complexity of structure in some cases. All 
these mycelial strands are capable of growth at the tip, sometimes 
extending for yards and branching and anastomosing freely. Their use 
is readily understood. Single hyphae are delicate and easily injured, as 
by insects. The rhizomorphs are usually tough and hard to damage. By 
their vigorous growth they permit of extensive spread. They are also, 
owing to their structure, able to withstand drying or other adverse con- 
ditions, much better than single hyphae; and their vitality is such that 
old, dried rhizomorphs, if brought into a moist atmosphere, can recom- 
mence growth and put out new branches even after some years. 



24 DISEASES AND PESTS OF THE RUBBER TREE PART i 

Instead of uniting to form long, cylindrical root-like strands, the hyphae 
of some fungi join into large, solid, more or less rounded and sharply de- 
fined masses, known as "sclerotia". These masses are very long lived and 
resistant to adverse conditions; their cells become filled with stores of 
reserve food; they usually separate off from the mycelium and become 
isolated and free; and they can resume growth when conditions become 
favourable, giving either a new mycelium, or in many cases producing the 
reproductive stage of the fungus. 

In the case of the important root diseases of rubber trees in Malaya, 
the following summary as to the formation of plectenchymatic tissues 
by the various fungi may prove of interest to investigators in other 
countries. 

F. lignosus forms external plectenchyma in the form of typical 
rhizomorphs, but does not produce internal plectenchyma, in attacked 
roots. 

G. pseudoferreum forms external plectenchyma as typical rhizo- 
morphs, which commonly unite to form a continuous rhizomorphic 
membrane, with a somewhat thickened outer skin. It also produces 
internal plectenchyma (a) in the form of occasional thin plates of 
tissue in the diseased wood, and (b) in typical fan-shaped masses of 
tissue in diseased roots just beneath the external skin formed by 
the rhizomorphic membranes. 

F. noxius has external mycelium but it is masked by consolidated 
masses of earth and stones around diseased roots, and so the formation 
of external rhizomorphs or membranes cannot easily be made out. 
Internal plectenchyma is formed in the shape of numerous thin plates 
of fungus tissue running through the diseased wood. 

8. repens has internal plectenchyma only, which occur as rhizo- 
morphic strands, and retain the appearance of typical rhizomorphs. 
Microscopic rhizomorphs ramify through the diseased cortical tissues. 
Macroscopical rhizomorphs grow between the wood and the cortex, 
and when found they are usually seen on the surface of the wood. 
Owing to the position in which they grow and having to withstand 
considerable pressure, they are flattened in form. 

U. zonata has internal plectenchyma only in the shape of numerous, 
prominent black plates of fungus tissue in diseased wood. There is 
no external plectenchyma and no suggestion of rhizomorphs either 
externally or internally. The rhizomorphic structures developed in 
pure cultures of both U. zonata and S. repens have been mentioned 
above. 



CHAP, ii CAUSATION OF DISEASE, ETC. 25 

CLASSIFICATION OF FUNGI 

The vegetative parts of fungi are comparatively simple in structure, 
but the reproductive portion is more complicated. In the higher 
forms, large numbers of varied and elaborate structures are built up 
by the ramification and intertwining of simple hyphae, when the 
reproductive phase is entered upon. The thin, simple brackets of 
Fomes lignosus and the thicker brackets of Ganderma pseudoferreum 
may be mentioned as examples, and these may be compared with the 
fructifications produced by an Agaric such as Marasmius palmivorus 
which causes a disease of the tapping panel. This again may be com- 
pared with the minute, reddish pustules or cases which form the per- 
fect fruits of Sphaerostilbe repens. Simpler forms of fructification, i.e. 
structurally more simple, are formed in fungi, such as Phytophthora 
palmivora, where single cells at the tips of simple hyphae become 
swollen and separated from the main body of the hypha by a cell- 
wall. In these, spores are eventually produced by the division of 
the protoplasm. 

The fungi are classified by the differences between their repro- 
ductive parts, as are all other large plant groups. The barest outline 
only can be given here. Fungi are divided into two large groups 
known as (a) Perfect fungi, (b) Imperfect fungi. 

Group (a) is subdivided into three large sub-groups which can be 
distinguished by the characteristic type of the fundamental repro- 
ductive structures. Group (b) is large and very heterogenous, con- 
sisting of fungi which cannot be included in the former group, because 
the reproductive structures typical of the three large groups of the 
perfect fungi are not present or have not been found. 

The three large groups into which the perfect fungi are subdivided 
are as under: 

I. Phy corny cetes. 
II. Ascomy cetes. 
III. Basidiomy cetes. 

These names refer to the characters of the groups. The suffix 
mycetes indicates fungoid, so that the three terms may be rendered 
as Phycofungi, Ascus fungi and Basidia fungi. 

The terms "phyco", "ascus" and "basidia" will be explained below. 

Phycomycetes. "Phyco" is a term signifying "related to the Algae", 
and this group comprises certain fungi which retain considerable 
resemblance to certain groups of Algae. It is subdivided into large 
sub-classes, the Oomycetes and the Zygomycetes. The lower forms of 



26 DISEASES AND PESTS OF THE RUBBER TREE PART i 

fungi included in the Oomycetes show but little complexity of vegeta- 
tive parts and may consist of a single cell only. 

In the Zygomycetes the mycelium is usually well developed. The 
hyphae may be septate or non-septate. Reproduction may be brought 
about by non-sexual or sexual spores, the former being usually pro- 
duced within differentiated portions of the hyphae, commonly occur- 
ring at the tips of branches, and termed sporangia. Again, in this 
class certain spores may be produced upon, or abstracted from hyphae, 
in which case the latter are termed conidiophores. It is common also 
to find motile spores, capable of active movement in water, formed 
for the purpose of reproduction. There are seven large orders in the 
Phycomycetes, of which only one, viz. the Peronosporales, is of special 
interest, because it contains the genera Phytophthora and Pythium. 

Ascomycetes. The fungi included in this class have one common 
characteristic, viz. the Ascus or spore-sac, generally containing a 
definite number of spores (ordinarily eight). Many varied types of 
asci are produced; they may be of a comparatively simple type 
closely resembling a simple sporangium. In many orders of this 
class, the asci may be formed within a bed of modified mycelial 
tissue, which is termed a stroma. But the different types of ascus 
fruits are so diverse in form and consistency that it is not possible to 
pursue the subject; but throughout all these varied types of fruit- 
bodies the ascus or spore-sac, with its enclosed spores, is the char- 
acteristic feature. The number of spores may be less than eight but, 
if enclosed in an ascus, the fungus would be regarded as an Asco- 
mycete. Again, there are numbers of fungi in this group having more 
than eight spores in the ascus, but in such a case the number is always 
some multiple of eight. The Ascomycetes contain a larger number of 
individual species than any other group of fungi. Conidial spore 
forms of manifold variety are known y and a single species may possess 
several conidial forms. The fungus causing mouldy rot is an asco- 
mycete with two conidial forms. The mycelium is usually consider- 
able, exposed or embedded in the substratum, and is septate. The 
fungi causing diseases in rubber plantations which fall in this class 
are Ceratostomella fimbriata, Ustulina zonata and Sphaerostilbe 
repens. 

Basidiomycetes. In general, the fungi included in this class are 
characterised by the type of fructification upon which the spores are 
developed. The form, size and shape of the fructifications exhibit 
great variation, but in every species the spores, four in number, are 
borne externally on the end of a swollen hyphal tip known as the 
basidium. The basidia are commonly closely crowded together to 



CHAP, ii CAUSATION OF DISEASE, ETC. 27 

form a definite layer known as the hymenium. The variation in the 
types of fructifications is well illustrated in the cases of Corticium 
salmonicolor, Fomes lignosus and Ganoderma pseudoferreum, all of 
which belong to the Basidiomycetes. 

In connection with this large group, mention must be made of two 
rather anomalous groups usually included in it: (a) the Hemibasidii, 
(b) the Protobasidii. The former is of considerable interest; it contains 
only two families, all the individual species of which are obligate 
parasites. These are generally spoken of as the "smut fungi". The 
Protobasidii include the most important single order of plant para- 
sites, the Uredineae or "rust fungi". Fortunately, the rubber planta- 
tions of the Middle East have never been troubled with attacks of 
smut or rust fungi, but the fate of the coffee plantations in Ceylon, 
which were devastated by the rust fungus Hemeleia vastatrix, is still 
well remembered by the older school of planters in Malaya, many of 
whom started their planting careers on the old coffee plantations in 
Ceylon. 

For purposes of simplicity, attention has been drawn only to the 
spores of perfect and imperfect fungi, without mentioning the fact 
that the spores produced during the development of the perfect stage 
arise from the culmination of a sexual act, i.e. the union of two nuclei. 
The perfect spores, therefore, are the sexual spores. Put shortly/ 
spores of imperfect fungi are asexual spores. The nature of the sexual 
process is movst clearly shown in the Phycomycetes , and if we consider 
the fungi directly concerned with rubber tree diseases, Phytophthora 
palmivora and Pythium complectens best show the special features. 
Fig. 34 (6) shows the smaller, male cell, the antheridium, closely ad- 
pressed to the larger, passive female cell, the oogonium. The nucleus of 
the antheridium passes over into the oogonium, comes into contact 
with its nucleus, and the union is completed when the two nuclei 
become completely merged with one another to form a single nucleus. 
It will be understood that the sexual process, carried through by a 
smaller, active male element and a larger, passive female one, is 
strictly comparable with the sexual act carried out in much more 
highly organised plants and animals. Although a form of fertilisation 
occurs, these features of the sexual act are not so clearly seen in the 
Ascomycetes and Basidiomycetes. It is well established that the forma- 
tion of perfect fructifications in the Ascomycetes is initiated by the 
union of sexual nuclei, and it has also been fully proved for the rust 
and smut fungi, which are classed as somewhat anomalous forms of 
Basidiomycetes . 

Fungi Imperfecti. This group of fungi constitute a heterogenous 



28 DISEASES AND PESTS OF THE RUBBER TREE PART i 

subdivision of the true fungi. The individual species pass their repro- 
ductive phase without the development of the structures found in the 
groups discussed previously. But many of these types may represent 
stages in the life cycles of the perfect fungi. However, until the 
perfect form of the fungus has been definitely established, the enor- 
mous number of secondary fruit forms cannot be classified except by 
creating this special, though very heterogenous group. Families such 
as Oloeosporium, Cytospora, Ascoshyta and Diplodia are included in 
the order, and these will prove of some interest because species of 
these families are associated with certain diseases of rubber trees. 

The large class of Fungi Imperfecti produce external spores which 
are budded off from more or less free hyphae and show no special 
arrangement as in the case of basidia (see Fig. 59 (d)). These spores 
are termed conidia, and the hyphae upon which they are developed 
conidiophores. Attention may be directed here to the asexual spores 
produced during the life cycle of Ceratostomellafimbriata. This fungus 
produces two distinct forms, which can be distinguished by the 
differences in wall thickness and the speed at which they are pro- 
duced. But both forms are alike in that they are formed endogenously, 
i.e. within the hyphae, and are extruded at the tip, which opens as 
spore formation is in progress. These spores are spoken of as endo- 
spores, and are not commonly formed as compared with the external 
spores which are simply abstricted or budded off by the large majority 
of fungi. 

Before spores can germinate successfully the requisite conditions 
must be satisfied. When optimum conditions are provided, the method 
of germination is similar in practically all cases, despite the varied 
methods appertaining to the initiation and production of fungus 
spores. A simple protrusion of one or more germ-tubes takes place, 
and as they increase in length branching begins, and after a time the 
elongating fungal filaments begin to ramify and intertwine with one 
another to form the vegetative portion of the fungus, the mycelium. 



CHAPTER III 

PHYSIOLOGY OF FUNGI 

Saprophytisrn and Parasitism Sproad of Fungi Immunity, Resistance and 
Susceptibility to Disease. 

SAPROPHYTISM AND PARASITISM 

ATTENTION has already been directed to the fact that the fundamental 
distinction between the fungi and all other plant groups is that they 
do not possess chlorophyll and so are unable to utilise the sun's 
energy in the matter of food synthesis. Therefore the carbon dioxide 
of the atmosphere is not available for the construction of the food 
materials necessary for their growth and development. As this source 
of carbon is denied to them they obtain it from organic combinations, 
and hence they are always associated with dead or living organic 
matter. In order to obtain the food material necessary for existence, 
fungi must break up complicated chemical compounds into much 
simpler forms. Carbohydrates form the principal and most important 
food material for fungi and these are broken down by the action of 
chemical substances known as Enzymes. 

The enzymes are peculiar in that they are able to bring about the 
decomposition of certain constituents of the medium without under- 
going any chemical change themselves, merely acting in an activatory 
capacity. The behaviour of an enzyme is different from that of an 
ordinary chemical agent, since the latter bring about alterations in 
other groups of atoms by their chemical affinity, so that the old 
combination is broken up and the separated portion enters into a 
new atomic grouping with a part of the active agent. Accordingly, a 
definite weight of the agent can only displace a definite quantity of 
other compounds, whereas in respect of enzymes their activity is 
practically illimitable. They do not combine with the products of the 
reaction but continue to react on the residual, undecomposed sub- 
stance. The reason for the important part played in industry by large 
numbers of fungi is that they often possess specific enzymes which 
influence chemical changes in a certain direction. 

Fungi are divided into two classes according to their mode of 
life. Those living on decaying vegetable matter are termed Sapro- 
phytes, while others which obtain their food material from the bodies 

29 



30 DISEASES AND PESTS OF THE RUBBER TREE PABT i 

of living organisms are termed Parasites. As regards the nutri- 
tion of fungi, we must, as with green plants, distinguish between 
the process of assimilation, i.e. the conversion of the absorbed food 
substances into body substance, and that of respiration, i.e. the varied 
phenomena of decomposition and degradation due to the vital 
activity of the organism. Just as in green plants, the two processes 
are intimately related to one another, but during the respiration of 
fungi, a large number of different nutritive materials are transformed, 
the final products being carbon dioxide and water. Speaking gener- 
ally, one may assert that constructive activity predominates during 
the nutrition of green plants, whilst destructive activity predominates 
in the case of fungi; the enzymes, which are of such general occurrence 
in the fungi, are the special destructive factors. 

With regard to parasites and saprophytes it should be realised that 
there is no sharp line of demarcation between the parasitic and sapro- 
phytic habit. Some fungi, which attain to their best development as 
parasites, are able to maintain themselves, and undergo a portion of 
their life cycle in a saprophytic manner. The converse is also true. 
Thus, four subdivisions may be recognised physiologically. These are 
listed below: 

(a) Obligate parasites. 

(b) Obligate saprophytes. 

(c) Facultative parasites. 

(d) Facultative saprophytes. 

The fungi classed in (a) can only maintain existence upon other 
living organisms as they are entirely dependent upon them for the 
requisite conditions for growth. 

The fungi classed in (b) can grow only on dead organic material, 
being quite unable to penetrate living tissues. 

The fungi classed in (c) are saprophytes, which occasionally, usually 
under very special conditions, may become parasitic. 

The fungi classed in (d) are those which normally pass through life 
as parasites, but which are capable of maintaining existence for a 
certain length of time in a truly saprophytic manner. 

Parasitic fungi can be subdivided into: 

(i) Holoparasites. 
(ii) Wound parasites. 

The terms are self-explanatory. Fungi in (i) can make a direct 
attack on the plant; those in (ii) can gain entry into the living organism 
only through wounds. Attention may be directed here to the diseases 



CHAP, in PHYSIOLOGY OF FUNGI 31 

of the tapping panel. The act performed in obtaining the latex by 
tapping gives the opportunity for the entry of certain wound para- 
sites, so that in the ultimate, the rubber tree, after being opened for 
tapping, must be considered to be in an abnormal condition, from a 
disease point of view. As a result of the possession of an adequate 
repair mechanism, no serious damage is done when normal tapping 
systems are used. 

SPREAD OF FUNGI 

The common method of spread is by means of spores developed in 
the special structures termed fructifications. In general, the state- 
ment may be made that spores are usually developed in large numbers 
by fungi, and in enormous numbers by some species, more especially 
by Basidiomycetes . Air currents play the most important role in the 
dissemination of the spores. But while air dispersal forms the general 
method there are many exceptions to the rule, as is well instanced 
by the diseases of rubber trees. In the case of the fungi causing panel 
diseases, viz. Phytophthora palmivora and Pyihium complectens, spread 
is brought about by free-swimming spores and therefore can only 
take place in the presence of moisture, though a thin film only is 
required. The spread of the fungus causing mouldy rot, Ceratosto- 
mella fimbriata, from one district to another which may be distantly, 
separated, is brought about by spores which are carried on coolies' 
clothing and implements, such as tapping knives. In the case of 
Ustulina zonata, which fungus produces a flat fructification with a 
copious development of conidia on the upper surface, it is quite 
possible that insects, in passing over the fructifications, would carry 
spores away on their various appendages. In the case of the fungus 
causing pink disease, Corticium salmonicolor, it is probable that dis- 
persal of small flakes of bark carrying minute portions of viable 
mycelium is largely responsible for its spread. The rhizomorphs 
developed by the various fungi causing root diseases of rubber trees, 
more especially in the case of F. lignosiis and O. pseudoferreum, pro- 
vide a method of vegetative spread which functions most efficiently 
when root-contact between neighbouring trees has become estab- 
lished, and as a result these fungi may travel from one diseased tree 
to numerous healthy ones. 

Large blocks of agricultural land planted up with but a single crop 
provide the most favourable conditions for encouraging the spread 
of disease-causing fungi. It is generally understood, and need not be 
dwelt upon here, that the host range of a parasitic fungus is usually 
limited. In numerous cases a fungus is limited to one particular host. 



32 DISEASES AND PE3STS OF THE RUBBER TREE PART i 

Of the fungi causing root diseases of rubber trees, Fomes lignosus has 
been reported as being found on large numbers of host plants, while 
similarly the host range for the fungus causing brown-root disease, 
F cymes noxius, is a wide one. The host range for Ganoderma pseudo- 
ferreum, on the other hand, is comparatively very limited, only a 
few plants up to date having been reported as hosts. The chief point 
is that in a plantation all the trees are largely of similar constitution, 
and if a certain parasitic fungus is present and conditions are suitable 
for its growth and spread, there can be no guarantee that any par- 
ticular tree in the plantation will escape attack. This point may be 
emphasised in connection with the future planting-up of high yield- 
ing material, vegetatively propagated, more especially in monoclone 
planting. All the individual trees in such blocks of rubber will be more 
closely related to one another than the trees planted in the past and 
present stands of mixed plantings. Consequently, while the latter 
may be considered largely of similar constitution, the trees propagated 
from a single rubber tree must be considered to approach much 
nearer to the ultimate end, i.e. an identical constitution. There is little 
doubt that the possibility of epidemic disease is much increased when 
bud-grafted trees are planted in monoclone blocks. It is recognised 
that individual trees might show varying degrees of susceptibility 
to attack or that there may be trees which show complete immunity 
under the prevailing conditions, but in general, and confining re- 
marks to rubber plantations, it can be stated with some degree of 
conviction that every tree in the plantation is subject to invasion by 
disease-causing organisms, more especially with such types as repre- 
sented by the fungi causing root diseases. If this statement is accepted, 
it is obvious that, as the change from balanced jungle conditions to 
plantation conditions is made, there are ever-increasing chances of 
a serious spread of disease. In the jungle, with a thoroughly well- 
mixed stand of different species of trees, each individual or small 
group of a particular species is separated from others of the same 
species by plants of probably several different species which are not 
susceptible to attack by the particular fungus. The simplest case is 
that provided by a fungus such as Ganoderma pseudoferreum, which 
spreads chiefly by contact of the roots of a diseased tree with those 
of healthy trees. It is obvious that, under jungle conditions, root- 
contact between plants of the same species is extremely unlikely, 
except in localised places where a small group of plants of one par- 
ticular species might have become dominant. Thus, under jungle 
conditions, a fungus such as G. pseudoferreum would develop in 
certain areas to form a "knot" of infected ground, and the spread 



CHAP, in PHYSIOLOGY OF FUNGI 33 

of the fungus would be confined within this knot. But on felling the 
jungle and planting-up a susceptible crop, every individual tree being, 
theoretically, equally susceptible, it is obvious that spread of the 
fungus will be encouraged to a practically illimitable extent. Thus 
the collection of plants, which have previously existed singly or in 
small groups, into large blocks of cultivation, is one of the most 
important factors to take full consideration of in connection with 
the spread of plant diseases. 

The important root diseases of rubber trees need mention at this 
point. When the jungle is felled, the stumps of the trees are usually 
left in situ, to undergo natural decay. These decaying stumps support 
a very varied, usually saprophytic, fungus flora, but a few species 
may exhibit parasitic potentialities for developing and extending 
upon introduced plants. As the stumps decay but slowly, there are 
favourable possibilities of infection of the cultivated plants when 
they exist over a long period of years as permanent crops. As experi- 
ence has shown in Malaya, the type of disease set up in such circum- 
stances is usually more serious in early than in later years, and as the 
years pass the disease continuously decreases in intensity if adequate 
control measures are undertaken. 

The characteristic knots of infected jungle areas are notably well 
shown in young rubber plantations in the case of Fomes lignosus and 
Ganoderma pseudoferreum. These fungi, in the jungle, may be com- 
paratively rarely seen and may cause but little damage, but when 
exceptional advantages for extensive spread are offered in young 
clearings, they quickly become prominent and demand attention. 
Similar remarks apply to the attacks made by white ants. 

IMMUNITY, RESISTANCE AND SUSCEPTIBILITY TO DISEASE 

A large amount of literature dealing with the wonderful results 
obtained by the breeding of resistant strains of cereals and other 
annual crops in common use as food supplies, must have come to the 
notice of all laymen during recent years. A clear conception of re- 
sistance and immunity is seldom obtained by the rubber planter, for 
the subject is not a simple one, and as there are few features directly 
concerned with rubber cultivation, there is little opportunity allowed 
for close contact. A few short remarks only will be attempted in this 
book. 

Immunity can be considered as the complete development of 
resistance. Resistant strains, varieties or species of cultivated plants 
have usually been discovered by chance, growing amongst a crop of 

D 



34 DISEASES AND PESTS OF THE RUBBER TREE PART i 

individuals some of which are infected by a particular disease. The 
resistant strain is then propagated and if the desirable disease- 
resistant properties do not interfere with other highly desirable pro- 
perties required in the profitable production of the crop, which is not 
always the case, then the resistant line may be successfully developed 
on a large scale. But resistance must not be regarded as fixed for all 
and every set of conditions. If conditions are materially changed, 
resistance may break down and the plant would become susceptible 
once more. 

It is an obvious truism that strong, healthy plants will be de- 
veloped only when they are grown under favourable conditions. As 
a result, a certain amount of disease resistance may be provided. 
But this statement must be modified to some extent according to the 
crop and the requirements thereof. For instance, the view that high- 
yielding rubber trees are more susceptible to brown bast disease is 
commonly held. There may be doubts as to this but a definite state- 
ment can be made, viz. that on poor types of soil, where the growth 
conditions for rubber trees are undoubtedly unfavourable and low 
yields are a direct consequence, cases of brown bast are seldom seen. 
However, a congenial situation will usually confer on plants some 
general power of resistance against disease attacks. There is no doubt 
that if unsuitable conditions are avoided and agricultural practice 
is kept up to the requisite standard, then the dangers of serious plant 
disease outbreaks will be considerably lessened. 

The aspects of the subject are innumerable and it would not prove 
profitable to dwell at length on any particular phase in this book. 
An extract from a recent address by Brown l may prove of interest 
as illustrating the extremely wide scope of this interesting subject, 
although, in the past, it has but touched the fringe of the disease 
problems encountered on rubber plantations in Malaya. 

The subject of disease resistance in plants, considered from the point of 
view either of academic or practical interest, is of too wide a scope to 
allow of adequate treatment in such an address as I propose to give. 
Relevant material could probably be culled from almost any paper deal- 
ing with a plant pathological subject. There is the variation of suscepti- 
bility from one plant or variety to another and the different behaviour 
of the same plant under different environmental conditions. Viewed from 
another standpoint, there are such matters of interest as the pathogenic 
range of various fungal parasites and the differences in virulence shown by 
strains, biological races, etc., of the same fungal species. Data of this type 
would all contribute to make up the full story of disease resistance, but 

1 Brown, W., 1934. "Mechanism of Disease Resistance in Plants." Pres. Address. 
Trans. Brit. Myc. Soc., vol. xix. Part I. 



CHAP, in PHYSIOLOGY OP FUNGI 35 

it is doubtful if any summary, covering the whole field, could be usefully 
attempted on this occasion. For those of you who might wish to read 
more generally on the subject, a number of papers might be cited, e.g. 
by Marshall Ward and Appel among earlier writers and more recently by 
Brooks and Walker. To the last mentioned I would specially refer you for 
a good and comprehensive catalogue of the types of relationship shown in 
parasitism. 

The variation of susceptibility in varieties of single species is men- 
tioned in the above extract. There are certain indications in Malaya 
that varietal disease susceptibility will need consideration in con- 
nection with bud-grafted plants. Two clones showing definite suscepti- 
bility in certain directions have been observed. Young trees of clone 
B.D.5 show susceptibility to lightning damage. This is attributed to 
the particular form developed by the young trees. The individuals of 
this clone have a late branching habit and, compared with trees of 
other clones of the same age, attain a considerable height before 
branching. It is suggested that owing to the long, unbranched stem, 
the trees of this clone attract lightning more readily. It will be 
difficult to prove the point, but there does not appear reason to doubt 
the fact that in this clone there is a preponderance of lightning 
damage. 

A much clearer case is reported on page 411. In 1932 three estates 
reported the same feature. Areas of mixed clones were damaged by 
the short-horned grasshopper, but only the individuals of the clone 
A.V.R.O.S.256 were attacked, and large numbers suffered complete 
defoliation, while all other interplanted clones escaped attack. 

There remains one item which deserves mention, and that is the 
question of disease caused by fungi introduced from another country. 
Many of the most serious epidemic plant diseases have originated 
as a result of an introduced parasite to which the particular crop has 
not been previously exposed. To further the prevention of the intro- 
duction of possible harmful fungi from outside, most countries with 
large agricultural interests now have rigid quarantine rules for im- 
ported material. Malaya cannot afford to be an exception. The ab- 
sence from the country of the fungus causing South American leaf 
disease is in itself enough to demonstrate this statement. 

It will also be appreciated that, in introducing plants intended 
for cultivation from countries abroad, indigenous fungi might find 
them very suitable hosts on which to maintain existence. In such 
cases also, very serious plant diseases may originate. 



CHAPTER IV 

EXTERNAL FACTORS AND RUBBER TREE DISEASES 

Outside Factors influencing Rubber Tree Diseases Tapping Systems and Panel 
Diseases Disease Symptoms in Rubber Trees. 

OUTSIDE FACTORS INFLUENCING RUBBER TREE DISEASES 

THE study of the host plant under cultivation introduces numerous 
complications into disease investigations, many of which are of the 
utmost importance; they often receive attention, however, only in 
a generalised sort of fashion. The importance of outside factors as 
they influence plant diseases has been generally recognised, as the 
following extract from an address given by Brooks in 1923 1 will 
indicate: 

Plant pathology is essentially abnormal plant physiology, in which a 
parasite is often the disturbing agency. Acting upon both host and para- 
site are environmental conditions which sometimes favour the one and 
sometimes the other. As Butler has indicated in his Fungi and Disease in 
Plants, these external factors are often of critical importance in the 
establishment of disease. 

The most important fact to note in the above statement is its 
qualified nature. With respect to the cultivation of the rubber tree 
and the diseases from which it suffers, the writer would withdraw 
all qualifications and definitely state that external factors must 
always be given an important place in the initiation and continuance 
of all serious outbreaks of the more important diseases. 

For the purposes of agricultural practice, the important distinc- 
tion in relation to plant diseases may be set forth in the form of the 
general statement made by No well, viz. as between those diseases 
which develop upon plants in normal condition, and those which 
occur to a serious extent only upon plants reduced in vigour by un- 
favourable circumstances, such as soil and climate, insect infestation 
or methods of cultivation. The various items mentioned in this 
general statement are well recognised in so far as they do exert a 
considerable influence on the course of specific plant diseases; but in 
spite of this, it is doubtful if sufficient attention has been devoted to 

1 Brooks, F. T., 1923. "Some Present-day Aspects of Mycology." Pres. Address. 
Trans. Brit. Myc. Soc., vol. ix. Parts I and II, Sept. 

36 



CHAP, iv EXTERNAL FACTORS AND DISEASES 37 

this aspect of disease investigations, more especially when permanent 
or semi-permanent crops are under consideration. It is important to 
recognise that while normal conditions for growth may be provided 
at the outset, natural phenomena may bring about important changes 
in the growth conditions, so that they may become abnormal and 
may ultimately favourably influence the invasion of the crop plants 
by parasitic organisms. 

In the special case of rubber cultivation an attempt will be made 
to show that the plant pathologist cannot legitimately attach greater 
importance to the organism causing a disease, or to the host plant, 
than lie can to the factors which influence the reactions of both. This 
fact emerges more plainly to the observer whose activities are mainly 
confined to the investigation of one particular crop. Malaya proves a 
very suitable country from this point of view, for the agricultural 
interests of the country are mainly bound up in the cultivation of 
rubber. All other Eastern countries growing rubber have large 
interests in the production of several different types of primary 
produce, and these crops demand attention, in addition to rubber. 

No well's statement may be accepted as a starting-point for the 
discussion to follow. To avoid diseases, plants must be kept in normal 
condition, which implies that normal growth conditions must be 
maintained. The conditions represented in the soil, and those of 
climate, are of the greatest importance, and if these remain constant, 
or around the optimum, within the higher and lower limits represent- 
ing normality, the plant will retain the normal condition, usually 
most antagonistic to injurious influences. 

It will be obvious that soil conditions will remain comparatively 
static as compared with climatic conditions; the latter undergo 
quick and often abrupt changes. On the point of changes in soil 
conditions, it will be interesting to institute a comparison between 
temperate and tropical countries. In the former, permanent tree 
cultivations are seldom commenced on virgin jungle soil; the soil 
benefits by the annual return of organic material in the shape of 
fallen leaves, and in the practical cessation of all vital activities, in- 
cluding water absorption, during the wintering period. Both the trees 
and the soil in which they exist have a favourable opportunity for re- 
cuperation during the winter period in temperate climates, and some 
definite benefit must result in both cases. The only injurious influence 
which is likely to affect the trees seriously during the winter resting 
periods is intensive freezing. 

The rubber areas in Malaya were mainly started on recently felled 
jungle areas, which can be considered fairly rich in humus material 



38 DISEASES AND PESTS OF THE RUBBER TREE PART i 

available as plant food. But given this advantageous commencement, 
neither the soil nor the trees planted have much opportunity for 
recuperation by the interspersion of a well-marked annual resting 
period the important favourable factor for plant development in 
temperate climates. The rich humus content of the original jungle 
soil is provided by the thick, shrubby natural undergrowth prominent 
in Malayan jungles, and once the light conditions are changed by the 
felling of the jungle, the plants of importance in the formation of 
humus disappear. As the jungle soil is comparatively favourable for 
the growth of the rubber tree in the early years, and as clean weeding 
operations favoured the supervision of labour, the latter operation 
became popular and firmly established in the early days of rubber 
planting. Although leaf-fall occurs on rubber plantations, it is in most 
years very irregular in Malaya, and as already stated there is no 
decided resting period. It may be taken for granted, therefore, that 
rubber trees, as cultivated in Malaya, are characterised by an un- 
interrupted growth period and that there is a practically continuous 
drain put upon the soil for the supply of food material. Thus, although 
virgin jungle soil may confer an initial advantage, the changes which 
take place in it soon become evident, and if plants of normal health 
are produced at the outset, they cannot maintain this condition if the 
soil changes indicated take place rapidly. This is generally the case, 
especially on hilly land, when no measures are taken to prevent soil 
erosion. It will be obvious that, unless measures designed to keep tne 
soil up to the original standard are undertaken, the conditions for 
outbreaks of plant diseases become more favourable as the years 
pass, because of deleterious soil changes brought about by natural 
factors working over a long period of time. 

So far, it has been assumed that all jungle areas in Malaya would 
prove equally suitable for growing plants in normal condition. This 
is, however, far from being the case, because the areas of land which 
could be considered first-class for rubber cultivation form only a very 
small proportion of the total. In all prosperous agricultural industries 
the best sites are sought for and taken up first, and these are likely 
to be the only ones which will form first-class properties. It is not, 
of course, always only the type of soil which determines choice of site, 
for locality and probable costs of transport are of importance from 
the point of view of costs of production. Again, if old cultivated areas 
with permanent buildings are available there is every reason why 
such areas should be considered for rubber cultivation, for there 
should be knowledge available as to whether the soil would prove 
suitable or not. While these considerations must be taken into account, 



CHAP, iv EXTERNAL FACTORS AND DISEASES 39 

the time inevitably comes, if the industry continues to prove pros- 
perous, when only ill-balanced soil areas are still available for plant- 
ing-up and the prosperity of the industry overrules any doubt there 
may be regarding unsuitable growth conditions. After a period of 
time, therefore, areas partially, if not wholly, unsuitable for the pur- 
pose in view are used for extending the area under cultivation, and 
according to the type of crop, the plants in these areas are very liable 
to contract disease, as compared with plants grown on the better 
areas. Once disease- centres become established there is little possi- 
bility of predicting the ultimate outcome. Rubber cultivators are 
fortunate that Hevea brasiliensis can be grown successfully under 
conditions showing very wide variations, a feature which accounts 
for the widespread range of many weeds. It is not too much to say 
that rubber trees show many of the characteristics of weeds. They 
have this in common: both are extremely difficult wholly to exterm- 
inate, even when growing under conditions obviously unfavourable. 

The above indicates that permanent tropical crops, such as rubber, 
can seldom be grown in habitats providing continuous conditions 
for ideal growth which are necessary to maintain continued health. 
The position might be better stated by saying that in rubber cultiva- 
tion innumerable chances arise for the successful development of 
disease-causing organisms, even if conditions for normal growth of* 
the host plant are provided at the outset. Slow deteriorative changes 
in soil conditions and quick changes in climatic conditions are taking 
place constantly, and these changes bring about lasting effects on 
the growth conditions of the plants under cultivation, which can have 
but one outcome, viz. that the plants will become more liable to 
attacks from disease-causing organisms. 

Up to this point, an endeavour has been made to state the case in 
the simplest possible way. The gradual changes in soil conditions 
with time, and the abrupt changes which may take place in climatic 
conditions, will be readily understood. Periodic changes in climatic 
conditions, which constitute an annual feature extending over a short 
period of time only, will not disturb the normal condition of the host 
plant to any great degree, if the fluctuations are confined within 
certain limits. But in Malaya, during certain years, the short, annual 
wintering period, during which conditions for growth may be con- 
sidered comparatively unfavourable, may be prolonged unduly, and 
the normal condition of the rubber plants might be expected to 
undergo some change. The change is not necessarily immediate and 
any external change may not, in a permanent crop, become apparent 
for some time, In such circumstances, cause and effect are difficult 



40 DISEASES AND PESTS OF THE RUBBER TREE PART i 

to associate with one another, but when disease symptoms are 
observed and fungi happen to become prominent, they are commonly 
considered to have played a part of primary importance as the cause 
of the trouble; indeed, it is not uncommon for them to be considered 
solely responsible. The position outlined above will, in the writer's 
opinion, ultimately be shown to be an outstanding feature in the case 
of lightning strikes on rubber plantations. The immediate damage 
done may be easily recognised in the trees affected, but the later 
effects which follow, on trees apparently unaffected in the first place, 
have not yet been closely followed up. These deferred results have been 
demonstrated clearly in connection with lightning damage in coconut 
plantations, and it is extremely likely that similar conclusions will be 
reached in rubber plantations with further work. 

Brierley 1 states the position very clearly, though in rather technical 
language, as follows: 

It will thus be evident that the complete understanding of a case of ill- 
health involves the genetic and physiological analysis of both host and 
parasite, and the physical and chemical analysis of the conditions under 
which both organisms have developed and at present exist. In actual 
practice one can only adopt a Baconian technique and rejoice if any 
single factor can be isolated and examined. Such investigation^ neces- 
sarily can only give very partial views, and a real comprehension of any 
particular case, considering the case of disease as an individual entity, 
requires that such partial views be synthesised as separate photographs 
are merged in a cinematograph film. An investigation of a disease is, as 
it were, a cross section of a process that is essentially a continuum, and a 
serious danger in plant pathology to-day is the tendency to accept iso- 
lated studies of a disease at any one moment as a true picture of the whole. 

The only observation the writer wishes to make on this quotation 
refers to the last paragraph. Studies of a plant disease in the tropics 
must necessarily be commenced on a line which would form an 
isolated unit. A danger certainly lies in the liability of an investigator 
feeling satisfied that the isolated study provides the true position 
of the whole, but this in fact seldom happens. Investigators engaged 
on phytopathological problems in the tropics have not usually the 
opportunity to carry on a line of work beyond certain limits. There 
are usually a superfluity of problems requiring attention, and as 
shortage of staff is commonly the limiting factor in every projected 
research, it is seldom that any investigator can commence a line of 
work and expect to carry it through successfully to completion. 

A detailed physical and chemical analysis of the climatic conditions 

1 Brierley, W., 1924. "The Relation of Plant Pathology to Genetics", Report of 
Proceedings, Imp. Bot, Con., p. 112, 



CHAP. IV 



EXTERNAL FACTORS AND DISEASES 



41 



in Malaya and other rubber-growing countries in the Middle East 
cannot be provided here. It will be sufficient to indicate the main 
features of the climate in Malaya and to call attention to some of the 
larger differences in climate existing between the different countries 
concerned, more especially in respect of the wintering seasons and 
the monsoon periods, in so far as they affect the disease position. 

Practically little of the rubber area in Malaya is affected by the 
onset of monsoon periods. The state of Kedah and a small area in 
Upper Perak is influenced by the North-West monsoon about 
February each year, but the only significant item is that they pass 
through a relatively long, dry wintering period at this time of the 
year, as compared with other rubber-growing districts. 

MCHES RAINFALL FOR KUALA LUMPUR IN INCHES. 



7\ 



V 



IQ29 
1Q3O 
1931 
1932 



V 



\ 















/ 



JAN FB MAR. APR MAY JUKI JUL AUG SEP OCT NOV DEC 

DIAGRAM I 

The uniformity and high humidity of the climate in Malaya is 
particularly noticeable. The only pronounced seasonal variations are 
those connected with rainfall. This is well distributed throughout the 
year, but has a distinctly higher incidence during the two periods 
April-May and September-December. Between these two periods 
there is a tendency for more open dry weather to occur, centring 
around February and July- August. The dry period centring round 
the month of February is usually considered to be a short, very dry 
period, compared with the longer but wetter period of July-August. 
The annual main wintering of the rubber tree coincides with the 
onset of the dry weather period in February. The advent of a suffi- 
ciently lengthy period of dry weather results in a regular wintering 



42 DISEASES AND PESTS OF THE RUBBER TREE PART i 

through which more than half of the trees are leafless about the 
same time. In Malaya such winterings are the exception rather than 
the rule. Usually, occasional wet days or a succession of wet days 
interfere with the defoliation process and the wintering becomes very 
irregular with some trees leafless, others partially defoliated and 
others fully clothed with leaves. It is estimated that in most years, 
about 15 to 20 per cent of trees do not winter in February, but carry 
over to winter in the later dry season around August, when a small 
secondary wintering takes place. An even wintering period, com- 
prising a long drought period, is viewed with considerable anxiety, 
for yields drop to comparatively low levels and there is a risk of 
serious damage being caused by the outbreak of leaf fires. Further, a 
wintering period may be experienced, during which the succession of 
rainless days may be broken by days on which light showers occur. 
Light showers of rain, occurring during a wintering period which for 
a certain length of time previously has been excessively dry, result 
in the refoliation process proceeding at a comparatively slow rate, 
and this feature provides ideal conditions for a virulent outbreak of 
Oidium leaf -fall. 

In Ceylon the sequence of events is somewhat similar, excepting 
that the May-July period is influenced by the breaking of the South - 
West monsoon, with the advent of very heavy rains, which are 
practically continuous over a long period. Fetch reports as follows: 

In the principal rubber districts of Ceylon, Hevea sheds its leaves at the 
end of January or early in February in the low country, and a few weeks 
later at medium elevations. Frequently, apparently more especially when, 
instead of the normal drought, heavy rains occur in January and February, 
the wintering is irregular. Neighbouring trees may winter at periods 
differing by two or three weeks, and even one side of a tree may drop its 
leaves and acquire new foliage before the leaves on the other side have 
commenced to change colour. In this normal leaf-fall, the leaflets are 
usually disarticulated and fall first, while the leaf-stalk remains attached 
to the branch and only falls later. 

With reference to Java, the writer is indebted to the Director, 
Proefstation, West Java, for information. Correspondence in relation 
to the disease caused by 0. heveae passed between the Proefstation 
and the Rubber Research Institute of Malaya, and the following 
details were provided: 

When considering the occurrence of 0. heveae in connection with the 
climate of Java, you should bear in mind that, generally speaking, we 
have three different climates here. There are striking differences between 
the west, the middle and the east of Java. Even in the case of West Java 



CHAP, iv EXTERNAL FACTORS AND DISEASES 43 

proper you cannot compare the estates on the west slope of the mountains 
with those situated on the east side. Moreover, in successive years great 
differences occur in the intensity of the monsoons. I think that this ex- 
plains the conflicting information brought to you from Java. 

The information given below refers to West Java only: (1) The actual 
time of wintering and refoliation runs from the middle of July to about the 
end of September. (2) The dry weather period begins in the month of May. 
As a rule, June and July are very dry. Then, beginning about the second 
half of August, rainfall is gradually increasing. November may be very 
wet. The wettest month, however, is January. (3 and 4) Unlike Malaya 
and N.E. Sumatra, there is only one dry season in Java. Accordingly a 
second wintering season is unknown here. (5) Oidium attack may be 
serious on estates above 200 metres. The higher the estate the more 
serious the attack. (6) Rainfall occurs in August and September chiefly 
during the late afternoon and the early hours of the evening. The number 
of rainy days varies considerably for the different localities. 

We read with great interest the article entitled "The Effect of Meteoro- 
logical Factors on the Virulence of Oidium heveae in Malaya", and the 
facts concerning the optimal conditions for the growth of O. heveae are 
in good agreement with our own observations on this subject. 

Climatic conditions often vary greatly in different countries which 
grow the same crop. In the rubber -growing countries of the Middle 
East the greatest difference lies between those countries directly 
affected by the rainy monsoon period and those which are slightly or 
even unaffected by monsoon periods. Even in the same country, the 
influence of the monsoon periods may bring about very different 
results from the disease point of view, on the crops cultivated, accord- 
ing to the topography of the country. This is well indicated in the 
copy of the letter given above, referring to cultivated areas in Java. 
A great influence on diseases of the rubber tree is exerted by the 
heavy and continuous rains which fall during the S.W. monsoon in 
Ceylon and S. India. Serious outbreaks of Phytophthora leaf -fall, 
which happen only during these wet spells in the countries men- 
tioned, are entirely absent in Malaya; at least, the most important 
rubber-growing districts in the country are entirely unaffected by the 
monsoon periods. Continuous high rainfall results in a constant high 
humidity, and this factor greatly increases the dangers from potential 
outbreaks of disease. 

The topography of a country naturally affects climatic conditions. 
Close proximity of plantations to the sea, where land and sea breezes 
are in daily evidence, has many advantages from the disease point of 
view. Ventilation is a potent factor towards reducing a high degree 
of humidity, and therefore daily winds will go a long way towards 
rendering climatic factors innocuous in the causation of disease. The 



44 DISEASES AND PESTS OF THE RUBBER TREE PART i 

presence of high mountain ranges has a profound influence on planta- 
tions as regards disease incidence, and it will usually be found in such 
situations that there are certain diseases of common occurrence which 
are not found in other districts in the same country. In fact, the 
limitation in area of any plant disease is practically a sure sign that 
climatic conditions are exerting an influence of magnitude in these 
areas. 

The most convenient method of presenting details of the effects of 
outside factors upon disease problems in the rubber plantations in 
Malaya will be to classify the various factors as under: 

(1) Outside factors influencing the important root diseases. 

(2) Atmospheric agencies. 

(3) Meteorological factors influencing stem, branch and leaf 

diseases. 

(4) Factors, including meteorological ones, affecting panel diseases. 

Outside Factors influencing the Important Root Diseases. The most 
important root diseases to be considered in this section are those 
caused by fungi of the Fomes type. This subject is dealt with in detail 
in the root-disease section and ample proof is there provided for the 
conclusion "that the three root diseases caused by Fomes lignosus, 
Ganoderma pseudoferreum and Fomes noxius and the problems they 
present, are entirely dependent upon the type of vegetation grown 
previously upon the areas now under rubber''. This statement will 
fully meet the position at the present stage, and the further remarks 
which remain to be made will refer to the disease caused by Sphaeros- 
tilbe repens. There is no definite information available relating to 
outbreaks of this disease beyond the fact that they are invariably 
associated with damage caused by the flooding of rubber areas. Most 
investigators agree that outbreaks are dependent on some unknown 
predisposing factor or factors, and of these flooding is apparently the 
chief. Up to date none of the numerous investigations undertaken on 
parasite or host have yielded any information of sufficient value to 
draw a definite conclusion. I am informed, however, by Dr. S. F. 
Ashby, that the association of the Sphaerostilbe disease with flooded 
areas is a noticeable feature in certain areas in the West Indies. 

Atmospheric Agencies. A whole section is devoted to this subject, 
under the heading "Scorching and After-effects'*. The direct effects 
of lightning on rubber plantations, only definitely established over the 
last two years, form the most important item. 

Several observers, including Fetch in Ceylon and Maas in Java, 
have briefly described the varied types of damage caused on coconut 



CHAP, iv EXTERNAL FACTORS AND DISEASES 45 

palms and rubber trees by direct lightning strikes. But there was 
little information available in respect of any crop, until the writer 
proved beyond doubt that lightning was the primary cause of practi- 
cally all apparent disease outbreaks on coconut plantations in Malaya. 
When it was possible to focus attention on Malayan rubber planta- 
tions, the important effects of lightning became more noticeable each 
year as additional experience was gained. The year 1933 was note- 
worthy for the large number of reports of lightning strikes on rubber 
plantations. The most important feature is the close association of 
lightning injury with patch canker at the collar of the tree. Further, 
the species of Diplodia causing "die-back" is always a prominent 
feature whenever scorching of the trees takes place, and there is now 
not much doubt that many of the early reports of branch damage, 
etc., with die -back supervening later, were merely descriptions of 
lightning effects. 

Attention is also directed to scorching effects caused by agencies 
other than lightning, There can be no opposition to the view that in 
cases where the direct effects of atmospheric agencies are obvious, 
the associated fungi must be given a secondary place. 

Meteorological and Soil Factors affecting Stem, Branch and Leaf 
Diseases. The rubber tree diseases which call for attention under 
this heading are (a) pink disease, (6) Oidium leaf-fall, (c) minor leaf 
affections. The Phytophthora leaf-fall as it occurs in Ceylon and 
S. India will also be referred to. 

The early experiences of pink disease in Malaya indicated that 
there was no reason why this disease should not spread throughout 
all the rubber-growing areas in the peninsula. The difficulties of 
accounting for the distribution of the disease was pointed out in 1913, 
and the statement was made that the disease was most abundant in 
the districts of heaviest rainfall and where large tracts of jungle 
remain. The distribution in 1913 is given on page 268, and the position 
is described in the following words: "But it is onlyin certain localities, 
where climatic conditions avourably affect the growth and spread 
of the fungus, that serious attacks occur. ... In Malaya, it might be 
said that all estates where serious attacks of pink disease occur are 
situated in proximity to large jungle reserves." In the writer's opinion, 
this is the most important feature in respect of attacks of pink 
disease, even at the present date. It is still confined to particular 
localities, but these change with time since the causal fungus is 
seldom prominent on areas carrying trees over ten years of age. A 
relatively high humidity will be maintained on young rubber areas 
completely surrounded by jungle because advantageous wind 



46 DISEASES AND PESTS OF THE RUBBER TREE PABT i 

breezes will be prevented from reaching them, and so effective 
ventilation will be prevented. This in itself will make the conditions 
exceptionally favourable for disease-causing fungi, and the cause of 
pink disease evidently finds them very favourable. It is a well-known 
fact that pink disease is of little importance and is seldom seen on 
coastal properties affected by daily variations in land and sea breezes. 
Judging from studies of distribution it cannot be doubted that, when 
serious attacks of pink disease occur, factors outside host plant and 
parasite are mainly responsible. 

The effects of external influences on the Oidium leaf-fall disease 
is dealt with fully in the section devoted to leaf diseases, and the 
results obtained in Malaya over the last few years prove beyond 
doubt that climatic factors play by far the most important part in 
the initiation of serious outbreaks. The same statement applies to 
this disease as it occurs in Java, as indicated by the letter received 
from the Director, Proefstation, West Java. A further point of 
interest is that when serious outbreaks of Oidium leaf- fall are re- 
ported in Malaya, the areas which show the worst affection are those 
where the soil is in poor condition through comparative exhaustion. 
Here again an example is presented of the potent influence exerted 
by unfavourable soil conditions in the successful development of a 
particular disease. 

The Phytophthora leaf-fall reported from Burma, S. India and* 
Ceylon is often referred to as "monsoon" leaf-fall, and the trees begin 
to shed their leaves about a fortnight after the monsoon rains have 
set in steadily. But Fetch records that in 1917 and 1918 the first cases 
of leaf-fall occurred at the end of January, long before the onset of 
the monsoon rains, and that the periods mentioned were characterised 
by abnormal heavy rains in some districts instead of the usual dry 
weather and, as a result, one or two cases of the disease appeared. It 
is apparent that the appearance and continuance of the disease is 
entirely dependent on long- continued heavy rains, and the absence 
of this disease from Malaya can be attributed to the fact that, even 
during the heaviest rain-periods, there are daily bursts of sunshine 
which effectually prevent the development of those fungi which 
spread by means of free-swimming spores, such as species of Phyto- 
phthora and Pythium. If climatic conditions proved suitable, there is 
no reason why rubber areas in Malaya should not suffer from attacks 
of Phytophthora, for Thompson has proved conclusively that there 
are, in Malaya, a considerable number of species, some of which would 
undoubtedly cause a leaf-fall under suitable climatic conditions. 

The only subject of interest remaining for consideration is that 



CHAP, iv EXTERNAL FACTORS AND DISEASES 47 

of the minor leaf affections. These probably form the best examples 
of the effects of unsuitable soil conditions, and it is doubtful whether 
they would be noticed at all if soil conditions were normal. This 
feature is well understood by planters in Malaya and is only men- 
tioned here for the sake of completeness. 

Factors affecting Panel Diseases. There is little necessity to go 
into details respecting the influence of external factors upon the 
fungi causing tapping panel diseases. The following points may be 
stated briefly: 

(a) The operation of tapping results in the development of a tree 
which must be considered as not in normal condition. Neither black 
stripe, brown bast nor mouldy rot diseases would have the slightest 
significance but for the tapping operation. 

(b) Black stripe and patch canker are caused by fungi producing 
free-swimming spores. The effects of daily bursts of sunshine in 
Malaya, upon this type of fungus, has been mentioned above. 

(c) Recent experience with mouldy rot in field experiments has 
proved that the humidity of the atmosphere exercises a profound 
effect on the development of the causal fungus, and this instance 
provides the clearest example for the writer's view that external 
factors can be considered of almost primary importance in most of 
the important rubber tree diseases in Malaya. Development of the 
fungus in the field is severely checked, if not entirely suspended, when 
a short, hot dry period of only forty-eight hours is encountered; at 
least all external signs of the fungus, which are always conspicuous 
under ordinary conditions, may to tally disappear. Taking the reversed 
condition, if the atmospheric humidity in diseased areas is increased, 
as would be the case if a natural cover of a mixture of plants were 
established under mature rubber trees, as is recommended by advo- 
cates of forestry methods, it becomes practically impossible to control 
the spread and development of the fungus. Methods of treatment 
which have proved wholly successful when diseased trees are growing 
under the common methods of cultivation, are useless. 

Before leaving this subject, the various points might be sum- 
marised so that the essential facts clearly emerge. The writer wishes 
to emphasise that the facts demonstrated must not necessarily be 
taken to apply in rubber plantations outside Malaya. They must be 
considered by competent authorities in other countries, and tested 
how far they apply to their own problems, and if climatic and other 
external factors show a considerable degree of similarity there is little 
doubt that the picture displayed in this section will be found worthy 
of careful consideration. 



48 DISEASES AND PESTS OF THE RUBBER TREE PART i 

The following points give shortly the gist of the position: 

(1) Root diseases are entirely dependent on the type of vegetation 
grown previously on the rubber areas. 

(2) All fungi associated with damage brought about by direct 
atmospheric agencies must be classed as of secondary importance. 

(3) The successful initiation and continued development of the 
important leaf and branch diseases is largely dependent on congenial 
outside factors; serious outbreaks of the important leaf-fall diseases 
caused by O. heveae and P. meadii respectively would never occur 
except under special climatic conditions, and in the case of the 
former, unsuitable soil conditions exert a significant influence in 
outbreaks of the disease, just as in the case of the minor leaf affec- 
tions. These would seldom be observed if soil conditions were normal 
and permitted the optimal development of the trees. 

(4) Outbreaks of panel diseases occur only because of the method 
of extracting the latex. Nevertheless, climate has a great influence, 
and if climatic conditions prove unsuitable to the free development 
of the causal fungi, serious outbreaks are seldom observed. In the 
case of the most serious panel disease of rubber trees in Malaya, 
i.e. mouldy rot, the extraordinary rapid disappearance of all the 
external signs of the fungus, when a short burst of sunny, dry weather 
occurs, indicated very clearly that the disease can only assume 
serious proportions during periods when atmospheric humidity is 
high. 

The subject has been dwelt upon at considerable length both here 
and in the preface. It only remains to be said, when undertaking 
investigations on cultivated crops in the tropics, it should never be 
forgotten that it is "the disease as it appears in the field" which is 
the important feature. Once this is fully realised, the importance of 
all factors outside host and parasite will receive the quota of recogni- 
tion which seems so desirable. 

TAPPING SYSTEMS AND PANEL DISEASES 

During the period circa 1910-12, and up to about 1920, which were 
prosperous years for the industry, when the price of rubber was still 
above the $1 per Ib. level, the primary idea which guided the 
industry in the selection of a tapping system was to obtain as much 
latex as possible from the tree; the suggestion that over-extraction 
of latex would predispose the trees to certain diseases naturally 
received very minor consideration. Thus, in 1910, ladder or monkey 
tapping, with several superimposed cuts over half the circumference 



CHAP, iv EXTERNAL FACTORS AND DISEASES 49 

of the tree, was commonly practised. In later years the practice 
became less frequent, and by 1916-17 two superimposed cuts on half 
the circumference was considered the limit; the vertical distance 
between the cuts varied. In the early years the cuts were started 
about a foot apart, but in later years the distance was increased so 
that the cuts were started about two feet apart. About 1917-20 the 
brown-bast scare supervened, and as the fact was gradually driven 
home that brown bast is a physiological affection which is initiated 
and maintained by over-extraction of latex, tapping systems, less 
drastic in operation, had to be considered very seriously. 

It was shown conclusively that, from the disease point of view, 
alternate daily tapping held an advantage over daily tapping. As any 
diminution of output occasioned by the adoption of an alternate 
daily tapping system could be compensated for by increasing the 
length of cut, no profits were lost unnecessarily. Alternate daily 
systems, over one-half or one-third of the circumference, were the 
systems most commonly adopted in Malaya, and these have retained 
their popularity to the present day; it is estimated that 30 per cent 
of the rubber trees in Malaya are still being tapped on an alternate 
daily tapping system. 

About 1922-23, tapping systems, based on a periodical cessation 
of tapping, were being experimented with. One of the first was termed 
the ABC daily tapping system, over one-half the circumference, for 
a period of twelve months; this meant that each block was tapped 
daily for a period of eight months and the trees were then rested 
from tapping for a four-months period. This system did not prevail 
long, for attacks of black stripe and brown bast became common 
after about three months' daily tapping, on estates where panel 
diseases had never been recorded previously. A similar result has 
been obtained experimentally in relation to brown bast, where it has 
been shown that under daily tapping systems bursts of disease 
activity occur at intervals of three to four months. 

Since 1931, tapping systems have been considered from one point 
of view only, that of economy. One system which has been introduced 
recently is known as the alternate monthly; the trees are tapped once 
daily over half the circumference for a month, then tapping is stopped 
for a month. This system undoubtedly encourages the growth and 
persistence of the fungus causing mouldy rot, for estates which have 
adopted this system are now finding mouldy rot more difficult to 
control than was the case formerly. There is sufficient evidence 
available to warrant the statement that, in Malaya, vigorous trees 
are unable to withstand more than three months' continuous daily 

E 



50 DISEASES AND PESTS OF THE RUBBER TREE PART i 

tapping before showing attacks of panel diseases. Generally, it can 
be definitely stated that all daily tapping systems, with a length of 
cut greater than a quarter of the circumference of the tree, predispose 
the latter to the onset of panel diseases. 

Cessation of tapping during treatment of diseased tapping areas is a 
factor of the greatest importance. It is absolutely vital in the case of 
brown-bast treatment, and of fundamental importance in the treat- 
ment of mouldy rot; in Malaya, cessation of tapping is not of such 
great importance in the treatment of black stripe. But a recommenda- 
tion to cease tapping for a longer or shorter period has never been a 
popular one at any time. It is obvious that, during prosperous periods, 
the output should be kept as high as possible in order to augment 
profits, and, therefore, as many trees as possible should be kept in 
tapping. This argument is countered by the fact that it is a foolish 
policy to risk permanent damage to valuable trees by continuous 
tapping while in a diseased condition. During periods of depression, 
the case is somewhat different and the situation cannot adequately 
be met. Since 1931, up to the present date (1933), Asiatic owners 
have been forced to tap their trees daily to obtain supplies of food, 
and the question of disease treatment is pushed into the background; 
indeed, it may be said that the pests and diseases enactment be- 
comes inoperative in Asiatic-owned plantations in Malaya during 
slump periods. On European estates, selective tapping has been 4 
adopted on most estates and only those trees which give an adequate 
flow of latex are tapped. As trees suffering from panel diseases usually 
give a diminished flow of latex, they are automatically left out of the 
tapping round. 

Now that a policy of restriction of output has been inaugurated, 
the cessation of tapping diseased trees becomes a subject of direct 
practical interest. It would be of direct benefit to the industry and 
also to the restriction policy if cessation of the tapping of such trees 
could be made compulsory. The machinery for doing so is already 
established. It is not, however, within the writer's province to pursue 
this matter further, but it may be commended to the authorities 
engaged in carrying forward restriction proposals. 

DISEASE SYMPTOMS IN RUBBER TREES 

The reactions of the rubber tree to attacks of the various diseases 
from which it suffers may be briefly commented upon. The visible 
reactions are generally confined to the stem and crown portions of 
the tree, owing to the fact that the ultimate action of disease- causing 



CHAP, iv EXTERNAL FACTORS AND DISEASES 51 

fungi on the rubber tree is to cause a diminution in the water supply 
to the above-ground portions. When the water supply is reduced 
beyond a certain limit to any particular part of the crown, the leaves 
affected are bound to wither and die. Thus, the direct response to an 
attack of root disease, which causes a reduction in the area of the 
root-absorbing system, is reflected in the crown by the death of the 
leaves and branches. 

The leaf reaction to root attack may be very different, however, 
according to the age of the tree and vigour of the fungus attack. It 
has been shown very clearly, in Malaya, that the two most important 
fungi causing root diseases are both present in the early stages of the 
plantations, i.e. infected plants are to be found when the plants are 
about one and a half to two years of age. The attacks ofFomeslignosus 
are comparatively sudden in onset and in intensity, and it usually 
reaches its apex in the fourth or fifth year; although even in later 
years the disease may still be prominent if the necessary precautions 
have not been observed. Usually, the attack commences to wane 
about the fourth year and the disease should be well under control 
by the sixth year. With Ganodermapseudoferreum, on the other hand, 
though the fungus is present in the original jungle, it gets little 
opportunity to spread from the primary centres until the roots of the 
rubber trees begin to make definite contact, and as its progress is 
definitely slow, it does not become very prominent on rubber planta- 
tions until towards the tenth year. 

While the symptoms of both diseases are primarily caused by the 
reduction in the water supply below a certain level, owing to the roots 
being killed, yet owing to increased tissue development in root, 
branch and leaf systems of the older trees, the response in the crown 
is very different in the two diseases. If we consider the crown of a 
young tree as equivalent to one branch of an older tree, then there 
is no real relative difference. In the young tree attacked by F. lignosus 
the crown of leaves continues to develop until the reduction in the 
amount of water from the roots to the leaves is felt; they suddenly 
wilt and in a few days they turn brown and fall off the tree, leaving 
bare branches. On the other hand, in the disease caused by Ganoderma 
pseudoferreum, the reduction in the amount of water supplied by the 
root system can only take place slowly, owing to the reaction of 
the roots to attack by this fungus. Attacked roots throw out enorm- 
ous numbers of healthy, absorbing, adventitious roots (Fig. 19 a-d). 
Although the fungus usually wins in the end, such an artificial increase 
in the root-absorbing system results in a very slow reduction in the 
water supply to the leaves. Thus, there is a gradual diminution in 



52 DISEASES AND PESTS OF THE RUBBER TREE PAKT i 

the leaf canopy, but the leaves produced at the tips of large branches 
become of smaller dimensions as the years go by, and finally large 
branches may become leafless. Mature trees, showing leaves of less 
than average size and large dead branches on one side of the tree, 
may usually be suspected of being attacked by O. pseudoferreum. 

In general, the above description may be said to apply to all root 
diseases of rubber. The symptoms may be not quite so definite as in 
O. pseudoferreum, and in the case of Sphaerostilbe repens they may be 
obscured by the entrance of boring beetles at the base of the stem. 
Following the comparison made between the crown of a young tree 
and the branch of a mature tree a step further, the symptoms of 
pink disease in advanced cases may be considered as brought about 
by a reduction in the water supply to a localised portion of the crown. 
Die -back disease falls in the same category. In both cases the fungus 
destroys the continuity of the large wood vessels in the periphery of 
the woody cylinder, which are most active in water conduction, and 
so this function cannot be performed efficiently. The leaves and 
woody twigs and branches above the attacked areas are denied a 
sufficient quantity of water for the metabolic processes to continue 
normally, and therefore death ensues. 

In the case of attacks by 0. heveae, the interference with water 
supply is of paramount importance, but in rather a different manner. 
It is generally held that the autumnal fall of leaves from plants grow- 
ing in temperate climates is a response to the reduction in the supply 
of water caused by the change in weather conditions; water absorp- 
tion by roots is greatly reduced by low temperature, and so during 
winter months the quantity of water absorbed is comparatively small 
in amount. The action of 0. heveae on leaves of rubber trees is to 
break up the continuity of the cuticle and epidermis of the leaf so 
that water evaporation, which is controlled by the stomata in the 
epidermis of the leaf, is greatly increased. Owing to the increased 
loss of water through the leaves, the physiological balance between 
the leaves and roots is badly upset and, as a result, the former are 
abstricted in a young, green condition and fall to the ground; in this 
way, excessive loss of water is for the time being avoided. 

In brown bast, the water balance in the cortical tissues is of the 
utmost importance. This disease is now considered to be a physio- 
logical affection brought about wholly, or in the main, by over- 
extraction of latex, the water content of which is about 60 per cent 
under normal tapping systems. When trees are over-tapped, the usual 
result is a percentage decrease in solid constituents and a consequent 
rise in liquid content, so that still higher percentage losses of water 



CHAP, iv EXTERNAL FACTORS AND DISEASES 53 

must take place. It is obvious that if such a situation is allowed to 
develop, the balanced condition of water relationship in the cortical 
regions must be upset, and this loss of balance is reflected in the 
symptoms of brown bast. 

The panel diseases may all be considered from the opposite point 
of view, for as a result of the parasitic activity of the fungi, only 
local areas of bark are affected, and the transport of elaborated food 
materials in these diseased bark areas will be interfered with. Of 
course, in cases of neglect, large areas of bark may be put out of 
action, and the damage done in such circumstances must be serious. 



PART II 
FORM AND FUNCTION 

CHAPTER V 

PLANT FORM 
St/om and Root Structure General Remarks on Loaf Structure. 

STEM AND ROOT STRUCTURE 

FOR the special purpose of this book it is considered desirable to give 
an outline, in the form of a very general account, of the tissues of the 
stem and leaves of a mature tree and to indicate the physiological 
activities with which they are connected. The terms covering Form 
and Function are Morphology and Physiology respectively. 

In order to study the morphology of any part of a plant thin 
sections of tissue have to be cut in certain definite planes. These 
sections are spoken of as: (a) Transverse sections, (b) Longitudinal 
Radial sections, (c) Longitudinal Tangential sections. 

The transverse section is self-explanatory; it is simply a cut made 
in the horizontal plane (Fig. 1). 

The longitudinal radial section is a vertical cut, which is made 
in a plane along a radius of a circular stem from the centre to the 
periphery (Fig. 4). 

The longitudinal tangential section is made in a plane which is a 
tangent of the radial plane and cuts across the radii of a circular 
stem (Fig. 5). 

All planters are aware that the stem of a rubber tree is composed 
of a central cylinder of hard, woody tissue surrounded by a softer 
cylinder of cortical tissue, which is covered externally by the corky 
bark. Between the inner cylinder of hard, woody tissue and the outer 
cylinder of cortical tissue, there is a single cell layer which is con- 
stantly dividing and giving rise to new tissues, both internally to the 
woody ring and externally to the cortical tissues; considerably more 
tissue is cut off internally to form additions to the wood than to the 
outer cortex. The tissues composing the cortical portions can be dis- 
tinguished as being formed of two parts, an inner portion nearest the 



56 DISEASES AND PESTS OF THE RUBBER TREE PART n 

cambial layer, i.e. the inner cortex, and an outer portion which com- 
prises all the tissues between the inner cortex and the outermost bark 
layers, i.e. the outer cortex. The latex containing cells are found in 
the inner cortex, usually very near the cambium. 

The study of Fig. 1 will clearly show the various tissue systems 
mentioned above. This photograph is one of a transverse section of a 
small root, but it can be taken as typical for a section of a stem. Apart 
from certain differences in the actively growing regions and in the 
portions where active absorption of water from the soil is taking 
place, the roots are similar to stems in cell structure. Growth in roots 
is carried forward by active division of cells at their extremities, and 
in this region they are very sensitive and so require protection when 
making progress amongst the soil particles. Protection is provided by 
the development of a covering layer, termed the root-cap. The grow- 
ing points of stems during development do not meet with obstacles 
of similar nature as the growing points of roots, so there is no necessity 
for constant protection by means of a protective covering layer, and 
nothing of the nature of a stem-cap is developed. In the roots, some 
of the epidermal cells, i.e. those of the external layer, in the absorbing 
areas, grow out and form elongated, hair-like growths, which are 
termed root hairs, 1 and these form the actual absorbing organs of the 
root system. The stem is different in structure in this respect because 
its function is not one of absorption. It is only in these two particulars 
that the root and stem structure differ materially. There is a definite 
distinction in the arrangement of the primary groups of wood, known 
as "protoxylem groups", in stem and root, but this feature need not 
be enlarged upon in this book. 

The illustrations show that the various tissue systems are com- 
posed of cell elements, very diverse in character. But the original 
cell-walls of all the individual cells in any tissue system are composed 
of the same material, i.e. cellulose. As growth and development takes 
place various secondary substances are deposited on the original 
cellulose walls, and by this means hard, woody systems, or softer 
cellulosic ones, are brought into being. 

The inner, woody cylinder is composed of varied cell elements, but 
the most important constituents, physiologically, are the large cells 
termed Vessels (Figs. 1, 2 and 3). 

The vessels are long, undivided tubes which are devoid of proto- 
plasm and are therefore dead, their main physiological function being 
the transportation to the leaves, of water and nutrient materials 
absorbed by the roots. It is only the outer, recently formed vessels 

1 See "Root Hairs" in Glossary. 



CHAP. V 



PLANT FORM 



57 



that are functional; a certain time after formation, vessels thicken, 
lose their functional capacity of water conduction and are then 




to 



FIG. 1. Transverse section of small lateral root of H. brasiliensis. 

Note. Extent of woody vascular ring, the most prominent component part being the large water- 
conducting vessels. External ring of large vessels indicates outer limits of vascular ring, which im- 
pinges directly on the cambial ring. (Fig. 2 shows an enlargement of cambial region.) Outside the 
cambium or cambial ring lies the inner and outer cortical layers, together forming the cortex. The 
cortical layers are bounded externally by the epidermis. 

R.W.P. = Rings of wood parenchyma showing as irregular rings in the vascular ring. They appear as 
dark rings because the cells are filled with starch grains. 

M. 11.^ Medullary Rays running radially from outer cortex through inner cortex and cambial ring to 
varying depths in vascular ring. The portions indicated by M.R, show the rays spreading out in the 
outer cortex to assume a fan-shaped appearance, commonly seen in woody plants. 

O.ll.W.V = Outer ring of wood vessels. 

CAM. - Cambium, immediately exterior to O.R.W. V. 

replaced by the vessels developed in the new wood, which is being 
formed continuously during the growing season by the actively 



58 



DISEASES AND PESTS OF THE RUBBER TREE FART n 



dividing cambium, situated between the woody cylinder and the 
cortical tissues. The woody cylinder is characterised by the deposition 
of a substance called lignin on the original, cellulose cell-walls, and 
this substance stains red with a dye named safranin. The technical 
term used for all the woody cells comprising the woody cylinder 
is Xylem. 

The cambium is a single layer of actively dividing cells, upon which 




FlO. 2. Enlargement of portion of transverse section of woody atom of H. 
brasiliensis, showing cambial layer (C.L.), with large wood vessels impinging 
directly on these actively dividing cells internally. The cells which divide off 
externally to the cambium, form parts of the cortex. 

The medullary rays (M.R.) are well shown to be continuous, passing from the cortical areas, through 
the cambial layer, into the woody, vascular cylinder. A single zone of wood parenchyma cells (W.P.) 
is shown, but this does not show up so conspicuously aa those shown in the transverse section of the 
root (Fig. 1), because the individual cells do not contain starch grains in such large numbers, x 120. 

all parts of the plant which undergo increases in girth are dependent 
for expansion (Figs. 2 and 3). 

Apparently, the illustration in Fig. 2 shows more than one layer 
of cells which might be engaged in active division. These appear to 
be four to six layers and, to avoid confusion in the layman's mind, 
these layers of cells form what is termed here, the cambial layer. The 
cambial layer comprises all those cells recently cut off by the single 
layer which is actually dividing. New cells cut off by the cambium are 



CHAP. V 



PLANT FORM 



59 



small, and growth leading to maturity results in the increase in size. 
But until full size is attained, they appear to form part of a definite 
layer composed of cells much smaller than normal fully grown ones, 
and they are arranged in radial rows. This radial arrangement is 
characteristic of all cell systems formed by cambial activity. Cells are 




FIG. 3. Enlargement of portion of transverse section woody tissue of vascular 
cylinder, showing typical appearance, in transverse section, of large water- 
conducting vessels, and zones of wood parenchyma (W.P.). x 120 

cut off by the cambium on the inner side to become wood or xylem 
elements, while cells cut off externally become bast or Phloem 
elements. The walls of the phloem elements, in general, retain their 
original, cellulosic character; as they age, they become thicker as a 
result of the further deposition of cellulose. Cellulose stains blue with 
a dye such as haemotoxylin. 
The most important cell elements in the phloem system are the 



60 DISEASES AND PESTS OF THE RUBBER TREE PABT n 

Sieve Tubes, their main function being to transport food materials 
elaborated in the leaves, downwards to all parts of the plant. The 
transverse walls which divide the length of a sieve tube are of a 
special nature and perforated, and are termed Sieve Plates. The ring 
of wood, plus the cambium and the phloem, form the Vascular 
Cylinder. 

A transverse section through the stem of a plant, one year old, will 
show that the thickness of the cortical tissues outside the cambium, 
i.e. the phloem and the remainder of the cortical tissues, is compara- 
tively small in extent compared with the woody ring or xylem tissue 
developed within the cambial ring. A similar section through the 
stem of a tree ten years of age will show a still larger discrepancy in 
favour of the woody ring. This is accounted for, not only by the fact 
already mentioned that more xylem than phloem elements are formed 
as a result of cambial activity, but also that the cortical tissues are 
being sloughed off continuously as bark. This is brought about by a 
cambium, termed the Phellogen or cork-forming cambium, which is 
laid down in the external cortical layers; division in this layer takes 
place in such a way that the great majority of new cells arising from 
the activity of the phellogen come to lie externally to it, and the walls 
of these cells become impregnated with a substance termed Suberin. 
This is a waterproofing substance and such cells are said to be 
suberised; the waterproof layer formed by the aggregation of these 
corky cells is the true bark. 

Two actively dividing, or meristematic layers have now been 
mentioned, the cambium forming the xylem tissues of the internal 
woody ring and the external cortical tissues, and the cambium form- 
ing the outer, corky, bark layers. There is a distinct difference between 
these two meristematic layers, for the cambium between the cortex 
and the wood is a permanent tissue-forming layer and it persists 
throughout the life of the tree; the cork cambium forming the bark, 
however, is replaced from time to time, after cutting off the external 
layers of cortical cells to form bark, by the formation of additional, 
successive, deeper-seated cambial layers, and these, in turn, cut off 
the tissues external to them. Thus, bark is not formed as a product 
of a single, persistent cambium, but from a succession of meristematic 
layers or cambia, formed at gradually increasing depths in the cortex. 

There is another type of cell, known as Stone-cells, usually developed 
in groups in the cortex. Planters are well aware of the difference 
between hard-barked and soft-barked trees. Normal yielding trees 
are usually characterised by a cortex which is sufficiently soft to 
allow the tapping knife to pass through without difficulty. Hard- 



CHAP. V 



PLANT FORM 



61 



barked trees are not tapped easily, because there is only a com- 
paratively thinly^developed cortical region, which contains a large 
proportion of cells which become thickened by deposits of lignin; in 
other words, they become lignified and form stone-cells. These cell- 
walls are often thickened up so strongly that the lumen of the cells 
are practically obliterated. It will be remembered that lignification 
characterises the formation of woody elements. 

Thus far, in dealing with a woody stem, the upward flow through 
the wood vessels of water and nutrient materials absorbed by the roots 
and the downward flow of elaborated food materials from the leaves, 
through the sieve tubes, has been mentioned. Water and elaborated 
food materials must be transported to all parts of the plant, and 
as the vessels and sieve tubes are located in definite, stationary 
positions, a conducting tissue system, suitably placed for radial 
conduction, seems necessary, if a complete circulatory system is 
to become established. This is provided by a system of cells known 
the Medullary Rays. These pass radially right through the wood, 
starting at varying depths, and through the cambium into the phloem 
elements and the cortical tissues (Figs. 4 and 5). Secondary or new 
medullary rays are constantly 
being laid down by the cam- 
bium as development pro- 
ceeds. 

The above is a very ele- 
mentary and abridged ac- 
count, but sufficient, it is 
hoped, to prove useful to the 
layman in enabling him to 
realise the terms attached to 
the elements forming the 
conducting systems, and the 
fact that these latter form a 
complete circulatory system 
within the plant. The illus- 
trations will be of interest 
to show the typical features 
of plant structure seen in a 
woody stem when sections 
are studied under the micro- 
scope. It should not be as- 
sumed that the circulatory system is in any way comparable to 
that in the animal organisation, where there is a central organ 




DIAGRAM II 

Medullary ray in combined L. Tangential and 
L. Radial section. To amplify Figs. 4 and 5. 



62 



DISEASES AND PESTS OF THE RUBBER TREE PART n 



which forcibly pumps the blood-stream through the largest arteries 
to the tips of the smallest veins. The circulation of water and 
elaborated food materials in plants is dependent entirely on purely 
physical forces, i.e. diffusion, osmosis, etc. This is a very complicated 
field and no point would be usefully served by entering into further 
description or discussion. 

The foregoing remarks apply generally to the great majority of 




w, 



FIG. 4. Longitudinal radial section of stem. 

Showing epidermis (Ep.); outer cortex (O.C.); inner cortex (I.C.); wood (W.); and medullary rays 
(M.R.), running radially from wood to cortex or vice versa. 

Note. The actual line of demarcation between the various tissue systems is not well shown in 
radial sections and the areas indicated must be considered to be merely approximate, x 120. 

woody plants which do not produce latex. In Hevea the latex is found 
in a tubular system, the elongated tubes or Vessels being formed by 
the absorption of the end walls of individual cortical cells; the water- 
conducting vessels in the wood are formed in a similar manner. Unlike 
the latter, they are not dead elements, for the laticiferous vessels 
retain their protoplasmic lining, which proclaims them as living. The 
laticiferous system is an additional development to the normal cell 
systems found in other plants, and it is very doubtful if those which 



CHAP. V 



PLANT FORM 



63 



have acquired a laticiferous system could continue to live without it, 
if it were possible to deprive them of it. The cell elements from which 
the laticiferous vessels in Hevea are formed are cut off by the cambium 
for the special purpose of latex formation in a very similar manner to 
the special cell elements of the cortex which ultimately form part of 
the special conducting systems, such as the sieve tubes and the 




FIG. 5. Longitudinal tangential section of stem, showing typical structure of 
medullary rays, x 120. 

medullary rays. As the differentiation of the laticiferous elements 
takes place rapidly after they are cut off by the cambium, they 
become recognisable as such before they have passed far from the 
cambial region, and this explains why the main seat of the laticiferous 
system of Hevea becomes established in the inner cortical layers 
(Fig. 6). In the early days it was generally stated that the laticiferous 
vessels of Hevea ran more or less vertically up and down the stem, 



64 DISEASES AND PESTS OF THE RUBBER TREE PABT n 

but it is now generally accepted that they are definitely situated at 
a slight inclination to the vertical, running some 5 to 7 to the right 
of the vertical line. 

For our elementary purpose, the plant world may be divided into 
two groups: (a) Laticiferous plants, (b) Non-laticiferous plants. The 
laticiferous plants form only a very small proportion of the great 
plant kingdom. They secrete the white fluid known as latex; this 




FIG. 6. Longitudinal tangential section through inner cortex, showing latex 
containing cells (laticiferous vessels), darkly stained. 

Note. The laticiferous vessels do not show up plainly when the usual cell wall stains arc used, as 
in the preceding figures. A special stain to show up the cell contents of the laticiferous vessels has 
therefore been used in order to bring out the typical appearance of the latex system of H. branliensis. 
It is only the latex which takes up the stain, and the walls of the latex tubes cannot clearly be made 
out in this illustration. 

substance may be contained either in laticiferous cells or laticiferous 
vessels. The method of formation of the latter has already been 
mentioned, and it is a system of laticiferous vessels which is formed 
in H. brasiliensis. Laticiferous cells are non-septate from the com- 
mencement and are formed as the result of the apical growth of 
certain cells which are differentiated in the seed. As the plants 
increase in size, a ramifying, branched latex system is built up by 
the apical growth and branching of the early differentiated, latici- 
ferous cells. Species of Euphorbia show this type of development in 
their laticiferous systems. 



CHAP, v PLANT FORM 65 

It is quite safe to say, whether we consider laticiferous cells or 
vessels, that our ignorance of the functions of the latex system in 
any laticiferous plant is most profound. The latex vessels in Hevea 
are situated in close proximity to both the sieve tubes and the 
medullary rays. The main constituent of the latex vessels is water, 
about 60 per cent by volume under ordinary tapping conditions. 
The following figures give the results of a normal analysis; they may 
be somewhat approximate but will serve the purpose in view: 

Water 

Per cent 
58-62 



llubber (Catouchouc) 


Protein 


Ash 


P.O. 


Per cent 
39-40 


Per cent 
2-2-5 


Per cent 
0-60-0-70 


Per cent 
0-175-0-250 



The high water-content of latex, as extracted from the tree, 
suggests that the laticiferous system of Hevea would act as a water- 
storage reservoir, given suitable conditions. This general view of the 
function of laticiferous systems in plants has been presented by many 
authorities; in support thereof is the fact that numerous plants of 
many different families grow under arid conditions, e.g. desert plants, 
and develop well-defined latex systems. But there is little definite 
knowledge on this complicated subject. Planters will note, however, 
that the extraction of latex includes the withdrawal of large quantities 
of water from the cortical tissues in the neighbourhood of the tapping- 
cut; thus the water relationships around the tapping areas, where 
tapping is in progress, must be very different from those functioning 
in the cortical areas of untapped trees. 

It is unnecessary to pursue this question further, but there is one 
suggestion which has become firmly implanted in the mind of many 
planters, and that is, that the laticiferous system functions as a pro- 
tective layer against insect attacks. The statement has been made on 
many occasions that white ants and boring beetles would not attack 
a healthy rubber tree. A categorical statement can now be made that 
this idea has been exploded, and there is not any semblance of a 
reason left to doubt the fact that white ants can directly attack 
healthy rubber trees. The position, with regard to the penetration 
of the cortical tissue by boring beetles, is substantially the same and 
is dealt with fully in the section dealing with insect pests. 



66 DISEASES AND PESTS OF THE RUBBER TREE PABT n 

GENERAL REMARKS ON LEAF STRUCTURE 

Foliage leaves are very varied in structure, therefore these remarks 
must be confined to a generalised explanation of a common type of 
leaf. 

Leaves usually show a clearly marked difference between the upper 
and lower portions, bounded by the upper and lower epidermis 
respectively. A diagrammatic section of a leaf is given below 
(Diagram III.). 

A foliage leaf is bounded on all sides by a typical epidermis. The 
epidermis is usually formed of a single layer of cells. These cells 




ep 



DIAGRAM III 
Transverse section of a leaf of Fagus sylvatica. 

ep, Epidermis of upper surface; ep", epidermis of under surface; ep'", elongated epidermal cell above 
a vascular bundle; pi, palisade parenchyma; s, collecting cells; sp, spongy parenchyma; k, idioblasts 
with crystals, in k' with crystal aggregate; st, stoma. (x3GO. After Strasburger.) 

secrete a substance known as cutin, and a transparent continuous 
layer, known as the cuticle, is formed as a result of the deposition 
of the cutin. The cuticle covers the aerial parts of the majority of 
herbaceous plants. Cutin is a substance which, chemically, is very 
impervious to water and a remarkably stable body, capable of resist- 
ing the action of various solvents which dissolve ordinary cellulose. 
The leaves have often been referred to as the breathing organs of 
plants. If the respiration of plants (i.e. the exchange of oxygen 
absorbed from the atmosphere and the expiration of carbon dioxide 
(C0 2 )) and breathing are considered equivalent terms, then the com- 
parison is not entirely correct, for all parts of green plants, roots, 
stems, branches and leaves, respire. It will be quite correct to say 
that the leaves are of paramount importance in gaseous exchange 



CHAP, v PLANT FORM 67 

between the plant and the atmosphere; but this exchange includes 
not only the function of respiration, but also that of transpiration, 
i.e. the escape of water vapour from the plant to the atmosphere, 
and the very important function of carbon assimilation, i.e. the 
exchange of C0 2 absorbed from the atmosphere and the expiration 
of oxygen, all of which are conducted entirely through the leaves. 
This gaseous exchange conducted during the function of carbon 
assimilation is the exact converse of that concerned in respiration. 

The leaves are enabled efficiently to perform these important 
phases of gaseous exchange because they possess a special type of 
regulatory mechanism in the shape of Stomata (sing, stoma). The 
stomata are situated in the epidermal layers, more especially on the 
under surface; they may be quite absent from the upper surface of the 
leaves in some plants. The stomata are, in fact, minute openings 
through the epidermis. These openings close automatically under 
certain conditions of light and humidity by the action of two guard 
cells. When the guard cells are turgid, i.e. full of water, the stomata 
stand open, and when turgidity is low in the leaves, the guard cells 
lose water, become less turgid, and the stomata then close and no 
further water vapour can be lost; neither can satisfactory gaseous 
exchange take place through them. The stomata average 100 to 300 
per square millimetre, and in exceptional cases they are as numerous 
as 100 to 700, and may even reach 2000 per square millimetre. 

The stomata are of paramount importance for the efficient regula- 
tion of the gaseous exchange apparatus in plants. They are delicately 
responsive to changes in light intensity, opening wider as light 
increases, contracting as the light wanes. They are in direct com- 
munication with the large intercellular spaces found in the spongy 
parenchyma, i.e. the tissue found immediately above the lower epi- 
dermis of the leaf, and by means of these spaces the gases are distri- 
buted throughout the plant to all living cells. The plant is, in fact, 
riddled with a continuous system of these fine spaces. Even the cells 
farthest from them are distant not more than a few tenths of a 
millimetre from an air passage. This system of intercellular spaces 
provides for the quick diffusion of gases throughout the entire plant. 

The tissue of the leaf-blade between the upper and lower epidermis 
and between the ribs or veins consists mainly of thin walled cells 
known as parenchyma and forms the tissue termed Mesophyll. The 
finer veins are embedded in it. Three different kinds of tissue can be 
differentiated in the mesophyll, as in Diagram III. 

(a) Palisade, parenchyma, underneath the upper epidermis, con- 
sisting of one to three layers of cells elongated at right angles to the 



68 DISEASES AND PESTS OF THE RUBBER TREE PART n 

upper epidermis. They possess abundant chloroplasts which contain 
the green colouring matter known as Chlorophyll and have very 
narrow intercellular spaces between them. 

(b) Spongy parenchyma, immediately above the lower epidermis, 
mentioned above; this layer consists of irregularly shaped cells with 
wide intercellular spaces and less chlorophyll than in the palisade 
tissue. 

(c) The Vascular tissue, comprising the finer veins or vascular 
bundles. 

The cells of the palisade tissue often converge in groups towards 
enlarged collecting cells situated between the upper palisade layers 
and the spongy parenchyma. These cells are sometimes known as 
the border parenchyma and form a sheath around the vascular 
bundles in the veins. The vascular bundles in the leaf- veins corre- 
spond on the whole to those seen in the stem, consisting of xylem, 
cambium and phloem, with the same arrangement of parts. 

As stated above, the roots absorb nutrient materials from the soil, 
in watery solutions. This is transported through the young vessels of 
the xylem to the tips of the finest veins. In the leaves, concentration 
of the nutrient solutions takes place by transpiration. The concen- 
trated nutrient solutions are then elaborated in the leaves into a 
suitable form for conduction and then transported to all parts of the 
plant, the most important route being the passage provided by the 
sieve tubes of the phloem. 



CHAPTER VI 

PLANT FUNCTIONS 

Carbon Assimilation Respiration Transpiration; Water Absorption Chlorophyll 
and Carbon Assimilation Respiration and Liberation of Energy Definition of 
Disease. 

THE important functions in plant life are four in number. They are 
termed: (a) Carbon assimilation; (6) Respiration; (c) Transpiration; 
(d) Water absorption. Carbon assimilation and transpiration are 
carried on entirely by leaf activity; respiration is carried out by all 
parts of the plant, while water absorption, as is well known, is purely 
a function of the roots. 

An endeavour will be made to give a simple outline of the some- 
what complicated vital processes of carbon assimilation and respira- 
tion, phenomena about which misunderstandings may easily arise. 
No special mention of transpiration by the leaves or water absorption 
by the roots is necessary, as there are no phenomena concerned in 
these comparatively simple processes which demand explanation. 
The writer fully appreciates, however, the difficulties of explaining 
the factors governing the ascent of sap in tall trees which are bound 
up with these two latter functions, which are, in themselves, readily 
understood. A few concise remarks on (a), (b) and (c) above will now 
be made. 

CARBON ASSIMILATION 

Carbon assimilation consists of the exchange between carbon di- 
oxide absorbed from the atmosphere and elimination of oxygen. This 
can only take place during the day, because the stomata close during 
periods of darkness and they form the main passage through which 
the exchange is made. 

As a result of carbon assimilation by green plants, organic sub- 
stances (e.g. starch) are manufactured from inorganic substances 
(e.g. carbon dioxide and water). Certain conditions are essential in 
order for the assimilation of carbon from the atmosphere to take place. 
Shortly, these are as follows: 

(1) Light of sufficient intensity is required. 

(2) Chlorophyll is necessary; this is not formed in the absence of 
oxygen. A sufficiently high temperature and a certain amount of iron 

69 



70 DISEASES AND PESTS OF THE RUBBER TREE PART n 

salts in the food are also necessities for the formation of the green 
colouring matter. 

(3) If a sufficiently high temperature is necessary for the formation 
of chlorophyll, this also holds for carbon assimilation. 

(4) Carbon assimilation, and the consequent formation of starch, 
does not go on if the cells are not supplied with potassium salts in 
solution. This can be easily proved by water cultures. 



RESPIRATION 

Respiration consists of the exchange between oxygen absorbed 
from the atmosphere and carbon dioxide liberated by the plant. This 
function is continuous throughout the twenty-four-hour daily period 
and is independent of the opening or closing of the stomata. It may be 
directly compared with the process of breathing in animals. Respira- 
tion takes place even in the roots, and if the free supply of oxygen to 
these organs is interfered with, terrestrial plants die of root suffoca- 
tion. It might be thought that these two opposite processes would 
balance one another; actually, however, carbon assimilation is far 
more rapid than respiration. During the course of a normal day, the 
plant absorbs considerably more carbon dioxide than it liberates and 
there is thus a balance of carbon in favour of the plant which goes to 
increase the weight of the plant body and of the manufactured foods 
stored therein. Further remarks on respiration are given later. 



TRANSPIRATION 

Transpiration consists of the elimination of water vapour from the 
leaves. While the stomata may not be wholly responsible for con- 
trolling the amount of water given off by the plant, yet when they are 
open a greater amount of water vapour would pass through them. It 
may be said that, in the main, stomatal transpiration only, is of 
importance in the typical land plant. It is usual, however, to dis- 
tinguish between stomatal and cuticular transpiration. In some cases, 
when the water supply in the soil is becoming low, continuous tran- 
spiration might become a real danger to the plant, and the ability of 
the plant to retard transpiration under such circumstances would be 
a matter of vital importance. 

Further remarks will be confined to two subjects: viz. (1) Chloro- 
phyll and Carbon Assimilation; (2) Respiration and Liberation of 
Energy. 



CHAP, vi PLANT FUNCTIONS 71 

CHLOROPHYLL AND CARBON ASSIMILATION 

The palisade layers of cells, found immediately underneath the 
upper epidermis, form the main seat of assimilatory activity. The cells 
of this tissue are thickly stored with cell plastids termed chloroplasts, 
which are bodies containing the green colouring matter, chlorophyll. 
The cell plastids and the green chlorophyll are separable, for the green 
colouring matter can be dissolved out from the plastid by alcohol and 
they then appear as before, but devoid of colour. The significance of 
the chlorophyll is that it arrests a part of the energy of the sun and 
transforms it in such a way that the chloroplasts can use it in food 
synthesis. The chloroplast, a specialised, aggregated portion of the cell 
protoplasm, does this work, but to do this it needs to be energised by 
the sun, and apparently this is what the chlorophyll is instrumental 
in bringing about. As it is the sunlight which furnishes the energy for 
food construction, the process is called Photosynthesis. The amount of 
photosynthesis taking place is influenced by the light intensity, and it 
cannot take place in the absence of carbon dioxide. The temperature 
may rise too high or fall too low for the continuation of this function; 
in the higher plants, on account of their waterproof epidermis, photo- 
synthesis must stop when a reduction in water-content in the cells 
of the leaves results in the closure of the stomata, for then the con- 
tinued inflow of carbon dioxide is prevented. 

The first visible food made by the chloroplasts from the carbon 
dioxide of the atmosphere and the nutrient materials absorbed by the 
roots is starch, in the form of minute grains. There is reason to believe 
that sugar is formed before the starch appears and presumably in the 
chloroplasts also, but it is soluble in the cell sap and probably does 
not long remain where it is first formed, but passes by diffusion from 
the chloroplasts into the cell sap that fills the cell cavity and then into 
the tissues devoted to food conduction. 

The main facts regarding the leaf functions may be briefly recapit- 
ulated. The epidermis is transparent and lets light through. The 
chloroplasts in the palisade cells absorb light and use approximately 
4 per cent of its energy in carrying on food synthesis. Light that escapes 
through the palisade parenchyma is arrested so completely by the 
spongy parenchyma tissue that not enough goes through the leaf to be 
useful to other leaves. The intercellular spaces of the spongy paren- 
chyma receive and distribute to all parts of the leaf the carbon dioxide 
that has entered through the lower surface. The border parenchyma 
or collecting cells (Diagram III), which border the veins, deliver 
water from them to the rest of the mesophyll and receive food from 



72 DISEASES AND PESTS OF THE RUBBER TREE PART n 

palisade and spongy cells and, together with the phloem elements of 
the veins, serve to transport it out of the leaf. 



RESPIRATION AND LIBERATION OF ENERGY 

In green plants all the organic substance produced by carbon 
assimilation is not used for purposes of construction and storage; a 
part of it is always broken down and returned to the state of inorganic 
compounds. This process is, in allrespects, exactly similar to that taking 
place in the animal organisation during breathing, i.e. the intake of 
oxygen and expiration of carbon dioxide during respiration. The 
significance of the process does not lie in the substances formed but in 
the liberation of energy which is essential for the life of the plant. By 
respiration, in its typical form, is understood the oxidation of organic 
material to carbon dioxide and water; this involves the absorption of 
oxygen from without. 

Though respiration goes on in every living cell, its intensity varies 
greatly in different organs and under various external conditions. 
Actively growing parts exhibit very active respiration. Among ex- 
ternal conditions which have an important influence on the intensity 
of respiration, the temperature and the amount of oxygen must be 
specially mentioned. An increase in temperature accelerates respira- 
tion as it does all the vital processes. With continued rise of tempera- 
ture, however, the respiration diminishes. 

At first sight respiration appears a contradictory process to carbon 
assimilation, since during the process organic material, which has 
been built up in assimilation, is again broken down. Its meaning only 
becomes evident when, turning from the aspect of changes of sub- 
stances, that of energy is considered. It is not the production of 
carbon dioxide and water which is important, but the liberation of 
energy. This is effected on the breaking-down of such substances as 
carbohydrates, for the construction of which, as has been seen, a 
supply of energy is requisite. On this liberated energy, the plant is 
dependent for the driving force in many of its vital phenomena. 
Movements of protoplasm, growth and movements due to stimuli 
cease on the withdrawal of oxygen from the plant. All these vital 
phenomena begin again on the restoration of a supply of oxygen, if 
this has not been too long delayed. It might have been expected that 
the organisms would possess arrangements by the help of which the 
external energy of light and heat could be employed as driving power. 
Practically, however, it is found that the plant proceeds to store up 
the energy of the sun's rays in the form of potential chemical energy, 



CHAP, vi PLANT FUNCTIONS 73 

e.g. building up of carbohydrates, and then utilises this at need. This 
method has the great advantage that the stored energy can be very 
easily carried to other places in the plant. It can thus reach, for 
example, the roots which grow in the dark and cannot directly trans- 
form light into chemical energy. Further, the stored energy can be 
employed at a time when the sun's energy is not available, e.g. at 
night. 

Thus, a green plant stores energy by the construction of organic 
substances such as carbohydrates formed during assimilation, but at 
the same time organic substances are lost during respiration in order 
to liberate energy which enables the vital processes to function 
normally. Assimilation and respiration are two distinct vital processes 
carried on independently by plants. While in the process of assimilation 
green plants alone, and only in the, light, decompose carbonic acid and give 
off oxygen, all plant organs without exception, both by day and by night, 
take up oxygen and give off carbonic acid. This view, first formulated 
by the famous botanist Sachs, forms the basis of all physiological 
experimental work in plants. En passant, non-technical readers should 
regard carbonic acid and carbon dioxide as equivalent terms. 

At the present stage, an outline only, and that of the barest possible 
kind, has been given of the important conducting conduits, and the 
movements of nutrient solutions and elaborated food materials along 
them. The movements of food materials from one part of a plant to 
another are naturally governed by the vital processes, to which some 
attention has been given. In healthy plants, the formation and 
transport of food materials can only take place in a normal way if the 
vital processes are working in a balanced state; any external factors 
which may have an overwhelming, depressing influence on one par- 
ticular process will upset the natural balance, and from this point of 
view, health in plants may be regarded as a state in which each organ 
performs its own function efficiently and in harmony with all others. 
Disease, in the broadest sense of the word, consists of any departure 
from that state. A condition of disease proceeds from a derangement 
of any physiological function, and in plants this most frequently 
follows upon derangement in structure. 



PART III 
DISEASES AND PESTS 

SECTION 1 
ROOT DISEASES 

CHAPTER VII 

GENERAL 

Systematic Position of the Fungi causing Root Diseases Wounding during Culti- 
vation Operations in Young Rubber Trenching, including Silt Pitting on Hilly 
Estates Low Cover Crops and Bushy Cover Crops susceptible to Fungus 
Attacks, more especially F. lignosus Liming, with special reference to F. 
lignosus Tree Surgery, with special reference to U. zonatdr Root Diseases and 
White Ant Attacks Yields from Trees attacked by Root Disease. 

SYSTEMATIC POSITION OF THE FUNGI CAUSING ROOT DISEASES OF 
HEVEA BBASILIENSIS 

FOR many years the exact systematic position of the fungi causing 
root diseases of rubber trees has been very obscure. Recent work by 
Corner has thrown much light on some points. In the writer's opinion, 
the name attached to a fungus causing a root disease of rubber trees 
is of little interest to the planter, for he considers the name merely 
as a handle, which is convenient to use when the subject happens to 
be under discussion. To the best of the writer's knowledge Table I is 
correct, giving the taxonomic position of the fungi causing diseases of 
roots of rubber trees, with their synonyms. 

A few remarks may help readers to understand the present taxo- 
nomic position more clearly. The fungus causing white-root disease 
was originally recorded as Fomes semitostus by observers in the 
rubber-growing countries of the Middle East, and before 1914 most of 
the literature dealing with this disease referred to the fungus by this 
name. It was then discovered that the original F. semitoslus is quite a 
different fungus. The above information is taken from Petch's 1921 
edition, and he adds that "the correct name of the species which 
causes this rubber root disease is Fomes lignosus". About 1914 Petch 
began to use the name Fomes lignoaus, Klotzsch, and it is by this name 

75 



76 



DISEASES AND PESTS OF THE RUBBER TREE PART in 



that it is now well known to the planting community. In 1923 Van 
Overeem declared that F. lignosus, as we know it, was only one form 
of a very variable fungus of world-wide distribution, and that over 
thirty varieties of the same fungus had received different names from 
different investigators; in other words, he claimed that the fungus had 
over thirty synonyms and had not up to that time been correctly 
named. He therefore proposed the name Rigidoporm microporus, 
Swartz. Van O. This proposal did not simplify the situation and the 



Common Name 



White -Root disease 



Red -Root disease 



Brown -Root disease 



Dry Rot disease 



Stinking Rot disease 
of roots 



TABLE I 



Present Name 



Pomes lignosus, Klotzsch 



Oanoderma pseudoferreum 
(Wakef.), V. O. et St. 



Fomes noxius, Corn. 
Ustulina deusta, Petrak 



Sphaerostilbe repens, 
B. & Br. 



Synonyms 



Fow.es semitostus, Berk. 
Rigidoporus m icroporus , 

Swartz. Van O. 
Polyporus zonalis, Berk. 

and according to Van 

Overeem, thirty -three 

other names. 

Fomes pseud of erreus, 

Wakef. 

Poria hypolateritia, Berk. 
Poria hypobrunnea, 

Fetch 
Trametes theae, Zimm. ' 

Hymenochaetae noxia, 

Berk. 
Fomes lamaoensis, Murr. 

Ustulina zonata (Lev.), 

Sacc. 
Ustulina maxima (Web.), 

von Wettstein 



problem demanded attention from other authorities. Fetch did not 
agree with Van Overeem 's conclusion, and he made a statement, in 
1928, that the fungus known to the rubber planter as F. lignosus is, 
as yet, an unnamed species. He remarks, "I am unable to visit Berlin 
and check this suggestion by inspection of Klotzsch 's type speci- 
men". Later, Weir stated that he has in his own herbarium a portion 
of the original specimen named by Klotzsch, and that in his opinion 
the name Fomes lignosus, Klotzsch, must stand. The writer is prepared 
to accept Weir's finding. 

The position is clearer with regard to Ganoderma pseudoferreum 



CHAP, vii GENERAL 77 

(Wakef.), V. 0. et St. When the disease was first reported in Malaya, 
only young and immature specimens of fructifications could be found. 
For purposes of convenience a name had to be found for the fungus, 
and this could only be done by consulting various works of reference 
dealing with tropical crops. The general symptoms appeared to 
correspond more closely to those described for the disease on Tea 
bushes known as reel-root disease, ascribed to Poria hypolateritia, 
Berk., than to any other known root diease. The disease thus became 
known in Malaya as Poria disease and is still referred to in this way. 
At a later date specimens of the immature fructifications were for- 
warded to Kew for examination by Miss E. M. Wakefield, who, 
although she was averse to supplying a name from such poor material, 
finally acceded to our continued requests and provisionally named 
the fungus Fomes pseudoferreus . This was an excellent determination 
for such unpromising material, although, later, Van Overeem trans- 
ferred the fungus to the Ganoderma section of the Fomes group as 
G. pseudoferreum, and to-day planters commonly speak of the Gano- 
derma disease. 

With regard to brown-root disease caused by Fomes noxius, Corner 
has published the latest information obtained during his recent 
researches. Up till about 1920 the disease was commonly spoken of 
as the Hymenochaetae disease because the causal fungus was con- 
sidered to be Hymenochaetae noxia, Berk. In 1917, Fetch found 
fructifications on jungle stumps, Tea and Hevea killed by brown-root 
disease, which he sent to Lloyd for identification, and this systematic 
worker identified the fungus as Fomes lamaoensis, Murr. After the 
most careful consideration Corner suggests that some confusion had 
arisen, arid points out that two similar, but different, fungi have both 
been included under the same name, which properly spelt, should be 
Fomes lamaensis (Murr.), Sacc. et Trott., and not Fomes lamaoensis, 
Murr. The fungus which is rightly named F. lamaensis is a harmless 
saprophyte; the other is a facultative parasite and is the true cause of 
brown-root disease of Hevea brasiliensis . This latter fungus is desig- 
nated by Corner as Fomes noxius, n.s. 

For the disease known as "Dry -Rot", the common name used for 
the causal fungus by planters, even at the present date, is Ustulina 
zonata. In 1924 Van Overeem brought forward strong evidence to 
show that Ustulina vulgaris, Tul., and Ustulina zonata (Lev.), Sacc., 
which hitherto had been considered to be two distinct species, were 
one and the same fungus. Ustulina vulgaris is known to occur all over 
the world and is a genuine cosmopolitan fungus, while U. zonata is 
only known to occur in tropical Asia (India, Ceylon, Malay Archi- 



78 DISEASES AND PESTS OF THE KUBBER TREE PABT in 

pelago). He suggests that these fungi should be referred to one species, 
to be known as Ustulina maxima (Web.), Von Wett. Fetch agrees 
that U. vulgaris and U. zonata are identical with each other, but 
points out that the name Ustulina deusta was suggested for the 
combination by Petrak^ in 1921; therefore the name should be Ustulina 
deusta, Petrak. This may be correct from the systematic point of 
view, but as the name of U. zonata is so well established among 
laymen, the writer feels there is sufficient justification for its con- 
tinued use. 

Referring to G. pseudoferreum, Corner remarks that this species 
comes very close to Ganoderma applanatum (Pers.), Pat., of which it 
may prove a variety. This is a very widespread and variable species. 
Further, Petch has shown that Van Overeem's citation of Poria 
hypobrunnea, Petch, Poria hypolateritia, Berk., and Trametes theae, 
Zimm., as synonyms for G. pseudoferreum, is false. 

The only fungus causing a root disease on rubber trees which has 
escaped adventures at the hands of the systematists is Sphaerostilbe 
repens, B. & Br. 

When comparing the above list with that given by Petch in 1921, 
it will be noted that he records red-root disease on rubber trees as 
being caused by Poria hypobrunnea, Petch. This record has never 
been made in Malaya and it is apt to lead to some confusion in this 
country, since the disease caused by G. pseudoferreum is now commonly 
referred to as red-root disease. It can be taken for granted, however, 
that G. pseudoferreum is the true and only cause of the typical red- 
root disease of H. brasiliensis found in Malaya. 

For various reasons, the writer is not following the same order of 
presentation of the individual root diseases as that adopted by Petch 
and Steinmann. It is most important that white-root, red-root and 
brown-root diseases should be treated as a closely connected group 
rather than to consider them as individual diseases of the type repre- 
sented by Ustulina zonata and Sphaerostilbe repens. The earlier 
description of these two individual diseases will also make for better 
continuity. To avoid misunderstanding, it should be understood that 
the above remarks apply more especially to Malaya and not to 
Ceylon, for in the absence of G. pseudoferreum from that country, it 
is difficult to gauge accurately the true position. 

The question of descriptive names such as white-root, red-root and 
brown-root diseases, has often been commented upon, usually ad- 
versely. While admitting the possibility of confusion arising, a forcible 
presentation to the layman of the main diagnostic symptoms of a 
particular disease, more especially if they are easily discernible, is 



CJHAP. vn GENERAL 79 

surely of the greatest value. It has been stated that wet -root rot is 
a misleading name for the disease caused byG.pseudoferreum, because 
F. lignosus may also on occasions cause a wet-rot in rubber roots. 
But the disease -situation in a permanent crop, during any particular 
period, may change as the seasons of the year show varying climatic 
conditions. The writer differs from other workers, who consider the 
term wet-root rot an unsuitable one. In the year 1916 a more suitable 
common name for the disease caused by Ganoderma pseudoferreum, as 
seen then only on trees approaching ten years of age, could not have 
been chosen. It is only recently, in 1931, since the discovery of young 
trees attacked by G. p8eudoferreum y that any definite reason for a 
change could be advanced. Steinmann remarks that the name wet- 
root rot was an injudicious choice for the G. psendoferreum disease, 
but the argument can be advanced that it would be extremely 
useful to planters to know that, in the majority of cases, trees 
approaching ten years or over, which show a wet-rot disintegration 
of the root tissues, are attacked by G. pseudoferreum. As Fetch, 
however, has attached the descriptive term of red-root disease to an 
affection caused by an entirely different fungus, it seems that con- 
fusion would be apt to arise whatever choice is made. But there is 
reason for changing the descriptive name in Malaya, from wet-root 
rot to red-root rot, because white-root rot and brown-root rot are 
names definitely established there and the change of name emphasises 
the close relationship of the three diseases, all caused by fungi of 
the Fomes type. 

When dealing with the general question of root disease on rubber 
plantations, there are several minor, though none the less practical, 
issues which have to be considered in relation to the main problems. 
Questions are often asked such as whether a thick growth of a cover 
crop in the early stages of a plantation will influence the spread of 
F. lignosus', and whether the cultivation operations such as weeding 
and forking, turning in of cover, etc., which might have to be under- 
taken to keep the cover in order, will result in extra wounding, thus 
giving the fungus an easier method of entry into the roots? Indirect 
factors such as these, which have been considered to influence the 
spread and control of the various root diseases, may be profitably 
dealt with at this point. If this is done, readers will be aware what to 
expect when the individual diseases are dealt with in detail. 

The following items call for mention: 

(a) Wounding during cultivation operations in young rubber. 

(b) Trenching. Also silt pitting, more especially on hilly land. 



80 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

(c) Low cover crops and bushy cover crops susceptible to attacks 
by fungi causing root diseases on rubber trees, more especially F. 
lignosus. 

(d) Liming, with special reference to F. lignosus, but also to all root 
diseases of rubber trees in Malaya. 

(e) Tree surgery, with special reference to treatment of old mature 
trees which have been badly diseased by U. zonata for a considerable 
time. 

(/) Root diseases and white-ant attacks. 

(g) Yields from trees attacked by root disease. 

Before taking up these issues individually, some remarks on the type 
of root system developed in Malayan soils by Hevea brasiliensis would 
be to the point. In suitable soils with a deep water-level, the tree 
produces a long tap-root which grows straight downwards through the 
soil to a depth of several feet. In low-lying ground, where the water- 
level is not more than two feet deep, as in practically all the coastal 
areas where rubber has been planted in Malaya, the tap-root does not 
grow below the water-level and a squat, rather rounded, terminal 
protuberance is formed. In such cases it is not difficult to under- 
stand that the lateral root system will be wholly confined to the upper 
two feet of soil. But even in areas of good soil, where the tap-root may 
grow to a depth of many feet, the majority of the large lateral roots, 
comprising most of the root system, are also found in the upper two 
feet of soil. This is of considerable importance in the treatment of root 
diseases; since, if treatment, for instance, by chemicals or manures is 
indicated, they can be applied with some assurance that they will 
reach the place intended. Trenches can also be dug with confidence, so 
that they will efficiently separate diseased from healthy trees. 

Since new areas have been opened up in the last few years for the 
purpose of developing high -yielding strains of rubber trees, the prac- 
tice of planting cover crops to prevent soil erosion and to provide 
soil shade, has been more carefully followed than in the past, during 
which period a policy of clean weeding has been very popular. There 
is no doubt that the young rubber plants are given better conditions 
of growth generally when a cover crop is grown successfully, but there 
is a certain disadvantage to be noted. The cover plants enter into 
competition for food with the young rubber plants, and the latter 
undoubtedly suffer retardation in growth as judged by the recorded 
increase in girth. This defect might be removed if the cover plants 
were turned in and incorporated in the soil. This operation is seldom 
carried out in Malaya, for it is expensive, and it is generally held that 



CHAP, vii GENERAL 81 

in view of the excessive rate of decomposition of green matter in 
tropical soils, there is but slight formation of humus and it is doubtful 
if much would be gained by this form of cultivation. The present 
practice in Malaya is merely to "ring weed" and keep the soil clear 
round each tree, in a circle of about 2-3 feet radius. A leguminous, 
low-growing cover plant is usually planted in Malaya. Bushy covers 
have never found favour as they have in Ceylon, where they are very 
popular, more especially in cultivations other than rubber. The book 
which should be consulted by planters for information on low or 
bushy ground covers is A Manual of Green Manuring (Dept. of Agri- 
culture, Ceylon, 1931). 

It has been the practice in former years, and will probably continue 
to be so, to set more plants per acre than is actually necessary and, at 
a later date, any superabundance can be removed. Mention of this 
will be made later. This procedure is undertaken chiefly to prevent 
too large a loss of stand from disease attacks. It is between the plant- 
ing and thinning-out periods that cultivation methods of various 
kinds have been put into operation, and it is quite possible that a 
significant amount of wounding has been done to the collar and root 
systems by the implements used. The writer believes that such 
injuries can be ignored in connection with diseases in rubber trees 
growing in suitable situations. It must be mentioned, however, that 
the fact of Ustulina zonata functioning as a wound parasite has been 
fully established. 

Readers will realise that in a book fundamentally devoted to 
diseases of the rubber tree, side issues such as establishing cover crops, 
cultivation operations, silt pitting, etc., can only be treated in a 
somewhat cursory manner, as limitations of space prevent a compre- 
hensive treatment. Only brief mention will therefore be made of 
the actual methods used and the objects which planters have 
in view. The items enumerated above will now be dealt with in 
their direct relationship to spread and control of root diseases of 
rubber trees. 

WOUNDING IN YOUNG RUBBER DURING CULTIVATION OPERATIONS 

Previous investigators have generally been inclined to believe that 
any wounds made on the young roots, or in the vicinity of the collar, 
would adversely affect the trees, in that they would become more 
prone to root diseases, presumably because they would be much more 
easily attacked by the various fungi concerned. Apart from the fact 
that H . brasiliensis possesses an exceedingly efficient repair mechan- 

G 



82 DISEASES AND PESTS OF THE RUBBER TREE PART in 

ism, which has been but recently recognised by the researches of 
the writer and Gunnery, it is now the firm opinion that the Fomes 
group of diseases are not favoured in the slightest degree by wounding 
of the roots or collar, for these fungi make a direct entry into roots 
without extraneous aid. Root-wounding can therefore be largely 
discounted as a source of trouble in the most important root 
diseases. 

Only two root diseases now remain to be considered in this connec- 
tion: those caused by Sphaerostilbe repens and Ustulina zonata. We 
have very little definite knowledge concerning the factors which 
influence the fungus in its entry into the plant in the case of S. repens, 
and the root disease caused by this fungus can be thus dismissed. 
This leaves but one disease (U. zonata) of importance for considera- 
tion, and in this also there is still much to be learned. This fungus is 
a wound parasite, not only in roots, but also in stems and branches. 
Collar infections, however, are the commonest type of the disease, 
but in these cases wounds made during cultivation operations with 
cover crops in the early stages of the plantations can have but little 
influence. The main factor influencing the increase in number of cases 
of collar disease caused by U. zonata is stated later when dealing with 
the fungus in detail. 

TRENCHING: ALSO SILT PITTING ON HILLY LAND 

Trenching has been generally recommended for treatment of root 
diseases on rubber plantations, and they were supposed to be pre- 
eminently useful in the control of Fomes lignosus in young rubber. 
Trenches for isolating disease patches are usually recommended to be 
dug two feet deep, and not less than nine inches wide. The type of 
soil may cause some modification of these figures, but the depth is the 
important unit, and this should not be less than two feet. 

Napper has recently shown clearly that isolation trenches are quite 
useless in the control of attacks of Fomes lignosus in areas of young 
rubber in Malaya. In fact, there is no reason at all for trenching for 
this disease, if a systematic root-disease inspection is periodically 
carried out, as will be explained later. 

A system of trenching can be recommended for treatment of areas 
affected by Oanoderma pseudoferreum when the diseased rubber trees 
are from ten to twenty years of age. The usual geometrical form of 
trenching will have to be abandoned, for the position of diseased 
groups of trees will, as detailed later, determine the size and configura- 
tion of the trenches. In the case of other root diseases, the most 



CHAP, vii GENERAL 83 

important matter is to get the soil free from all diseased material, and 
in order to accomplish this, a trench which includes the whole of the 
diseased area may prove to be of some utility. 

Silt pitting may be dealt with here. Silt pits are discontinuous 
trenches, made much wider than the ordinary trenches dug during 
disease control work. They are dug about 2 feet deep, 2 feet 6 inches 
wide, and are made usually about 6 to 8 feet long, running along the 
contours of hilly land. They are placed in a suitable position so that 
all the suspended soil which is washed downwards during storms is 
caught, and loss of the important top soil is thus prevented to a large 
extent. Silt pits are made much wider than disease trenches so that 
soil erosion can be prevented successfully. 

When a system of silt pits is installed in mature rubber there is 
often a marked increase in the number of cases of Ustulina zonata, 
owing to the cutting of large lateral roots, which are left untreated 
or treated carelessly. All roots cut during silt pitting operations should 
have their ends trimmed straight, and the exposed tissues should then 
be dressed by a reliable wound cover. This will prevent any spread 
and increase in number of cases of U. zonata. 

In addition to their useful function on hill land, silt pits help to 
improve soil aeration in most types of Malayan soils. On hilly land, 
the capacity of the silt pits should be sufficient to retain the heaviest 
rainfall during any period. One of the most important features in 
mature rubber, where attention has been definitely given to keeping 
the silt pits in good condition, is the possibility of utilising these in a 
trenching scheme when trees attacked by Ganoderma pseudoferreum 
are found. Of course, expert advice would have to be sought, but the 
method has been tried out successfully. 

Low COVER CROPS AND BUSHY COVER CROPS, SUSCEPTIBLE TO 
ATTACKS BY FUNGI CAUSING ROOT DISEASES ON RUBBER TREES, 
MORE ESPECIALLY F. LIGNOSUS 

In a later section, considerable attention is given to the desira- 
bility of maintaining soil conditions in a state suitable for the growth 
and development of the rubber tree to full maturity, i.e. to as great 
an age as possible. It must be admitted that soil shading and preven- 
tion of soil erosion is eminently desirable if the natural life of a rubber 
tree is to be prolonged to obtain the fullest economic utility. In 
Malaya these desiderata are usually provided in young areas by 
establishing a light-loving, low-growing, leguminous cover crop. As 
the rubber tree grows to maturity, more and more shade is thrown 



84 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

on the ground, so that the light-loving, low cover naturally dis- 
appears, for the intensity of the light is decreased enormously under 
normally developed, mature rubber trees, as compared with the 
amount of light available for cover crops in the first to the fourth 
years. Concurrently, soil shade is provided which will keep the soil 
at a normal temperature. 

But, under the circumstances, there seems to be no adequate 
provision for preventing soil erosion, and as the trees make more 
demands on the soil as they grow larger, every possible advantage 
should be taken of increasing the humus content of the soil, so as 
to make it a more suitable medium for plants which are possibly 
exacting in so far that they may require large amounts of food 
material. Shade prevents the adoption of the methods used in the 
early stages when plenty of light is available, and only shade-loving 
plants can be utilised as a cover crop under mature trees. Up to date, 
only shade plants growing under natural conditions have been found 
suitable, and those which maintain a succulent habit, without becom- 
ing definitely woody, are chosen for development and multiplication. 
The development of natural growths as cover plants under mature 
rubber has led to the exploitation of similar ideas in young rubber 
areas, and cover crops, consisting of plants which appear naturally, 
have been successfully established in a few areas in Malaya. 

It can be stated at once that some low-lying and bushy leguminous 
covers are subject to attacks by Fames lignosus (Fig. 7). 

Details need not be given here, and it will be sufficient to remark 
that the conditions under which cover crops might be expected to 
promote root disease are found on areas where Fomes lignosus is 
abundant, and then only when the cover, natural or leguminous, 
develops into a thick, impenetrable mat. The word in italics should 
be noted especially, for Napper, as a result of his recent researches, 
says: "It is probable that the disease [on rubber trees] in a young 
clearing is less under a cover crop than in clean weeded areas". This 
statement can be taken to apply generally, for wherever cover crops, 
of whatever type, susceptible to F. lignosus are established, they exert 
a kind of "baffle" action and retard the rapidity of spread of the 
fungus amongst the rubber trees, although the actual amount of 
viable mycelium may possibly be considerably greater. So it appears 
that while a knowledge of this effect may be useful in so far that 
attention to the activities of the fungus might be deferred as long 
as the rubber trees themselves are not affected, yet if the fungus 
appears on the roots of the rubber trees more time and trouble must 
be spent finally. During a period when money is difficult, any policy 



CHAP, vii GENERAL 85 

which defers expenditure is helpful, but not always to the ultimate 
advantage of the people interested. 

The question of root diseases in mature areas under a thick natural 
cover brings up again the subject of the latter exerting a "baffle" 
action and retarding the spread of the more important root diseases, 
more especially that caused by Ganoderma pseudoferreum. This ques- 
tion is a recent development and some comment is necessary since 
claims have been made that immune strains of rubber trees may be 




FIG. 7. Showing rhizomorphs of F. lignosus growing and ramifying amongst 
leaves and debris in the plantation. 

developed if they are grown for a sufficiently long period on soil areas 
permeated with G. pseudoferreum. It may be said at once that there 
is no evidence to indicate the possibility of immune strains of H. 
brasiliensis developing under any set of growth conditions. It seems 
more probable at the present time that favourable conditions for 
rubber trees are just as likely favourably to affect the various disease- 
causing fungi. There is one case known where, if there is not careful 
supervision, a fungus disease will definitely act as a limiting factor on 
mature rubber growing under the more favourable conditions pre- 
sumably provided by a dense natural cover. 



86 DISEASES AND PESTS OF THE RUBBER TREE PART in 

APPLICATION OF LIME, WITH SPECIAL BEFEBENOE TO CONTBOL 
OF F. LIGNOSTJS 

It is commonly held amongst a large number of planters that 
liming should be undertaken for the purpose of controlling outbreaks 
of root disease. Fetch, in his 1921 edition, recommended the use of 
lime, because the majority of fungi prefer an acid medium. It was 
therefore held that by rendering a soil more alkaline, the fungi causing 
root diseases on rubber trees would suffer a definite check. Bryce, in 
1922, showed that this view could not be supported in the case of 
Fames lignosus in Ceylon, and work carried out in Malaya has con- 
firmed his conclusion. Nothing will be gained by liming the soil on 
diseased areas, but there may be special circumstances in which 
lime may be used profitably, as in badly drained areas where the trees 
are sickly and offer little resistance to the heavy attacks which often 
develop in such localities, in spite of the depressing effect on the 
fungus of the sourness of the soil. Under these conditions it is probable 
that the beneficial effect of liming (combined with adequate draining) 
upon the growth of the host plants, will outweigh any detrimental 
effect which may follow the concurrent increase in the activity of 
the parasite in the soil. For these reasons it is suggested that the 
application of lime to the soil may be of utility when dealing with 
localised areas, which have carried trees suffering from the diseases 
caused by Sphaerostilbe repens and Ustulina zonata for a considerable 
length of time. The above must not be considered a general recom- 
mendation, but if advice can be obtained on the point, it is worth 
while enquiring whether lime would or would not be beneficial. 

TBEE STJBGEBY, WITH SPECIAL BEFEBENCE TO THE TBEATMENT OF 
OLD MATUBE TBEES WHICH HAVE BECOME BADLY DISEASED AT 
THE COLLAB BY ATTACKS OF USTULINA ZONATA 

This subject has received more attention in Ceylon than in Malaya. 
The writer's views will be given when the control of the fungus is 
being discussed. In Malayan rubber plantations, tree surgery methods 
could not be adopted with any degree of success except for filling 
large holes caused by breaking of large branches, which afterwards 
become infected by U. zonata, or for filling cavities caused by hacking 
away diseased tissue at the collar, caused by U. zonata. From an 
economic point of view there seems little to recommend the adoption 
of tree surgery in Malaya, but some readers may be interested, so a 
short extract from Fetch is given: 



CHAP, vii GENERAL 87 

The idea of filling tree cavities is not a new one, but it is only com- 
paratively recently that methods have been adopted which are likely to 
prove successful. Stopping tree cavities is analogous to dentistry, and two 
cardinal principles must be observed, viz. all decayed tissue must be cut 
away, and the filling must completely fill the hole, so that water cannot 
lodge behind it or fungus spores and insects obtain an entrance. 

It is doubtful whether this method can be advantageously applied, in 
the case of Hevea, to large cavities in the upper parts of the tree. The wood 
of Hevea is brittle, and the excision of all the decayed tissue would prob- 
ably weaken the stem to such an extent that it would break off. On the 
other hand, if such cavities are not treated, the stem will ultimately break 
off owing to the progress of the decay. In this respect prevention is better 
than cure; and more attention should be given to correct pruning and 
periodic tarring of wounds. 

Cavities at the base of the tree, however, could safely be treated. All the 
diseased wood must be cut out (this is easier said than accomplished); 
otherwise the fungi will continue to destroy the wood behind the filling. 
Successful treatment depends chiefly on the thoroughness with which the 
diseased wood is removed. It should then be painted with a coat of white 
lead paint and afterwards be filled solid. Creosote or Brunolinum, etc., 
followed by a coat of tar may be used instead of white lead paint. (In 
Malaya, a solution of Solignum has proved to be one of the most useful 
wound covers for this purpose.) 

Various mixtures are used for the filling. Bricks, stones, and cement is 
the most usual, the cement being mixed with two parts of fine sand. 
There should be no spaces left between the filling and the wood, and the 
outer face of the filling must be finished off smooth with the cement. The 
bricks and stones merely add bulk to the material; the lining next the 
wood should be cement, and the bricks, stones, etc. embedded in the middle 
of the cavity. After the filling has set it is left for a day or two, and then 
covered with coal tar to prevent cracking. The filling must not be brought 
level with the outer bark of the tree. What is desired is that the callus 
from the edges of the wound should grow over the cement, and either cover 
it completely or at least cover it at the edges so that it holds it in position. 
Hence the filling should only be brought to the level of the cambium. 

In the case of cavities in branches in which rain water collects, care 
must be taken to see that they are quite dry before filling is attempted. 
If they are very deep, an auger hole should be bored into the branch to 
reach the base of the cavity so that any Water will drain out. 

On branches which are liable to bend and sway in the wind, a cement 
filling may crack and fall out. In such situations a mixture of asphalt and 
sawdust is used, in the proportion of one part of asphalt to four parts of 
dry sawdust. The sawdust should be from hard wood. The mixture is 
prepared by stirring the sawdust into boiling asphalt, and it is applied 
before it has cooled. 

The writer has little confidence in the suggested methods for use 
on Malayan plantations. There are great practical difficulties attend- 



88 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

ant upon clearing away all the diseased tissue, and this is sufficient 
to make anyone, well acquainted with the conditions, hesitate before 
recommending such a course of treatment. 

If further details are required, the report by Stoughton-Harris, 
which is given in the table of literature, should be consulted. 

ROOT DISEASE CAUSED BY FUNGI AND WHITE ANT ATTACKS 

This will be dealt with under the section dealing with white 
ant attacks, but a brief reference may be made here. Most entomo- 
logical workers have referred to the subject and their opinion 
has usually been that white ants never or very rarely attacked a 
healthy rubber tree. There was general agreement that they were 
often found associated with the root diseases caused by Fome# lignosus 
and Ustulina zonata, but it was usually held that the fungus had made 
the prior attack. During the last two years, researches in Malaya 
have proved undoubtedly that these insects will attack a healthy, 
un wounded rubber tree, and will kill it in a very short space of time. 
There is therefore no reason for any further misconception on this 
point. 

YIELDS FROM TKEES ATTACKED BY ROOT DISEASE 

Fetch states that the effect of root disease on the yield of latex (in 
Ceylon) is highly variable. In Malaya, the general opinion is 'that 
trees suffering from root disease are usually, until a large proportion 
of the root system is definitely put out of action by the parasite, 
exceptionally good yielding trees. It is a common saying that all the 
trees which have been in tapping for any length of time and which 
happen to be the ones first found suffering from an attack of red-root 
disease, are the good yielding trees. There is a very good reason why 
this should be so, as will be explained later. 

The position in respect of other root diseases is not so clear. Forties 
lignosus can be ruled out of court in Malaya because the main attack 
should be under control, if no't wholly wiped out, before the trees are 
opened up for tapping. Fomes noxius is of small account, but attacks 
of Ustulina zonata and Sphaernostilbe repens are often found on trees 
yielding well above the average. The writer has vivid recollections of 
one of the first fields of eighteen-years-old rubber, which was giving 
the high yield of nearly 1000 Ibs. per acre per annum, and had done so 
over a period of five years. About 1916-17, S. repens became very 
prominent in this field and, in conjunction with a boring beetle 
attack, practically wiped out every tree. 



CHAP, vn GENERAL 89 

The various sections following and included under Root Diseases 
will be self-explanatory and will not present any complications, 
excepting the concluding one. This section is devoted to the question 
of replacing areas of mature rubber, which have become uneconomic 
units at the present date. The question has become prominent, since 
it has been largely accepted that greatly increased yields may be 
obtained from old rubber areas if good, cultivable soil is planted up 
with good stocks of rubber plants, on to which individuals of those 
clones which have been proved to possess all the desirable qualities 
are bud-grafted. The common terms used for replacement of old areas 
are rejuvenation and replanting. This subject has been dealt with by 
Taylor, in so far as it is a problem facing rubber plantations in Ceylon. 
As the section on root diseases is studied by readers, it will become 
increasingly evident that there are many features in Ceylon and 
Malaya which are essentially different. In Malaya, this particular 
problem arises fundamentally from the fact that groups of trees 
become diseased by root contact when they have reached fifteen to 
twenty years of age, and replacement in such areas can be done only 
by undertaking replanting. In Ceylon, Taylor draws attention to the 
possibility of rejuvenating areas of old rubber trees by allowing good 
yielding trees to remain in situ while tapping is continued on these 
trees. Poor yielding trees in these areas, giving below 10 Ibs. per tree 
per annum, which amount is considered to be the economic yield, 
should be replaced by bud-grafted individuals, which have been 
proved capable of yielding 10 Ibs. per tree in their first year of 
tapping. Taylor's views for Ceylon focus the problem largely as an 
agricultural one, and perhaps for this reason the subject should not 
be included in a section devoted to root diseases. But the writer feels 
impelled to include the subject in this section rather than to defer it 
to a later stage, because in Malaya the question is so absolutely de- 
pendent on the root disease problem, more particularly in connection 
with the disease caused by Ganoderma pseudoferreum, a disease which 
has not yet been reported from Ceylon. The position in Java is similar 
to that in Malaya. 



CHAPTER VIII 

USTULINA ZONATA SPHABROSTILBE REPENS 
USTULINA ZONATA, LEV. SACC. 

IN Malaya the disease caused by this fungus is found on old rubber 
areas in every part of the peninsula. It has been recorded attacking 
Hevea in Java, Fiji and Ceylon. In the latter country, it has been 
known for many years as the cause of the commonest root disease on 
Tea. 

The disease has not shown up prominently on young trees, though 
occasional attacks on trees not more than two to three years of age 
have been recorded. It is seen in its several forms in mature areas 
over twenty years of age, but is commonly found in trees not more 
than ten years old. This fungus, in conjunction with Ganoderma 
pseudoferreum, has been the main factor in destroying the economic 
efficiency of the older stands of rubber, but in this respect 0. pseudo- 
ferreum stands pre-eminent. 

The disease is usually discovered on old trees as a "collar rot". On 
one side of the stem a hollow at the base may be formed due to the 
rotting tissue disintegrating under the influence of the weather and 
falling away. If a cut is made below the surface at such a point, it 
will be found that the rotting tissue has spread to a distance of three 
to four feet above ground-level. It is seldom that the fungus gains a 
greater height than this, for by this time most of the tissues at the 
base of the stem will have become involved, with a consequent restric- 
tion in the amount of water supplied from the roots. One case 
examined in 1916 showed the fungus travelling from the collar up 
through the heart wood of the stem into the lower branches, some 
twelve feet high. This infection might have been a double one: (a) a 
branch infection travelling down the stem, and (6) a collar infection 
travelling upwards, with the two infections eventually joining up. If 
an attacked root system is examined, it will be found that the tap- 
root and some of the larger laterals are involved, and as a result water 
conduction will be stopped along these roots and the crown of the 
tree must suffer, gradually going out of commission. 

The characteristic symptom of the disease is the ' 'Dry-Rot " set 
up in the attacked tissues. In some cases, conspicuous black lines can 

90 



CHAP, via 



UCTUL1NA ZONATA 



91 



be seen on the outer surface of the wood; if the lines are followed care- 
fully, it will be found that they form thin black plates running through 
the internal tissues of the woody stem, their edges showing as black 
lines on the exterior (Fig. 8). 
A longitudinal section taken 
through the collar of a diseased 
tree shows these black lines 
running irregularly in the rot- 
ting tissues, often forming 
circles surrounding dark- 
coloured patches of diseased 
wood. The black lines are com- 
posed of aggregated fungus 
tissue, formed by the massing 
of hyaline hyphae; this mass- 
ing always commences in the 
medullary ray cells. Tracts of 
connecting cells between the 
rays later become filled with 
similar tissue and a continu- 
ous line is formed. What 
appears to be carbonaceous 
material is deposited in the 
infested cells after the aggre- 
gation therein of the fungus 
hyphae, and as time passes it 
is difficult to detect the exact 
origin of the lines. The cells 
bordering the black lines 
are crowded with hyaline 
hyphae. 

Such aggregations of fungus 
hyphae might be considered 
rhizomorphs, but as they are 
strictly confined to the 
diseased tissue they have not 
the power of growing freely 

along the exterior of the root and so cannot effectively function 
as organs for vegetative spread in area. But they retain their 
vitality for considerable periods and if portions of diseased wood, 
containing black lines, become scattered about in the soil, there 
is a definite chance that roots of healthy trees, which come into 




FIG. 8. Wood of diseased root exposed, 
showing typical appearance of "black 
lines" of U. zonata. 



92 DISEASES AND PESTS OF THE RUBBER TREK TAUT m 

contact with such infective material, will contract the disease. 

There is no external mycelium associated with roots suffering from 
this disease, though fan-shaped, white patches of a felt-like mycelium 
may be sometimes observed on the exterior of the wood, when the 
bark is removed. 

It should be noted that other fungi, more or less closely related to 
U. zonata, also produce similar black lines in dead and decaying wood 
found lying about the plantations. Thus in diseased rubber trees, 
reliance can only be placed on the black lines as a diagnostic character, 




FlG. 9c/. Incipient white tipped aggregations of mycelial hyphae (Rhizomorphs?), 
of U. zonata developed in plate cultures. (From Anns, of App. Biol.) 

when the trees show the typical dry-rot in the woody tissues, either in 
the root or stem system. 

The possible relation between the aggregations of fungus tissue, 
which form the black lines, and rhizomorphs, is referred to above, and 
also in Part I. The mycelial aggregations in the form of minute strands 
of fungus tissue which are developed in pure cultures, is shown in 
Fig. 9c. These are very similar to the strands developed in pure cultures 
of Sphaerostilbe repens, and it is now realised that this fungus freely 
produces microscopical rhizomorphs, of typical form, in invaded 
cortical tissues of rubber roots. 

The progress of the disease is slow, after infection has taken place. 
This is connected with the fact that the water-conducting vessels are 
comparatively little affected by the activities of the fungus developing 



CHAP, vin USTULINA ZONATA 93 

in the attacked tissues. During its progress through the woody 
tissues, the fungus is largely confined to the medullary ray cells and 
the fibres of the wood. Quick travelling fungi use the long, tubular 
vessels of the wood as their route for moving from one part of the 
plant to another, for there are no cross walls to intercept their pro- 
gress. The death of large, heavily infected trees may be delayed for 
many years, and if the yields of latex do not fall to any great extent, 
there is no real reason why such trees should be taken out of the 
tapping round. Finally, however, trees attacked by U. zonata dis- 
appear from the tapping round, either because the yield of latex 
becomes too small for their profitable retention, or they are blown 




FIQ. 9 a. Fructification of U. zonata developed on diseased rubber root. 
Note typical zonation. 

down during the heavy wind and rain storms which occur so com- 
monly in Malaya during certain periods of the year. 

Fructifications. The fructifications are often produced in profusion 
at the base of the stem, before the death of the tree (Figs. 9 a and c). 
The young fruit body commences as a small, yellowish-white plate 
closely addressed to the bark. It emerges through the bark as a short, 
white column and spreads out in all directions flat on the surface, 
being attached to the bark only at the point of origin. The plate 
increases in size and the surface darkens to a greenish -grey colour, 
owing to the formation of a thick layer of conidial spores. These are 
borne on erect stalks which are closely compacted to form a continu- 
ous surface (Diagram IV, 1). 

As the spores are borne superficial!} 7 they are easily blown away by 
wind, and insects walking over the flat plate would probably transport 



94 DISEASES AND PESTS OF THE RUBBER TREE PART in 

the spores on their appendages. This phase may continue for about 
one week, and during this period the plate is soft and easily cut. As 
the conidial layer disappears, the flat fructification becomes darker in 
colour; gradually it becomes more leathery in consistency and ulti- 
mately becomes brittle and quite black. Typical young specimens 
gathered outside in the field show a well-defined zoning on the surface, 
hence the name of U. zonata (Figs. 9 a and c). When fully developed, 
the plate-like fructifications are several inches in diameter. A number 
of plates may fuse together, until several feet of the diseased stem 
may be covered with the fructifications. When the plates are black 




FIG, 96. Flat fructification of (/. zonata, growing together with Kretschmaria 
type of fructification. The Ustulina plates of typical form were growing out 
at the edges into the Kretschmaria forms. 

and brittle, a close inspection will show that they bear scattered, 
minute, slightly elevated points. These are the openings into small, 
globose cavities, the perithecia, from which the black ascospores are 
ejected. After ejection, the groups of ascospores may often be seen 
resembling small, black heaps of dust, surrounding the ostioles of the 
perithecia. 

When a mature fructification is cut or broken across, several 
distinct tissue layers can be distinguished. The conidial layer has 
disappeared, and the upper layer is black, composed of compact tissue 
very similar to that forming the black lines running through attacked 
woody tissues; below this black, compacted layer, is a white, loosely 



USTULINA ZONATjl 

Compacted zone, in which the globular perithecia are formed, and 
below this is a broader band, grey in colour and leathery in consist- 
ency, and finally the lower surface is reached, this being formed by 
a continuation of the outer black zone on the upper surface (Diagram 
IV, 2). 

The globose perithecia communicate with the exterior by very 
narrow channels. The first formed elements of the perithecia can be 
recognised in suitably stained sections very early in the development 
of the fructification, long before the production of conidia; these 
elements stain more deeply 
with protoplasmic stains than 
surrounding ones, and appear 
as small, circular patches of 
spirally running hyphae. 

In the early stages of de- 
velopment the outer, black 
zone is not present in the 
fructification. Whilst the 
stroma is still soft and yel- 
lowish, the walls of patches 
of the loosely compacted 
layer, irregularly distributed, 
but at the same depth, be- 
come impregnated with car- 
bonaceous material. Later, the 
walls of the fungal cells of the 
loosely compacted layer inter- 
vening between the black 
patches, become impregnated 
with similar material, their cell 
contents darken, and a continuous black, brittle zone is formed. 

The greenish-grey conidial layer is formed about the time the black 
zone is completed, while the fructification, though leathery, is still 
soft. In many cases the conidial layer can be found on the younger, 
growing edge of the fructification, while the older parts in the middle 
are showing the ostioles of the perithecia. The conidia, when examined 
singly, are hyaline, but when present in large numbers and compacted 
to form a continuous surface, they give the upper surface a greenish- 
grey appearance. They measure 4/z, x 2^. 

The perithecial openings can be observed as minute black spots 
almost immediately after the disappearance of the conidial layer. By 
this time, the black zone is continuous, and the spore chambers are 




FIG. 9c. Fusion of flat fructifications of 
U. zonata, covering two square feet of 
stem at the base. 



DIAGRAM IV (after Steinemann). 




$4), 



4 ( x 



Ustulina Zonata 

Fig. 1. Section through conidial layer of young fructification. Diagrammatic repro 

sentation of upper surface with conidia. x 287. c=conidia. 
Fig. 2. Section through older fructification. Showing upper surface after disappearance 

of conidial layer. Note globose perithecia in the substance of the fructification. 
Fig. 3. Enlarged view of interior of perithecia, showing asci, with ascospores and 

paraphyses. x 54. 
Fig. 4. Enlarged view of Fig. 3. x 287. P= paraphyses, osaHci, jo Hsrnsporos. 



CHAP, viii USTULINA ZONATA 97 

developed just below this zone, in the more loosely compacted tissue. 
The asci are numerous with paraphyses (Diagram IV). 

The ascospores, when first delimited from the remainder of the cell 
contents in the ascus, are hyaline, with no special contents. Later they 
darken, become almost black, with two or three oil drops. The mature 
ascospores measure 28-32/1 x 7-10/*. In the writer's experience, the 
ascospores do not germinate readily, but germination of the conidia is 
more easily obtained. 

There is much variation in the form of the fructifications. Fetch 
reports the same feature from Ceylon. There is a solitary stalked 
form, the conidial layer being produced only on the top and continued 
for a short distance down the side. The commonest variation is the 
Kretschmaria type of fructification, in which the heads of a stalked 
form are crowded together to form a continuous, flat upper layer. 
Several investigators have considered a fungus named Kretschmaria 
micropus (Fr.), Sacc., to be a wound parasite on H. brasiliensis. The 
ascospores of this fungus measure about the same as those of U. 
zonata, as given above. Fetch gives three records, viz. 28-33/x x 6-7/x, 
29-34/z x 0-9/x and 28-32/u, x 9-1 1/u,, in an article entitled "Xylariaceae 
Zeylandica", published in the Annals of the Royal Botanic Gardens, 
Peradeniya, vol. viii., May 1924. This close agreement in size of the 
ascospores raises suspicions as to the specific identity of K. micropus, 
for both Van Overeem and the writer have called particular attention 
to the Kretschmaria stage of U. zonata, for it is often found both in 
pure culture and in close association with the ordinary plate-like form 
of the fructification in nature (Fig. 96). There seems no adequate 
reason in the present stage of our knowledge for considering the 
Kretschmaria fungus associated with symptoms similar to those 
attributed to U. zonata as other than an expression of the extreme 
variability of the external growth forms of the fungus. Fetch gives a 
detailed description of different Kretschmaria species in the above- 
mentioned article, but the details are unlikely to interest planters; it 
should be consulted by any investigator who is desirous of finally 
settling the question. 

There is another form of U. zonata which closely resembles a foliose 
lichen; this has not yet been found to produce spores. 

Distribution. The disease is disseminated by wind-borne spores, 
which are formed in great profusion. It can only gain entry into the 
tree through wounds; the characteristic symptoms shown by stem 
Ustulina are a clear example of this. In its mode of life and the type 
of damage done in the root system of H. brasiliensis the fungus U. 
zonata differs considerably in its salient characteristics from the Fomes 

H 



98 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

group of root diseases. According to Napper, the main points of 
practical significance are: 

(1) U. zonata develops on all sorts of rotting debris, whereas the 
species of Fomes, causing root diseases on rubber trees, can only 
develop in those trees they have attacked parasitically. 

(2) U. zonata spreads aboveground by wind-blown spores, whereas 
the other type of diseases spread underground by means of special 
vegetative organs, the rhizomorphs. 

(3) U. zonata is a wound parasite and can only penetrate through 
wounds or through unhealthy tissue. The other type, Fomes group, are 
not fettered by this restriction. 

Reasoning from (1) and (2), it is seen that the centres of infection 
and the mode of propagation of U. zonata are both practically un- 
controllable, and from (3) that control can immediately be effected 
by avoiding the development of unprotected wounds. In all these 
respects the disease caused by U. zonata differs diametrically from the 
root diseases caused by the Fomes group of fungi. 

One observation of interest was made during 1933, when several 
cases of lateral roots of H. brasiliensis showed a mixed infection of 
Ustulina zonata and Sphaerostilbe repens, the characteristic symptoms 
of both fungi being quite obvious. The intimate nature of the mixed 
infection was such that there was no clear indication where U. zonata 
ended or began. The succession along the root was 8. repens -> U . zonata 
->$. repens. 

Control. The method of infection and spread must be understood 
before control measures can be advised. All authorities in Ceylon, 
Java and Malaya are agreed that the commonest seat of infection is 
at the collar of the tree. The original infection is brought about by 
wind-borne spores, and Steinrnann gives his opiuion that the tree is 
often more or less seriously wounded at the base during changkolling, 1 
and that it is probably due to this cause that most infections are 
found at the root collar. In Malaya, a general opinion is held that the 
accumulation of rubber as bark or earth scrap at the base of the tree 
for a long period of time, results in the suffocation of the cortical 
layers beneath, for such rubber pads are wholly air-tight, and it is 
believed that the best conditions for attack by U. zonata are thus 
provided. The fungus becomes established below the pads, spreads 
deep into the bole and along the adjacent laterals, giving rise to the 
dry-rot infections so frequently seen in mature areas. 

The evidence for spread by root contact is given by Fetch, who 
says: 

1 Changlcola, native hoe used in cultivation operations. 



CHAP, vin USTULINA ZONATA 99 

The prevalence of Ustulina zonata as a root disease of tea is due to the 
practice of growing Qrevilleas through the Tea and felling them when they 
have grown too large. The fungus develops on the stumps of Grevillea 
robusta and travels down its lateral roots, passing on to any Tea root 
which happens to be in contact with the Grevillea roots. To a lesser extent 
the same happens when Albizzia moluccana is felled, but another root 
disease is more usual in that case. The first case of Ustulina as a root 
disease of Hevea in Ceylon was in an old Tea field where the Tea had been 
abandoned and allowed to die out. In that case the Ustulina undoubtedly 
spread from the dead Tea roots to the Hevea. In another case Albizzia and 
Lunumidella (Melia dubia) had been planted as shade trees along the road- 
sides of a Tea estate, and the Tea was subsequently interplanted with 
Hevea] after some years the shade trees were cut out, and in numerous 
instances the course of their lateral roots was marked by a line of dead 
Tea bushes and one or two Hevea either dead or attacked by Ustulina. 
On another estate Albizzia had been planted at the same time as the 
Hevea, and cut out later; many Hevea trees were subsequently attacked by 
Ustulina , and clear cases of infection of the tap root just below the laterals 
were demonstrable, where a dead lateral root of the Albizzia was in con- 
tact with a Hevea. 

As U. zonata develops its fructifications luxuriantly on old rubber 
stumps and logs left after thinning, it is obvious that careless thinning- 
out would influence and encourage its prevalence to a marked extent. 
This latter remark also applies to Ganoderma pseudoferreum. Large 
fructifications of U. zonata have moreover been found on old jungle 
stumps ten to twelve years after felling the jungle. 

The two most important factors which influence the prevalence of 
the disease are (a) the presence of pads of rubber scrap at the collar 
of the tree which may remain untouched for many years, and (6) 
allowing rubber stumps and logs to remain in situ after thinning-out. 
Injuries caused during cultivation operations must, of course, also be 
taken into account. If, therefore, all felled rubber timber and logs are 
thoroughly cleared out during the thinning-out operation, and the 
remaining trees are cleared of the earth-scrap at the base periodically, 
there would be few reports of serious attacks. 

When the price of rubber is sufficiently high, planters are not keen 
on cutting out diseased trees which may be yielding a normal supply 
of latex on one side. The danger is obvious, for fructifications often 
develop on the diseased side. Several estates have undertaken the 
collection of fructifications as soon as possible after they develop. 
Some attempts have proved quite successful or, at least, the results 
have been considered satisfactory. Others have not had satisfactory 
results, the chief reason for failure lying in the personal equation. 
This factor is of the utmost importance and, in Malaya, it must 



100 DISEASES AND PESTS OF THE RUBBER TREE PART in 

always be taken into account when offering recommendations for 
disease treatment on a large scale. After much patient work and a 
considerable amount of success, a certain line of treatment is recom- 
mended to planters, some of whom may be more or less indifferent to 
the outcome. The only remark that needs to be added is that the 
usual result of careless or indifferent treatment must be practical 
failure. 

Most observers who have been in close contact with the collar 
disease on Hevea, caused by U. zonata, have considered the question 
of the application of tree surgery methods in dealing with individual 
cases. In 1914 the writer tried cutting out the diseased tissues and 
filling in with cement, concrete and brick-work. The chances of suc- 
cess were considered somewhat remote at the time. Some thirty cases 
were dealt with successfully but none of the trees are standing at the 
present date. The Rubber Research Institute of Ceylon recommended 
a method of this type from 1924 onwards, and described it and the 
possible reasons for non-success. The financial aspect again rules the 
situation and the method could not be considered economic at present- 
day prices of rubber (1933). Future developments will rule out the 
application of expensive methods of treatment designed to save 
individual trees now over twenty years of age; that, at least, is the 
opinion of the writer. 

The development spoken of as "stem Ustulina", where entry to the 
stem of the tree is gained through large branches being broken off, is 
dealt with in the section headed Stem Diseases. 

Fetch says the treatment of this root disease should follow the usual 
rules for root disease in general, i.e. complete removal of infected 
lateral roots from the soil and running a trench round the infected 
area, while dead trees or stumps of any kind should be dug up and 
burnt. At the present date, more especially on old properties, the 
point that must be kept prominently in view is to clear the soil of all 
infective material. In treatment of individual trees, therefore, if it 
is desired to maintain the tree in the stand, the lateral roots which are 
found to be diseased should be cut off as close to the trunk as possible. 
They should then be followed up to their extremities and completely 
extracted from the soil. Any lateral roots from neighbouring trees 
with which the diseased roots come into contact, should be examined 
at the point of contact and, if found diseased, should be followed and 
completely removed from the soil. The soil area in which the roots 
have been ramifying should then be dug over to a depth of one and a 
half to two feet. 

In treatment of this type it is most important that the diseased 



CHAP, vni USTULINA ZON AT A SPHAEROSTILBE REPENS 101 

trees should be inspected every week or so, so that any fructifications 
which might grow from the diseased tissues in the trunk can be quickly 
removed. 

After some time, diseased trees will die or be blown over. The 
diseased tap-root and laterals should then be completely removed 
from the soil and destroyed, along with the stems and branches, 
unless, as sometimes happens, the estate is suitably located so that a 
market for firewood can be conveniently established. As remarked 
above, old rubber timber should be removed as quickly as possible. 

The fungus Xylaria thwaitesii has been reported as the cause of a 
root disease of rubber trees in Ceylon (page 176), and it may serve 
some useful purpose to add here a few remarks by Weir. He states: 

During estate visits planters have pointed out black, spike-like fructi- 
fications from one to two inches high growing on dead wood of wounds at 
the base of trees. These fungi belong to Xylaria, a genus closely related to 
Ustulina, and they also produce black lines in the wood. They frequently 
follow up wounding from sunscorch, leaf fires, mechanical wounds, or may 
sometimes be associated with Ustulina, in the same canker. As a rule, these 
fungi are not of much importance. The treatment is the same as that for 
Ustulina. The species so far recorded on dead wood of living rubber are 
Xylaria multiplex, X. plebeja and Xylaria deserticola. 

It is interesting to note that the fungi cultivated by certain of the mound - 
building termites number among them species of Xylaria. In one case 
there was a definite connection between a nest from which X. phbcja was 
isolated and an infection by the fungus on the roots of a tree. 

SPHAEROSTILBE REPENS, B. BR. 

The disease caused by this fungus is often known as stinking root 
disease, for attacked rubber roots and the surrounding soil have a 
particularly foul smell. 

The first record of its occurrence in Malaya was made by Richards 
in 1912-13. In 1914 Brooks investigated it for a short time, but the 
only important conclusion which could be drawn from his work was 
that attempts at artificial inoculations were unsuccessful. The fungus 
is well known in Ceylon, both on rubber and on tea plantations, and 
was first found there in 1907. Fetch says this fungus has never caused 
any widespread damage in Ceylon. 

In Malaya, the disease is most commonly found on low-lying 
coastal or riverine areas. In fact, it is best seen following the flooding 
of areas carrying rubber trees, and Sphaerostilbe practically always 
causes extensive damage under such circumstances. The first large 
area found showing diseased trees attacked by S. repens after flooding, 



102 DISEASES AND PESTS OF THE RUBBER TREE PART in 

was practically wiped out and resulted in the total destruction of 
nearly 200 acres of rubber. Since that date many cases have been 
notified. During 1931 the bund at Port Swettenham burst and the 
river flooded a few neighbouring areas for several days. A fortnight 
later, the water had cleared away and soon afterwards numerous 
trees attacked by S. repens were found. More recently, an area was 
deliberately flooded for several days with a view to aiding white ant 
control. The insecticidal powder, Paris Green, was being used to 
control the insect attacks, and this had been applied before the 
water was allowed to enter the areas. A few weeks elapsed, and 
hundreds of cases of the root disease caused by S. repens were found. 
An attempt was made to fasten the entire blame on the use of the 
insecticidal powder, but even if it was ancillary to the outbreak of the 
fungus, there is no doubt that if enquiries had been made as to the 
advisability of flooding, a negative answer would have been returned, 
and the danger of a severe attack of root disease caused by S. repens 
would have been predicted. But it is interesting to note that there 
were but few records of rubber trees being attacked by S. repens after 
the Pahang floods of 1926, which were extremely severe and prolonged. 
A few remarks relative to the Pahang floods are given at the end of 
this section. 

The disease has seldom been found on high ground in Malaya, 
though Petch states it is not confined to the low country in Ceylon. 

Brooks reports that the foliage of rubber trees affected by S. repens 
becomes thin and the branches gradually die back. The progress of 
the fungus being slow, a considerable time sometimes elapses before 
the whole of the collar or all of the lateral roots become affected, with 
the subsequent death of the tree. Although this may be the case with 
individual trees, in the most noteworthy attack seen by the writer, 
the attacked trees shed their leaves rapidly. Ten days before the leaf- 
fall began, there were no signs of the fungus attacking the roots, as 
indicated by the gradual dying-back of portions of the crown, and it 
was only the occurrence of sudden and heavy leaf- fall which led to an 
enquiry into the cause of the trouble. 

Symptoms. If the roots of a rubber tree affected by S. repens are 
examined, they can (if the affected roots have not been too long 
diseased) be distinguished from all other root diseases by the black, 
flattened rhizomorphic strands, which are usually found between the 
bark and the wood. The edges of the black, flattened strands may be 
tinged with pinkish pustules which are the imperfect fructifications of 
this fungus (Plate I). 

When a suspected case of 8. repens is being investigated, the foul 



CHAP, vin SPHAEROSTILl 103 

smell of the soil which is being dug over will be the first indication of 
the probable cause. When the diseased roots are inspected no external 
rhizomorphs will be found, but if the cortex is lifted, the black, 
flattened, usually radiating rhizomorphs will show up prominently on 
the surface of the wood. Even when the rhizomorphs have decayed, 
their former position is often indicated by the presence of correspond- 
ing dark lines on the wood. 

The rhizomorphs are not confined to one r position, i.e. between the 




FIG. 10. .Radiating rhizomorphs of Sphaerostilbe repens, in cortex of diseased 

Hevea root. 

wood and the outer cortical tissues, but they grow freely through the 
cortical tissues, and can often be found just under the external scaly 
bark (Fig. 10). 

The aggregation of hyphae to form rhizomorphic strands of a micro- 
scopical character in the cortical tissues of an attacked root, as does 
8. repens, is a somewhat unusual feature in fungi. The centre of 
these microscopic rhizomorphs is either hollow or may consist of a 
few hyphae very loosely compacted together; these are surrounded 
by a layer much more closely compacted, and the latter is covered 
externally by an extremely dense layer of hyphae, which appear to 



104 DISEASES AND PESTS OF THE RUBBER TREE PART in 

form a tough outer covering. They move through the cortical tissues 
of the host, splitting them apart as if a peg was being driven into 
them (Fig. 11). The appearance presented by sections of the cortical 
tissues of rubber roots attacked by this fungus is quite typical, and 
even if macroscopic rhizomorphs are few or entirely absent, the 
features described should be sufficient to establish its identity. A 
small rhizomorph is shown in longitudinal section in Fig. 11, while 
one in transverse section is seen in Fig. 12. 

The rhizomorphs, as seen between the bark and wood, are usually 
about 2 mm. broad, but may reach a breadth of 5 mm. As explained 




FIG. 11. Longitudinal section through microscopical rhizomorph of 8. repens 
in diseased cortical tissues. 

above, the rhizomorphs may be microscopic, or may mass together to 
form large plates. When fresh and growing vigorously the general 
background of colouring of the large plates is greyish- white, with a 
reddish tinge in places, imparted by the presence of mostly imperfect 
fructifications. Later, they appear redder in colour, but as the root 
decays, so do the strands, and the latter become black. If the strands 
are not dead or moribund, they stand out prominently above the 
wood, but in old, decayed roots they may appear as a mere impres- 
sion on the wood. 

Fetch describes the fusing of the rhizomorphs into a continuous 
sheet on a specimen found between the wood and bark of a decaying 
"Dadap" log (Eryihrina lithosperma). It is evident that his remarks 
apply equally well to the fungus as found on H. brasiliensis in 
Malaya. He says: 



CHAP. VIII 



SPHAEROSTILBE REPENS 



105 



In that case the rhizomorphs are much broader and they have fused 
behind into a continuous sheet. The outer surface of the rhizomorphs are 
marked with a peculiar herring bone pattern. When the bark was separated 
from the wood, these thick strands were often split horizontally, and the 
white internal tissue then presented a fern-like appearance. The patch 
of mycelium was over a yard in length and about eight inches broad, the 
separate rhizomorphs being evident only at the margin (Fig. 13). 

Fructifications. Sphaerostilbe repens, B. & Br.,is a fungus belonging 




FIG. 12. Transverse section through microscopical rhizomorph of S. repens. 

to the Ascomycetes and so produces the perfect form of fructifica- 
tion characteristic of the genus Sphaerostilbe. These are small, dark 
red, globular perithecia, the asci therein containing eight one-septate 
spores. There is also a conidial form of fructification typical of a 
genus Stilbum which is placed in the Fungi Imperfecti. There are two 
other species of Stilbum found growing on rubber trees; one, 8. mnum, 
Massee, is common on dead branches; the other, S. cinnabar mum, 
Mont., being, according to Fetch and Brooks, the conidial stage of 
Megalonectriapseudotrichia, Schw. These species of Stilbum are much 
the same as the conidial form of S. repens, in having red stalks and 



106 DISEASES AND PESTS OF THE RUBBER TREE PAKT in 




Fio. 13. Mat of rhizomorphs of *S'. repens, formed by fusion. Found in diseased 
cortical tissues of roots. Note mat about to break up at edges into individual 
rhizomorphs. Also pink spores masses of Stilbum fructifications. 



CHAP, viii SPHAEROSTILBE REPENS 107 

red or pinkish heads, but the stalk of the latter is hairy, whereas the 
stalks of the two former are quite smooth. 

In the ordinary course of natural development the Stilbum stage 
of S. repens is the first to appear. It takes the form of short, erect, red 
stalks from 2 mm. to 8 mm. high and \ mm. to 1 mm. in diameter, 
surmounted by a white or pinkish, globose head, 1-1 \ mm. in diameter 
(Fig. 14). They are formed in large numbers and can be easily seen 
when present. The stalk is hairy at first, but later becomes smooth in 
the lower half. 

The writer doubts whether previous accounts of the development 




Fi. 14. Typical appearance of Xtilhum fructifications of S. repens, on rubber 
root. Natural size, slightly enlarged. 

of the fructifications of S. repens can be considered to be more than a 
cursory statement, and further work must be undertaken before the 
position can be accepted as satisfactory. The actual method of the 
origin of the conidial fructifications, which has not been specially 
illustrated previously, is shown in Fig. 15. The section was taken 
longitudinally through a rhizomorph carrying the conidial fructifica- 
tions. It will be seen that the upright masses of conidial hyphae arise 
not from the rhizomorph which is apparent on the surface but from 
the microscopical, submerged rhizomorphs which are formed in the 
cortical tissues of diseased roots; the surface rhizomorphs joining up 
the individual conidial heads also take their origin from a similar 
position. It appears as though the surface rhizomorph puts down root- 
like structures at varying distances, and from these the heads of the 



108 DISEASES AND PESTS OF THE RUBBER TREE PART in 

conidial fructifications grow upwards. It is a matter of considerable 
morphological interest but space will not allow further comment. The 
spores which arise at the extremities of the Stilbum type of fructifica- 
tion are hyaline, oval, 10-20^ x 5-9/x in size. 

The perithecial stage of the fungus follows the conidial stage on 
diseased roots, but is not always to be found, for under certain condi- 
tions this type of fruit-body is not produced. Recent cases have been 
examined where there were numerous perithecia but no signs of the 
Stilbum stage. The perithecia are small, red bodies, rounded below and 
conical above, globose, about 0.6 mm. high and 0.4 mm. in diameter. 




FIG. 15. Section through diseased cortex of rubber root showing the Stilbum fructifi- 
cations. Note their development from submerged rhizomorphs and that they are 
joined together by surface mycelial tissue, x 45. 

The ascospores are contained in asci, 190-220/^x 9/x in size, and the 
spores are eight in number, one septate, pale brown to reddish-brown, 
oval, slightly constricted, and measure 19-21/^x Sp,. 

Both Fetch and Brooks state that S. repens can live entirely on 
dead plant tissues as a saprophyte. The writer has never specially 
noted this feature and it seems that further evidence would be 
required before the statement could be accepted. 

Brooks, working in Malaya in 1914, successfully established pure 
cultures, and endeavoured to fix the status of the fungus as a parasite 
or saprophyte by artificial inoculations. In his pure cultures, sessile 
aggregations of spores of a yellowish-pink colour arise on both media 
(potato agar and rubber wood blocks), and these are often arranged 
in concentric zones. These spores were hyaline, oval and very variable 



CHAP, viii SPHAEROSTILBE REPENS 109 

in size, the average limits being 16-20/x x 6-8/z, though some are much 
smaller. 

In these cultures, spherical, thick-walled, resting spores were 
formed in the hyphae and at the ends of short branches; these spores 
are brown in colour when mature, and measure 9-10/i in diameter. 

In the inoculation experiments, sixteen plants were inoculated but 
after five months none showed signs of infection. This points to the 
possibility that some condition which predisposes some plants of 
H.brasiliensisto susceptibility must exist before the fungus can invade 
a healthy tree. The most probable factor is the inadequate aeration of 
the soil in areas where the requisite conditions are not provided for 
adequate drainage. 

Dissemination. The fungus can be freely spread by the wind for 
the spores are produced in large numbers on the conidial fructifica- 
tions. Spread by root contact may be possible but this is not a promi- 
nent feature, as it is in Ganoderma pseudoferreum. Since it is fairly 
obvious that the fungus can successfully attack Hevea only within 
very narrow limits, it will evidently never cause serious damage 
unless the necessary conditions are provided. 

There is not the slightest doubt that the requisite conditions are 
provided during, and after, flooding of low-lying plantations. It is a 
practical certainty that, if rubber trees remain standing in water, to 
a depth of nine inches or more, for a period of seven to ten days, the 
direct outcome will be a more or less severe attack of S. repens. Once 
a good hold is obtained by the fungus upon the roots, little can be 
done beyond extracting the diseased trees as far as possible. 

Even when there has been no flooding, a single individual, or even 
three or four diseased specimens in close proximity, may occasionally 
be found. Dead trees must be dug up and burnt in such cases, and 
diseased stumps and lateral roots extracted. The fungus seldom 
attacks young trees; mature trees are usually the victims and as root 
contact has probably been made, it will be advantageous to trench 
around diseased trees in the customary manner. Further, as most of 
these cases occur on areas with heavy clay soils, the application of lime 
can be usefully recommended, for the soil acidity will be reduced, and 
flocculation of the clay particles will take place so that the soil can be 
broken up more easily. Both of these points are important if the 
denuded area is to be re -supplied. 

The latest contribution to our knowledge of S. repens is from Ceylon, 
in 1929, by Small and Bertus. The discussion of results in this paper 
introduces the subject of the fungus Rhizoctonia bataticola in rela- 
tion to root diseases of plantation crops, including rubber, and may 



110 DISEASES AND PESTS OF THE RUBBER TREE PART in 

perhaps be usefully quoted at this point while comment upon the 
controversial issues may be reserved. It will be seen that in respect of 
S. repens the position in Ceylon is very much the same as that in 
Malaya, though if a "consequent suffocation of the roots of affected 
woody plants" is taken as the main predisposing factor which en- 
courages infection in rubber plants, it is difficult to explain why no 
reports of trees killed by S. repens were received after the subsidence 
of the Pahang floods, for all forms of life must have been suffocated 
by the tremendous amount of silt deposited. The extract is as follows: 

The results of the above experiments showed that Sphaerostilbe repens 
was able to attack arrowroot, Canna and papaw under the conditions im- 
posed and that it was unable to attack the healthy roots of woody plants 
like tea, rubber and dadap, or of rubber and cacao seedlings, even with the 
supposed help of wound entrances to tissues and close contact between 
inoculum and host surfaces. 

From the practical point of view the question of the attack of Sphaero- 
stilbe on roots of woody plants is of greater interest than the question of 
Sphaerostilbe disease of arrowroot, Canna and papaw, and the remainder 
of this discussion therefore deals with the woody-plant aspect of the sub- 
ject in hand. The lack of positive results in experiments with woody plants 
agrees with the negative results obtained by Brooks in experiments with 
rubber in Malaya. The investigator is forced thus to the conclusion that 
successful Sphaerostilbe attacks on the roots of woody plants is conditioned 
by the previous operation and effects of adverse physiological conditions 
which are presumed to produce in the exposed plant such a state of de- 
generation or lack of resistance that Sphaerostilbe is enabled to assume 
a parasitic role. In nature the adverse conditions seem to be supplied most 
frequently by lack of drainage and a consequent suffocation of the roots 
of affected woody plants, and it is possible that a moist or wet soil is the 
most suitable substratum for Sphaerostilbe. On the other hand, it is to be 
noted that the attempt to imitate natural moist soil conditions in the 
experiments did not lead to Sphaerostilbe attack on woody roots and that 
the fungus is found in nature in plantation soils which do not suffer from 
lack of drainage. It is not forgotten that the attempts to imitate moist soil 
conditions in the experiments may have fallen far short of natural con- 
ditions in their results. At the same time, it may be doubted if the moist 
soil conditions said to be required for successful Sphaerostilbe attack are 
in constant and regular operation in nature. 

It is, therefore, in order to enquire into the possible presence and opera- 
tion of other factors which may cause the necessary preliminary degenera- 
tion or unhealthy condition of woody roots required for Sphaerostilbe 
attack, and it has to be reported that, as already mentioned, a root disease 
factor is present with such frequency in Ceylon cases of Sphaerostilbe root 
disease that it must be taken into account. In short, it is probable that 
in many cases of Sphaerostilbe attack on woody roots, if not in all, the 
entrance and advance of the Sphaerostilbe is preceded by a diseased condition 



CHAP, vin SPHAEROSTILBE REPENS 111 

induced by Ehizoctonia bataticola attack. The grounds on which the attack 
of the Ehizoctonia is assumed to be prior to that of other fungi found on 
diseased woody roots have been discussed with reference to Fomes, Poria 
and other forms, and they need not be repeated in this place. The writers, 
therefore, do not deny that Sphaerostilbe attack on woody roots may be a 
secondary phenomenon which follows upon moist or sour soil conditions, 
but they think it is necessary to lay stress upon the necessity for investiga- 
tion into the possibility of the presence of Rhizoctonia bataticola either with 
and without the abnormal soil conditions. 

Remarks on the Pahang Floods, 1926-1927. The Pahang floods of 
1926-27 will always be remembered by those who went through that 
terrible experience. It will be interesting to give a typical record 
obtained on a rubber estate, taking one from near Kuantan, in 
Pahang, as a suitable centre. The important point is that after 
extremely severe flooding few records of rubber trees attacked by S. 
repens were received. In view of the importance attached to flooding, 
some attempt must be made to account for this, though in typical 
cases of 8. repens attacks following flooding, the floods are not usually 
severe or of long duration. 

The estate in question was flooded on four occasions between 
December 21st, 1926, and March 4th, 1927; they are described as 
follows: 

Dec. 21st-24th, 1926 . . . Normal floods 

Dec. 26th, 1926-Jan. 7th, 1927 . . Abnormal ,, 

Jan. 23rd-25th, 1927 . . . Normal 

March 6th-10th, 1927 . . . Normal 

The so-called normal floods gave a depth of water in the fields 
varying from 4 ft. to 30 ft., while, during the abnormal flood, the 
depth of water varied from 60 ft. in the deepest part to 2 ft. in the 
lowest. An acreage of 2300 acres was affected by normal floods and 
one of 3000 acres by the abnormal flood. 

After severe and prolonged flooding very serious damage might be 
expected. During the Pahang floods a large quantity of silt was carried 
down and the depth of silt deposited in the depressions on the rubber 
plantations varied from 6 ins. to 16 ft. The average height reached by 
the deposited silt was 4 ft. to 5 ft. 

The chief troubles recorded were as follows: 

(a) Pink disease and claret-coloured bark canker became prominent 
when mature trees were submerged for a lengthy period, while those 
deep in slime showed a splitting of the bark with the free exudation of 
latex. The latter trees recovered after about one month. 



112 DISEASES AND PESTS OF THE RUBBER TREE PAKT.III 

(6) Submerged trees show the cortex affected just below and above 
the tapping cut, and in a few instances the affection descended to 
ground-level. Where the cortex had died down to the wood, soft pads 
of coagulated latex were formed between the wood and cortex, while 
both wood and cortex were of a blue -black colour. 

(c) Trees were blown down by the cyclonic winds usually experi- 
enced during heavy flood periods, more especially on estates with 
loose soil, and as a result large numbers of other trees were injured by 
branches being broken away from the stems. 

The deposit of large quantities of silt will undoubtedly have a 
suffocating action on all organisms living in the soil, and will neces- 
sarily have a very effective retarding influence on any new develop- 
ment of root disease below soil-level, caused by fungi. Silt will be 
easily removed from the trunks and branches of trees during ordinary 
rainy periods and there need be little fear of the bark or cortex being 
severely damaged as a result of silt remaining too long on the trunks 
and branches. Young trees are more affected by submersion over a 
lengthy period than mature trees, and in the majority of cases are 
killed out. The general amount of damage done on areas affected by 
severe flooding is usually large, but it is fortunate that in the par- 
ticular case described, the deposit of fine silt filtered into the soil, 
changing the soil conditions to such an extent that they begame 
distinctly unfavourable to the growth and development of any fungi 
which might cause dangerous root diseases. 

Even if the trees are not blown prostrate during severe flood 
periods, the swaying of the trees during heavy winds on estates with 
a loose soil may result in the root systems being considerably 
damaged. Reductions in yield of 100 Ibs. per acre were reported 
from estates affected by the Pahang floods by this cause, and many 
months elapsed before the trees recovered to give their normal yield 
by the development of new, small feeding rootlets. 



PLATE 1 





CHAPTER IX 

FOMES LIGNOSTJS GANODERMA PSEUDOFERREUM FOMES NOXIUS 
FOMES LIGNOSUS, KLOTZSCH 

(White-root Disease) 

THE root disease caused by this fungus has been prominent in Malaya 
since the first plantations were opened up. During the years 1910-16 
this disease was by far the most important which had to be dealt with, 
and the losses were often so numerous that, before the disease could 
be brought into subjection, large sums of money had to be expended 
in control measures. Steinmann reports: 

In recent years, two Sumatran estates with an area of 2750 acres, about 
70,000 trees, were destroyed and another estate lost about 15,000 trees. 

In Malaya, we have recently dealt with areas showing a percentage 
loss of nearly IS per cent over 700 acres. It is now known that much 
of the money expended in the past on control measures for the 
disease caused by F. lignosus was not profitably spent, for the results 
obtained did not prove to be of permanent value, and any control 
established was really due to natural factors, chiefly those affecting 
the manner of growth and spread of the fungus. This subject will be 
enlarged upon later when presenting treatment of the root diseases 
caused by Fames spp. 

Fetch states: 

This disease was first recorded in Malaya by Ridley at Singapore in 
1904. In Ceylon it was first recorded in 1906. The absence of any previous 
record in Ceylon is doubtless due to the fact that much of the earlier 
Ceylon rubber was planted among Tea or Cacao, and that some of the 
earliest plantations were established on land which had been cleared of 
almost all the jungle stumps prior to planting. 

The fungus has been reported from South India, Java, Sumatra and 
Borneo and in West Africa and the Congo region. The disease does not 
appear to have been recorded from the Western Hemisphere, but as the 
fungus is known to occur throughout the tropics, it will, no doubt, ulti- 
mately be found wherever it (rubber) is grown. 

The disease is not often prominent on mature areas in Malaya, 
though losses due to F. lignosus are common on some coastal proper- 

113 I 



114 DISEASES AND PESTS OF THE RUBBER TREE PART in 

ties. But wherever and at whatever period a recrudescence of new 
planting occurs, the disease springs into prominence. During the last 
few years, a considerable amount of new planting of bud-grafted 
rubber has been undertaken, and an opportunity has thus arisen for 
studying this disease intensively. 

Symptoms. The fungus is readily identified by its external rhizo- 
morph system. The white hyphae of the fungus become aggregated 
together to form stout, smooth cords, which are firmly attached to 
the surface of the roots (Figs. 17 a and 6). They run more or less longi- 
tudinally along the root and unite here and there to form a network. 
These cords may vary slightly in colour according to the colour of 
the soil in which the rubber plants are growing, but in artificial 
cultures the rhizomorphs of F. lignosus are pure white. In the field, 
however, they may be white, or yellowish-white, or in red laterite 
soil, reddish. They vary in breadth, but the thickest are seldom more 
than \ in. thick. The rhizomorphs may spread out into forms of 
hyphae which unite into a continuous sheet; this usually takes place 
at the point of the limit of growth of the fungus on the root, and 
forms the younger, growing parts. This type of mycelial aggregate 
is often found at the collar of the plant, but the fungus seldom 
appears above soil level. Even if it does, it is seldom conspicuous, for 
the strands become subdivided into finer threads or even separate 
hyphae which can only be detected with difficulty at the base of the 
stem. The writer has, however, recently seen specimens showing a 
conspicuous white mycelium, which formed a complete cover from, 
ground level to a few inches up the stem. After careful examination 
it was concluded that the mycelial cover, in this case, was a type of 
Thread Blight (page 286). 

The typical rhizomorphs are more or less rounded on the upper side 
and consequently stand out conspicuously on roots which have been 
affected for some time. The external cords give rise to threads which 
penetrate into the roots and bring about their decay. But this pene- 
tration is not immediate. 

Fetch recognised this feature many years ago for he says: 

The superficial mycelium frequently spreads for some distance along a root 
before penetrating it. 

Because of this there exists the possibility of treating and saving 
roots which are already showing the external rhizomorphs, by scraping 
the latter away with some sharp instrument. So that for a certain 
length of time the fungus is merely attached to the bark of the root 
in the manner of an epiphyte. Recently, De Jong has published some 



CHAP, ix FOMES LIGNOSUS 115 

work relating to field inoculations and has pointed out that in two 
field experiments, 57 trees, 3J-4J years of age, and 126 trees, 5-7 years 
of age respectively, were found to be infected naturally; they had 
mycelium of F. lignosus on the roots but they did not show decay. In 
60 per cent of these cases, the mycelium disappeared without any 
treatment and without doing any harm. This is a very different result 
to the one from which Fetch draws his conclusion when he says: 

Taking all circumstances into consideration it is probable that the majority 
of trees attacked die within twelve months. 

De Jong draws the conclusion from his observations that the fungus 
is but weakly parasitic on rubber trees and that it can cause extensive 
decay only under special environmental conditions. Weir states an 
opposite view as follows: 

Studies on the parasitism of Fames lignosus, Fames lamaaensis and 
Oanoderma pseudoferreum conducted under controlled and uncontrolled 
conditions show that Fames lignosus is strongly parasitic and is capable 
of causing the death of six-months-old rubber without the supplementary 
action of any other organism. 

Therefore it appears that the later work of Weir would support the 
views held by Fetch, but the field work done in Malaya over the last 
three years supports De Jong's observations. 

It is very important to realise that the percentage number of trees 
showing mycelium on the roots is not a suitable criterion for the 
results of field experiments; the only reliable one is the percentage 
number of trees actually lost as a result of becoming infected with the 
fungus. This very critical basis of computation has been adopted in 
Malaya, as will be seen in Tables II and III. While accepting De 
Jong's results and conclusions, it must be kept in mind that the 
reaction of young roots to the presence of the fungus may be very 
different to that found in roots of trees which are several years older, 
in so far as it may be possible that the epiphytic stage remains more 
persistent in younger or older trees, as the case may be. 

Apart from the external rhizomorphs, attacked lateral or tap-roots 
show no particularly distinguishing features. As stated previously, a 
wet-rot may be found in cases, but if it is not a mixed infection with 
white ants, the infected wood remains fairly firm, but obviously pene- 
trated with mycelium. Where white ants are common, mixed infections 
are frequently found. 

The spread of the fungus in the roots of young trees progresses up 
to a point when the supply of water to the leaves is greatly reduced. 
Whilst the leaves are green a sufficient quantity of water to maintain 



116 DISEASES AND PESTS OF THE RUBBER TREE PART m 

life is passed up the tree, but when the limit is reached and the root 
system cannot supply the necessary amount of water required, the 
leaves wilt rapidly, turn brown, and death ensues within a few days. 

Attention should be 'directed here to the fact that rhizomorphs of 
fungi other than those of F. lignosus are found in the soil of rubber 
plantations and even on rubber roots. The rhizomorphs of F. lignosus 
can be distinguished because they are tightly attached to the root, 
while the others are only loosely attached and easily removed. These 
saprophytic fungi which form rhizomorphs are quite common in the 
soil; the cords are usually slightly coloured in shades of purple or 
yellow. 

Fetch reports that, in Ceylon, when F. lignosus was first found, the 
fungus was most frequently associated with stumps of Jak (Arto- 
carpus integrifolia) or various species of Ficus. Hence it was presumed, 
at one time, that it would be unnecessary to remove all stumps in 
order to avoid the occurrence of this disease, and that it would be 
sufficient to adopt a method of selective stumping and to get rid of 
the stumps of trees which were known to serve as hosts for the fungus. 
Bancroft, in Malaya, later concluded that this fungus occurred in- 
discriminately on all kinds of stumps. The fructifications have been 
found on various plants, including several species of palm. 

The following host plants are notified by Van Overeem: 

Anona squamosa, L.; A. glabra, L. 

Areca catechu, L.; Artocarpus sp. 

Artocarpus integrifolia, L.; Afzelia sp. 

Bambusa sp.; Bambusa spinosa, Roxb. 

B. vulgarise Berry a sp.; Bombax sp. 

Cordya mixa, L.; Cyclostemon sp. 

Cocos nucifera, L.; Coffea sp. 

Cinnamomum sp.; Cinnamomum camphor a, Nees 

Derris sp.; Dendrocalamus sp. 

Erythrina indica, L.; Ficus sp. 

Ficus benjamina, L. 

Qliricidia sepium (Jacq.), Steud. 

Hevea brasiliensis, Mull. Arg. 

Koompassia sp.; Leucaena glauca, Benth. 

Livistona cochin-chinensis, Mart. 

Mangifera indica, L.; Malotus sp. 

Manihot TJtilissima, Pohl 

Oncosperma sp.; Oncosperma filamentosa, Blume 

Palmaei Pterocarpus sp. 



CHAP, ix FOMES LIGNOSUS 117 

Polyalihia sp.; Shorea guiso (Blanco), Blume 
Strychnos nux-vomica, L. 
Theobromae cacao, L.; Tkea\ Vitex sp. 

Fetch supplies the following list, several of which are included in 
Van Overeem's citations: 

Common Name Scientific Name 

Meranti Shorea sp. 

Merbau Afzelia palembanica, Baker 

Kumpas Koompassia malaccensis, Maing 

Bombax Bombax malabaricum, D.C. 

Dadap Erythrina umbrosa, H.B.K. 

Halmilla Berrya ammonilla, Roxb. 

Denis dalbergioides, Baker 

Ceara rubber Manihot glaziovii, Mull-Arg. 

Serdang palm Livistona cochin-chinensis, Mart. 

Nibong palm Oncosperma filamentosa, Bl. 

Giant bamboo Dendrocalamus giganteus, Munro 

The fungus has also been recorded as causing a root disease on Tea, 
Camphor, Liberian and Robusta coffee, Tapioca, etc. Fetch remarks 
that the records cover such a wide range of flowering plants that any 
selective method of stumping is impossible. This is quite true, but in 
the writer's experience in Malaya, "Kumpas" trees are by far the 
worst for harbouring F. lignosus. Cases have been observed where the 
rhizomorphs could be removed in huge quantities from the neighbour- 
hood of the buttress roots of "Kumpas" trees. In areas where these 
trees have been numerous in the jungle, special attention should be 
given to their stumps as a source of propagation from which F. 
lignosus commences to spread. 

White-root disease begins to come into prominence between the 
first and second year. It has been known to cause considerable losses 
in seedling nurseries, but in the field the plants reach an age of about 
eighteen months before any definite signs of the fungus can be 
observed. Development from this point is rapid, and if the area is 
heavily infected and control measures are neglected the loss of stand 
may be very large. This is of more immediate importance at the 
present time than formerly, for newly planted areas are invariably 
filled with good planting stocks upon which expensive material is 
bud-grafted later. 

The infection spreads from diseased jungle stumps and rotting 
jungle material derived therefrom, which exists in the soil at the time 



118 DISEASES AND PESTS OF THE RUBBER TREE PART m 

of felling and burning. F, lignosus is an exceedingly vigorous and 
mobile fungus, with a diffuse, far-spreading, rapidly growing rhizo- 
morph system. The fungus is a quick-acting wood destroyer and the 
affected roots rot away rapidly after felling. The attack on the suc- 
ceeding rubber plantation therefore develops quickly after planting, 
is widespread and usually dies down before the trees reach maturity. 
For these reasons the disease is represented characteristically on 
immature areas, but should any factor delay the rotting away of the 




FIG. 10. Showing rhizornorphs of F. lignosus growing amongst roots 
of cover crops. 

infected jungle timber, or if control measures are neglected until trees 
are of an age when their roots form an interlacing system all over the 
planted area, then the disease may cause excessive damage in the 
mature stand. 

Napper considers that only those stumps of the trees which were 
attacked in the jungle before burning are of any importance in spread 
and that stumps of trees which were free from the fungus in the jungle 
are no longer dangerous after burning, for they cannot be infected by 
wind-borne spores of F. lignosus and therefore cannot act as hosts. 
This definite statement appears to be directly contrary to the state- 



CHAP, ix FOMES LIGNOSUS 119 

ments made by Fetch in his 1921 edition. In addition, the latter 
investigator makes a definite statement in relation to the independent 
travel of the mycelium through the soil which Napper does not agree 
with. Fetch's statements, therefore, can be conveniently extracted 
and considered at this point: 

The spores of the fungus are blown on the exposed wood of the stump, 
and if the weather conditions are favourable they germinate and their 
hyphae grow down into it. These hyphae continue growing in the dead 
tissue until they have permeated both the stem and the roots, and then 
they spread from the roots of the stumps to the roots of adjacent living 
trees. Some fungi can only spread to other plants if the roots of the latter 
are in contact with those of the host stump; others, however, can spread 
freely through the soil, drawing food from the supply in the stump which 
served as a base. Each stump thus affords a centre of disease, spreading 
disease in ever- widening circles. 

Later he states, with reference to F. lignosus: 

Thus, the time when the disease is first evident on the rubber depends 
to a great extent upon the time taken by the fungus to destroy the jungle 
stumps, or perhaps more correctly, on the time taken by it to accumulate 
to such a degree that it is able to spread further afield. It may also be 
dependent upon the time taken by the rubber to develop lateral roots since the 
fungus will then have a shorter distance to travel to reach them. It is not, 
however, necessary that the lateral roots of the rubber should come 
in contact with the diseased roots of the stump, because the mycelium of 
F. lignosus can travel independently through the soil. 

Fetch further states: 

It is the fact last mentioned which makes this disease so formidable and 
makes its eradication so difficult. The majority of fungi can only advance 
within dead wood, but the strands of F. lignosus can travel for a few feet 
at least through the soil unattached to any root or dead wood, except, of 
course, at their starting point. It is always attached to its base, i.e. the 
stumps on which it originated, and it must derive its food from that source 
until it meets with other dead wood, or a living plant which it can attack. 
In all probability it will die if separated from its base, unless it soon meets 
with fresh material from which it can derive nourishment. 

Free mycelium is usually found in the uppermost foot or eighteen inches 
of the soil, etc. etc. 

On the same point Steinmann states: 

The danger of White-Root mould (F. lignosus) is aggravated by the 
fact that detached pieces of mycelial strands (so-called rhizomorphs) can 
remain alive in the soil for a long time even when lacking organic food and 
so can spread from a bit of dead wood left in the soil. 



120 DISEASES AND PESTS OF THE RUBBER TREE PART in 

Napper's recent researches in Malaya lead him to consider that, as 
far as that country is concerned, the disease becomes first evident 
when the tap and lateral roots of the young rubber trees have attained 
sufficient length to penetrate into the disease knots, formed by the 
presence of diseased jungle stumps and timber left after felling and 
burning. This is the prime feature of importance with regard to the 
origin of the disease. As shown by the extracts, other investigators 
do not particularly emphasise this feature, though Fetch evidently 
recognises the possibility of the growth in length of tap and lateral 
roots being of some importance in the spread of the disease. Emphasis 
is usually laid on the spores being blown on the exposed wood of 
stumps, which then becomes infected on the germination of the spores, 
or upon the question of the independent travel of the mycelium 
through the soil, which is said to make the disease very formidable 
to control, and its eradication difficult. The recent work in Malaya 
provides exceedingly strong evidence that these features can be con- 
sidered, at most, of very minor importance. Hundreds of diseased 
trees have been carefully opened up, even to depths of four feet, and 
in every case, without a single exception, the diseased material, from 
which infection has spread, has been found in contact with the 
diseased roots at some point. This diseased material is always either 
a jungle stump or material derived therefrom, which is actually being 
rotted by the fungus penetrating the internal tissues, and it is found 
in contact with rubber roots which were previously healthy, but 
which have become infected at the point of contact. Some typical 
cases of diseased jungle roots, in contact with rubber roots which have 
become badly infected as a result, are shown in Fig. 17 a-c. 

In many cases the source of infection was difficult to detect, but as 
experience was gained the diseased jungle roots, carrying infective 
material, were always found. There is no doubt in the writer's mind 
that, for Malaya, Napper's evidence on this particular point can be 
fully accepted, and that possible infection of stumps by wind-blown 
spores and independent travel of the mycelium or rhizomorphs 
through the soil can be entirely subordinated when considering the 
most suitable method of control. Even if it was admitted that the 
mycelium and rhizomorphs of this fungus had power of independent 
movement through the soil, it would be difficult to consider this of 
any great importance. There has been such a large number of serious 
outbreaks which have been dealt with entirely successfully by simply 
keeping in mind that digging must be continued until the actual source 
of infective material has been discovered and extracted. In every 
single case where operations have been guidedby this recommendation 



CHAP. IX 



FOMES LIGNOSUS 



121 




FIG. 17 a. 

FIG. 17 a, b, e. Illustrations showing infected jungle timber in disease "knots", 
with roots of rubber trees which have contracted infection as a result of increase 
in length by natural growth. 

Note photograph (a): the piece of Infected jungle timber lay some nine inches below the lateral root of 
the rubber tree and it was difficult to detect the point of contact between the two pieces of infected 
material for the lateral root of the rubber tree was undoubtedly infected. At point marked A, a minute 
hair root, hardly discernible in the photograph, was found descending from the rubber root to make 
contact with the infected wood below. The appearance in the field was that here was a case of the spread 
of the infection by the free passage of a rhizomorph from jungle timber to a rubber root. However, a 
transverse section quickly showed the typical root structure surrounded by the mycelial felt of the 
fungus. 




FlG. 176. 



CHAP, ix FOMES LIGNOSUS 123 

feet in length, may be formed by the close intergrowth of single 
fructifications (Plate II and Fig. 18). When fresh, the fructifications 
grow out horizontally to form the typical bracket shape, but when dry 
the edges curl up and the fresh deep orange colour of the upper 
surface fades to a dull grey. A resupinate form of the fructification is 
often found. 

The brackets, when fully formed and in the fresh condition are 
leathery or even woody in consistency, with a more or less definitely 




FICJ. 18. Illustration showing development of fructifications of F. lignosus 
growing at the collar of old rubber tree. 

zoned, orange-yellow, upper surface. When the zoning is not very 
definite, the upper surface usually shows a deeper colour (Plate II). 
There is often a radial, fibrous appearance on the upper surface, 
and the edges of the fructification form a definite, bright yellow, 
or yellowish-white rim. The under surface is coloured orange. The 
size of the brackets vary considerably; the usual size is between 2 
and 5 ins. in the longer axis and 1 and 3 ins. in the shorter. When the 
fructifications dry out, the colour becomes duller, the upper side 
turns pale yellowish-brown, the bottom side red-brown, and the 
yellow colour of the rim fades away, and the edge turns downwards. 
If one of the fructifications is cross -sectioned, two clearly defined 



122 



DISEASES AND PESTS OF THE RUBBER TREE PART in 




FIG. 17 c. 

Note (c). This shows a tap-root infection from a small piece of infected wood, only about one foot 
long, and no other infected wood eonld be found in the vicinity. This also illustrates the depth to which 
digging had to be carried before the sources of infection could be found, in many cases. 

the results have been considered satisfactory from an economic 
standpoint. It seems an undoubted fact therefore that, for extensive 
spread in rubber plantations, there must be a continuous chain of 
living, susceptible roots in direct contact with diseased jungle timber. t 
Fetch makes two remarks which might be quoted here: 

(a) Infection by spores has been considered improbable, because when 
the fructifications have been examined they have been found to bear very 
few spores, or in some cases, none at all, 

and 

(6) this is probably merely a matter of examining the fructifications 
at the right stage. 

Napper has recently set all doubts at rest on this point in Malaya, 
for he has found copious spore discharge at certain periods of the 
year. Judging from Steinmann's book, there has never been any doubt 
upon this point in Java. 

Fructifications and Spores. The fructifications, as seen in nature, 
are of the usual, bracket-shaped Fomes type, unstalked, being 
attached to the substratum by a broad base. Simple, single fructifica- 
tions are the most common, but compound fructifications, several 



CHAP, ix FOMES LIGNOSUS 123 

feet in length, may be formed by the close intergrowth of single 
fructifications (Plate II and Fig. 18). When fresh, the fructifications 
grow out horizontally to form the typical bracket shape, but when dry 
the edges curl up and the fresh deep orange colour of the upper 
surface fades to a dull grey. A resupinate form of the fructification is 
often found. 

The brackets, when fully formed and in the fresh condition are 
leathery or even woody in consistency, with a more or less definitely 




FIG. 18. Illustration showing development of fructifications of F. lignosus 
growing at the collar of old rubber tree. 

zoned, orange-yellow, upper surface. When the zoning is not very 
definite, the upper surface usually shows a deeper colour (Plate II). 
There is often a radial, fibrous appearance on the upper surface, 
and the edges of the fructification form a definite, bright yellow, 
or yellowish-white rim. The under surface is coloured orange. The 
size of the brackets vary considerably; the usual size is between 2 
and 5 ins. in the longer axis and 1 and 3 ins. in the shorter. When the 
fructifications dry out, the colour becomes duller, the upper side 
turns pale yellowish-brown, the bottom side red-brown, and the 
yellow colour of the rim fades away, and the edge turns downwards. 
If one of the fructifications is cross-sectioned, two clearly defined 



124 DISEASES AND PESTS OF THE RUBBER TREE PART in 

layers, each of a different colour, can be seen; an upper, whitish, light- 
coloured layer, built up of closely interwoven hyphae, and below an 
orange- coloured layer of tubes or pores in which the spores are formed 
and from which they are discharged when ripe. The upper light- 
coloured layer and the lower orange -coloured layer may be taken 
as distinctive for F. lignosus by the planter, for there is no other 
Fomes species in the plantations showing these characteristics; at 
least, none has been reported up to date. 

The pores are 45-80ju, in diameter, bright orange-yellow when fresh, 
and on drying up, discolour to a dirty grey. The length of the pore 
tube varies considerably. While some doubt has persisted in Malaya 
in past years as to the fertility of the fructifications, there is now no 
reason to believe that they are sterile. They produce viable spores in 
large numbers under certain climatic conditions, which probably 
occur at least once a year and last for a considerable period. The 
occurrence of infection, as a result of the wind dispersal of spores, may 
therefore be considered highly probable in Malaya, but further work 
is necessary correctly to value how far this method of propagation 
influences the spread of the disease. 

The spores are colourless, spherical, 2-8-8/x in diameter, and 
according to Steinmann are always present in large numbers in young 
fructifications. The spores may have completely disappeared from old 
fructifications. 

The basidia are thick-set, colourless, and at the tip bear four fine 
sterigmata on which the basidiospores are borne. They are about 16/A 
long and 4-5-5/i thick. Among the basidia, club-shaped, colourless, 
thin-walled cystidia are to be found here and there. 

Control and Treatment. It has already been emphasised that the 
future treatment of the Fomes group of root diseases in Malaya must 
be of a comprehensive nature, for these diseases are closely linked 
under field conditions, and treatment for F. lignosus cannot be under- 
taken without reference to the root disease caused by Oanoderma 
pseudoferreum. The latter becomes prominent after the disease caused 
by F. lignosus has reached its peak and is on the decline. The position 
is different in Ceylon, for the disease caused by G. pseudoferreum has 
not yet been recorded; at least it is not included in the list of rubber 
diseases of Ceylon published by Murray in 1930. 

In order to deal with this group of root diseases in the manner 
defined, it will be necessary to detail the various points which have 
influenced recent investigators in Malaya to take up almost an 
opposite attitude to previous workers. In addition, the views gener- 
ally held up to a recent date may be stated here; these are given in 



CHAP, ix FOMES LIGNOSUS 125 

paragraphs (a), (6), (c), (d) and (e), which follow. The general theory 
is dealt with at this point because the important features came into 
prominence when investigating F. lignosus. 

(a) All the fungi of the Fomes group which cause the main group of 
diseases of the rubber tree have evolved a successful means of vegeta- 
tive propagation by means of rhizomorphs. 

(6) In the past, it has been generally stated, particularly in the 
case of F. lignosus, that the rhizomorphs can travel independently 
through the soil. 

(c) That each jungle stump affords a centre of disease, spreading 
disease in an ever- widening circle. 

(d) That spores of the disease-causing fungi are blown on the 
exposed wood of jungle stumps and, under favourable conditions, 
the spores germinate and the hyphae grow down into them. The roots 
of these stumps thus become permeated with the fungus, and it 
spreads from them to the roots of adjacent living rubber trees. Some 
fungi can only spread to other plants if the roots of the latter are in 
contact with those of the host stump; others, however (such as F. 
lignosus), are supposed to spread freely through the soil. 

(e) On the above basis, isolation trenches to prevent spread of the 
disease in area were indispensable. 

As a result of his recent work, Napper puts forward the following 
suggestions: 

(1) That the centres of infection which appear in the plantations 
represent the places in the jungle where the disease-causing fungi 
have attacked individual trees or groups of trees before the felling of 
the jungle is undertaken. 

(2) These disease centres, where the fungi have gained dominance 
in the jungle, are absolutely fixed by the acts of felling and burning, 
and they are considered to form a kind of network the meshes of 
which would conform to uninfected areas of land which did not carry 
previously infected jungle trees, while the knots of the meshwork 
represent areas of ground in which infected jungle stumps would be 
found. Hence, distribution of root disease in the jungle at the moment 
of felling governs entirely the distribution of centres of infection in 
the subsequently planted crop. 

(3) With the networks thus predetermined in size or area, and the 
"meshes" being smaller or larger, and the "knots" of infection fewer 
or greater according to the varied activities of the fungi concerned, 
the only method of spread is by contact of healthy roots with infect- 
ive timber. It is thus the growing roots of the planted rubber trees 



126 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

which disclose the "knots'* of infection at a greater or less period of 
time. 

(4) This leads to the interesting conclusion that in the early years 
of the plantations, until root-contact amongst the stand of rubber 
trees is established, isolation of diseased trees by trenching is un- 
necessary, and is really waste of money. When root-contact between 
neighbouring trees is fully established and knots of infection are still 
present in the soil, then trenching can be effectively undertaken. 

(5) Thus, in the early years, the apparent spread of the disease 
amongst the rubber trees is, in reality, a false spread, as it is entirely 
governed by the spread in ground area of the roots of the rubber 
trees brought about by natural growth. The disclosure of the infective 
knots thus brought about by natural increase in length of roots is a 
sound conception, for only time is required ultimately to bring a 
healthy root into contact with infective material in one of the knots, 
and no system of trenching can prevent this. 

From these premises Napper draws the following conclusions: 

The first relevant point is that the old conception of root -disease fungi 
as living and moving freely in the soil must be discarded, and with it the 
cognate idea that the function of an isolation trench is to separate diseased 
soil from healthy soil. The SOIL is always healthy, even if it contains in- 
fected timber. The root-disease parasites live in decaying wood, riot in the 
soil itself, even their organs of propagation, the rhizomorphs, being un- 
able to make direct entry into the soil, but being constrained to travel 
along the surfaces of buried roots. If this is so, isolation trenches are 
successful only in so far as they cut through the chains of roots between 
infected and uninfected areas. In a young area, before root -contact has 
become established between neighbouring rubber trees, isolation trenches 
perform no useful function whatever. 

The second point to notice is that the centres from which root disease 
develops in a clearing are determined in position and extent before ever 
the jungle is felled. While it was held that root-disease fungi could live and 
move freely through the soil and could spread also by the infection of the 
exposed ends of jungle stumps by wind-blown spores, disease patches were 
looked upon as the outcome of simple radial developments of sporadically 
occurring point sources of infection. The practice of throwing isolation 
trenches around the sites of dead trees was therefore entirely justified, 
as it aimed at preventing unlimited development of these point sources. 
It is now known, however, that the centres of infection are the knots of 
jungle-tree infection and are therefore neither point sources nor sporadic 
in occurrence, but are already delimited at the time of felling. No amount 
of trenching can prevent their * 'spreading" to their predetermined size. 

The type of "spread of infection" typical of the early days of an attack 
is therefore a false spread. It does not represent enlargement of the in- 
fected areas, but the gradual disclosure of these areas as the* expanding 



CHAP, ix FOMES LIGNOSUS 127 

rubber-tree root systems make closer and closer contact with the buried 
infected timber within the limits of the knots. It is obvious that isolation 
trenches must be powerless to prevent spread of this kind. 

It is only when the full extent of the knots of jungle infection has been 
unfolded that true spread of infection, controllable by the use of isolation 
trenches, can begin, and even then it is dependent upon the existence of 
free root-contact throughout the stand of rubber trees. 

These specific conditions are not fully satisfied in a rubber plantation 
until the stand is 12-15 years of age. During the first five or six years after 
planting neither condition is fulfilled and isolation trenches are therefore 
worthless, while during the subsequent five to ten years they become 
gradually more and more useful until full practical utility is reached at 
the age stated above. In younger stands, say up to ten years of age, the 
use of isolation trenches, even where they can be justified, should be 
entirely subordinated to a policy of discovering and eradicating the knots 
of jungle infection. Such a policy is fully practicable (it has been tried 
out already on a field scale), and of course would obviate both the present 
and future need for isolation trenches by removing the actual sources 
from which infection arises. 

There has been considerable divergence of opinion in the past as 
to whether the money spent on the treatment of white-root disease 
would be economically disbursed. On the majority of estates in 
Malaya, the position is much the same as that described for white 
ants (page 377). The disease appears in the early stages of the planta- 
tion: during subsequent years there is a sudden increase in numbers 
of trees attacked until a peak is reached about the fifth year, when a 
decline sets in and the disease either practically disappears or at least 
is not prominent to any great extent. The doubts respecting the 
economic treatment of the disease caused by F. lignosus are quite 
justifiable, more especially when the procedure followed is to plant a 
sufficiently large number of trees per acre to allow for disease losses, 
so that not too large a proportion of the stand could possibly be lost 
before the trees were ready for tapping. If an optimum stand per acre 
can be ensured, this may be considered a good and sufficient reason 
for continuing this method. 

In Malaya, the position has been entirely changed by the writer's 
discovery that Ganoderma pseudoferreum was capable of attacking 
the youngest trees, and Napper, following on this, demonstrated that 
it was present in the earliest stages of the plantations, just as in the 
case of F. lignosus. Attention is drawn later to the fact that young 
rubber trees in Java were found suffering from the root disease caused 
by 0. pseudoferreum in 1930. They were reported by E. Von Zboray, 
who gave their age as four and a half years old. The only difference in 
the two fungi is that F. lignosus is a quicker-growing fungus, becom- 



128 DISEASES AND PESTS OF THE RUBBER TREE PART in 

ing prominent from the second to fifth year, whereas G. pseudoferreum 
does not attain prominence until about the tenth year or even later. 
The enormous amount of damage brought about in old rubber areas 
in Malaya must be put down to G. pseudoferreum, and if the future is 
to be assured, a scheme of control is necessary which will reduce 
losses to a minimum from both F. lignosus and G. pseudoferreum. A 
suitable scheme has been worked out and all preventable losses from 
root disease should now be accounted for. If this optimistic view of 
the future is realised, then the expense of early treatment of root 
disease will be fully justified. 

The following remarks regarding early treatment must be taken to 
apply equally for the disease caused by G. pseudoferreum and that 
caused by F. lignosus, although the latter shows up more prominently 
in the early stages. If the situation is taken in hand about a year after 
planting, much can be done before diseased trees begin to appear. At 
this stage the connections and contacts between the jungle-root 
systems can still be traced with ease, while infected jungle roots still 
bear unmistakable evidences of infection. If, therefore, a systematic 
collar inspection is made of all jungle stumps, it is possible, at this 
early stage, to map out the "knots" of infection and, by digging out 
all the infected stumps, entirely to eradicate root disease of all kinds 
once and for all, before any appreciable loss of stand has occurred. 
This method has already been tried out on a large scale, and on one 
estate is proving satisfactory. 

If control measures are deferred until their need becomes apparent, 
i.e. until rubber trees begin to die, the opportunity of making this 
single clean sweep of root disease will be lost. The connections between 
the jungle roots will rot away, thus rendering it difficult or impossible 
to trace infection from stump to stump, while the progressive decay 
of the stumps themselves will make it difficult to distinguish between 
uninfected and infected stumps which have lost the traces of the 
rhizomorphs which originally caused their infection but have not 
yet begun to develop rhizomorph systems of their own. In such cases, 
methods have to be devised by means of which the infected timber 
is discovered and removed piecemeal. The simplest of these is the 
method of periodic tree-to-tree inspection, with treatment which will 
lead to the tracing and removal of the sources of infective material. 
This generally consists of bits of rotting timber lying at various 
depths in the soil, usually not deeper than two feet, though cases have 
been observed where the infective material was found at a depth of 
four feet. In order to guarantee complete control with this system, 
tree-to-tree inspection is absolutely essential. 



CHAP, ix FOMES LIGNOSUS 120 

It is impossible to detect an infected tree on leaf symptoms alone, 
until it is beyond hope of treatment. The tree can then neither be 
saved itself nor can its own removal as a source of infection be of any 
great benefit to its neighbours, since each infection in a young stand 
is a separate one, the decay of the ''knots" having left each one an 
area of scattered, unconnected infective material. It is a case, there- 
fore, of every tree for itself, and it is only by making a tree -to -tree 
inspection that infected trees can be caught at an early enough stage 
to yield to treatment. Furthermore, the treatment must be periodic, 
since a tree which is healthy at one inspection may, within a few 
months, as its root range increases, make contact with hitherto un- 
touched infective material in its vicinity. As regards frequency of 
treatment, the rounds must be frequent enough to ensure that, in the 
interval between consecutive rounds, the number of trees becoming 
too heavily diseased to yield to treatment is small compared with the 
number which can be treated successfully. In practice, an interval 
of four months between inspections works well, even in cases of very 
heavy infection. 

It has been stated above that the discovery and eradication of the 
jungle knots of infection is of vital importance if a successful system 
of control is to be developed, and that the disease knots of both 
F. lignosus and O. pseudoferreum must be removed as completely as 
possible. The actual method of procedure may now be given in detail. 
We will select for treatment a young budded area the soil of which is 
covered with a thick cover crop of Oentrosema pubescens, and control 
measures should be started when diseased trees are first found. The 
following instructions should be carefully noted: 

(1) In order to avoid damaging the trees all excavations in the 
vicinity should be made by a wooden shaft, which is shaped like a 
spade at one end and pointed at the other. 

(2) The cover crop must be removed to a distance of three feet all 
round the trees. 

(3) The root systems of the inspected trees must be laid bare to a 
depth of eighteen inches to two feet below the collar and laterally 
three feet from the stem. 

(4) A thorough examination of the exposed roots is now made. If 
they prove to be infected, the source of infection should be sought 
for. Commencing at the stem of the tree, the various lateral roots are 
bared to their entire length until contact is made with the infecting 
stump or piece of rotting timber. Any stumps which have to be 
removed are usually found with the white rhizomorphs growing on 

K 



130 DISEASES AND PESTS OF THE RUBBER TREE PART in 

the surface. Usually a tree is infected from one stump only, but this 
must be carefully checked, as there may be other seats of infection. 
The soil surrounding the stump and the infected tree or trees is then 
dug over to a depth of eighteen inches and small fragments of jungle 
timber removed. Enormous quantities of this are often found and are 
usually covered with the mycelium. 

(5) When the roots of the rubber trees are found carrying the white 
rhizomorphs, the latter should be carefully removed by means of a 
clasp-knife or other sharp instrument, and the underlying cortical 
tissue carefully examined to see if it is discoloured owing to the pene- 
tration of the fungus into the tissues. If there is no discoloration and 
the cortical tissues seem healthy, the root system should be completely 
drenched in a solution of 2 per cent copper sulphate. The roots are 
then gently rubbed to remove all traces of infection. 

(6) Paragraph No. (4) refers to trees in which the mycelium has not 
penetrated into the underlying plant tissues, i.e. the fungus is in the 
epiphytic state. When the fungus has penetrated into the root, dis- 
coloration of the underlying tissues will be observed. Such cases 
demand the removal of the diseased root, and the application of a 
wound cover such as tar or asphaltum-kerosene mixture on the cut 
end. When this procedure has been thoroughly carried out, the earth 
is replaced and packed down in its original position around the roots. 

(7) It is advisable to distinguish between (a) trees inspected and 
(b) trees found diseased. A black mark is suitable to indicate the 
former; a red mark to indicate the latter. 

The following is typical of a detailed analysis of a tree -to -tree 
inspection. A patch (A) was examined which contained 327 trees, 
bud-grafted exclusively with clone A.V.R.O.S.50. The majority of the 
trees presented a vigorous and healthy outward appearance with 
good growth and girth for age. Prior to the commencement of the 
tree-to-tree examination, two cases of white-root disease had been 
located and treated. 

Fifteen trees were found to be infected by F. lignosus on the first 
examination =4- 6 per cent. Some trees carried a heavier infection 
than others, but none appeared beyond the aid of treatment. When 
the infection is light and there is no penetration of the root tissues by 
the fungus, there is no difficulty and most of these trees seem likely 
to survive. 

In the more heavily infected trees, certain of the lateral roots had 
to be removed, the exposed wood surface being treated with tar. The 
costliness of the operation depends on the degree of difficulty entailed 



CHAP, ix FOMES LIGNOSUS 131 

in the search for submerged timber harbouring the mycelium. In 
some cases cartloads of heavily infected timber have been found 
and removed, whereas in others the surrounding ground has been 
found to be comparatively free, apart from the actual disease "knot" 
itself. 

Of the 15 cases found it should be noted that all were single trees 
except in one instance where two infected trees were found together. 
These were somewhat evenly distributed over the area and there 
was nothing which indicated the presence of disease prior to the 
actual examination of the root systems. In practically every case the 
foliage carried was ample and of healthy appearance. Incidentally, 
the sporadic appearance of diseased individuals strongly supports 
Napper's contention that the disclosure of the infected area is brought 
about by the expansion of the root system; as the roots grow in length 
they, at some time or other, come into contact with infected material, 
and infection is not brought about owing to independent travel of the 
white rhizomorphs through the soil. If the white rhizomorphs could 
travel independently through the soil to any large degree, the result- 
ant distribution of diseased trees would obviously be of a grouped 
character. 

A second patch (B) containing 484 trees budded with clone 
A.V.R.O.S.49 was treated in a similar manner to patch A. The trees 
were all thoroughly healthy in appearance, but the branching and 
girth development were not so good as that of the bud-grafts of 
A.V.R.O.S.50. Again, the large majority of the trees found to be 
infected were single cases. Two cases of two adjacent infected trees, 
and one group of seven infected trees, were found. The amount of 
submerged timber uncovered again varied largely. 

The percentage of infected trees found in this patch was approxi- 
mately 8 per cent = 38 out of 484 trees. This is a heavier percentage 
infection than in patch A, and in addition the individual cases 
appeared to be more heavily infected. All the treated cases in patch 
A appear to be maintaining a healthy foliage after treatment, but 
three in patch B died after treatment. 

Over the areas examined, the sources of infection in the disease 
knots were usually found at a depth of 2-3 ft., although, occasionally, 
digging to a depth of 4 ft. was necessary. Thus it is obvious that the 
expense of these operations will vary considerably according to the 
depth at which the infective material is found. Expenses will also vary 
according to the age of the trees; it is much more costly to open up 
the root system of a four- to five-year-old tree than a two-year-old tree 
because of the much greater extent of the former. Further, expenses 



132 DISEASES AND PESTS OF THE RUBBER TREE PART in 

will vary according to type of soil; it is much more expensive digging 
in heavy clay soils than in open sandy loams. 

An analysis of the records received from an estate which has been 
systematically treating root disease, under supervision by Napper, 
shows many interesting pointers. The experiment is in progress on an 
estate of 3000 acres, divided by purely artificial boundaries into three 
clearings, each roughly 1000 acres in extent, planted in 1928, 1929 
and 1930 respectively. The land is constant in type throughout the 
whole area and originally carried heavy jungle. 

The site has many advantages from an experimental point of view, 
In the first place, the uniformity of the site makes it reasonable to 
assume that the jungle carried, before felling, a uniform incidence of 
root disease throughout, and that the differences which have since 
developed between the types of attack in the three clearings have been 
due solely to the differences in manipulation to which they have been 
subjected. Since the areas compared are as large as a thousand acres, 
the error involved in making this assumption should be small. A 
second advantage is that the clearings are in distinct age classes 
with equal class intervals; and a third that, when the experiments 
were begun two years ago, Clearing No. 2 (planted in 1929) was just 
two years old and therefore at the period of maximum root-disease 
activity, while Clearing No. 1 (planted in 1928) was well beyond the 
maximum, and Clearing No. 3 (planted in 1930) well short of it. 

The experiment was started in October 1931 and took the simplest 
form, viz. the application of a standard method of treatment over the 
whole estate. The method employed consisted of periodic rounds of 
tree-to-tree inspection and treatment as outlined above, the rounds 
following one another at intervals of three to four months. Treatment 
consisted in opening up infected trees, following the rhizomorph 
systems to their points of origin, removing the sources of infection 
(rotting jungle roots) and treating the roots of infected trees with a 
weak solution of copper sulphate. 

The work has been wholly in charge of the Manager, and has, in 
fact, been carried out as a purely commercial operation under estate 
conditions. Personal visits have been paid as often as possible to 
discuss the progress of the work. 

Up to the present (February 1934) there have been six rounds of 
treatment in Clearing No. 1, and five each in Clearings No. 2 and 
No. 3. Detailed records have been kept by the Manager for each round 
of treatment, showing the results of the previous round (i.e. recoveries, 
deaths and re -treatments), the amount of new infection and the cost 
of treatment. These records have been summarised in the following 



CHAP, ix FOMES LIGNOSUS 133 

table (barring costs, a full statement of which is not yet available): 

TABLE II 



Clearing 


Present 
Age (in 
years) 


Age at 
which 
Treat- 
ment 
began (in 
years) 


Length 
of Time 
under 
Treat- 
ment (in 
years) 


Loss of 
Stand 
before 
First 
Treat- 
ment 
(per cent) 


Recover- 
ies since 
Treatment 
began 
(per cent) 


Loss of 
Stand 
since 
Treat- 
ment be- 
gan (per 
cent) 


Total 
Loss of 
Stand 
since 
Plant- 
ing (per 
cent) 


Present In- 
cidence of 
Infection 
(per cent) 


No. 1 (700 


5 


3 


2 


15-9 


7-7 


2-2 


18-1 


0-67 


acres) 


















No. 2 (1200 


4 


2J 


1J 


8-9 


7-7 


2-3 


11-2 


049 


acres) 


















No. 3 (1100 


3 


11 


U 


3-7 


5-7 


2-0 


5-7 


0-99 


acres) 



















Allowing for the fact that Clearing No. 1 has received one extra 
round of treatment, the figures for the different clearings are remark- 
ably consistent among themselves, and agree closely with expectation 
based on the present theories of root disease. It may be difficult at 
first to understand why the recoveries (and also the losses since treat- 
ment began) in Clearing No. 3 are not a good deal higher than in 
No. 2, and in No. 2 than in No. 1. The explanation is as follows. In 
young clearings, where the root systems of the trees are small, 
individual pieces of infected jungle timber are unlikely to infect more 
than one tree before being discovered and removed during treatment. 
In older clearings, however, the root systems are large and wide- 
spreading, and individual pieces of infected timber stand a good 
chance of infecting two or more trees before removal. In each clearing 
the treatment has saved a considerable number of trees from be- 
coming infected, although there is no means of showing this type of 
"recovery" in the records. It is certain, however, that the number is 
much higher in Clearing No. 3 than in No. 2, and in No. 2 than in 
No. 1. 

Table II indicates very forcibly the advantage of beginning treat- 
ment early. In Clearing No. 1, at three years old, in the complete 
absence of treatment, loss of stand had reached the alarming figure of 
over 18 per cent, yet in No. 3, at the same age, after being under 
treatment for eighteen months, the loss was barely a third of this 
figure, i.e. 5-7 per cent. 

De Jong's recent work should be kept in mind at this stage, for if 
we accept for the time being that in 00 per cent of infected cases the 
mycelium disappears without causing harm, then the 18 per cent of 
total losses would represent a total infection of over 40 per cent. The 



134 



DISEASES AND PESTS OF THE RUBBER TREE PART in 



point made by De Jong is of considerable interest, but is not of great 
importance when considering control, as will be explained later. 

A more accurate measure of the relative success of the treatment 
when begun at different times after planting is provided in Table III, 
which shows the state of affairs at the same age (i.e. three years after 
planting) in each clearing: 

TABLE III 



Clearing 


Age before 
Treatment 
began 
(in years) 


Loss of 
Stand 
before 
Treatment 
began 
(per cent) 


Length of 
Time under 
Treatment 
before Stand 
3 years old 
(in years) 


Loss of 
Stand 
during this 
Period 
(per cent) 


Total Loss 
of Stand 
at 3 years old 
(per cent) 


No. 1 (700 acres) 


3 


15-9 


.. 




15-9 


No. 2 (1200 acres) 


2i 


8-9 


1 


1-8 


10-7 


No. 3 (1100 acres) 


li 


3-7 


H 


2-0 


5-7 



Although the experiment has not yet been completed there can be 
no doubt that, from a scientific point of view, it will prove a complete 
success. As regards costs, a full record is not yet available except for 
Clearing No. 1, and this will be given here as they are the most 
important. The total cost of five rounds of inspection and treatment, 
including the cost of cultivating the sites of dead trees, amounts to 
3.20 dollars per acre. Considering that the total cost of bringing this 
particular clearing into bearing is estimated at 200 dollars per acre, 
and that for under 2 per cent of this expenditure an immediate saving 
of at least 15 per cent of the stand has been effected, to say nothing 
of the subsequent saving on account of the early removal of centres 
of infection of Ganoderma pseudoferreum (an even more important 
factor), there can be little hesitation in pronouncing the experiment 
a complete success also from the financial point of view. 

It is stated above that De Jong's point when considering control is 
not of much importance. All cases affected, whether in the epiphytic 
stage, which would include De Jong's 60 per cent of harmless cases, 
or in the more advanced ones where penetration of the host tissues by 
the fungus has actually taken place, must be treated according to the 
routine laid down. It would obviously be dangerous if the treatment of 
epiphytic cases were delayed, for exposure of the root system should 
be of short duration, therefore the earth must be returned to cover the 
roots which are carrying, or have carried, epiphytic mycelium, as 
soon as possible. If left untreated, a serious attack may eventually 
result, for, as De Jong emphasises, the fungus mycelium can cause 
extensive decay only under special environmental conditions, and if 
such eventuate, any epiphytic mycelium may take on an active phase, 



CHAP, ix FOMES LIGNOSUS 135 

during which period penetration may take place. It must be remem- 
bered that environmental conditions are never static, but are continu- 
ously changing at different periods of the year. For this reason, it 
seems most undesirable that the figures given by De Jong should be 
allowed to influence any recommendations for control. Just as at 
certain periods of the year, and not at others, there is a profuse pro- 
duction of viable spores, in the same way, the passage of the mycelium 
on the roots from the epiphytic to the parasitic stage may be entirely 
under the influence of the climatic conditions prevailing at any 
particular period. 

If De Jong's investigations can be confirmed by observations in 
Malaya, it is obvious that on lightly infected areas the disease caused 
by F. lignosus will not call for special treatment, and that it may be 
possible, as certain planters claim, to limit treatment to removing the 
roots and stems of the trees killed by the fungus and re -supplying 
immediately. But if this type of treatment is undertaken and no 
attention is given to eradicating disease knots of Ganoderma pseudo- 
ferreum in the early years, then it can only be expected that more 
time must be spent and further expense incurred when the trees are 
about the age of ten years. It cannot be emphasised too often that 
the recommendations now being made for treatment of F. lignosus 
are largely dependent on the fact that such treatment will also result 
in the early extermination of disease knots of G. pseudoferreum. 

Much prominence has been given to the recent work of De Jong on 
the subject of Rigidoporus microporus (=F. lignosus). This investi- 
gator has carried out his investigations in Sumatra, while Napper has 
been working on the same subject in Malaya. The two investigations 
have practically coincided in time, but while the one in Malaya was 
devoted mainly to obtaining results which would prove useful in the 
control of a general root-disease problem, that in Java was con- 
sidered from a different angle, for De Jong states specifically in the 
extract following that 

no attempt is made to deal with the practical side of the question, since 
it is considered that the Rigidoporus problem is one that can only be 
intelligently solved with a view to the peculiar conditions obtained in 
any particular locality and the results thus obtained are largely of local 
significance only. 

It will be noticeable to readers that our conceptions of the root- 
disease problem in Malaya are mainly based on the very extensive 
damage which has been done generally in the old rubber areas by the 
root disease caused by 0. pseudoferreum, and that, if it were not for 
this factor, De Jong's statement would meet the situation in Malaya, 



136 DISEASES AND PESTS OF THE RUBBER TREE PART in 

with respect to the root disease caused by F. lignosus. There are many 
important results recorded in De Jong's work which, for all practical 
purposes, may be considered identical with those obtained in Malaya 
by Napper. Therefore, a copy of the most relevant portion of the 
English summary of De Jong's paper is given below for comparison 
with the points raised in the foregoing account: 

The foregoing inoculation results experiments appear to indicate that 
the fungus in question is only weakly parasitic to rubber. The presence 
of mycelium alone on the roots of an infected tree does not necessarily 
indicate the subsequent development of decay, and the presence of decay 
is not always followed by the death of the tree. Observations to this effect 
have not only been obtained from the inoculation experiments but also 
from trees that have become naturally infected in the field. Of course there 
is no doubt that Rigidoporus microporus is frequently responsible for 
deaths in stands of Hevea, but such cases are probably associated with 
special environmental conditions that affect the virulence of the fungus 
and the susceptibility of the tree. 

It would appear that the following factors are of importance in con- 
nection with the development of Rigidoporus decay in Hevea: 

a. The presence of Rigidoporus decaying wood in close contact with the 

roots of the tree. 
6. The size and/or quantity of the inoculating material. Probably the 

nature of the inoculating wood is also important. 

c. Extent of decay of the inoculating material. 

d. The size of the rubber tree involved, as small trees can be killed more 
quickly than larger ones. 

e. Variation in resistance to the disease among rubber trees. This may be 
the result of predisposing environmental conditions. 

/. Previous history of the area, with special reference to the vegetation it 
formerly supported. In this connection, epidemics have been observed 
in red soil areas that were formerly planted with Ficus dastica, also in 
red soil and sand "permatang" areas previously planted to coco-nuts. 
White soil areas that formerly supported coco -nut palms are apparently 
not particularly subject to the disease. The literature contains refer- 
ences to the effect that rubber planted on sites previously occupied by 
Koompassis Malaccensis and Artocarpus elastica is especially subject 
to the disease. 

g. The situation with respect to ground cover. In this connection Napper 
reports that the incidence of the disease is reduced through the presence 
of cover crops, "blukar", and avoiding clean clearing in opening new 
areas. Although the importance of these factors is not precluded, they 
cannot be considered as definitely established, especially since Napper 's 
method for estimating the status of the disease is open to question. 

h. Characteristics of the soil. The rubber on red soil and sand "permatang" 
areas appears to be especially subject to the disease, where its incidence 
is very much higher than in the case of white soil stands. As far as 



CHAP, ix FOMES LTGNOSUS 137 

conditions on the H.A.P.M. are concerned, there appear to be no direct 
relationships between the incidence of the disease and: 
I. the >H of the soil; 

II. the titratable acidity of the soil after shaking with a potassium 
chloride solution; 

III. the phosphate of the soil; 

IV. the humus content of the soil; 

V. oxidation characteristics of the soil. 

i. Manuring treatment. In this connection, however, an experiment in a 
red soil stand of young rubber showed no significant differences in the 
disease situation following the application of the common artificial 
manures and certain combinations thereof, except in the case of treat- 
ment with a combined manure containing nitrogen, phosphate and 
potash, together with manganese sulphate, where an increase in the 
incidence of the disease was obtained. Even in this instance, however, 
it is considered that confirmatory evidence is required before accepting 
the fact as established. From another experiment it appeared that the 
use of a mixture of cow-dung and soil for filling the planting holes 
caused a slight increase in the incidence of disease among the young 
trees planted in this manner. 

In the present paper no attempt is made to deal with the practical side 
of the question, since it is considered that the Eigidoporus problem is one 
that can only be intelligently solved with a view to the peculiar conditions 
obtaining in any particular locality, and the results thus obtained are 
largely of local significance only. At the same time, certain aspects which 
have been brought out in the present paper should not be overlooked in a 
practical study of the problem: 

(a) An estimation of the disease situation in any particular area should 
not be based on the incidence of mycelium infections only, since the 
presence of mycelium is not necessarily followed by decay. 

(b) The same is true with regard to judging the status of disease from 
a single examination as to the incidence of Rigidoporus decay, 
because such decay may stop of its own accord, even without 
treatment. 

(c) The only satisfactory manner in which to estimate the disease situa- 
tion in any particular locality is through repeated examinations 
that show the progress of decay, or better still, an accurate record 
of the mortality due to the disease. 

Summary of Treatment. It may be advisable, for the sake of the 
planter, to give a summary of the views expressed in the foregoing 
paragraphs. 

Napper believes that if the situation is taken in hand not more 
than a year after planting, much can be done to deal with infected 
jungle knots before diseased rubber trees begin to make their appear- 
ance. As stated, this method has been used with beneficial results on 
a large scale on one estate, yet the writer's opinion is that it will prove 



138 DISEASES AND PESTS OF THE RUBBER TREE PART m 

of limited application, because the personal factor will enter into the 
proposition to a very great extent. Usually, it is only when diseased 
trees are being discovered that the question of control is seriously 
considered. 

The following fact has already been emphasised and explained in 
detail and should now be clearly understood by all readers; viz. that 
in a young area, before root- contact between neighbouring rubber 
trees has become established, isolation trenches cannot perform any 
useful function. 

That the centres of infection are the "knots" of jungle -tree infec- 
tion already delimited at the time of felling, and no amount of 
trenching can prevent their spreading to their predetermined size. 

Further, spread of infection in the early days of an attack is not an 
actual spread and is really a gradual disclosure of diseased areas by 
the expanding rubber-tree root systems making closer and closer 
contact with the buried infected timber within the limits of the 
' 'knots". Isolation trenches cannot prevent spread of this kind. 

Isolation trenches can only become useful when the full extent of 
the "knots" of jungle infection has been disclosed, and then their 
utility is entirely dependent upon free root-contact throughout the 
stand of rubber trees. 

Thus, isolation trenches can be considered worthless during the 
first 5-6 years; during the next stage covering another 5-6-year period 
they will become more and more useful, until at the age of 12-15 years 
they will reach full practical utility and, as will be obvious later, wiU 
be specially useful in the control of the disease caused by G. pseudo- 
ferreum. Up to the age often years the use of isolation trenches should 
be entirely subordinated to a policy of discovering and eradicating 
the knots of jungle infection. 

Three points may be briefly emphasised: 

(1) It is obvious that there should be no trenching. 

(2) There is no necessity to use lime except under special circum- 
stances. 

(3) Wounding of healthy trees around the collar during cultivation 
operations is not considered to be of any special significance in aiding 
the fungus to attack the root system. 

Treatment of F. lignosus should be commenced by exposure of the 
root system, and if diseased roots are found, the source of infection 
must be found and extracted. Infected stumps should be removed as 
far as practicable. Soil surrounding diseased stumps or infected rubber 
trees should be dug over to a depth of eighteen inches and small 
fragments of jungle timber removed. 



PLATE II 







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S -w> 

S 3 



J (S 

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CHAP, ix GANODERMA PSEUDOFERREUM 139 

Rubber roots carrying rhizomorphs should be examined carefully 
to see if the fungus is in the epiphytic state, i.e. not penetrating the 
root tissues. This is done by carefully scraping the mycelium from the 
roots with some sharp instrument, and if there is no underlying dis- 
coloration in the cortical tissues, the root system is well drenched in 
a solution of 2 per cent copper sulphate, and roots which have carried 
any traces of the fungus are gently rubbed to remove all traces of the 
infection. Other materials beside copper sulphate have been used with 
successful results. If the underlying cortical tissue is found to show 
the slightest discoloration whatever, the root must be cut off, the cut 
being made in healthy tissue, while the healthy tissue exposed by the 
cut should be protected by the application of a wound cover such as 
tar or kerosene and asphaltum mixture. When this work has been 
completed, the earth should be replaced and packed down in its 
original position around the roots. 

The writer fully appreciates that, during depressed financial periods, 
the advice given cannot be followed because of depleted finances. 
In such cases, some modification of the main routine will have to be 
undertaken or the disease must be left to take its course. Any modifica- 
tion which might be possible can only be discovered by the personal 
visit of an expert plant pathologist, and if expert advice is available, 
this should be obtained. It has already been shown that there are 
many dangers to be expected if the disease is allowed to take its 
course owing to lack of money or for any other reason. 

GANODERMA PSEUDOFERREUM (WAKEF.), VAN. 0. ET ST. 
(Red-Root Disease) 

This particular disease was first reported upon in Malaya, in 1916, 
by Belgrave. The reason for the early names of Poria disease coupled 
with wet-root rot, later Fomes pseudoferreus , and at the present time 
Ganoderma pseudoferreum coupled with the common name, red -root 
disease, is detailed in an earlier section. In connection with the latter 
name it must again be mentioned that Fetch describes in the 1921 
edition of his book a red-root disease on rubber trees, caused by Poria 
hypobrunnea. This disease is quite distinct from that caused by G. 
pseudoferreum, and has not been found in Malaya, and according to 
Murray it is one of the most uncommon to which Hevea is prone in 
Ceylon. Red-root disease is very common in Malaya and is respon- 
sible for a large amount of damage in old rubber areas. It is found in 
Java and was first reported in 1920. Steinmann states that in western 
Java it is one of the most frequently occurring and most widely 



140 DISEASES AND PESTS OF THE RUBBER TREE PART in 

distributed root diseases of H. brasiliensis , and that it would not be 
exaggerating to say that there is scarcely a single estate on which 
there are not at least a couple of trees that show infection by this 
fungus. In East Java the disease seems to be less general. Accord- 
ing to official reports, the disease caused by G. pseudoferreum has 
not yet been found in Ceylon. 

The following quotations may be given from Steinmann's book, 
after which points of difference, as seen in Malaya, may be appreci- 
ated more readily: 

Red-root fungus occurs most frequently on heavy clay soils, on estates 
that have trouble with water in the sub-soil, in depressions in the land, in 
the vicinity of rivers, etc., and especially in old fields; this fact is connected 
with the progress of the disease. In the initial stages of the disease there 
are no outward signs. The trees continue to appear healthy and fresh; this 
is due to the fact that the infection as a rule is confined to one side of the 
root system. Outward signs only appear after a lapse of years; the tops 
die back, the crowns become sparse and the leaves wither and turn yellow. 
But during this time the fungus has had an opportunity of spreading all 
over the field and for preventive measures it is then too late. It may happen 
that fields that outwardly look healthy, in the end turn out to be com- 
pletely infected with red-root fungus. It is the slow rate of spread of the 
disease which makes it more especially dangerous. The red-root fungus is 
often found with the white-root fungus together on the same root; con- 
fusion may then take place as the disease symptoms are then mixed. 

In Malaya, red-root disease occurs commonly in mature areas on 
most types of soil and little can be said in respect of the fungus, 
showing preference for certain types of soil or any particular situation. 
On plantations possessing both hilly and flat land areas carrying 
mature rubber trees, serious root-disease losses may be met with in 
both types of land. In such cases it may be found that the losses on the 
flat land areas are due entirely to Fomes lignosus, while those on the 
hilly areas, over the same estate, will be found to be caused by G. 
pseudoferreum. On a neighbouring estate, the exact reverse situation 
may be encountered with G. pseudoferreum as the common cause of 
the losses on the flat land areas and F. lignosus predominating 
largely on the hilly areas. When both fungi are present in the circum- 
stances indicated, the exact situation can never be predicted with 
certainty, but it is seldom that a mixed infection is found. 

In 1917 Belgrave recorded that only one estate had had its young 
rubber badly attacked by Poria, and the death of isolated trees which 
had been attributed to F. lignosus or brown-root disease was really 
caused by G. pseudoferreum. But though this report was made so 
early, the true status of this fungus as a parasite on the roots of young 



CHAP, ix GANODERMA PSEUDOFERREUM 141 

rubber trees was not fully realised until 1931-32. Belgrave's record 
of 0. psendoferreum attacking young trees was the only one up to 
November 1930, when E. von Zboray, in Java, reported that he had 
found true red-root disease on trees four to five years of age. A copy 
of this article is reproduced in a later section (page 202). All investi- 
gators had considered the typical attack, as seen on mature trees, to 
be of major importance. 

This attitude can well be understood, for until recently there were 
two outstanding facts difficult of explanation, viz. : (a) that the 
disease, omitting the exceptional attacks found on young trees before 
1930, seldom became prominent until trees were about ten to twelve 
years of age; (6) that most of the attacked trees were, or had been 
considered to be, good yielding trees. 

Steinmann says, "It is especially the slowness of the progress of the 
disease which makes it so dangerous". This general statement has 
been accepted to account for (a), assuming that "slowness of growth" 
under the conditions prevailing was an inherent quality of the 
fungus. The fungus undoubtedly develops comparatively much more 
slowly than F. lignosus in time, but this fact does not allow for a 
complete explanation. 

In 1931, while supervising a trenching system in a badly infected 
area, the number of diseased roots which showed the proliferation of 
large masses of adventitious roots was very noticeable (Fig. 19). 

Fig. 19 shows the typical appearance of diseased roots with ad- 
ventitious roots springing from them. In one it is obvious that the 
rubber root has recovered naturally as the result of the adventitious 
root development, for further penetration of the fungus has been 
prevented successfully. 

The prolific production of adventitious roots on attacked trees led 
to a natural conclusion which has proved to be correct. The assump- 
tion that the production of healthy, absorbing, adventitious roots is 
a common reaction to the attacks of G. pseudoferreum led to the 
conclusion that the absorptive area of the root system would be 
increased substantially, and the general physiological reaction to the 
fungus attacks would be the absorption of an increased supply of 
water and food materials in solution. Further, the rate of the progress 
of the fungus through attacked root tissues would be considerably 
retarded when the general vigour of the plant is maintained at a 
normal level, because adequate supplies of food materials are avail- 
able owing to the development of a copious supply of adventitious 
roots. 

Thus, if trees are attacked in the earliest stages of the plantation, 



142 DISEASES AND PESTS OF THE RUBBER TREE PART m 







FIG. 19. Oanoderma pseudoferreum. Illustrations showing proliferation of 
adventitious roots from roots of rubber trees severely attacked. 

a, Attack on tap-root of young tree. Note ring of adventitious roots produced at reirion of collar 
growing vertically, straight downwards, into soil. g r collar ' 

6, Surface, lateral root of old tree showing common appearance, with extensive development of 
adventitious roots. 

c, Affected lateral root of old tree. 

d, Showing root in c, split open. The fungus attack has been entirely checked and the diseased wood 
cut out thoroughly, by the development of the ring of healthy adventitious root". 



CHAP, ix GANODERMA PSEUDOFERREUM 143 

there is no reason to expect external symptoms in the crown to appear 
at once, for the response of the attacked plant is the production of 
numerous adventitious roots from the unaffected root tissue, and 
these readily absorb water and food materials. As the disease remains 
entirely subterranean, only trees of mature age, not less than ten 
years old, are likely to be found showing typical symptoms. But it is 
perfectly plain on this reasoning that G. pseudoferreum will be present 
on rubber trees much younger than the age mentioned, and that it 
might be found in the earliest stages of the plantation. 

The above would also provide a probable explanation for the 
assertion often made by planters, that their best yielding, trees are 
always the first to be found attacked by red-root disease. The profuse 
proliferation of healthy adventitious roots, capable of water absorp- 
tion, would result in increased absorption of water and nutrient 
solutions, and increased yields of latex may be expected to follow 
naturally. 

It is now fully established in Malaya that 0. pseudoferreum is 
present in the earliest stages of the plantations. A diligent search 
resulted in the disease being found on trees four to five years of age 
(Fig. 20 a and b). Subsequently trees not more than three years of age 
were found attacked by the fungus, and more recently still Napper 
has shown that the "knots" of disease are very well defined and 
compact, and that diseased trees can be found at the same time as the 
first cases of Fomes lignosus, when the plantation is carrying trees 
not more than one and a half to two and a half years of age. There is 
no doubt that large numbers of young trees which have developed 
diseased roots have been diagnosed as F. lignosus in the past, whereas 
the proper diagnosis should have been G. pseudoferreum. 

Symptoms. In mature trees, the woody tissues of attacked roots 
degenerate into a soft, spongy mass from which water can be squeezed 
under the pressure of the fingers. This "wetness" of diseased wood is 
independent of situation, but is not very obvious in young plants. In 
addition to the wetness of diseased tissues, attacked roots are charac- 
terised by the formation of red rhizomorphs on the external surface. 
These rhizomorphs are formed from simple, red, mycelial strands 
which later fuse together to form a continuous membrane. The rhizo- 
morphic membrane and individual rhizomorphs are not always easily 
seen when first extracted from the ground, as portions of the soil 
remain attached, being held by the rhizomorphs; it is therefore 
necessary to wash the soil away before the red rhizomorphs and mem- 
branes can be recognised. In diagnosing the disease on young trees, 
the only reliable guide is the presence of red mycelial strands or 



144 DISEASES AND PESTS OF THE RUBBER TREE *ABT in 

membranes. When the strands and membranes are young they are 
light red; when drying the red colour fades to a dirty white, but the 
colour reappears after moistening. When older, the colour is deep 
claret and remains unchanged by drying. When the roots are entirely 
rotten, the colour of the rhizomorphic membranes approaches a 
blackish violet colour and single, separated rhizomorphs are found 
only occasionally (Plate I). 

The production of a complete, external skin of fungus tissue by the 
union of blood-red rhizomorphs appears to be a constant feature of a 
certain phase. This external skin is never found on the upper parts of 
diseased lateral roots exposed to light and air, though it may be found 
occasionally on the under-side of such surface roots, which are in 
contact with or slightly buried in the soil. 

The progress of the disease in surface roots is always more marked 
along the under-side; the lower surface in contact with the soil may be 
completely rotted, while the upper half remains free from attack. In 
roots which have the upper surface exposed to the atmosphere, the 
line between healthy and diseased tissues is well marked even exter- 
nally. This is caused by the development of a well-marked line of 
"callus growth" from the healthy tissues on the upper surface. In 
vigorous trees, the callus development may proceed so far as to 
completely occlude the diseased woody tissue, and in some cases the 
fungus is prevented from penetrating further along the root by 
this means. The common response shown by attacked roots is a 
profuse proliferation of adventitious roots, and this is a striking 
feature in mature trees. But even in young trees, which show roots 
attacked by this fungus, the proliferation of adventitious roots is 
pronounced and appears often as a sort of digitate branching, as shown 
in Fig. 20 a and b. 

The young, diseased root illustrated was split open longitudinally 
in the laboratory on the day it was extracted from the soil. When it 
was split open, only a small portion of the under-side of the root, the 
portion marked (a), showed the typical dark brown colour of red-root 
rot (Fig. 20 a and b). The split root was left exposed to the air for a few 
days when the portion marked (b) was found discolouring; first, from a 
white healthy-looking state to a light brown colour, which later be- 
came darker brown, and on the third day after splitting no further 
discoloration took place. This portion of the wood, which appeared 
quite healthy when split, never attained the dark brown colour of the 
wood obviously diseased at the time of splitting. However, when 
examined microscopically, the hyphae of the fungus could be made 
out quite easily and they were present in plenty. The subject is not 




Fia. 20. Photographs illustrating first case of roots of young rubber tree 
found attacked by O. pseudqferreum. 

The specimen illustrated was found on a tree 3J years of age; it was 9 inches below soil level and 
the diseased tissue in the root was confined to the under surface. Note apparent digitate branching, 
due to proliferation of healthy roots from healthy tissue on upper surface. 

a, Kcgion of root marked A indicates diseased under surface. 

t>, Kcgion of root marked A shows healthy upper surface, from which adventitious roots spring. 
c. Same root a* in a and ft, split open. A ~ badly diseased under surface. B== slightly diseased area, 
with discoloured wood not very prominent in photograph. C--- healthy tissue on upper surface. 



146 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

one of special importance and may be left without further comment. 
Should any investigator desire to obtain the details in respect of the 
investigation of diseased tissues, the article by Belgrave should be 
consulted. 

In addition to the main symptoms already described here, Belgrave 
also draws attention to the following minor details: 

(h) The presence of brown, not black, lines in the wood. The lines are 
very thin and sharply defined, and as a rule run nearly straight, without 
the reticulation characteristic of the lines of Ustulina. They sometimes 
curve to enclose small islands, which are more decayed than the surround- 
ing wood. The lines are really the edges of plates of hard brown tissue seen 
in section. 

(i) The presence of discoloured light brown areas in the wood. Such areas 
usually occur near the junction of healthy with diseased tissue, and are 
often limited on the healthy side by a distinct, darker brown band (cf . with 
description of split root given above). 

(j) Honeycombing of the wood of Hevea roots, though rare, is sometimes 
seen, and is frequently, though not invariably, due to F. pseudoferreus 
(G. pseudoferreum). Such honeycombing is of common occurrence on jungle 
wood. 

As will be seen later, Fetch and Murray, working in Ceylon, call 
attention to the above features described by Belgrave for G. pseudo- 
ferreum, but they are described in connection with root tissues 
affected by brown-root disease. Numerous, thin brown lines are easy 
to see in cases of typical brown-root disease in Malaya, and they 
conform to the above description. Honeycombing of the wood of 
Hevea roots is also ascribed to brown-root disease in Ceylon. 

The woody elements of attacked roots may finally become so 
completely disintegrated that diseased roots resemble "mummified" 
roots. These pseudo-roots have dried out, and are composed of a well- 
developed, external "red-skin" surrounding an aggregated mass of 
fungus tissue, which simulates a false, parenchymatous tissue. None, 
or very few woody elements, can be found in the pseudo -roots by the 
use of the usual wood stains. 

When diseased roots showing the later stages of red-root disease are 
opened up and exposed to the atmosphere, the decaying mass is found 
to be already invaded by many species of non-pathogenic fungi. 
After twenty -four hours of exposure the decayed roots are often 
covered with a brilliant blue-green Penicillium species. In other cases 
diseased roots are, at certain periods, often grown over externally 
with a thick white fungus cover, often half an inch thick. This fungus 
is Echinodia theobromae, Pat., and is characterised by the fact that the 



CHAP. IX 



GANODERMA PSEUDOFERREUM 



147 



surface, if examined, will be found to be covered with upright 
outgrowths resembling small teeth, upon which the spores are 
borne. 

Fructifications. Both in Java and Malaya, a considerable period 
of time elapsed before the fructifications of G. pseudoferreum were 
definitely recognised on rubber trees. Corner took up the question of 
the identity of Javan and Malayan specimens of this fungus in 1931, 




FIG. 21. Transverse section through root badly attacked by G. pseudoferreum, 
though not in the' final state of disintegration. 

A == Showing structure of external rhizomorphic membrane. 

B = Mass of filamentous fungus tissue beneath the external membrane, without definite cellular form. 

C Similar masses of filamentous fungus tissue as in B, but placed much deeper. 

Between B and C are distinct, cellular tissue developments, fan-shaped in appearance. These are 
offshoots of root tissue in rapid division, as shown by the radial distribution of the cells of which they 
are composed. This represents an attempt to cut out the fungus tissues external to these developing 
fan-shaped portions of root tissue. But the fungus has penetrated well below this level, as shown by the 
clumps of fungus tissue marked C. 

and as a result of his examination of the fungus from both countries, 
he concluded that they were alike in every respect, and that the name 
must be Ganoderma pseudoferreum (Wakef.), Van 0. et St. 

Corner reports this species as common on dead stumps in the 
Singapore Botanic Gardens and also in the lowland forest of Malaya. 
He has found it parasitic at the base of several large trees in the forest 
in Johore and Pahang, and has found the fructifications on Myristica 
sp., Pterocarpus sp. and Arenga saccharifera in Singapore. Van 



148 DISEASES AND PESTS OF THE RUBBER TREE PART in 

Overeem records Metroxylon sp., Alhizzia sp. and Durio zibethinus 
(Durian) as other hosts on which the fungus is parasitic. 
In his 1925 edition Steinmann remarks: 

Up till recently the fruit-bodies of G. pseudoferreum were practically 
unknown on our rubber estates, and the reason for this was that the fruit- 
bodies appear only at a late stage of development, when the vegetative 
mycelium has in most cases already rotted away; it may also be due to 
premature blowing-down of diseased trees. This also explains why fruit- 
bodies are seldom seen on those estates where diseased trees are treated 
immediately after discovery. 

In Malaya the fructifications have recently been found developing 
freely on old logs of diseased rubber trees which had been felled and 
allowed to remain in situ for a considerable time. 

The fructifications develop occasionally at the base of diseased 
trees which are still standing. They are commonly found developing 
on the bole of the tree at ground-level, between two large lateral roots. 
The fructifications, in the early stages, appear as a round or spherical 
knob-like proliferation, which is usually known as the "primordial 
knob", and may be 1-2 ins. in diameter. At the slightest touch, 
yellow or brown spots appear. The basal part, during further de- 
velopment, turns grey and brown and finally brownish-black, white 
the crust becomes more or less smooth. The white, spherical, prim- 
ordial knob now starts growing out into a hood. Sometimes it widens, 
but little or no growth in width may take place at the base; in such 
cases, a distinct stalk is formed. Usually, however, there is no definite 
stalk formed and the fructifications are sessile, but abnormal cases 
have been recorded of stalk and fruit-body with a total length of 
12 ins. approximately, the length of the stalk being about 7J ins. 
Plate II and Figs. 22 and 23 are illustrations of the fructifications. 

During the development of the bracket or pileus from the prim- 
ordial knob, the under surface remains completely white and small 
shallow pores develop. In most cases the brackets develop singly but 
compound fructifications are quite commonly met with. These com- 
pound fructifications closely resemble those of Ganoderma applanatum 
(Pig. 23). Corner's remarks, that 0. pseudoferreum comes very close 
to G. applanatum and that it may prove to be a variety, have already 
been noted. 

The following unpublished report by Napper is of interest in con- 
nection with the development of fructifications and spores in Malaya. 
To make the information complete, the full description of mature 
fructifications is later taken from Corner's article, which may not be 
readily available to other investigators. 



CHAP. IX 



GANODERMA PSEUDOFERREUM 




FIG. 22. Fructifications of U. pseiuloferreum developing at base of old infected 

rubber tree. 




FIG. 23. Ganoderma pseudoferreum. Imbricate form of fructification, resembling 
that of O. applanatum. (From Quart. Jour. Itubber Research of Malaya.) 

Napper made observations on the fructifications of G. pseudoferreum on 
an estate where for some five years little was done towards destroying the 
root systems of trees which had become casualties owing to attacks by 
the fungus. Trees were felled when they died and the boles extracted and 



150 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

allowed to rot in situ. During the latter half of March [1933], immature 
fruit- bodies of G. pseudoferreum were seen on a few of these rotting boles, 
and their development was watched closely. During April, young fruits 
were seen more frequently, and at the beginning of May, a general fruiting 
season had commenced all over the property. By the middle of the month 
nearly every old diseased bole bore its quota of fruit-bodies. Up to May 
24th, all fructifications seen conformed to a definite and unmistakable 
pattern. They were dead white on the under-side, with a conspicuous edge 
of the same hue, while the upper surface was dully lacquered, and zoned 
in shades of dark tawny brown, merging into black. On the above date, a 
new type was seen, which at first sight appeared to belong to a different 
fungus altogether. The pore surface was the same white colour, but the 
edge was brown instead of white, and the upper surface was a uniform dull, 
light brown in colour instead of being lacquered and zoned in shades of 
dark brown. In fact, the fruit -bodies looked as though they had been 
generally sprinkled with cocoa powder. The analogy is a good one, for, 
on examination, the deposit was found to consist entirely of spores. On 
scraping or washing the surface the dark zoned appearance was re- 
generated. This new type was found to represent the stage in development 
at which growth had stopped (no white edge), and the profuse sporing 
phase has begun. The rate of deposition of spores was very rapid. Glass 
slides placed beneath the fruits for an hour were found on removal to 
carry a heavy deposit of spores. In one extreme instance, the deposit was 
plainly visible as a brown film on the slides. Similar attempts to obtain 
spore deposits from the younger fruit-bodies had met with very dis- 
appointing results, although microscopic examination showed that spore 
development was progressing rapidly. 

The spores are golden brown in colour, elliptical to egg-shaped, 6-8/z x 
45^t, borne in a pendulous manner from long sterigmata. The point of 
attachment to the sterigma is at the smaller end, this being the part re- 
motest from the hynienium. The basidia are colourless, above 14/x high 
by lOjit broad, each bearing four sterigmata in the form of a crown. The 
long axes of the spores are slightly inclined outwards from the normal to 
the surface of the hynienium, making it appear as though the basidia 
are rotating slowly about an axis perpendicular to the hynienium (cf. 
governor balls). 

The spores are thick-walled and possess a remarkable capacity for 
withstanding desiccation. Fifty per cent germination was obtained from 
the spore deposit on the surface of one of the fruits. This fruit was the 
highest bracket on a prostrate bole (being about two feet from the ground), 
and the spores on its surface must have floated up from below after a 
lengthy journey through the air. Some of the spores which germinated 
must have been exposed for more than 24 hours to the drying action of 
sun and wind. The rapidity of deposition, purity and vigour of germina- 
tion of this spore deposit, can be judged by the fact that the cultures 
obtained by smearing the tip of a wet brush over the surface of the fruit- 
body and then over corn-meal agar in a Petri dish, remained pure long 
enough to enable an isolation of O. pseudoferreum to be made. 



CHAP, ix GANODERMA PSEUDOFERREUM 151 

Strong evidence was also obtained that the spores need a considerable 
amount of desiccation before they will germinate. Although such free 
germination was obtained from the well-dried spores on the surface 
of the fruit -body, no germination was obtained from spores deposited in 
a closed damp chamber, or on slides exposed for a short period of time in 
the field. Spores deposited in an open dry chamber had germinated, how- 
ever, on the dry surface of the slides after 24 hours. A more precise de- 
termination of the limits of desiccation between which germination is 
possible will be made. 

The main points of practical interest which arose from the observations 
were: 

(a) Fructifications of O. pseudoferreum on rubber trees are rarities in 
this country [Malaya], merely because infected wood is usually destroyed 
before it reaches the stage of rotting at which the formation of fruiting 
structures begins. This stage is reached after three or four years exposure 
in the field. Fruiting is particularly favoured by long periods of wet 
weather, such as we have recently experienced, and continues inter- 
mittently over many years, for the older rotting boles bear the disin- 
tegrating skeletons of several previous batches of fructifications. In 
a normal year in Malaya, there are probably two fruiting seasons, viz. 
April-June and October-December respectively. 

(6) The mature fructifications bear viable spores in great abundance, 
and the spores can withstand a high degree of desiccation. 

There is nothing therefore in the mechanism of spore development and 
dispersal in G. pseudoferreMm which could inhibit the free spread of red- 
root disease by means of spores. It will be necessary to determine whether 
such spread actually takes place in plantations, as if it does, the destruc- 
tion of fruit- bodies will become a vital part of any control scheme. 

From previous experience, however, it is probable that fruit destruction 
will not be necessary. No diseased tree has yet been seen whose infection 
could not be traced to root contact with buried infected timber, and 
further, the mode of origin and spread of red-root disease in a stand of 
rubber is typical of a purely vegetative means of propagation. Some factors 
connected with germination and infection probably operate to preclude 
successful spore infection in the field. 

The most likely factors are: 

(1) Sensitivity to competition, which would tend to inhibit (a) the 
establishment of the fungus as a pure saprophyte in the soil, (6) the colon- 
isation of wounds and (c) the infection and colonisation of exposed stumps. 

(2) Inability of the spores to produce germ- tubes sufficiently long and 
vigorous to effect direct penetration of healthy bark. Even penetration 
hyphae developing from the under-surface of rhizomorphs are unable to 
do this when their vigour of growth is insufficient to break through the 
defences of the host. 

The full description following is taken from the article by Corner: 

The fructifications may be sessile or only short stalked. This is the most 
common type. They may be flattened out, horizontal or ascending, often 



152 DISEASES AND PESTS OF THE RUBBER TREE PART in 

overlapping as the tiles of a roof, up to 21 cm. in radius and 31 cm. 
wide. 

The upper surface is smooth or covered with a velvety coating of fine 
soft hairs, rather dull, with small grooves, often with irregular excres- 
cences on the surface. The colour of the upper surface is fuscous-amber, 
or blackish with crowded cinnamon, brownish-olivaceous or khaki- 
coloured, narrow wavy zones and with a conspicuous bright, chestnut- 
brown, sub-resinaceous zone (2-10 mm. wide) near the margin; eventually 
dull brown from deposited spores. Margin white, thick and tumid at first, 
becoming thin, sub-acute, and often lobed or proliferating small pilei. 

Stem, when present, sub-cylindric or flattened, expanding gradually 
into the pileus, up to 6 cm. long x 1-5-8-5 cm. wide, the same colour as the 
upper surface of the pileus. If a radial section from the point of attach- 
ment to the margin of the pileus is taken, it will be found that the flesh 
of the pileus varies from 16-45 mm. thick at the base (point of attach- 
ment), relatively thin in the mature pilei (5-10 mm.), at half-way to the 
margin, cinnamon hay-brown in colour, and darker over the pores, 
mostly very pale near the upper surface, darkening with age, with narrow, 
alternating dark and light zones, developing thin fuscous or blackish 
crustaceous lines, 0-2-1 mm. thick from the base to the margin, with a 
thin blackish crust 0-2-0-5 mm. thick on the upper side. 

The pores or tubes, the openings of which are seen on the under surface, 
are up to 10 mm. long at the base, fuscous or blackish brown, drying to the 
same colour as the flesh; pores white, small, circular, entire, 100-1 50ft 
wide, with dissepiments 40-100/x thick. 

Spores, dark ferruginous when seen in mass, ellipsoid, sub-truncate at 
one end appearing minutely echinulate, 6-7-5/x x 4-5-5^, with one large 
gutta, 1-5-2-5/u, wide. 

Smell strong, like mice and cheese when kept for a few days. 
The pale- coloured flesh in the upper half of the pileus appears to be 
as characteristic as the variously coloured zones on the surface, but both 
features disappear with age. The zones are ultimately obscured by the 
thick deposit of spores which settle on the pilei, and the flesh darkens in 
colour as the crustaceous lines develop centrifugally. The upper side is not 
shining or laccate, as in O. lucidium, though the chestnut- coloured zone 
near the margin is sometimes sticky and sub-resinaceous. 

The thickness of the flesh varies considerably according to the size of 
the primordia, but well -developed pilei are always relatively thin and never 
become hoof-shaped. 

The growth of the fruit-bodies appears to be rather slow, at least three 
or four months being required for the pilei to reach a size of 12-15 cm. 
Sporing begins at a late stage, not until the pilei are 5-15 cm. in radius, 
and the tubes are 3-8 mm. long. (Steinmann says basidia and spores are 
rather hard to find and in younger stages are usually searched for in 
vain. However, at the right time, when conditions are favourable, thick 
deposits of spores are formed, and in the compound fructifications the 
upper surfaces of the pilei situated in the lower positions are covered with 
a thick layer of spores which change the colour of the upper surface.) 



CHAP, ix GANODERMA PSEUDOFERREUM 153 

Fruit- bodies which have developed in open situations often assume 
irregular shapes, since their growth is interrupted by spells of dry weather; 
they consist of the original primordial knob, 1-6 cm. in diameter, at the end 
of which other knobs, lobes or rudimentary pilei have developed with or 
without intervening short layers of tubes. These abortive specimens are 
seldom fertile, but they can be identified from the characteristic colour- 
ing. They are the forms most likely to be met with on rubber estates. 

The fruit -bodies always develop low down near the base of infected 
trees or from the roots, and similarly on dead stumps. Those of G. applana- 
tum, on the other hand, may develop from a considerable height, up to 
20 feet or more above the ground. 

The same explanation is given by both Steinmann and Napper for 
the rare occurrence of fructifications of G. pseudoferreum on diseased 
rubber trees in Java and Malaya. 

Corner's and Napper's descriptions in general tally with one 
another very closely, though the former's is given in much more 
detailed form. 

Control and Treatment. The writer hopes that it has been made 
clear that the control of the root diseases caused by species of the 
Fames type is a broad general problem confronting the rubber 
cultivator. Ganoderma pseudoferreum is present from the opening-up 
of the plantations (a feature long recognised in the case of F. lignosus), 
and the early tree-to-tree inspection and systematic removal of 
infected jungle timber, recommended for the control of F. lignosus, is 
as important, and probably more so, for successful control of G. 
pseudoferreum in later years. 

For areas of young rubber, the plan of campaign for controlling the 
spread of G. pseudoferreum in the plantations has been set out in the 
form of recommendations given for treatment of F. lignosus. But 
while the latter lias reached its peak about the 4th-5th year and the 
percentage infection is on the wane, the same cannot be said of 
G. pseudoferreum, for, unless special attention is given to the diseased 
patches to be found in earlier years, the disease caused by this fungus 
attains greater prominence year by year after the trees are ten years 
of age. It has already been indicated that a system of trenching will 
become of full utility in mature areas, but if these have received the 
early treatment recommended, diseased areas which require trenching 
should be small in both extent and number, and as a consequence the 
expenditure required would be comparatively small. 

The condition of diseased areas will definitely determine the treat- 
ment to be recommended in the matter of trenching. On areas with 
trees twenty to twenty-five years of age, where the disease has been 
rampant for years, no economic system of trenching could be recom- 



154 



DISEASES AND PESTS OF THE RUBBER TREE TART m 



mended; the only undertaking which would meet the case would be 
replanting. On areas with trees ten to fifteen years of age, where little 
attention has been paid to treatment in the early stages, a system of 
trenching, which is rather expensive, can be undertaken. Whether 
this would prove to be an economic success would depend entirely on 
the price of the commodity. A trenching scheme has been worked 
upon by one estate in Selangor and complete details have been pub- 




FIG. 24. Ganoderma pseudojerreum. Dissection of soil area in field of old 
rubber, size 5 feet by 4 feet. 

Roots of flvc different trees are in contact in this small area and all have contracted the disease 
from the one tree which became diseased originally. Root grafts have been formed at A, B and C. 

lished; these are given later. It is sufficient to say at this stage that 
the results were considered satisfactory, probably because only a 
single diseased tree has been found during ten years in the treated 
area of over forty-six acres. 

The progress of the disease in attacked roots is practically entirely 
subterranean; the underground habit of the fungus makes it a greater 
menace than it would be otherwise. The method of spread is entirely 
by root-contact, even though fructifications and spores may be pro- 
duced profusely. This bald statement gives but little idea of the 
extremely slow and intricate nature of the root systems of the trees 
in a field of twenty -year-old rubber. 



CHAP, ix GANODERMA PSEUDOFERREUM 155 

Fig. 24 shows the roots of five trees crossing in a soil area covering 
only five feet by four feet; they are in such close contact that root 
grafts have developed between three of the trees. The formation of 
root grafts was found to be quite a common development in this badly 
diseased area. At first there was only one tree with a diseased root; at 
a later date the roots of the other four trees contracted the disease 
from this one. In another case, a diseased root was traced to a distance 
of forty-five feet away from the stem, and this one infected the roots 
of five other trees with which it came in contact. 

The investigator who first studied red-root disease intensively in 
Malaya was Belgrave. He detailed his findings in a special bulletin 
issued by the Department of Agriculture, Federated Malay States, in 
1919. This bulletin is now out of print and it is difficult to obtain a 
copy, but in order to show the unanimous opinion of all Malayan 
investigators, more especially with regard to the method of spread of 
the disease from tree to tree by root-contact (cf. Rhizoctonia batati- 
cola), it will be advantageous to give a short extract from the work at 
this point: 

Large numbers of similar cases have since been found, abundantly 
proving the spread of the fungus under plantation conditions to be by 
contact of the roots, either with the diseased roots or stumps of jungle 
trees, or with other diseased Hevea roots. F. pseudo-ferreus has been found 
to attack all kinds of jungle woods, both hard and soft, white and red, 
being in fact, especially in early stages, one of the normal fungi causing 
decay of jungle timber in Malaya; hence no system of selective clearing 
can be devised to afford protection to Hevea. 

All the symptoms of an attack of the fungus so far described have 
referred to parts of the plant normally invisible, viz. roots and lower part 
of the collar; opening up is necessary to find the disease while the tree is 
yet standing. Added to this invisibility, shared with all root diseases, 
F. pseudo-ferreus has a slowness of advance into healthy tissues peculiarly 
its own, with the result that a tree may be badly diseased for many years 
without showing it. The persistence of diseased trees is aided by the par- 
tiality of the fungus for "heart- wood" which has ceased to function in 
water conduction, and by the fact that the attacks are as a rule confined 
for a long time to one side of the collar. As a result, the water supply is not 
sufficiently reduced to cause general wilting. There is one sign, however, 
by which badly attacked trees may often be discovered, viz. the occurrence 
of bare tips (usually on the highest branch), looking like slight attacks of 
"die-back". When such tips are seen, at a season which excludes winter- 
ing, and the "die-back" does not spread, F. pseudo-ferreus may be sus- 
pected, and the tree opened up. 

As an instance of the elusiveness of F. pseudo-ferrem may be taken the 
Government Plantation at Kuala Lumpur, where the 17 -year-old rubber 
has been found to have about 30 per cent of trees attacked; and this was 



156 DISEASES AND PESTS OF THE RUBBER TREE PART in 

only accidentally discovered when a tree-to-tree examination (for other 
purposes) was in progress. 

In fields of old rubber which have received little attention from the 
point of view of root -disease treatment, the total disease percentage 
can never be guessed correctly without full disclosure of the root 
system. In a field with groups of trees which are obviously affected and 
require extraction, there will be a high percentage which are lightly 
attacked, the diseased tissues being still confined to the lateral 
root system. In one case already mentioned, the total disease per- 
centage was 56; of this total 26 per cent were obvious cases for 
extraction, the fungus having reached and penetrated into the 
tissues of the bole of the tree; 30 per cent were lightly affected cases 
which could be saved by excision of diseased lateral roots. This vital 
point has to be kept in mind when considering treatment. The number 
of obvious cases may reach a high percentage of the total stand, but 
it is probable that there is a higher percentage of lightly affected cases 
still left in the ground. 

The progress of the disease in old neglected areas is well shown 
in Diagram V. The disease spreads in ever- widening circles, those 
marked A-K representing typical diseased patches where the fungus 
has been active and allowed full play. As the direct result of the 
removal of a large number of diseased trees, a serious decline in yield 
ensues, and ultimately it may become unprofitable to tap those which 
remain. 

In a special bulletin published in 1931, before sufficient evidence 
had been collected definitely to conclude that 0. pseudoferreum must 
be accepted as a root parasite of jungle trees (falling in the same 
category as F. lignosus and therefore likely to be found on young 
rubber trees equally early), the writer recommended a system of 
trenching on mature rubber estates, assuming that individual cases 
of root disease caused by G. pseudoferreum might be found when the 
trees were about the tenth year of age. As further experience has been 
gained, it is obvious that the single system of trenching described 
below will satisfy all cases, and the above-mentioned system must now 
be discarded. 

Trenching has been recommended for treatment of root diseases of 
rubber from the earliest days of the industry, but judging from the 
present-day position, trenching systems have been used with but 
doubtful success. This is not because of any inherent defect in the 
method, but because it has been carried out in ignorance of the true 
state of affairs existing below the surface of the soil. It is useless to try 
to guess where a trench should be made by looking at the foliage of 



GANODERMA PSEUDOFERREUM 



157 



the trees at the edge of a diseased patch. Trees infected by G. pseudo- 
ferreum may linger on for years before they show signs of the disease 
in the foliage, and by the time they do so the advancing rhizomorphs 

ROOT DISEASE EXPERIMENTAL AREA. 



K 

x x 74 
3 23 28 48 52 x 


/ 

77 
78 

X 

x 98 

x 97 


102 
103 

104 


133 194 220 
x 134 160 x x 219 
* * * 192 * 218 
131 x 155 x 191 gg 217 
130 x 157 i6l 190 197 ** 
> x x Kg |89 198 x 


X 
X 

X 

1 

223 

2W 


252 

X 

251 253 

9 Z75 


302 332 
301 331 335 
277 300 303 330 336 

278 * x *% 
279 #7 538 

x 29o 304 328 x 

280 295 x 327 x 






255 




b 326 x 
325 339 






25o 


A ^ 


4 x 


x 4o 53 73 


79 x 


105 


155 164 200 










226 

227 


245 257 x 


X X > 


324 x 


x 22 


72 


80 x 




128 138 154 x 185 x 214 


7 ' 




N 




x x xgx x x x 


2*7 x 2 
24o x 275 
245 258 x 
244 x 272 
243 x 27 

2*2 x 27C 
259 


x 293 307 x 340 


L/*] 

x 20 
> 19 

x 


x 44 H 

x 43 x x 


81 * 

82 > 

x 93 


100 
107 
108 

109 

X 


x x x )o5 154. x x 
x 139 x x |fl3 201 x 


x 32 306 x x 

x x X x 34.1 

xTx x x 342 
x x 309 322 x 

) x x x x 343 


x x x x 2 x 213 


X X X X | X xfA* 

I2o 153 \J 
125 x 152 x 180 x*^x 


x 


7 18 

x 16 
x 15 
8 U 
13 
12 
II 
10 
9 






[s 




2t* 




c 321 x 

(XX 


30 42 y 70 
31 X 58 X 


x 91 
x 90 


x 141 150 x x 203 212 

122 ^ x x |78 x 211 


* 


239 * * 
236 " x 


X X > 


282 x 3 


x 344 


32 40 59 x 
33 x 60 & 
34 x x x 
x x 61 67 


83 S9 
x 88 

/T 


no 


120 W3 149 x (77 x 210 


229 

f 


237 x x 233 x > 
236 x ^* 284 x > 

x 260 263 x 286 ' 

??5 -- , , 


< X 

345 

318 
2 x 3*6 

317 
< 316 

< aj< 


j x x x x x| |7o * x 
xTx x x*^|68 x x 208 
115 117 W6 x) Ib? x x 207 


^-% x 

x 2W x 


..* * 3 

U 3 
li x x 

X X 


x 39 x x 


85 x 




x W /* x x x x 


jy,, ..,.,. 


35 38 b2 " i"*" x 


X 


" "G" " " * / 


233 x x 


285 x 


x 37 63 yA xxx 


x x x x x y; 204 


x 


232 x at. 


I x x 


34 



x - POSITION Of TREES REMOVED. 
A-K - TYPICAL DISEASE PATCHES DUE TO FOMES P5EUDOTOQEUS. 

DIAGRAM V. 

will have travelled ahead at least one, sometimes two, three or even 
more rows of trees, all of which may appear healthy. Neither the size 
nor even the shape of the true patch of infection can be judged by 
visual inspection, and no trench can be expected to be satisfactory 
unless it is dug in conjunction with a method of root inspection. 



158 DISEASES AND PESTS OF THE RUBBER TREE PART in 

The necessary root inspection is carried out in quite a simple way. 
The main requirement of an isolation trench is that it shall be cut 
outside the advancing limits of the patch. If, therefore, in cutting the 
trench all the roots severed are healthy, the trench must be fulfilling 
this requirement. If, however, diseased roots are encountered, the 
trench is known to be incorrectly placed, and must now be taken in 
a direction which will include the tree showing the diseased roots, 
within the trenched area. The diseased roots are the indicators for the 
location of the trenches, and these must be taken further and further 
away from the diseased patch until all roots severed are healthy. 

Near the advancing edges of a diseased patch, the rhizomorphs are 
in their freshest, most vigorous and most easily recognisable condi- 
tion. It would be difficult to overlook a root rotted by this fungus, for 
when cut it will not yield any latex, while of the roots which do yield 
latex, the infected ones carry on their surface fresh, vigorous rhizo- 
morphs which cannot possibly be mistaken for the clean surface of a 
healthy root. It is well to have a bucket of water handy where this 
work is being carried out, for the soil usually adheres closely to 
infected roots, and this must be washed away, when the rich red 
colour of the rhizomorphic membranes will be seen in the form of a 
tough skin covering the surface of the bark and easily detachable 
from it. 

In isolating a diseased area, the trench should be dug in such a way 
that at least one row of standing trees comes between the trench and 
the denuded central portion. As the trench progresses round the 
patch, all severed root sections must be examined and, where 
diseased roots are found, the trench must be extended outwards to 
include other trees from the next row as required. Since it is necessary 
that the trench should be deep enough to sever all lateral roots cross- 
ing its line of progress, it should be dug midway between the rows of 
trees, as here the depth of penetration of the roots is at a minimum. 

The cut ends of healthy roots which are severed during the 
progress of the trench should be covered with Asphaltum-Kerosene 
mixture. 

No attempt should be made to confine the trenching system to a 
rigid geometrical pattern. The trench will wander through the trees 
in a somewhat crazy fashion, including trees here and there as they 
are found diseased. The trenches should be at least two feet deep, but 
it would be safer to aim at a depth of three feet. They should be 
inspected periodically and should be always kept open. 

Treatment of the trees in the isolated areas can be decided on the 
spot. As there is little chance of spread by wind-blown spores, tapping 



CHAP, ix GANODERMA PSEUDOFERREUM 159 

can be continued on any trees producing a fair yield of latex. In the 
writer's opinion, the trees within the isolated areas should be tapped 
as heavily as possible and, when the yield falls off owing to the pro- 
gress of the disease in the tissues, they should be taken out. The tap- 
root should be removed completely to three feet below ground-level, 
and all diseased lateral roots should be followed up, taken out of the 
ground and destroyed, if possible by burning. 

There is an obvious danger in the method recommended, and this 
lies in the wholesale cutting of lateral roots, which will possibly result 
in an increase in the number of cases of Ustulina zonata. This disease, 
however, can be dealt with comparatively easily and there should be 
little danger if the cut ends are treated quickly and then covered by 
the soil. 

The above method, with modifications according to local condi- 
tions, can be put in operation on most estates, irrespective of their 
location or of the type of soil. It can be said to be of fairly general 
application. The important point is that the scheme demands an 
exceedingly careful examination of the lateral roots which are cut 
through when digging the trench. 

Careful costings in relation to the method recommended above have 
been made on one estate in Selangor and, though expensive, the 
results obtained justify the expense, so that these measures enter the 
realm of practical politics. Up to date, our knowledge of root-disease 
treatment has been largely empirical; there has been no index by 
which the success or failure of the remedial operations could be 
gauged. In this connection, the number of trees in the first row outside 
the trench, which are found with diseased lateral roots, provides a 
definite indication of the results to be obtained by treatment. Exci- 
sion of slightly infected lateral roots not only saves a valuable tree, 
but removes a definite and serious danger, as such trees left untreated 
would become in a few years centres of infection. The cost details are 
given below: 

(1) Area of field treated =46 acres 

(2) Total cost of disease treatment = $155-09 

(3) Cost per acre over whole field = 3-40 (app.) 

(4) Approximate ratio of diseased area to area 

of the whole field is 8-7 per cent (say 10 

per cent) =4-6 acres 

(5) Cost of treatment over 4-5 acres =$31-20-$39-00 per acre 

(6) Percentage number of diseased trees found 
in first row of trees outside the trench 
(treated and saved by severance of lateral 

roots), in total number of trees opened up = 14-3 per cent 



160 DISEASES AND PESTS OF THE RUBBER TREE PART in 

The fact that 143 per cent of the total number of trees opened up 
are in the first row, are found lightly affected and can be saved by 
excision of the diseased roots, forms a primary consideration when 
making recommendations for control. If such a high percentage 
should be found in the majority of cases, this alone would justify a 
recommendation in areas known to carry mature trees suffering from 
Ganoderma pseudoferreum that trenching operations should be under- 
taken as early as possible. 

Soil treatment is as usual. The trench should be at least two to 
three feet deep and one foot wide, and the soil from the trench must 
be thrown on the ground inside the area bounded by the trench. 
When the diseased trees have been completely removed, the whole of 
the soil in the isolated area must be dug over to a depth of twelve to 
eighteen inches and, as far as possible, all rotting vegetable material 
should be collected and burnt. 

It will be fully appreciated that costs of trenching will vary con- 
siderably according to soil type and situation. The costs given above 
were obtained by working typical laterite soil on slightly undulating 
ground. The work was carried out in 1931, and since that time only a 
single case of G. pseudoferreum has been found, and it is possible that 
this was a case of a lightly affected tree missed during the trenching 
operation. 

The particular case published refers to an area in which the disease 
had been allowed to develop for a considerable time before a system- 
atic attempt was made to deal with the situation, and, from a patho- 
logical point of view, was completely successful. Whether it will 
ultimately prove to be an economic success there is reason to doubt, 
but even from this point of view the results are so far considered to be 
satisfactory. But if the full combined scheme for F. lignosus and G. 
pseudoferreum is carried through from the early years when the former 
first becomes prominent on the young rubber trees, there is no reason 
left for doubting the economic outcome. 

FOMES NOXIUS, SP. N. 

(Brown-Root Disease) 

Up to 1917 this disease was supposed to be caused by a fungus 
named Hymenochaete noxia. From that year to 1932, the causal 
fungus was considered to be one of the typical Fomes type which was 
named Fomes lamaoensis, Murr. In 1932 Corner's article, entitled 
"The Identification of the Brown-Root Fungus' ', appeared, and he 
concluded that the true cause of brown-root disease was a new fungus 



CHAP, ix FOMES NOXIUS 161 

which had previously been confused with F. lamaensis ( = Lamaoensis), 
which he named Fomes noxius, sp. n. 

This work of Corner on the fungus causing brown-root disease of 
many tropical cultivated plants, including rubber trees, has swept 
away much confusion. The disease has been known for a longer period 
than any other root disease on rubber, and specimens of the fungus, 
obtained from Bread-fruit trees in Samoa, were examined by Berkeley 
in 1875. It was recorded on Tea in India, in 1887, by Cunningham; 
in later years, on Hevea and numerous crops by other investigators. 

It is rather difficult to explain the present position succinctly, and 
the best way to put forward a clear presentation will be to summarise 
the established details. Before summarising, it is legitimate to remark 
that many statements made by various investigators in the past must 
be doubted. The writer cannot support Weir's observations in Malaya, 
though he has had the subject under close observation since 1931. 
Further investigation is required, but as the disease is of little prac- 
tical importance in Malaya, it is likely to be some time before further 
attention can be given to it. However, there is need for reinvesti- 
gation of this root disease in Malaya whenever time permits. 

SUMMARY. Cause. The history relating to the determination of 
the fungus as Fomes lamaoensis, Murr., is given in detail in Petch's 
article, page 171. 

Corner's conclusions may be recorded as follows. The fungus 
causing the brown -root disease of rubber trees and tea bushes is not 
F. lamaoensis, Murr., but is a distinct species which is named F. noxius, 
sp. n. It is also the suspected cause of the stem-rot of Elaeis (Oil- 
Palms) in the East. 

F. noxius differs morphologically from F. lamaensis in the wider 
hyphae, in the absence of hymenial setae and in the structure of the 
upper surface, and biologically in being a facultative parasite, and in 
growing in open situations, rarely, if ever, in the deep forest. F '. lama- 
ensis is a saprophyte in the forest and is very rarely found under 
estate conditions in Malaya. Murray, in his manual published in 1930, 
states that the fructifications of F. lamaoensis are very rarely found 
in Ceylon; this supports Corner's findings in Malaya. 

Symptoms. Roots attacked by brown-root disease, more especially 
the tap-root, are encrusted with a thick covering of earth and small 
stones 3-4 mm. thick (Fig. 25 6); this varies according to the type of 
soil. The mass is cemented to the roots by the mycelium of the fungus, 
which consists of tawny brown threads collected here and there into 
small sheets or nodules. In the early stages the predominating colour 
is brown, but as it grows older the fungus forms a black, brittle, 

M 



162 



DISEASES -AND PESTS OF THE RUBBER TREE FART in 



continuous covering over the brown masses of hyphae. In all stages, 
however, the disease is distinguished by the encrusting mass of 
stones and earth, which cannot readily be washed from the root. 

The diseased woody tissue is soft and permeated by fine brown 
lines which are the edges of plates of brown fungus tissue (Fig. 25 a). 




FIG. 25. (a) Tap-root of young rubber tree affected by brown-root disease. Split 
open to show fine, brown lines of fungus tissue developed in diseased woody 
tissues. (6) External appearance of rubber roots attacked by brown-root 
disease, showing thick, earthy covering encrusting diseased roots. 

When the decay is advanced, this brown tissue may form honeycomb- 
like structures in the wood. 

It has been mentioned above that the encrusting mass of soil and 
stones is cemented to the roots by the mycelium of the fungus. The 
hyphae of the mycelium have the power of secreting mucilage, 
possibly in copious amounts, and the production of this substance, 
capable of binding the soil and stones tightly together, results in the 
appearance of the typical symptoms. Many fungi possess this power 
of secreting mucilage in the presence of adequate quantities of water; 



CHAP, ix FOMES NOXIUS 163 

this was demonstrated in 1922, in relation to brown-root disease 
itself, by the writer. It seems very probable, therefore, that any soil 
fungus, with brown hyphae capable of secreting mucilage, might pro- 
duce typical symptoms of brown-root disease, if associated with 
individual trees of any particular crop. This fact may have some 
significance in connection with the large number of plants which have 
been reported as hosts for brown-root disease, a list of which is given 
at the end of this section for those people interested. 

Spread and Control. Few remarks are necessary under this 
heading. Spread is entirely by root-contact. The Fome# group of fungi 
causing root diseases of rubber trees are thus seen to constitute a 
series in which spread is entirely by root-contact, and the chief 
distinguishing features which characterise the three root diseases 
caused by F. lignosus, G. pseudoferreum and F. noxius are rapidity of 
appearance and extent of spread in area. Our experience of F. noxim 
on young trees in Malaya is that the disease appears only in single 
cases; thus, as long as root-contact has not been established in young 
plantations, there is no reason to fear active spread. 

The only control action necessary is to remove dead trees and roots 
of diseased trees as completely as possible. 

FURTHKR INFORMATION. The foregoing summary provides the 
gist of the reliable information obtained up to date, which is appli- 
cable to rubber plantations in Malaya. More detailed information 
respecting the disease generally is given in the following quotations. 

The first extracts are copied from Corner's article and include the 
full description of F. noxius. This is followed by Fetch's description of 
brown-root disease in Ceylon and Weir's remarks on some observa- 
tions on the disease in Malaya. 

(1) FOMES NOXIUS, CORNER 

That it is the true F. lamaensis and that F. williamsii is a synonym, as 
Bresadola first noted, I have checked by microscopic examination of the 
types. Both types are in the herbarium at the New York Botanic Gardens 
and were collected by R. S. Williams on the Lamao River, P.I. They were 
described by Murrill in the same paper and on the same page in terms that 
are almost identical, though Murrill seems not to have noticed any simi- 
larity, and in the next year he assigned F. williamsii to F. endothejus, 
Berk., which, as Bresadola and Lloyd remarked, is utterly false, since 
F. endothejus is a species with brown spores and without setae. The de- 
scription of F. lamaensis came first and this name therefore has priority. 
Bresadola substituted the name "williamsii", in which he was followed 
by Patouillard, apparently on the ground that the fruit-bodies in the type 
collection of F. williamsii, being larger than those in the type collection 



164 DISEASES- AND PESTS OF THE RUBBER TREE PART in 

of F. lamaensis, represented what he called "status adultus", those of 
F. lamaensis being the ''status juveniiis" of the species. But this notion 
seems to have arisen from a remarkable misunderstanding. In the first 
place, the term "adult" cannot be applied to fruit-bodies of the Fomes 
kind which are virtually of unlimited growth and which continue to pro- 
duce basidiospores from a very early stage, unless it is reserved for those 
fructifications which do produce basidiospores and so must then be ap- 
plied to every state but the primordial knob, in which case the terms 
"mature" and "immature" seem more appropriate. But the fruit-bodies 
in the type collections of both species are all mature, though in neither 
can they be regarded as full-grown, since the fruit-bodies are perennial 
and much larger ones are easy to find elsewhere. In the second place, it 
seems that the terms' "status juveniiis" and "status adultus" (which can 
mean only immature and mature) were confused with the terms "im- 
perfect state" and "perfect state" in their mycological sense, and thus the 
rule of procedure for the radically different proposition when a fungus 
imperfectus is joined with an ascomycete or basidiomycete was applied 
also. It is important that this point should be clear, or it may become law- 
ful to substitute many other names for the singular reason that they were 
given to bigger specimens of the same species. 

The species name, taken from the place of discovery, Lloyd changed to 
"lamaoensis", which etymologically may be the more correct, and he has 
been followed by others. But one must keep to the original spelling, as it 
is clearly no misprint. The orgin of the name "lamao" is, moreover, un- 
certain. Is it a native word, or is it derived from the Spanish "lama", 
meaning "mud" or "flat swampy land" (Latin, lama-ae), or as seems most 
likely, from "la mano", meaning the hand, which has suffered contraction 
and fusion into "lamao", for there is also a Point Lamao? 

Lloyd has explained the late discovery of this species, which is so com- 
mon in the East. It was mistaken for F. ignarius. In the herbarium at 
Leiden he found many collections which had been sent from Java nearly 
a hundred years ago and thus referred. 

With reference to the fungus which he considers the actual cause of 
brown-root disease, i.e. Fomes noxius sp. n., Corner states: 

That this species is the cause of the brown-root of rubber trees, I have 
proved by examining specimens of the fungus from diseased trees in 
Malaya, as well as one of the collections from Ceylon which Petch sent 
to Lloyd for determination. I presume that it causes the brown-root of 
tea- bushes too, though I have not had the opportunity of examining 
specimens. It is also the suspected cause of the stem-rot of the oil-palm 
(Elaeis guineensis) in the East Indies. I examined several specimens from 
diseased palms which Thompson submitted for identification, and it is the 
species referred to in his paper as "Fomes sp. resembling F. pachyphloeus, 
Pat." (I was first struck by the large size of the extrahymenial setae in 
the dissepiments, which are like those of F. pachyphloeus rather than F. 
lamaensis.) Lately I have examined other specimens from diseased oil- 
palms in Sumatra and found them to be the same species. It is probably 



CHAP, ix FOMES NOXIUS 165 

a widespread parasite both in Africa and the East, since I have little 
doubt that the diseases which have been attributed recently to F. lamaen- 
sis will be found to have been caused by F. noxius. 

The only other case which I have met with is that of a Flame of the 
Forest tree, Delonix regia, in the Singapore Botanic Gardens; the fungus, 
which had evidently entered by the roots, developed fruit-bodies at the 
collar of the tree and caused the branches of the tree to die- back to such 
an extent that the tree had to be cut down. I have not seen it parasitic 
in the forest. 

FOMES NOXIUS SP. N. 

Effuso-reflexed, pilei applanate, dimidiate, slightly ascending, up to 
13-5 cm. radius, 25 cm. wide; resupinate part spreading up to 35 cm. wide. 

Upper-side as in F. lamaenms, rapidly glabrescent; growing margin white, 
creamy -ichite or pale ochraceous. 

Flesh 6-19 mm. thick at the base, rarely up to 5 cm. thick, 1-5-12 mm. 
at 5 mm. from the margin; 0-5 2 mm. in the resupinate part, texture and 
colour as in F. lamaensis\ crust 0-5-1 mm. thick; black crustaceous lines 
and mycelial strands as in F. lamaensis. 

Tubes short in the first season, 2-5 mm. at the base, 0-3-1-5 mm. at 
5 mm. from the margin, developing 2-5 layers each 1-3 mm. thick with a 
thin intervening layer of flesh 0-5-1 mm. thick with a total thickness up 
to 11 mm., carbonaceous, concolorous with F. lamaensis\ pores as in F. 
lamaensis, rather smaller, 80-1 10/z wide, dissepiments 40-100/1 thick. 

Spores as in F. lamaensis, rather larger, 3-5-4-5 x 3-03-5, with one 
gutta 1 2-5/i wide. 

Basidia and cystidia as in F. lamaemis, cystidia sparse. Hymenial 
setae none. 

Extrahymenial setae in the flesh up to 600/t long x 4-10/1, wide, in the 
dissepiments up to 100/x long x 9 16/z wide. 

Generative hyphae 2-5 5/x wide. 

Hal), saprophytic or parasitic at the base of trees in clearings, estates or 
secondary jungle. 

I made several observations on the rate of development of the fruit- 
bodies as they came up on some logs in the Botanic Gardens; I had the 
logs put in a shady place and well watered except in rainy weather. 

The primordium appears on the surface of the wood as a minute, 
creamy- white, villose speck, 0-5-1 mm. wide. It does not develop straight- 
way into the hemispherical primordium of the pileus even on vertical 
surfaces, but it grows at the periphery over the surface of the wood to 
form a circular, or irregular, resupinate patch about 0-5 mm. thick. The 
rate of marginal growth of this patch, i.e. the rate of increase in radius, 
varies considerably according to the supply of water, the humidity of the 
air and the age of the patch. The maximum rate which I obtained was 
2 mm. per diem (24 hours). If conditions are favourable, it appears that a 
rate of 1-1-5 mm. per diem, is soon reached and may be maintained until 
the patch is 10 cm. wide and possibly more. But if the air is dry, growth 
is much impeded and the rate falls to 0-1-0-3 mm. per diem\ in several cases, 



166 DISEASES AND PESTS OF THE RUBBER TREE PART in 

even though the logs were watered heavily twice daily, growth ceased 
altogether in sunny, rainless weather. 

When the resupinate patches are 10-16 mm. wide, pores develop over 
the centre and a pore-field travels centrifugally at a distance of 2-3 mm. 
from the margin. On vertical surfaces pilei do not develop until the patches 
are 2-4 cm. wide, and in some cases not until they are 12 cm. wide. If the 
resupinate patches developed on the under-side of the log, then no pilei 
were formed, of course, until the margin of the resupinate part had spread 
on to an ascending surface. 

The pilous arises as a short horizontal ridge 2-12 mm. long, from some 
part of the resupinate patch through the proliferation of the hyphae of 
the dissepiments, occasionally at the margin. The rate of marginal growth, 
i.e. the increase in the radius from the centre of attachment to the free 
margin of the bracket, corresponds with that of the resupinate part. The 
maximum rate which I observed was 1-6 mm. per diem. The growing 
margin of the pileus is as susceptible to dry air as that of the resupinate 
part, being very easily checked by a rainless day or two, though similarly, 
under favourable conditions it appears that a rate of 1-1*5 mm. per diem 
is soon attained. I did not succeed in growing pilei larger than 3-5 cm. in 
radius and 6-8 cm. wide, but one of these had a rate of marginal growth of 
1-6 mm. per diem when 3-2 cm. in radius. Doubtless in large specimens the 
rate declines even under the most favourable conditions, as in F. levigatus. 

When marginal growth is arrested for several days, the surface of the 
fruit-body blackens owing to the agglutination of the hyphal ends, and 
the fruit-bodies may remain in this state for any length of time up to 
three months at least and still be able to revive on the return of wet 
weather. In reviving, lateral hyphae sprout from the margin and under- 
side, sometimes from the upper-side also, and cover the fruit-body with 
a fresh, creamy-white down; then the radial growth of the limb and the 
down-growth of the tubes continue. These successive additions can easily 
be recognised in the structure of the fruit- bodies, since a thin crustaceous 
line extends through the flesh from the upper surface to the tubes where 
marginal growth has been arrested, and there are often thin layers of 
flesh between the successive layers of tubes. 

These observations on the rate of growth are confirmed by Thompson's 
on the development of the fruit- bodies on the trunks of oil-palms. A 
bracket, 5 mm. in radius, took two months to develop, that is to say, at 
an average rate of marginal growth of 0-8 mm. per diem. On account of 
the slow growth and the extreme susceptibility to dryness, the fruit- 
bodies which develop under estate conditions, like those of Oanoderma 
jjseudoferreum, are usually stunted and small, often abortive and mostly 
resupinate and have several short layers of tubes. The resupinate state 
might easily be mistaken for a Poria, as Patouillard mistook a similar 
state of F. lamaensis, and the species may have been described previously 
as a Poria. And as Fetch has shown, the superficial sterile mycelium, 
which has projecting extrahy menial setae, was put originally in Hymeno- 
chaete with the nomen nudum, H. noxia, Berk. 



CHAP, ix FOMES NOXIUS 167 

(2) BROWN-ROOT DISEASE 
(Fomes lamaoensis, Murr.) 

This disease appears to be the most widely-spread root disease of culti- 
vated plants in the Eastern Tropics. It was originally found on Bread- 
fruit trees in Samoa, where it was said to cause serious damage. The next 
report of it was on Tea in Northern India; in this case the principal feat- 
ures of the disease were described by Cunningham, and though he did not 
discover what the fungus was, it is clear from his description that he was 
dealing with this disease. Similarly, Zirnmermann found it attacking 
Coffee in .Java, but was unable to ascertain the identity of the fungus 
which caused it. 

It was first recorded on Hevea in Ceylon, and it is probably the com- 
monest root disease of the Rubber tree in that country. Yet, except under 
special conditions, it does not cause so much damage as Fomes lignosus. 
The latter can spread independently through the soil from a jungle stump, 
and may attack a number of trees in one spot before any of them is so 
seriously affected as to show signs that there is something amiss. Brown- 
root disease, on the contrary, spreads very slowly, and, for all practical 
purposes, only along the roots of the tree; consequently it only infects 
the neighbouring trees when their roots are in contact with those of the 
diseased tree, and the progress of the fungus is so slow that, as a rule, the 
first affected tree is dead before the neighbouring trees are attacked. In 
general, therefore, only one tree is killed at each centre of infection, 
unless the dead tree is left standing for a long period. 

When the dead tree is dug up, the special characters of Brown-Root 
disease are usually immediately evident, and, as a rule, there can be no 
mistake in the diagnosis. The roots are encrusted with a mass of sand, 
earth and small stones to a thickness of three or four millimetres; this 
mass is fastened to the root by the mycelium of the fungus, and con- 
sequently, cannot be washed off. The mycelium consists of tawny, brown 
threads, which are collected here and there into small sheets or loose 
masses, either on the surface or embedded in the crust of soil and stones. 
The colour of the mycelium varies, and one frequently finds brownish- 
white, or almost white, masses intermingled with the tawny brown. In 
the early stages the predominating colour of the mycelium is brown, and 
this is usually the case when the roots of a dead tree are examined. 
Hence the name Brown-Root disease. But when the disease has been 
established for. a long time, and the fungus has grown older, it forms a 
black, brittle, continuous covering over the brown masses of hyphae, and 
the diseased root then appears chiefly black, The brown mycelium is, 
however, immediately discernible if the black crust is cut. 

In all stages the encrusting mass of earth and stones, intermingled with 
brown threads, serves to distinguish this disease. The root looks as though 
it had been dipped in glue and then had soil and stones scattered over it. 
Bancroft stated that the surface of the root becomes dark brown and 
almost black, and for that reason the coolies in Malaya know the disease 
as "Sakit hitam". 



168 DISEASES AND PESTS OF THE RUBBER TREE PART in 

In the case of young trees the encrusting mass is usually most strongly 
developed on the tap-root, and it may ascend up the stem for several 
inches. On old trees, however, the appearance may be different, especially 
if the tap-root is the part first attacked. In that case, owing to the slow 
effect of the disease, the tap-root may be in an advancing state of decay, 
before the fungus has spread to the laterals sufficiently to cause any 
marked symptoms in the crown. The cortex with its covering of earth and 
stones may by that time have disappeared completely from the tap-root, 
owing either to decay or to the attacks of white ants, and it is then neces- 
sary to examine the laterals to find the characteristic external appearance 
of the disease. But even when the outer crust has disappeared the disease 
may usually be identified by the appearance of the wood. 

In some cases, after the tap-root has been attacked, the tree produces 
new roots at the collar, and these grow down vertically and take the 
place of the missing tap-root. As Bancroft has pointed out, this is an indi- 
cation of the slow progress of the disease. I have, however, seen the same 
thing in a case of Fomes lignosus, where the disease had for some unknown 
reason been arrested after the tap-root had been destroyed. 

If the encrusting mass is cut away, the cortex on the diseased roots is 
found to be brown, or brown mottled with small white patches internally. 
The diseased wood usually shows characteristic markings, though these 
may be of two entirely different types. In the one case the wood is soft and 
friable, with a network of fine brown lines, and even with a hand lens it 
can be seen that these lines are composed of brown hyphae. Thin sheets 
of brown hyphae run through the decaying wood, and these appear as 
brown lines when the wood is cut. This is the more frequent appearance 
in the lateral roots. In the other case the wood of the root is comparatively 
hard, and traversed by rather broad brown bands in which no hyphae 
are discernible. This may occur in the lateral roots, but is more usual at 
the base of the stem. There is some evidence that the appearance first 
described follows the second. In either case the wood in an advanced 
stage of decay may be honeycombed, the brown plates persisting after 
the tissue between them has almost completely decayed. 

A few narrow black lines are usually present in the diseased roots, but 
the brown lines are more numerous. In advanced cases, black circles are 
sometimes found when the cortex is stripped off a diseased root. 

Brown-Root disease, in its most general form, might be regarded as a 
"dry rot", but I have seen advanced cases where the honeycomb struc- 
ture was well developed, in which the cells of the honeycomb were filled 
with water. 

This disease often appears on old trees as a "collar rot", i.e. an area of 
rotten, decayed bark, more or less triangular in outline, and broadest 
below, extends upwards from ground-level on one side of the stem for a 
height of a foot or so. The wood behind this region is decayed and rotten, 
and may weather away, leaving a large cavity at the base of the tree. 
This effect is produced by an attack of the fungus on a lateral root, and 
its advance along the lateral to the base of the stem, which is attacked 
round the point of origin of the lateral. This mode of attack is very com- 



CHAP, ix FOMES NOXIUS 169 

mon in cases where the fungus first develops on Cacao stumps and spreads 
from them to Hevea, and in such cases it is easy to pick out the affected 
trees by the rotten patch of bark at the base, before any effect is observ- 
able in the crown. Ustulina zonata frequently works in the same way. 

When the fungus has first attacked the tap-root, it often advances up 
the centre of the stem and causes a "heart-rot", i.e. it affects the central 
heart wood more rapidly than the outer, younger sapwood. A more or less 
conical decayed region extends up the centre of the stem, sometimes for 
a length of a couple of feet, the boundary being discoloured and evidently 
diseased, but still solid, while the inner parts are converted into a honey- 
comb structure with brown walls, with white fragments of the decayed 
wood in the cells. If such a stem is cut across above the evidently diseased 
part, a white covering of mycelium usually appears in the centre of the 
section within a few days. 

A curious variant of the foregoing was recorded in one case. The tree 
had apparently had what is known as a "heart shake", i.e. the wood had 
split near the centre of the tree along the line of an annual ring. When 
the fungus grew up the stem it filled the crack with a thick felt of brown 
mycelium to a height of about three feet. 

As indicated above, this disease is not confined to Hevea, but attacks 
cultivated plants of all kinds, except (as far as is known at present) the 
short-lived annuals. In Ceylon it has been recorded on Ceara Rubber, 
Castilloa elastica-, Cacao, Tea, Dadap (Erythrina), Caravonica Cotton, 
Camphor, Cinnamomum cassia, Erythroxylon coca, Brunfelsia americana, 
The^pesia populnea, Hura crepitans, Grevillea robusta, Codiaeum variega- 
tum (Croton), Brownea grandictps, Jak (Artocarpus integrifolia). 

In the Federated Malay States it has been found to attack Hevea and 
Camphor; Brooks and Sharpies state that it is infrequent on the former, 
and usually attacks trees under two years of age, though Bancroft re- 
corded that it appeared to be fairly common on certain areas. It has been 
recorded from Samoa on Hevea, Castilloa, Cacao, Bread-fruit and Albizzia 
stipulata, and from Java on Hevea, and Coffee. In Southern India it is 
known to occur on Tea, on Hevea, and in Northern India on Tea and various 
shade trees. In West Africa it attacks Hevea, Cacao and Funtumia. 

On new clearings the fungus spreads to the Rubber trees from decaying 
jungle stumps and rotting timber, and this may go on as long as either 
of these remain. In one case (on Tea) the fungus was found to spread to 
the Tea from decaying stumps of Na (Mesua ferrea), the Ceylon Iron- 
wood, which were at least fourteen years old. But by far the greater 
number of cases which occur in Ceylon are on old Cacao land, after the 
Cacao has been felled. 

Brown-Root disease is the only root disease of Cacao known in Ceylon. 
Comparatively few Cacao trees are killed by it, but the fungus develops 
freely on the Cacao stumps whenever the Cacao is cut down. In 1905 this 
occurred on several estates on which alternate lines of Cacao had been 
cut out to make room for Rubber, and in some cases it proved difficult to 
eradicate, owing to the large number of Cacao stumps, each of which was 
a potential centre of disease. When writing on this disease in 1911, it 



170 DISEASES AND PESTS OF THE RUBBER TREE PART in 

was pointed out that where Hevea and Cacao had been interplanted it 
would ultimately become necessary to remove the Cacao; and when that 
step had been decided upon the Cacao should be uprooted, not merely 
cut down, if attacks of Brown- Root disease were to be avoided. Recent 
events have amply justified that statement. On several estates where the 
Cacao has been removed during the last five years, by merely felling the 
trees and leaving the stumps, Brown-Root disease has been rampant, 
upwards of ten per cent of the trees having been attacked. In such cases 
the cost of treating the disease has been much greater than the cost of 
removing the Cacao stumps originally would have been. 

Another instance of the association of Brown-Root disease with the 
stumps of cultivated trees recently came to light in Ceylon. On one group 
of estates, the boundaries and roads were planted up with the white 
cotton, or Kapok tree, Eriodendron anfractuosum. Naturally, with such a 
large and rapidly growing tree, it soon became evident that they had 
to be taken out, and when that was done they were simply felled, and 
the stumps allowed to remain. In the course of a year or two, numbers of 
these stumps became centres of Brown- Root disease, which spread to and 
killed the adjacent Rubber. 

Brown-Root disease has also been found to spread to Rubber from a 
felled Hevea log which had been accidentally buried during the construc- 
tion of a road. 

In the most general case Brown-Root disease spreads from one tree to 
another, or from a dead stump to a neighbouring tree, only when the roots 
of the two are in contact. Instances of this may be quite commonly seen 
where the disease has originated on Cacao stumps. But it may be worth 
while putting on record two cases which give some evidence that it might 
be possible for the mycelium to spread through the soil, at least for a short 
distance. In one case a Rubber stump was planted in a flower-pot at the 
laboratory, and in course of time the mycelium extended from the stump 
to the wall of the pot on one side, binding together the particles of soil 
in a mass about two inches thick. But it did not pass through the wall 
of the pot, as the mycelium of Poria hypobrunnea will do under similar 
conditions. In the other case the mycelium spread along dead leaves, etc., 
at the collar of a diseased Brownea grandiceps for a distance of about four 
inches all round. When this case was found, the mycelium had lost its 
hyphal character and had formed, on the under-side of the dead leaves, a 
black film covered with a brown powdery layer. This powdery layer can 
frequently be observed overlying the black crust on diseased roots; it 
consists of a number of minute spore -like bodies, which, however, do not 
appear to be true spores. 

Though, as already stated, this disease is often associated with decaying 
stumps and timber, there are very many cases in Rubber, or Tea, or on orna- 
mental trees in Botanic Gardens, in which no stump or decaying timber 
can be found anywhere in the immediate neighbourhood. In such cases it is 
obvious that infection must take place by means of spores conveyed to 
the plant by wind or other agency. But here, we were until quite recently 
faced with the difficulty that no one had been able to find the spores of 



CHAP, ix FOMES NOXIUS 171 

the fungus, or, indeed, had met with the fructifications of the fungus 
in other than a rudimentary condition. As a rule, a dead tree is found and 
dug up before the fructifications have developed, and the treatment which 
will cause the production of the fructification of, say, Forties lignosus, in 
the laboratory from diseased roots is usually unsuccessful in the case of 
Brown-Root disease. Even when dead trees have been left standing for 
some years, until they have finally disappeared owing to the attacks of 
white ants, no fructification has been formed. 

On young Rubber, or other small trees which have been killed by this 
disease, the fungus sometimes ascends the stem externally above the 
collar, and there forms a tawny or dark brown crust, free of earth and 
stones. In Ceylon these patches are usually small, not more than an inch 
or two in diameter, but in some countries they are said to cover the stem 
all around for a length of several inches. Bancroft stated that the only 
fructification he obtained in Malaya was a badly developed specimen 
on Camphor, but that he had seen specimens on Cacao from West Africa 
in which the brown crust ringed the stem at the collar for a distance of 
about three inches. These brown patches are minutely velvety, being 
covered with very small projecting bristles or setae. Such structures are 
characteristic of the genus Hymenochaete, the species of which form, as a 
rule, flat, encrusting, brown plates, velvety with the bristles in question. 
Hence it has been customary to consider that the fungus of Brown-Root 
disease is a Hymenochaete, and to adopt for it the name Hymenochaete 
noxia, which is that given by Berkeley to the fungus on Bread-fruit in 
Samoa. 

But during the last few years, more particularly during 1917, perfect 
fructifications have been found in Ceylon on several occasions, on jungle 
stumps, OH Tea and Hevea killed by Brown- Root disease, and on rotting 
Hevea logs. These show that the fungus is really a Pomes, and that the 
brown patches hitherto observed, the supposed Hymenochaete, are merely 
abortive attempts to produce the Forties sporophore. This Forties is bracket- 
shaped, often irregular, and consisting of several brackets fused together. 
The separate brackets are three to four inches broad, and about one third 
of an inch thick, and very hard. The upper surface is purple-brown, 
usually concentrically grooved, and glabrous. The lower surface is dark- 
brown, or almost black when moist. When broken in two it is seen to 
consist of a hard, dark, outer crust, with lighter brown tissue internally. 
The internal tissue usually shows a concentric zoning, with curved trans- 
verse lines parallel to the margin. The pore or tubes on the under surface 
are lined with setae, similar to those which occur on the supposed Hymeno- 
chaete patches. The fructification is peculiar in that its internal tissues are 
built up of two kinds of hyphae, the one thin- walled, like fungus hyphae 
in general, the other thick-walled and resembling the setae in structure. 
The name of this species is Fomes lamaoensis. It frequently occurs in 
resupinate form, i.e. lying flat on the root or stem. 

The discovery of the Forties fructification clears up the difficulty of 
accounting for the distribution of the disease. It is now evident that 
infection can be conveyed by wind-borne spores from the fructifications 



172 DISEASES AND PESTS OF THE RUBBER TREE PART in 

on decaying stumps or timber in the jungle or elsewhere. But in Ceylon 
the fructification is by no means common, and it would seem that special 
climatic conditions are required for its development. 

In illustration of the rate at which the disease spreads the following 
instance may be cited. Hevea was planted, 14 feet apart, in a single line 
round the boundary of an old-established Cacao estate. When the trees 
were eight years old, one of them died, from Brown- Root disease as was 
subsequently discovered. The tree was left standing and allowed to decay. 
Two years later the next tree in the line died and was likewise left to decay. 
After a further period of two years had elapsed, the next tree in the same 
direction along the line failed to recover after wintering and was evidently 
dying, and an examination of this tree and the two old decaying stumps 
proved that they had all been killed by Brown-Root disease. Some of the 
neighbouring Cacao was also killed during the four years, but the path of 
the fungus from one Hevea to the next had been along the rubber roots. 

Anstead has recorded an experiment in which a diseased root was 
buried in contact with the roots of a healthy tree, with the result that the 
latter was infected and died. 

Dead trees should be dug up, with as much of the roots as possible, 
and burnt. Any neighbouring stump should be similarly treated. The 
affected spot should be dug over, all dead wood collected and burnt, and 
lime forked in. In general, practically all the fungus is removed with the 
dead tree, and in many cases trenching has been dispensed with. But owing 
to the uncertainty of removing all lateral roots, it is better to err on the 
safe side, and to trench round the affected area. 

When extensive attacks of Brown-Root disease occur on old Cacao, 
the decaying Cacao stumps must be dug up and burnt. This will 
generally entail forking over the whole area. It should then receive a 
dressing of lime at the rate of at least a ton an acre, in addition to the 
application of the usual quantity, sixty pounds, to the site of each dead 
tree. In such cases it is usually possible to detect many trees in an early 
state of the disease by noting the occurrence of patches of decayed bark 
at the collar where a diseased lateral joins the tap-root. These cases should 
be treated by removing the decayed lateral root and all diseased wood 
and bark at the base of the stem. The cavity should then be tarred, and 
it would be advisable to fill it up with cement or concrete. 

The experiment of immediately replanting a tree of the same species 
in the place where one had just been killed by this disease was tried at 
Peradeniya several years ago, and the "supply" has remained healthy. 
It would therefore appear probable that vacancies might be filled as soon 
as all dead wood has been removed and the ground limed. But it would 
perhaps be safer to wait for about six months. 

(3) FOMES LAMAOENSIS 

Fomes lamaoensis originally described from the Lamao River, Luzon, 
Philippines, and the cause of the brown-root rot of rubber has been found 
on almost all the estates visited and is shown to be a much more serious 



CHAP, ix FOMES NOXIUS 173 

cause of decay than was formerly believed. It has been found to cause the 
death of Mangosteen, Rambutan and Soursop by direct attack at the root- 
collar. It is chiefly responsible for a serious collar and tap-root decay of 
Guttapercha and Jelutong in the regions studied. The fungus has been 
found in four instances to cause a serious decay in the forks of rubber, 
resulting in the breakage of the branches at that point. These infections 
were due to spores carried either by wind or insects. The spore-producing 
capacity of the fungus, as determined by spore print-tests, is great and 
may continue indefinitely, but the fructifications are usually rapidly 
destroyed by insects. The mycelium of the fungus has been found to 
extend through the soil a distance of sixteen inches from a major infection 
and to attack the mature parts of a neighbouring root. This means of 
spread, which is favoured by the gelatinous nature of the hyphae and 
which causes the adherence of sand and gravel, explains the isolated spot 
infections. 

List of Plants reported as Hosts of Brown-Root Disease 

Artocarpus incisa, L. Bread-fruit tree 

Thea sinensis, L. Tea 

Coffea spp. (various) Coffee 

Hevea brasiliensis, Miill-Arg. Rubber 

Manihot glaziovii, Miill-Arg. Ceara Rubber 

Theobroma cacao, L. Cacao 

Castilloa elastica, Cerv. Ule, or South American 

Rubber Tree 

Erythrina, spp. 1 Dadap 

Oossypium barbadense, L. Caravonica Cotton or Sea 

Island Cotton 
Cinnamomum camphor a, 

T. Nees & Eberm. Camphor 

Cinnamomum cassia, Blume. Cassia bark 

Erythroxylon coca, Lam. Coca 
Brunfelsia americana, L. 

Thespesia populnea, Sol. Mahoe 

Hura crepitans, L. Sand-box tree 

Grevillea robusta, A. Cunn. Silky Oak 

Codiaeum variegatum, Blume Croton 

Broumea grandiceps, Jacq. ? B. coccinea, Jacq. is the 

Mountain Rose 

1 There are several species of Erythrina known in the tropics. E. lithosperma, 
Blume, is known as " Dadap " in Burma and Malaya ; E. indica, Lan., is also known 
Under the same name. The true " Dadap" of Java is E. hypophlorus, Boerl, while 
E. umbrosa, H. B. & K., is the "Immortelle" of the W. Indies. I am indebted to 
Dr. S. F. Ashby for this information. 



174 



DISEASES AND PESTS OF THE RUBBER TREE PAET in 



Artocarpus integrifolia, L. 

Albizzia stipulata, Boiv. 

Funtumia (elastica ?), Stapf. 

Mesua ferrea, L. 

Eriodendron anfractuosum, D.C. 

Qarcinia mangostana, L. 

Nephelium lappaceum, L. 

Anona muricata, L. 

Palaquium oblongifolium, Burck. or) 

Palaquium obovatum, Engl. J 

Dyera laxiflora, Hook. 

Elaeis guinnensis, Jacq. 

Delonix regia, Rafin. ) 

Poinciana regia, Bojer. j 



Jak 

Sail 

Lagos Rubber Tree 

Iron -wood 

Kapok 

Mangosteen 

Rambutan 

Soursop 

Guttapercha 

Jelutong 
African Oil -Palm 
Flame of the Forest- 
Flamboyant 



CHAPTER X 

OTHER BOOT AFFECTIONS AND SOME PROBLEMS RELATING TO ROOT 

DISEASES 

Root Affections reported by other Investigators Remarks regarding Fungi forming 
Rhizomorphs Thinning-out, a Factor closely affecting the Spread of Root 
Diseases caused by Fornea spp, Root Diseases in Rubber Areas planted on 
Land previously cultivated in other Crops Root Diseases of Rubber in Malaya 
and Khizoctonia bataticola (Taub.), Butler Replanting of old Diseased Areas in 
Malaya Costs of Replanting on old Rubber Areas. 

ROOT AFFECTIONS REPORTED BY OTHER INVESTIGATORS 

THERE are records of other fungi causing root diseases of rubber 
trees in Java, Ceylon and Malaya, but none of these are of importance 
in Malaya at the present time. Steinmann, in Java, records Xylaria 
thwaitesii, Cooke, as a root disease of rubber and also described an 
unnamed root-rot. Fetch and Murray record the same fungus disease 
in Ceylon, and the latter remarks that though it is of extremely rare 
occurrence, it is considered worthy of mention owing to its severity 
in the cases recorded. The fungus, Poria hypobrunnea, Fetch, is 
recorded from Ceylon as the cause of a root disease on rubber, but 
this again, according to Murray, is one of the most uncommon to 
which Hevea is prone. Brooks, in Malaya, recorded Polyporus rugu- 
losus, Lev., as the possible cause of a root disease, but this has not 
been confirmed. Small in Ceylon has recently made strong claims for 
the parasitism of Rhizoctonia bataticola ( = MacropJiomina phaseoli), 
but these have not received support from comprehensive work since 
carried out in Java and Malaya. 

With the object of covering the ground thoroughly, the following 
short descriptions of the above-mentioned diseases are taken from 
Murray's Manual of rubber diseases. 

(a) PORIA HYPOBRUNNEA, FETCH 

Red-root disease caused by this fungus is, in Ceylon, one of the most un- 
common to which Hevea is prone. It originates from old jungle stumps 
and more particularly from Hevea logs. 

Symptoms. The appearance of diseased roots varies somewhat ac- 
cording to the age of the tree attacked. On young trees the mycelium 
forms stout red strands on the exterior of the tap-root. If cut, these 
strands are seen to be white internally. When old the strands turn black. 

175 



176 DISEASES AND PESTS OF THE RUBBER TREE PART m 

The root is often found encrusted with stones and earth as in Brown- 
Root disease, though never to so great an extent. The diseased wood is 
soft and friable and permeated with red sheets. 

In older trees the diagnosis is often more difficult. The mycelium may 
all have turned black though red strands are sometimes found on a 
recently attacked lateral root. The diseased wood is generally soft and 
wet and exposed wood surfaces are red-brown in colour. 

The fructification is uncommon but is sometimes found at the collar 
of a diseased tree. It forms a flat plate closely applied to the surface of 
the root or stem. When young it is yellowish-white but subsequently 
turns reddish -brown. The upper part consists of a layer of small tubes 
which are seen in a surface view as small holes. 

Control. The treatment is the same as for Fomes lignosus. 

It should be noted here that this fungus causes a disease which in 
some respects is similar to that caused by F. lamaoensis. If the disease 
is uncommon and only single cases are found, the method of control 
would be as given for brown-root disease rather than for F. lignosus. 

XYLARIA THWAITESII 

X. thwaitesii, as a cause of root diseases of Hevea in Ceylon, is of ex- 
tremely rare occurrence. It is considered worthy of mention, however, 
owing to its comparative severity in the few cases recorded. The disease 
has only been reported from the Kegalle district in Ceylon; it also occurs 
in Java and Indo-China. 

Symptoms. The external mycelium of the fungus is represented by 
flat irregular bands of variable width on the surface of affected roots. 
These are white when young and are thus seen on the growing margin of 
the mycelium. They soon, however, become black and form an extensive 
network over the root, the bands coalescing in places to form irregular 
black patches. In this condition the external appearance is somewhat 
similar to an advanced case of Brown- Root disease. 

The inner cortex is yellowish-brown in colour, and friable. Where the 
tap-root or a large lateral is attacked, latex is often found to have exuded 
from the cortex in numerous places and formed large lumps of black scrap. 

In advanced cases the appearance of the wood of diseased roots is quite 
characteristic. On splitting the roots longitudinally the central region is 
sometimes found to be greyish-brown in colour, the wood being hard yet 
moist. This region may be delimited by a black line from the outer wood, 
which is yellowish- brown in colour and somewhat more decayed. It is 
noteworthy that the wood remains quite hard until the final stages of 
decay. The extreme wetness of thoroughly diseased roots is a striking 
feature; on breaking a root, water will often spurt into the face. This 
combination of hardness and wetness is quite distinct from the effect 
produced by any other of the root fungi. The fungus appears to spread 
very slowly and in this respect is comparable with Fomes lamaoensis, the 
cause of Brown-Root disease. 

The fungus will apparently not attack exposed portions of roots. 



CHAP, x OTHER ROOT AFFECTIONS 177 

Where an affected root comes to the surface the portion lying on and 
under the ground is diseased, while the upper part exposed to the air is 
quite healthy. The margin of the diseased tissues is sharply delimited 
and becomes marked by a line of callus growth from the healthy portion. 
It is along this line, i.e. where a diseased root cbmes to the surface, that 
the fructifications are mostly found. 

The fructification consists of a cluster of club-shaped growths, arising 
from a basal mass. Three or four stout stalks arise which may divide into 
numerous finger-like protuberances. When found in the field the "clubs" 
are usually a dirty white at the extremity, darkening in colour down to 
the base. Subsequently they turn black. The fructification is usually one 
to three inches in height and the basal mass about two inches in diameter. 
When mature, the upper part of the club-shaped stroma bears perithecia 
containing spores. 

Control. As for other root diseases. 

RHIZOCTONIA BATATICOLA = MACROPHOMIN A PHASEOLI 

It has already been mentioned that the importance of this fungus as a 
cause of a root disease of Hevea is not yet clearly known. Ehizoctonia is 
probably capable of attacking healthy roots under certain conditions, 
and since future experiments may prove it to be of greater importance 
than it is now commonly regarded, it is as well that the planter should be 
acquainted with the symptoms of disease and appearance of the fungus 
in rubber roots. The fungus has been identified as Macrophoniina phaseoli 
and should correctly be called by this name. To avoid confusion, however, 
the former name of Ehizoctonia bataticola will be used. 

Symptoms. Ehizoctonia enters the root system via the small feeding 
roots and thence travels slowly upwards into the longer roots. It is in the 
fine laterals that the fungus is most commonly found. It produces no 
conspicuous vegetative mycelium either externally or in the tissues of the 
root and will therefore often escape the eye of even the trained observer. 
In an affected root the inner layers of the cortex are attacked, and the 
latter, therefore, usually lies as a loose sheath over the wood. If the cortex 
is removed the wood is found to be hard, dry and brittle, and is studded 
throughout with very minute black spots. These are sclerotia, or resting 
bodies of the fungus, and are also found on the inside of the cortex. Fine 
black, dark-brown lines are also sometimes seen in the wood. The symp- 
toms are the same in large roots though larger sclerotia may be found. 
Attacked roots are undoubtedly killed and rendered functionless, but it 
has been argued that it is only after the tree has been weakened by other 
fungal attack or by some physiological cause that Ehizoctonia is able to 
gain entrance. 

Control. In the present stage of our knowledge no control measures 
can be suggested, beyond increasing the vitality of the trees by cultiva- 
tion methods. 

The small, black, rounded sclerotia from which the fungus takes 
the name Rhizoctonia bataticola (Taub.), Butler, are not spores nor 

"NT 



178 DISEASES AND PESTS OF THE RUBBER TREE PART m 

spore-producing fructifications, but are simply aggregated masses of 
mycelial tissues which can resist adverse conditions. This subject has 
already been mentioned, and is dealt with in some detail later. It may 
be pointed out here, however, that if spores are ever found to be 
developed by the fungus, a change in name according to the nature 
of the spore-form will be required. Thus, the name given to the im- 
perfect, pycnidial spore-form, i.e. Macrophomina phaseoli (Taub.), 
Ashby, would be used in preference to R. bataticola by systematic 
workers. But certain investigators are still uncertain as to whether or 
not the name M . phaseoli can be accepted. 

POLYPORUS RUGULOSUS 

Brooks describes this possible fungus affection as follows: 

On several occasions another polyporoid fungus was seen growing at the 
collar or upon exposed lateral roots of diseased rubber trees and it seemed 
likely that this fungus was the cause of the disease from which the trees 
suffered, although inoculation experiments are needed to settle this point 
definitely. The tissues of the host near the fructifications were invariably 
decayed, the foliage of the affected trees became thin, and the branches 
died back after the manner of trees attacked by a slowly growing root 
parasite. I saw this disease in trees which were in tapping, and it appeared 
to be more frequent in badly-drained, low-lying estates than upon 
undulating land. One tree severely attacked by this fungus had been 
previously invaded by white ants. 

The fructifications of this fungus are often densely imbricate and, in 
the aggregate, form large masses, several inches across, although a single 
pileus is only an inch or two in diameter. The upper surface is smooth, 
brownish and zoned; the under pore-bearing surface is white when young, 
becoming yellowish -brown with age; the pores are minute; the substance 
of the fructification is thin, and although fleshy when young is leathery 
at maturity. Both in the colour of the pores and in the much thinner 
substance, the fructifications of this fungus differ markedly from F. 
llgnosus. 

I am indebted to Miss Wakefield of the Royal Botanic Gardens, Kew, 
for kindly identifying this fungus as the Polyporus rugulosus of Leveille. 
The type specimen of this fungus was obtained from tree-trunks in Java, 
and was described by Leveille in 1844. Saccardo has since placed the 
fungus in the genus Fames, but on account of the texture of the fungus 
when young it is preferable to retain the original name. I have been unable 
to find any previous record of this fungus on rubber trees. 

I have seen no confirmation of this finding in Malaya. 

As the fungus must be of rare occurrence, treatment should be on 
the same lines as for F. noxius, i.e. eradication of diseased trees and 
roots from the soil. 



CHAP, x OTHER ROOT AFFECTIONS 179 

Steinmann reports a "root-rot" in a general sort of way, and the 
following translation is taken from his book: 



ROOT- ROT 

This is the effect of the influence of stagnant water on the root system 
of Hevea. It occurs exclusively in low-lying lands with heavy soils. The 
symptoms, collectively called root-rot, are caused by unfavourable con- 
ditions of the soil, especially in connection with supply of air; a character- 
istic is the absence of mycelium. The structure of the soil, of course, plays 
an important part. Most cases of root-rot are found on heavy clay soils 
which suffer from lack of air supply and from excessive moistness; it is 
less common on loose porous sandy soils which are better able to stand 
the disastrous consequences of temporary flooding. 

Progress of the Disease. In some cases of root-rot the above-ground 
parts of the tree do not show any abnormal signs and the disease does 
not become apparent before the trees are blown down. In most cases the 
crowns are sparse on top and start dying back. Cases such as happened in 
1918 on an estate in Sumatra where, owing to a flood lasting two months, 
about 100,000 trees of six to eight years old were killed, fortunately are 
an exception. 

The roots are usually blue-black to black on the outside; their bark is 
completely rotten owing to the action of anaerobic bacteria due to lack 
of oxygen. The very first measure to prevent root-rot is proper drainage 
to ensure thorough earrymg-off of the water. On such low-lying land it is 
advisable to dig wide, straight parallel drains following the slope of the 
land. In accordance with the volume of water to be carried off and the 
fall of the land, these main drains must be made 8-20 feet wide and (U 8 ft. 
deep to lower the level of the ground water to that depth. In low flat land, 
the number, width and depth of the secondary drains depends on the 
character of the soil. If the soil is clayey, the distance between them must 
be less than is needed in sandy soils; with marshy soils it may even be 
necessary to dig drains between all rows or every second or third row. For 
the rest we refer to what has been said on this subject in the Hand buck 
voor de Rubber Cultunre, p. 72. 

Van Overeem in 1924 recorded a case of the black-root disease 
(Eosellinia sp.) affecting rubber and coffee. His English summary is 
as follows: 

In a rubber and coffee estate in Kediri some cases of the black-root 
disease affecting coffee were stated and also a single case of the same disease 
attacking Hevea. Obviously the latter had been infected by the coffee. 

Already as early as 1910, Zimmermann gave detailed description of the 
black -root disease in coffee but the fungus could not be identified. An 
affection of Hevea by this disease has, until lately, never been observed. 
The fungus forms on the roots of the trees fine, black, slightly flattened 
strands which in some places were profusely ramified and formed a kind 



180 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

of netting which is a characteristic of Eosellinia. The specific name of 
the fungus is probably E. bunodes (Berk, et Broom), Sacc., but absolute 
certainty on this point could not be obtained, organs of fructifications being 
absolutely wanting. The symptoms shown by the roots of coffee were 
less typical; however, we do not doubt in the least that the disease was 
caused by the same fungus. 

The attack of Hevea by the black-root disease should not give rise to 
alarm, as Rosellinia occurs everywhere and up till now not a single case 
of this fungus affecting Hevea was mentioned. 

The name black-root disease is to be remembered for the above-de- 
scribed disease, the identical organism being known under the same name 
for tea and coffee. For Sphaerostilbe repens, this name must be rejected as 
the use of it might cause confusion, and in this species the strands are not 
black. 



REMARKS REGARDING FUNGI, FORMING RHIZOMORPHS 

It will now be appreciated that the production of rhizomorphs by 
root-disease fungi is a subject of considerable importance to both 
investigators and laymen. It may be more interesting to the former, 
because there is very little information available in the literature, 
even from the structural point of view. Every student of fungi is 
aware of the typical formation of rhizomorphs by the fusion of hyphae 
running longitudinally (well shown in Fomes lignosus)', the habit of 
longitudinal growth by means of an apical meristem (well seen in 
Sphaerostilbe repens)', the habit of anastomosing to form a network 
(seen in F. lignosus and S. repens); whilst in some cases, individual 
rhizomorphs grow together so closely as to form continuous mem- 
branes (shown by Ganodermapseudoferreum). The typical structure of 
the common rhizomorph is best shown by S. repens (Fig. 11). 

An attempt will now be made to impart some further general infor- 
mation. All the important root diseases of rubber trees in Malaya are 
characterised by the possession of some form of aggregated mycelial 
structures. These bodies should prove of utility in resisting adverse 
conditions, a function considered to be one of the main attributes of 
rhizomorphs, and four of the five fungi concerned produce these 
structures in typical form. 

Root diseases caused by fungi which form rhizomorphs are not 
confined to Malaya, nor to the rubber tree. The remarks which follow 
naturally refer chiefly to Fomes lignosus and Ganodermapseudoferreum, 
but many observations may be taken to apply to rhizomorphs 
generally. 

The root diseases under consideration are liable to occur in any part 
of the world in woody crops planted on land recently cleared of virgin 



CHAP, x OTHER ROOT AFFECTIONS 181 

forest. The actual parasites concerned and their relative importance 
vary in different countries and in different crops. 

The group has attained its maximum economic importance in the 
tropics, where the climate favours the evolution of vegetative pro- 
pagation, and where the first crops taken on virgin land are quickly 
maturing tree crops such as rubber, coffee, tea and cocoa, etc. 

In Malaya, the rhizomorphs of F. lignosus and G. pseudoferreum 
obviously provide an efficient means of vegetative propagation. 
Therefore the production of fructifications and spores may be con- 
sidered a laborious process in these two cases, and the formation of 
rhizomorphs provides a special means of short-circuiting the slow 
development of the fructifications. 

The question is often asked why the root parasites never seem to do 
any obvious damage in standing jungle although they have such an 
effective and easy method of propagation at their disposal. It has 
already been stated that the jungle conditions represent a delicate 
state of equilibrium established over very long periods of time. Now 
the root-disease fungi, along with their neighbours, are kept in check 
by natural competition. They only obtain dominance here and there, 
and the damage done is not noticeable. When the jungle is felled, the 
equilibrium is destroyed and the rhizomorph-forming fungi find the 
new conditions entirely to their liking from the point of view of 
spread. 

Before a Malayan jungle area is felled, the various root-disease 
fungi form, through their rhizomorphs, continuous individual ''net- 
works", extending over the whole area. The size of the "meshes", i.e. 
the extent of infection, depends in the lie of the land, type of soil, 
rainfall, etc., but largely on the individual characters (such as vigour 
and mobility) of the particular parasites concerned. This latter factor 
also determines the size of the individual "knots", i.e. of the spots 
in the jungle where the fungi have obtained dominance over their 
competitors. In undisturbed jungle these "networks" are continually 
changing their form through rhizomorph activity. 

The three root diseases on rubber trees caused by F. lignosus, 
G. pseudoferreum and F. noxius differ fundamentally only in regard 
to the development of maximum activity, i.e. whether they are 
rapidly or more slowly developing fungi. It may be useful to repeat 
that F. lignosus is an exceedingly vigorous and mobile fungus 
with a diffuse, far-spreading, rapidly growing rhizomorph system 
resulting in the formation of jungle networks which are ill-defined, 
the meshes being small and the knots numerous, diffuse and almost 
merging into each other. The fungus is a quick-acting wood-destroyer 



182 DISEASES AND PESTS OF THE RUBBER TREE PART in 

and the infected roots rot away rapidly after felling. The attack on 
the succeeding rubber plantations therefore develops very soon after 
planting, is widespread, and usually dies down before the trees reach 
maturity. 

The cause of red-root disease, Ganoderma pseudoferreum, is on the 
other hand a more compact, slowly acting fungus and the jungle 
networks are therefore wide -meshed, the knots being relatively few 
and restricted in size, and taking a long time to rot away after felling. 

This disease, therefore, develops from widely spaced, concentrated 
centres in the subsequent stand of rubber, but the onslaught is spread 
over a long time. In the immature stand, where the chance of spread 
of the disease from tree to tree by root-contact is slight, the loss of 
trees is small in number, but in the mature stand the disease becomes 
a serious menace. The infected jungle timber remains active long 
after the roots of the rubber trees have become closely intertwined all 
over the clearing, and under favourable conditions the disease spreads 
gradually from tree to tree away from the knots of jungle infection, 
thus forming the disease patches so familiar in present-day stands of 
old rubber. Red-root disease is therefore typical of old areas, although 
it does occur to a small extent in immature stands. 

Brown -root disease, caused by F . noxius, does not call for any 
special comment, for it occurs but rarely on rubber trees in Malaya 
and therefore is of little practical importance to planters in that 
country. 

The root parasites of the rubber tree, capable of forming rhizo- 
morphs, possess in these organs a powerful weapon of attack and 
propagation. The rhizomorphs have, however, many limitations, and 
these can be taken full advantage of when planning a scheme of 
control for root disease. The main limitations are: 

(a) They cannot grow freely exposed to the air, hence their penetra- 
tion of a host cannot take place above soil-level. 

(b) They cannot grow straight through the soil, but require a 
continuous chain of roots along which to spread. It will be clear from 
(c) below that "chain of roots" refers to both living and dead roots. 
This does not greatly hinder the development of the fungus in the 
jungle, or in a planted clearing where the soil is full of interlacing 
roots. The need of a chain of roots, however, affords a line of treat- 
ment, viz. the relatively simple expedient of removing all buried 
timber from an infected area. This removes both sources of infection 
and rhizomorph system, making a clean sweep of infected material, 
and leaving the soil perfectly free. 

In connection with the statement that rhizomorphs require a con- 



CHAP, x OTHER ROOT AFFECTIONS 183 

tinuous chcain of roots along which to spread, it should not be forgotten 
that most investigators incline to the view that Fomes lignosus has 
the power of free growth through the soil, and this seems to be gener- 
ally accepted. Sufficient evidence has, however, been gathered to 
justify the above statement in respect of root diseases investigated in 
Malaya, but absolute evidence, which would settle this point definitely, 
is not yet forthcoming. Evidence obtained recently in young planted 
areas strongly favours the view that a continuous chain of roots is 
required for the rhizomorphs to spread freely in area. 

(c) Although rhizomorphs can travel equally readily along the 
surface of dead or living roots, they can only penetrate and obtain 
nourishment from living roots. In a newly felled jungle area, there- 
fore, the only potential sources of infection are the root systems of 
those trees which were infected by root disease before felling, and it is 
possible, without recourse to the costly alternative of complete clean 
clearing, to trace and remove all potential sources of infection before 
a loss of stand commences in the subsequent crop. This is a sound 
argument theoretically, and in one particular case it has proved so in 
practice. The same argument also applies to the treatment recom- 
mended for old rubber areas which have been heavily infected with 
root disease and are to be replanted. 

The fundamental facts for root-disease control in Malayan rubber 
plantations may be shortly restated. As the root-disease fungi 
reside in decaying wood and not in the soil, the removal of infected 
roots from the soil by digging will completely eradicate root disease 
from an infected area. Soil sterilisation by the surface application of 
fungicides can never hope to control root disease. It may kill the 
growing rhizomorphs but it will only sterilise the surface of the sources 
of infection. As soon as the rain washes away the fungicide, new rhizo- 
morphs will form, and parasitic activity will recommence. It will be 
well to emphasise that the use of copper sulphate solution, as recom- 
mended on page 130, is not for the purpose of soil sterilisation. 

The digging of isolation trenches to hold up the spread of root 
disease is sound as long as certain conditions are fulfilled: 

(a) Each separate jungle knot of disease must be completely en- 
circled by the trench. This is easily attained in mature areas when 
treating red-root disease, but almost impossible to ensure when 
treating white-root disease. Trenches dug within the limits of a knot 
are useless. 

(b) The trench around each knot must be dug beyond the limits of 
the advancing rhizomorph systems. This cannot be attained with 
certainty by digging trenches according to some arbitrary, geometri- 



184 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

cal pattern. Trenching must be accompanied by root inspection. 

(c) The trench must be deep enough to sever completely all root- 
contact between one side of the trench and the other, and must be 
kept open. 

The subject of rhizomorphs has been treated at considerable 
length from one point of view. It is a very wide subject, however, and 
offers scope for many speculative considerations. In connection with 
the root diseases of rubber trees, all investigators will admit that four 
of the five important fungi dealt with produce rhizomorphs; three of 
them produce structures of the typical form, but in Fomes noxius the 
rhizomorphs are somewhat atypical, being masked by the thick 
covering of soil and stones found on diseased roots. Ustulina zonata 
does not produce rhizomorphs, but arguments will be advanced to 
show that from the functional standpoint this fungus does not differ 
greatly from the other fungi causing root diseases. An attempt will 
now be made shortly to put forward various points which appear of 
interest in this connection. 

The first question to be answered is: How did rhizomorphs arise 
and for what purpose were they produced? It has been clearly stated 
that rhizomorphs are fundamentally aggregations of fungal hyphae, 
which, as seen at the present day, are of the greatest utility in the 
life-history, and especially in those fungi causing root diseases. They 
are the product of evolutionary change, as is the case in all organic 
developments. Certain authorities state "that rhizomorphs serve, as 
will be shown in the Basidiomycetes, for the transport of food". If 
food transport was originally the important function of these struc- 
tures, they must have existed in saprophytic forms prior to any 
indication being given in the evolutionary sequence towards parasit- 
ism. In parasitic fungi, food transport has become a very subsidiary or 
secondary function of rhizomorphs in comparison with those of (a) 
preventing desiccation and (6) permitting extensive spread in area, to 
which major importance must be attached. All aggregations of hyphal 
tissue will help towards the former function (a). It appears legitimate, 
therefore, to consider that rhizomorphs were a common feature in 
saprophytic fungi for purpose of food transport, prior to the period 
when protective tendencies, which would prolong the continuity of, 
and ensure the spread of the species, were found to be developed in 
parasitic fungi. 

If this view is accepted, the evolutionary transition from sapro- 
phytism to parasitism would most probably be through an inter- 
mediate stage of semi -parasitism. Because of its epiphytic phase, 
F. lignosus may well be considered to be a semi-parasitic fungus, for 



CHAP, x OTHER ROOT AFFECTIONS 185 

during the epiphytic periods the parasitic activities must be sus- 
pended. This may be said to be due to the antagonistic influences of 
the host plant dominating the opposing ones possessed by the rhizo- 
morphs. Ganoderma pseudoferreum is a definite holo-parasite and 
presumably F. noxius falls in the same class. Sphaerostilbe repens and 
Ustulina zonata do not fall within this group, but F. lignosus can 
definitely be considered the starting point of a series, followed by the 
more specialised forms of Ganoderma pseudoferreum and Fomes 
noxius. 

After the parasitic habit has become stabilised, the main effort of 
parasitic fungi is directed to the one end-aim of all organic life, viz. 
preserving the continuity of the species. Extensive spread in area, 
permitted by the development of rhizomorphs in parasitic root fungi, 
is but a step towards this desired end. It may be as well to recall that 
methods of vegetative propagation, when effective, generally tend to 
replace methods of sexual reproduction necessitating the production 
of elaborate fructifications and spores. 

A parasitic root fungus producing rhizomorphs must avoidany factors 
retarding its development, and its greatest danger lies in drying-out, 
i.e. desiccation. Therefore, the production in any particular species of 
special structures which will prevent desiccation will mark an advance 
upon others which retain their original form. It is remarked above 
that any aggregation of fungal hyphae, whether in the typical rhizo- 
morphic form or not, may be considered an advance on simple hyphae 
in the matter of preventing desiccation. Gaumont and Dodge suggest 
the use of the term plectenchyma for aggregations of hyphal tissues. 
Thus when the question of prevention of desiccation is being con- 
sidered, rhizomorphs are merely plectenchymatic tissues which 
assume a definite form. 

Rhizomorphs may be considered as external plectenchymatic 
tissues in F. lignosus, G. pseudoferreum and F. noxius, or as internal 
plectenchymatic tissues when they are developed internally as in 
Sphaerostilbe repens. Internal plectenchyma will also apply to any 
aggregations of hyphal tissue in the form of black lines in Ustulina 
zonata and the brown lines in F. noxius. 

All rhizomorphs are effective organs for the purpose of preventing 
desiccation, when they are allowed freely to develop in their natural, 
underground habitat. But when diseased roots are exposed to the 
atmosphere, distinctive differences between the various fungi con- 
cerned are noticeable. When the more severe conditions resulting 
from exposure have to be resisted, external fungal tissues, without 
special protective devices, will suffer to the greatest extent. Fomes 



186 DISEASES AND PESTS OF THE RUBBER TREE TART in 

lignosus has no special devices and provides a typical example of a 
rhizomorph-producing fungus which is quickly dried out on exposure. 
Ganoderma pseudoferreum produces rhizomorphs which have a 
thickened outer skin, and this, as compared with F. lignosus, is more 
efficient in preventing rapid desiccation. The rhizomorphs of F. noxius 
are intermixed with a thick binding of soil and stones, and such a 
covering would form a very effective measure for preventing drying- 
out. The internal development of the rhizomorphs of Spkaerostilbe 
repens will result in more efficient protection than if they were 
developed externally, and the maximum protection will be enjoyed 
by fungi developing plates of plectenchymatic tissue internally, more 
especially if they are deeply placed in the diseased tissue, as is the 
case in Ustulina zonata. Fomes noxius also develops this type of 
internal plectenchyma, while G. pseudoferreum follows suit, though 
only to a limited extent. 

From a functional point of view, it may be taken that the fungi 
causing the root diseases of the rubber tree form a series, with F. 
lignosus as the starting point, the least specialised against desicca- 
tion. From the point of view of withstanding desiccation, F. noxius 
and S. repens both stand in a comparatively favourable position, and 
neither fungus can really be given precedence in this respect. 

On the above reasoning, the order in the series would fall as follows: 

(1) F. lignosus 

(2) G. pseudoferreum 

(3) S. repens 

(4) F. noxius 

(5) U. zonata 

If development of typical, external rhizomorphs is taken as the 
main criterion, then F. noxius becomes third in the list and S. repens 
fourth. 

There is much evidence which would support the above views, while 
some could be quoted as antagonistic. But enough has been written 
to show that plant diseases of a particular type developing on the 
same crop should not be envisaged as isolated units, having little in 
common. In other words, the physiological aspects of the pathological 
problems under consideration should hold a much more important 
position than is usually thought to be necessary. The source of our 
present knowledge on root disease really developed from a short 
investigation by the writer on the fungi isolated from diseased roots of 
Camphor, and from diseased roots of rubber trees obtained from 
Ceylon and Malaya. All these showed typical symptoms of brown- 



CHAP, x OTHER ROOT AFFECTIONS 187 

root disease, in so far as the thick encrusting, external mass of soil and 
stones, tightly bound to the roots, was a well -developed feature in all. 
All three fungi isolated were different morphologically, but were alike 
physiologically, for all excreted mucilage freely when grown on blocks 
of rubber wood in the presence of adequate supplies of moisture. This 
venture into the quest for the cause of brown-root disease formed 
merely a prelude for a much wider investigation of root-rots of rubber 
trees, but the opportunity did not arise until quite recent years, and 
the results arc shown in full for the first time in this book. 

THINNING-OUT, A FACTOR CLOSELY AFFECTING THE SPREAD OF ROOT 
DISEASES CAUSED BY FOMES SPECIES 

Reference has already been made to the methods followed when 
planting up in Malaya, the outstanding feature of which is the prac- 
tice of planting more trees per acre than is necessary. This ensures a 
sufficient number of trees remaining available to produce the most 
economical results when the time arrives to start tapping. The 
number of trees per acre must therefore be reduced at some time or 
other. Losses through root disease are usually expected even if not so 
numerous as to cause much anxiety. There are no fixed limits to the 
number of trees to be planted. It will probably be dictated by local 
fancy, but a common number lies between 150 and 200 per acre. 
Neither is the number of trees to be thinned-out at any particular 
period a fixed one; the number taken out is mainly directed by the 
fact that it is desirable to maintain the yield of latex at as high a level 
as possible. There is one guiding principle. The number of trees per 
acre must not be so reduced that a noticeable decrease takes place in 
the amount of dry rubber per acre obtained. 

The disease losses in the early years are caused mainly by Fomes 
lignosus ; the number lost by attacks of this fungus normally reaches 
a peak between the fourth and fifth year and from this time onwards 
the number of disease losses should decrease annually. Rubber planters 
may consider themselves fortunate that this feature is well marked in 
Malaya, but it must not be forgotten that the closely spaced disease 
knots formed by Fomes lignosus are not the only heritage left by 
the felled jungle. The wide-spaced disease knots, characteristic of 
Ganoderma pseudoferreum, still remain, and these are of primary 
importance in mature stands. 

It has been stated that although rhizomorphs have certain limita- 
tions they form a very efficient means for effecting spread in area, if 
left undisturbed to continue their natural habit of growth below soil- 



188 DISEASES AND PESTS OF THE KUBBER TREE PART in 

level, especially if a close, intertwining, continuous chain of roots 
exists. It has been emphasised that a continuous chain of roots is a 
necessity for the efficient spread of the root diseases caused by the 
Fomes type of fungi. The method of thinning-out of rubber trees 
usually adopted in the past was to cut them at ground-level, remove 
the trunk and branches from the plantation, often by burning, and to 
leave the tap-roots and the lateral roots to decay in situ. This method 
was adopted on the ground of expense, but while it saved immediate 
costs it provided ideal conditions for encouraging the spread of root 
diseases. As losses due to Fomes lignosus should be decreasing rapidly 
as the time for thinning-out approaches, the only root disease which 
needs serious consideration is that caused by Ganoderma pseudo- 
ferreum. 

Another point to remember is that a vigorous rubber tree displays a 
certain amount of resistance to attacks of G. pseudoferreum by the 
production of adventitious roots, but there is no resistance offered by 
the parts of a rubber tree left in the soil after the upper parts have been 
removed by thinning-out. When the trunk of a tree is removed, the 
roots do not necessarily die with great rapidity. However, they 
become moribund and ultimately death follows. The loss of resivstance 
to the attacks of the fungus may be considered an additional factor 
which will lead to the rapid spread of root disease after thinning-out. 

The modus operandi of spread of root disease in thinned-out rubber 
areas may now be shortly described. The rhizomorphs will quickly 
withdraw from tissues where food material is becoming scarce, such 
as the roots of rubber trees left in the soil after thinning. Neighbour- 
ing healthy trees will then become infected rapidly, that is, if root- 
contact becomes definitely established between them and the non- 
extracted affected lateral roots of thinned-out trees, in which perhaps 
disease had been unsuspected. Thus the original jungle areas in which 
G. pseudoferreum had gained dominance are maintained without any 
evident increase in area until root-contact by healthy trees is made. 
This is governed by the spacing of the trees, but root-contact will be 
established between the fourth and the sixth year. Following this 
period, a slow spread in area may be expected until thinning-out is 
undertaken; afterwards a rapid acceleration will be effected as 
detailed above. About the eighth to the tenth year the disease be- 
comes prominent and numerous diseased specimens may be found at 
this stage. It seems fairly obvious that there is little cause for fearing 
large losses of mature trees if the original disease knots can be 
removed in the early years and if thinning-out is done thoroughly, 
i.e. by extracting tap-roots and lateral roots. 



CHAP, x OTHER ROOT AFFECTIONS 189 

In a general consideration of the root-disease position in Malaya, a 
great change has been brought about by the comparatively recent 
discovery that Ganoderma pseudoferreum was present in the earliest 
stages of the plantations, i.e. foci of diseased trees, affected by this 
fungus, could be found when they were not more than two years of 
age. But owing to its slow growth and underground habit, the 
" disease-areas" escaped detection for eight to ten years. Given such 
foci of infection and exceedingly favourable conditions for rapid spread 
by root-contact, it is not surprising to find large areas of old rubber 
now being killed by G. pseudoferreum. This is owing to the method of 
thinning-out adopted in the past. As noted previously, the position in 
the old rubber areas in Ceylon is, according to the records, materially 
different from that in Malaya. In that country, the fungus responsible 
for most of the damage in old rubber areas is Fomes lignosus. 

ROOT DISEASES IN RUBBER AREAS PLANTED ON LAND PREVIOUSLY 
CULTIVATED IN OTHER CROPS 

The root-disease problems which arise on Malayan rubber planta- 
tions as a result of the trees being planted on land which was 
previously under jungle, have been fully described. But in Ceylon 
cultivation of other crops was being carried on long before rubber 
planting was started; for instance, the cultivation of Coffee was a very 
profitable undertaking as long ago as 1870. Before the inception of the 
rubber industry, Malaya was a country not too well known from an 
agricultural point of view; in fact, there was very little agricultural 
development in the country. The prospects for the new industry 
appeared very bright when the profit-earning stage was reached by 
the first rubber plantations, and its full expansion and development 
could not possibly be estimated. 

The crops chiefly grown in Ceylon before rubber were Coffee, Cacao 
and Tea. Of these crops, European planters were endeavouring, some- 
what unsuccessfully, to cultivate Coffee in Malaya over rather limited 
areas. Sugar estates were also organised on some coastal areas in 
Malaya, usually under European supervision, but the area under this 
crop was not extensive. In Malacca and Kedah, there were fairly large 
acreages of Tapioca, chiefly by Chinese cultivators. When the rubber 
industry began rapidly to expand, the comparatively unprofitable 
Coffee, Sugar and Tapioca crops were quickly abandoned and the 
popular new crop substituted. The position was different in Ceylon, 
because the crops under cultivation were still profitable at the time. 
Profitable crops could not be rapidly abandoned without incurring 



190 DISEASES AND PESTS OF THE RUBBER TREE PART in 

considerable risk, hence in order to be on the safe side, they were 
interplanted with rubber, until the heavy shade from the growing 
trees began to interfere with the normal development of the individual 
plants of the preceding crop. When this occurred, the latter were 
extracted and rubber was left as the sole crop. But in addition to 
establishing rubber plantations by interplanting areas carrying other 
crops, it is probable that rubber plantations exist in Ceylon which 
were planted directly on recently felled jungle land. If this be the 
case, then a true comparison is possible between rubber plantations 
in Ceylon and Malaya. 

For Malaya, the statement can be made without fear of contradic- 
tion, that the state of the jungle soil in which the young rubber trees 
are planted, predetermines the future behaviour of these areas in 
respect of root diseases. It might be expected that the more general 
remark will apply, i.e. that in any country, any growth precedent to 
rubber, whether jungle or plantation crop, must have a very import- 
ant influence on the types of root diseases which will develop in the 
new crop. Keeping in mind that 0. pseudo/erreum has not been 
recorded in Ceylon (though it causes practically the whole of the 
damage in old rubber areas in Malaya), and that brown-root disease 
can be considered rare in Malaya, the paragraph on page 109, copied 
from Fetch's book, is of considerable interest. It refers to the common 
occurrence, in Ceylon, of brown-root disease on rubber trees planted 
upon old Cacao land, and indicates that the true explanation of the 
comparative rarity of brown-root disease on rubber trees in Malaya, 
viz. that, except in an experimental fashion, Cacao has never been 
planted up in the country. It may be added that the writer has never 
heard of one of the Cacao experiments proving successful. 

There seems little doubt that whatever the type of land utilised for 
the planting of rubber, the root-disease problems which are likely to 
be encountered will depend entirely on the previous planting history 
of the areas. When rubber plantations replace other crops, either by 
being interplanted or by direct replacement, the root diseases which 
the plants are likely to contract will be those to which the replaced 
crop plants were susceptible, and which the latter contracted origin- 
ally from jungle soil. So that root-disease problems might be expected 
to vary according as to whether the areas under consideration were 
previously under Coffee, Cacao, Tea, Sugar or Tapioca, or any other 
growth which might be mentioned, for all will probably show wide 
differences as regards their susceptibility to the fungi persisting from 
the original jungle and which are capable of causing root diseases. 
Thus, there are very strong reasons supporting the expectation that 



CHAP, x OTHER ROOT AFFECTIONS 191 

root diseases may be very different on rubber plantations in Ceylon 
and Malaya. 

If economic crops are planted successively, the perpetuation of a 
root disease caused by a fungus which is active in the original jungle 
is brought about only if the first or succeeding crops are susceptible 
to the particular fungus. If none of these are susceptible, the fungus 
can only continue existence as long as any undecayed jungle timber 
remains, and once this is removed, danger disappears. Jungle stumps 
and timber, in areas where they are allowed to decay naturally, are 
not prominent after a period of thirty years, though there may be 
some remnants of the largest, hardwood stumps still persisting. 
Therefore after thirty years the only disease centres remaining are 
those formed by the crop plants which have contracted the disease. 
If rubber-planting has been undertaken on areas where the original 
jungle stumps and timber have rotted away completely owing to the 
lapse of time, and a crop or crops of non-susceptible plants have been 
cultivated before the rubber, reports of root disease would probably 
be non-existent. 

A special case in point may be mentioned here. Tapioca was 
extensively cultivated before the rubber era in certain districts in 
Malacca and Kedah. These old tapioca areas were allowed to become 
derelict, in some cases for many years, after being abandoned, and 
they became covered with a heavy, coarse growth of "lallang" grass 
(Imperata arundinacea, Cyrillo). Many of these areas were later 
planted up with rubber, and usually there were few signs of jungle 
stumps or timber remaining when the work was put in hand. Some of 
the estates in the Malacca district are large properties, and practically 
no reports of root disease have ever emanated from those opened up 
on "lallang" land. It is a well-known fact that a vigorous growth of 
Fomes lignosus is often found on tubers of Tapioca, but it does not 
seem to do a great amount of harm to them. If rubber had been 
planted directly following the Tapioca crop, there is little doubt that 
white-root disease would have appeared; but a long enough period 
having been allowed to elapse when the conditions were unfavourable 
to the development of the fungus, the disease was conspicuous by its 
absence. 

The foregoing remarks apply to rubber plantations in Ceylon, com- 
menced on old coffee land. This crop was going strong in 1870. 
Rubber-planting became a general proposition in the Middle East in 
the decade 1900-1910, so that there was ample time for the total 
disappearance by natural decay of jungle stumps and timber from old 
coffee areas. 



192 DISEASES AND PESTS OF THE RUBBER TREE PART m 

In Malaya, during recent years, attention has been directed to the 
fact that small-holdings apparently show far less root disease than 
the large estates under European supervision. This has led to con- 
siderable correspondence as to the merits of Native versus European 
planting methods. Such a controversial matter cannot be dwelt upon 
at length in this book, but the statement has repeatedly been made 
by the writer that there is no doubt that patches of red-root disease 
can be commonly found in small rubber holdings under native con- 
trol. The view has never gained full acceptance and has been ignored 
entirely by ardent supporters of forestry methods. Up to 1934, little 
reliable evidence could be produced in support of the view; it was a 
statement based on personal experience in the country. The most 
recent official announcement, however, from Malaya, is made by the 
Economics Branch of the Department of Agriculture, on Small 
Rubber Holdings in 1934, and this report states, inter alia: 

In Perak, persistent reports of damage by root disease were received 
which will receive further investigation; there would seem to be little doubt 
that in some localities, root disease probably mainly Ganoderma pseudo- 
ferreum is more prevalent in small holdings than has been supposed to 
be the case. 

Further evidence for the view that root diseases are common in 
native rubber holdings can be quoted as coming from Java, for 
Leefman wrote in 1933 as follows: 

that owing to the prevalence of bark and root diseases, 20% 30% of 
the Hevea rubber trees in the older native plantations in the Tapanoeli 
Residency, in Java, have become unproductive. 

The evidence for the writer's views, given above, strongly empha- 
sises the suggestion that the differences in the prevalence of root 
diseases in native small-holdings and European estates will eventu- 
ally be found to be more apparent than real. Asiatic small-holdings 
are usually opened on land which has previously been planted up 
with trees not susceptible to red-root disease. As the fungus will die 
out in course of time if susceptible trees are absent, there are very few 
signs of red-root rot in mature trees growing in native holdings. 
Numbers of rubber trees are often planted up in kampongs (native 
gardens), which usually carry a mixture of fruit trees, coconut 
palms, etc. The only common fruit tree recorded as being susceptible 
to Ganoderma pseudoferreum is the Durian (Durio zibethinus, Murr.), 
and if rubber trees were planted intermixed with durian trees, there 
is little doubt that red-root disease would be commonly found. The 



CHAP, x OTHER ROOT AFFECTIONS 193 

above remarks must be taken as applying only to Asiatic small- 
holdings in Malaya. 

The next point for consideration is the status of Rhizoctonia batati- 
cola (Taub.), Butler, as a causal agent of root disease of rubber trees 
in Malaya. 



ROOT DISEASES OF RUBBER IN MALAYA AND RHIZOCTONIA 
BATATICOLA (TAUB.), BUTLER 

Exceedingly wide claims were made by Small to the effect that 
R. bataticola was the cause of root disease of plantation crops in 
Ceylon. The crops specially mentioned by him were "two plants of 
great economic importance in Ceylon, namely, Tea and Rubber". The 
fungi mentioned by this investigator as being under suspicion are 
the following: 

(a) Fomes lignosus (d) Poria 

(6) Fomes lamaoensis (e) Rosellinia 

(c) Ustulina (/) Diplodia 

No good purpose will be served by stirring up the pool of dissension 
created by Small's articles; this now seems to have settled down, and 
for the time being a smooth surface is showing. The writer feels 
justified in alluding to the subject only in so far as the root diseases of 
rubber in Malaya are concerned. 

Small's claims were that the fungi, formerly considered to be the 
cause of the important root diseases of rubber and tea, were only of 
secondary importance. The basis of this statement rested on the 
discovery made by Small of the presence of R. bataticola in diseased 
rubber and tea roots, and in most cases one of the fungi mentioned in 
the above list was also present. He considered that, in all cases where 
R. bataticola was found, this fungus must be considered to be of 
primary importance, though he admits that "in the absence of the 
results of inoculation experiments there is a certain amount of conjec- 
ture which is unavoidable at the moment". Small's attitude is perhaps 
best indicated by the following short extract from his first article on 
this subject: 

I therefore continue to regard all the plants involved in an outbreak 
of root disease, whether large or small, as having been attacked in the 
first place by Mhizoctonia bataticola, and I hold that trenching and stump- 
ing are of little, if any, value as treatment of the outbreak because they 
do not affect in any way the incidence of the spread of the Rhizoctonia, 
a fungus which does not move from plant to plant by contact, does not 

o 



194 DISEASES AND PESTS OF THE RUBBER TREE PART in 

spread through the soil by creeping mycelium and is widely distributed 
in Ceylon soils. 

It appears, therefore, that if evidence can be produced to show that 
the important root diseases of rubber trees do spread by contact in 
Malaya, SmalPs views may be considered of little importance in 
connection with the root-disease problems encountered in that 
country. Overwhelming evidence has already been given to show that 
the diseases caused by Fomes lignosus and Ganoderma pseudoferreum 
in Malayan rubber plantations do spread by contact. 

No evidence has been obtained over the last three years to support 
the claims of Small in relation to rubber diseases, either in Java or 
Malaya. Even if the evidence provided by the illustrations in the text 
is alone considered, no doubt can exist in the mind of any practised 
observer in Malaya that the two important fungi causing root diseases 
spread by root-contact. In the case of white-root disease, Napper has 
carefully dug out hundreds of cases of diseased trees, and in every 
case, without exception, the source of infection has proved to be a 
jungle stump or a piece of jungle timber, the latter often of small 
dimensions, which is being rotted away by F. lignosus. R. hataticola 
was never found, though a close examination for this fungus was 
always made. The difficulties attendant on this comprehensive field- 
work were enormous, for the soil had occasionally to be dug out to a 
depth of four feet, in a circle round a tree, with a radius of fifteen feet 
or more. However, the evidence secured is so convincing, that full 
compensation for the hard labour involved was obtained. There is not 
the slightest doubt remaining that the root disease caused by F. 
lignosus spreads by root-contact, once the roots of the neighbouring 
rubber trees have grown sufficiently long to come into contact with 
infected jungle timber or with roots of a diseased tree. 

With reference to O. pseudoferreum, any investigator who has 
worked in a diseased field of mature rubber in Malaya cannot pos- 
sibly come to any other than the same conclusion. When a large, badly 
diseased lateral root is followed up to its outward extremity, it will 
usually be found to come into close contact at various points with 
lightly affected roots belonging to other trees. If these roots are 
examined carefully at the point of contact, it is obvious that the 
earliest infection is made at these points, for the whole of the tissues 
of the lightly affected roots are here involved; the fungus then spreads 
along the root in both directions with the amount of diseased tissue 
gradually decreasing as a greater distance is passed from the point of 
contact, until finally the diseased tissue cannot be found at all. 
This method of infection and spread is such a commonplace feature 



CHAP, x OTHER ROOT AFFECTIONS 195 

that it is quite unnecessary to postulate the presence of another 
fungus. 

The only possible conclusion to be drawn is that, in Malaya, the 
two most important root diseases spread by root -contact. Further, 
no evidence has been obtained to indicate that R. bataticola is 
associated with these root diseases either in a primary or even a 
secondary capacity. 

There are other matters which might be commented upon. The 
writer is of the opinion that Small's discovery of R. bataticola on 
diseased roots of rubber and tea is of the greatest interest, but the 
finding of this fungus in Ceylon is no more surprising to Malayan and 
Javan investigators than the complete absence of Ganoderma pseudo- 
ferreum in that country on mature rubber. An attempt to account for 
fundamental differences such as these, which are evident in different 
countries, should be made, and a tentative explanation is given above. 
With respect to Small's reference to trenching methods being of little, 
if any, value as treatment (in control of root diseases), the recent 
work in Malaya indicates that, in the early stages of the plantation, 
there may be some truth in this statement; but later, when spread 
by root-contact between neighbouring trees becomes effective, the 
immense value of trenching immediately becomes obvious. 

REPLANTING OF OLD DISEASED AREAS IN MALAYA 

It is only to be expected that, during the prosperous periods of the 
past, rubber estates with available jungle reserves would endeavom 
to bring them into the profitable bearing stage. For this reason, the 
majority of old estates in Malaya have at the present day no jungle 
reserve land available. Further, the allotment of areas of jungle 
reserve for the purpose of planting rubber has been officially pro 
hibited in the three states where the rubber plantation industry has 
been most extensively developed. Numerous estates on which red-rool 
disease on the old rubber areas has been allowed to develop withoul 
restriction, now possess areas of rubber which have become un 
economic units owing to disease, and if it is wished to place these 
areas in the economic list once again, they are practically forced tc 
consider replanting. The re-conditioning of the soil of such blocks o: 
land for the purpose of rubber-planting is more expensive than the 
felling of jungle and planting-up on virgin soil, and the ensuing results 
might be expected to be more problematical. There are two reasons 
for this: 

(a) The areas to be replanted have carried badly diseased trees, 



196 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

and the soil must be considered to be riddled with infective material 
(mainly diseased rubber roots); if the prospects of successful re- 
planting are to be ensured, this must be totally removed as far as 
possible. 

(6) The soil which has been under cultivation with rubber for a 
period between twenty and thirty years may be expected to be in a 
comparatively exhausted condition, for during their period of growth 
rubber trees are continuously drawing on the nutritive material pre- 
sent, and comparatively little return of organic material to the soil is 
made in the way of leaf-fall, etc. It might be worth stating here that 
the soil of rubber estates in Malaya may be considered definitely poor 
in nutritive materials from the outset, and at the end of twenty to 
thirty years' growth its condition must have become decidedly 
worse. 

Under these conditions, we may justly enquire why, during de- 
pressed financial periods, a policy of replanting uneconomic areas 
should be undertaken. The reply is found in the probable yields of 
rubber to be obtained by utilising modern methods of planting-up 
bud-grafted material, i.e. trees which have been proved definitely 
superior and found to possess all the desirable properties. These strains 
of rubber trees are expected to give greatly increased yields, even to 
the extent of twice or three times the amount given by the ordinary 
mixed material planted in past years. The writer has stated on more 
than one occasion in the past, that if only the question of increased 
yields from bud-grafted material can be confirmed by the production 
of sufficient credible evidence, it seems only a matter of time before a 
bud-grafting policy will be forced on all rubber estates which have 
reserve funds available. The time does not seem far distant when 
estates with an eye to the future will be utilising the modern methods 
of bud-grafting to the full, in spite of the recent introduction of 
restriction which, incidentally, brings rubber into line with most 
other primary commodities. This modern development is by far the 
most prominent feature which emerges from all the research work 
done on the planting side of the industry during recent years. 

Reference to the two terms rejuvenation and replanting have 
already been made, and no further comment is needed. The only 
policy worth considering in Malaya is replanting, and there is only 
one distinction to be made, viz. as to whether large or small areas 
should be dealt with at any particular period. This entirely depends 
on the question of adequate financial resources. 

In view of the extremely favourable reports obtained from bud- 
grafted areas, the most business-like policy to pursue, if funds are 



CHAP, x OTHER ROOT AFFECTIONS 197 

adequate, is to replant all old areas which are definitely uneconomic, 
i.e. producing not more than 300 Ibs. of rubber per acre per annum. If 
yields can be doubled, overheads will be halved automatically and 
costs of production will be largely decreased. 

But there are so many estates which show badly diseased patches 
in their old rubber areas, and a large number of them do not possess 
adequate monetary reserves to undertake a comprehensive scheme 
of replanting in large blocks, so some possible alternative recom- 
mendation must be made. The only alternative is to concentrate 
attention on the diseased patches, and to defer work on the healthy 
areas to a later date. 

For estates of limited means, the best scheme for facilitating re- 
planting would be to treat the diseased areas in such a way that any 
expenditure incurred would be a direct contribution to a more com- 
prehensive scheme. Therefore the work should be designed to clean up 
any diseased areas in advance of the main replanting scheme, so that 
when the latter programme is commenced, most of the more strenuous 
part of the work will have been completed. 

Whatever policy is adopted, the treatment of the diseased areas, 
actually carrying large numbers of diseased trees, should be the same. 
The tap-roots of diseased trees must be removed to a depth of at least 
three feet, and all the lateral roots must be extracted as completely 
as possible. The diseased timber and the remains of the trees, if not 
required for firewood, must be destroyed by burning in situ, if 
possible; it will be of advantage if the ashes left after burning can be 
scattered about over the area, in order to utilise the potash content. 
The soil over badly diseased areas must be dug over to a depth of at 
least 18 inches, and if any small lateral roots are encountered, they 
must be gathered and burnt. 

The spread by root-contact results in the formation of diseased 
patches which can be demarcated quite clearly from healthy areas. 
The clearing work on healthy areas need not receive the meticulous 
attention which is necessary on diseased areas and the soil need not 
be dug so deeply: 9-12 ins. will suffice. Thus expenditure on healthy 
areas should be considerably lower than on diseased ones, owing to 
the lighter work involved. 

Many objections have been raised to the effect that such recom- 
mendations would not result in the complete removal from the soil of 
the infective material. The possibility of a 100 per cent removal being 
effected is very remote. In the first place, the expense likely to be 
incurred by adopting such a proposal would be practically prohibitive. 
An attempt at the complete removal of all the infective timber on 



198 DISEASES AND PESTS OF THE RUBBER TREE PART in 

areas which are to be replanted because of root disease would involve 
digging to a depth of three to four feet and general sifting of the soil. 
Even when this had been accomplished there could be no guarantee 
that the desired end had been effected. On one experimental plot 
three acres in extent, this operation was undertaken at a cost of over 
400 dollars per acre. A second drawback which seriously affects the 
young crop is that deep digging results in considerable disturbance of 
the infertile subsoil, usually found on Malayan plantations, which is 
raised to the surface and becomes mixed with the fertile top-soil. As 
a result of this the young plants make very poor growth. It may seem 
somewhat remarkable, but it appears that a large proportion of sub- 
soil which is raised remains on the surface, while a large portion of the 
fertile top-soil becomes buried where it is not readily available until 
the roots of the young plants have grown considerably in length, and 
are able to penetrate to lower levels. The setback thus occasioned is 
very obvious, and, as judged by the above-ground development, it is 
from twelve months to two years before the plants commence normal 
growth. The recommendations made above will result in the removal 
of a good 95 per cent of infective material at a comparatively small 
cost, and if they can be followed by the systematic treatment for root 
diseases from the earliest stages, as detailed for Fomes lignosus and 
Ganoderma pseudoferreum, there is no reason to fear large losses of 
expensive planting material owing to outbreaks of root disease, even 
though a small percentage of infective material still remains in the 
soil after the main clearing is finished. The detailed report given later 
will provide all the information required on this point. 

It will be perfectly plain to all planters that, if the policy of re- 
planting small patches of badly diseased areas is adopted, an import- 
ant fact must be kept in mind, viz. each replanted patch must be 
protected from the competition of the old rubber trees around its 
boundaries. This applies not only to (a) root competition, but also to 
the equally important factor (6), the effect of the shade cast by old 
rubber trees on the outer rows of trees in the replanted areas. The 
latter effect is difficult to counteract, and the only recommendation 
that can be made is that the patches dealt with should be as large as 
possible, for the larger they are, the smaller will be the proportion of 
replanted trees affected by the shade. In the writer's opinion, small 
replanted areas should not be less than \ an acre in extent, and should 
be in a square block if possible; a larger sized block would be still more 
preferable. Many planters have replanted areas not exceeding of an 
acre in size, and claim that good results are likely to ensue. There is 
little doubt, however, that if the areas are sufficiently large, there are 



CHAP, x OTHER ROOT AFFECTIONS 199 

good prospects for the central portions at any rate producing well- 
developed trees. 

To prevent root competition in small replanted areas, an isolation 
trench should be preserved at the periphery of the patch. There is no 
necessity to keep the trench permanently open, but it should not be 
too strictly limited in size, either in depth or breadth. If it is not kept 
open, it is necessary to re-dig the trench at intervals, in order to 
prevent the old trees sending down vigorous, newly developed 
absorbing roots into the replanted areas. 

Whatever policy of replanting is adopted, there remains the question 
of obtaining the highest possible yields of latex from the standing 
trees. If a wholesale policy is undertaken over areas not less than ten 
to twenty acres in extent, as many cuts as will yield latex may be put 
upon the tree. But where financial exigencies entail a waiting period, 
it will be dangerous to commence a tapping system which will prove 
too exccvssive, for this would lead to considerable trouble from out- 
breaks of panel diseases, and these must be avoided as far as possible 
if it is considered desirable to tap the trees for a lengthy but indefinite 
period. Excessive tapping systems can be used with safety only when 
the future of the replanting policy can be clearly viewed and the time 
of commencing is definitely fixed. Systems of excessive tapping can 
be recommended which will give enormously increased yields, and in 
Malaya expert advice can always be obtained as to which method of 
tapping would be most profitable under any particular set of circum- 
stances. On one estate, two years' normal crop of rubber was obtained 
in six months, the trees giving a yield under the excessive tapping 
system used, calculated to be at the rate of 1700 Ibs. per acre per 
annum. 

Where the soil conditions happen to be unfavourable for the 
development of rubber trees, disappointment may be met with. This 
will not be a common occurrence except in areas where the soil has 
been badly eroded in the past. But the soil in any area which has sup- 
ported rubber trees for the past twenty to thirty years cannot be 
expected to compare in suitability with the soil ready for use in 
newly felled jungle areas. Therefore, immediate steps must be taken 
to improve soil conditions by planting of cover- crops, etc., for it is of 
primary importance in starting replanted areas; if a suitable cover-crop 
can be easily established it can be taken for granted that the replant- 
ing will be successful. During the first four years, enough light will be 
available for the successful working of cover- crops, and periodical 
turning-in of green material will result in some soil improvement. 

Even, however, if a cover-crop is established successfully, on soil 



200 DISEASES AND PESTS OF THE RUBBER TREE PART m 

which seems not unsuitable for rubber-growing, the young trees may 
appear to develop well in the early stages, but later show a very 
definite lag in growth. The only manner of surmounting this is by the 
use of inorganic, chemical manures. In fact, chemical manures are 
likely to become of the greatest importance in the successful de- 
velopment of replanted areas, for it is very doubtful whether normal 
growth can be maintained in the early years by a green cover-crop 
only. Further, if the high yields of latex are to be obtained, as 
anticipated, they can only be kept up by utilising larger amounts of 
nutritive materials from the soil than did the previous trees, and some 
compensation must be made to the soil for this continuous drain. In 
the writer's opinion, this will be done only by the working out of a 
complete manurial scheme in which chemicals will play the chief part. 
The following scheme is taken from an estate report signed by 
R. P. N. Napper: 

In the planting hole . 4 oz. per tree Young Rubber Mixture 

After 6 months . . 3 oz. 



,, 1 year . . 8 oz. 

,, 2 years . 1 Ib. 

,, 3 years . . 1 J Ib. 

4 years . . 2 Ibs. 

He adds further: 



Enpekay 

}> 
Sulphate of Ammonia 



Permanent improvement in soil conditions can be taken in hand by 
encouraging the growth of a natural or planted shrubby cover between 
the rows. A legume like Lamtoro (Leucaena glauca) or Tephrosia, would 
probably require assistance with a fertiliser at the start, and for this 
reason a natural cover might be preferred. The planting rows should be 
kept clean- weeded up to 7-8 feet width, to minimise the competition 
between the cover and the young rubber trees. Fertilisers intended speci- 
fically for the rubber trees should be applied only within the limit of those 
clean-weeded rentices and maximum benefit will be obtained if they are 
restricted to a circle, or rather to a ring around each tree, coinciding with 
the main absorbing area of its root system. These rings will of course 
expand as the trees increase their root range, and should be estimated 
at each application. 

The writer agrees with this advice in the main, but would add the 
following remarks, merely to express personal preference. The seeds 
or the cuttings of a green cover-crop should be inserted as soon as 
possible in all places where clearing has been finally accomplished. 
Immediately the cover-crop shows signs of successful development, 
the stumps or seeds of the rubber plants can be planted, but if the 
soil conditions prevent the initial successful growth of the cover-crop, 
then it is more than likely that the young rubber plants will suffer 



CHAP, x OTHER ROOT AFFECTIONS 201 

adversely. The best criterion for judging whether the soil conditions 
over a replanted area are suitable for the planting of the young 
rubber plants appears to be the success or otherwise of the cover-crop, 
and planting-up should not be attempted until definite signs of suc- 
cess are obtained. Bushy covers, such as suggested, could no doubt be 
used in conjunction with a green cover with very satisfactory results, 
but the suggestion to use natural covers does not meet with the writer's 
present approval. It is admitted that the development of natural 
covers must be considered haphazard and therefore somewhat un- 
scientific, although an enthusiast might make even a comparative 
success along these lines. But the future developments in rubber 
planting will necessitate the abolition of haphazard methods. 

In concluding this portion on replanting, the WTiter would mention 
that little has been heard of the recent activities in this line. However, 
reports of the annual general meetings of two important rubber 
companies appeared in the Malay Weekly Mail dated May 23rd, 1935. 
Definite references to "future policy" were contained in these reports. 
The portion dealing with a programme of replanting on one estate is 
reproduced below, and it seems clear that the methods recommended 
herein are being taken into serious consideration. 

Turning to the question of our policy for the future, the board is in- 
vestigating the advisability of embarking upon a programme of replanting, 
with a view gradually to replacing our older areas with bud-grafted rubber. 

The extent of such a programme is limited by enactment to a total of 
20 per cent of one's planted area, during such period as rubber regulation 
may remain in force; but, in any case, the board's views are that the ques- 
tion should be tackled gradually and that no larger programme should 
at present be embarked upon than can be comfortably financed from our 
existing reserves. 

When any particular problem is under review, it is always of 
interest to compare the position in Malaya with that existing in other 
rubber-growing countries in the Middle East. An article was published 
by E. von Zboray in 1930, and the extracts clearly indicate that, with 
reference to the close interdependence between the red-root disease 
caused by Oanoderma pseudoferreum and replanting of old areas on 
estates which have no reserve jungle areas available for new planting, 
the position in Java is exactly the same as in Malaya. Readers will 
appreciate many minor points of difference, but this does not require 
comment, for much progress can be recorded since the article was 
written. The points of agreement on the major issues are so obvious, 
however, that they must be considered to hold the greatest signifi- 
cance. 



202 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

The writer states, inter alia: 

Among the many rubber problems still unsolved, the red -root rot takes 
a very forward place. I doubt if in the present slump in rubber there are 
many more important problems waiting for solution than the combating 
of one rot or another. A problem that is always cropping up is: What must 
we do with our fields to make them pay? Other tapping systems, more 
trees per acre, tap to death our present plantations and replace them by 
better material by re- clearing or rejuvenating; or is the solution to be 
sought elsewhere? Naturally everyone would have as good producers as 
possible on his estate. Unfortunately old plantations are in very many 
instances giving only a very moderate yield or are going back. Everyone, 
then, is busily transforming poor fields into valuable high -yielding gardens. 
In places where there is no root disease, replanting requires no particular 
care. But where the soil is infected with root disease, it is a much more 
difficult question. We have here to deal with a great unknown problem. 
For it is not yet known how soon the red-root disease (Ganoderma pseudo- 
ferreum) attacks newly planted trees nor can we say with certainty how 
long a time a tree, attacked by red-root disease, takes to die. 

In practice it is impossible to make soil infected with red-root disease 
entirely free from timber in re- clearing. In Bantan, an original clearing 
from which all rubber was removed to a depth of one metre, cost 400 
guilders per bouw (nearly dollars Straits 150 per acre). Notwithstanding 
this high cost, it still cannot be said definitely that there is not a stick of 
timber left in the ground to become a source of infection later. 

It is thus an outstanding question whether soils where root disease is 
present, can be completely cleared of timber or rendered sterile before 
new rubber is planted. For this question to be answered definitely, we 
must first know how a rubber tree does in infected soil. 

It is known that young plantations suffer from white-root disease; 
however it is usually not so bad, and after some treatment the percentage 
of trees attacked falls and as the trees grow older the disease completely 
disappears. Red-root disease on the other hand is considered to be a 
disease of old plantations. But what happens to the red-root disease in 
young plantations, and similarly in re- clearing works? 

Following on the above, the writer gives details to prove that five 
years after planting rubber trees in soil areas which had carried old 
trees suffering from red-root disease, they had become infected with 
the same disease. He goes on to state: 

Within five years after the attack, the trees die off. There may be 
hundreds of infection centres in infected soil, from which it is theoretically 
possible that all trees planted are destroyed within five years. The danger 
of red-root rot in re- cleared gardens is thus not illusory, and it is very 
possible that just at the time the trees become tapable, a number of them 
will die off. How big the wastage will be naturally depends upon very many 
factors the number of infection centres left in the ground, the thickness 
of the stand of plants, growth conditions of the disease, etc. 



CHAP, x OTHER ROOT AFFECTIONS 203 

I think this shows quite emphatically that in re- clearing or rejuvenating 
the soil ought to be purified of all possible root-remains. Eventually the 
soil must be disinfected by chemical means. Although costs are now so 
high, this money must be spent, unless we are to run the risk of finding 
in five years' time the plantation dead as it stands. 

(Conclusion. From the above facts the conclusion may be drawn that 
young Hevea trees under certain circumstances may die off of this disease. 

Whether under conditions more favourable to the disease the process 
will run its course in a shorter time still, is naturally not ruled out. The 
converse is also possible, namely, that an affected Hevea tree may offer 
resistance for longer than five years. 

The fact that an affected tree can die within five years demands the 
greatest care in re-clearing or rejuvenating of old plantations where red- 
root rot prevails. 

COSTS OF REPLANTING ON OLD RUBBER AREAS 

Costs of replanting vary according to locality. One estate favour- 
ably situated has replanted one area at a nominal cost, by arranging 
that all the felled timber could be taken away for sale in exchange for 
the labour required to undertake the preliminaries of felling, digging 
of soil, collection of all timber, etc. etc., and the manager calculates 
that the only cost to the company will amount to not more than 30 
dollars per acre. The schedules given, however, will enable planters to 
estimate what prices should be paid for the work in their own parti- 
cular districts, when let out on contract to Chinese contractors. The 
work is very heavy and Chinese seems more suitable than Tamil 
labour. Schedule (A) gives itemised costs for replanting small, vacant 
spaces, and Schedule (B) gives the same items in a more detailed 
form, for replanting in a wholesale manner over a large acreage. It 
will be noticed here that fifteen acres have been felled and cleared 
free of cost. 

SCHEDULE (A) 
Cost of replanting Vacant Slices 

(1) Felling and removing tap-roots to a depth of 3 feet $ c. 
and burning, 55 trees per acre (o> 40 cents . . 22.00 

(2) Chengkolling to a depth of 18 inches and removing all 
timber and roots and burning same, per acre . 30.00 

(3) Holing, Filling (size of hole 2J ft. deep by 3 ft.) 16' x 

17' 160 trees per acre 2| cents . . . 4.00 

(4) Planting budded stumps (own budwood), 160 @ 4 

cents . . . . . . 6.40 

(5) Contour drains 15 chains to an acre (size of drains 

2 ft. by 2 ft.) @ 50 cents per chain . . . _7.50 

Total per acre . . "$6SL90 



204 



DISEASES AND PESTS OF THE RUBBER TREE PABT in 



SCHEDULE (B) 

Cost of replanting 30 Acres of Old Rubber 
FELLING 

Felling and clearing timber on 15 acres free of 
cost; timber being given in lieu of payment 
Felling and burning timber on 15 acres @ 70 
cents per tree (645 trees) .... 

Broadcasting ash ..... 

Pruning overhanging branches of trees along 
boundary ...... 

2 Trewhella jacks ..... 

Transport and repairs to jacks 



DIGGING 

Digging over 30 acres @ $30 per acre 
Digging over diseased patches and old bungalow 
compound second time and breaking up the 
cement floor of the old bungalow . 



LINING 

Lining 30 acres 18'xl8'xl8' (triangular) 
HOLING 

4415 holes @ 2 cents each . 

Extra payment on laterite area 



$ c. 
Nil. 

451.50 
1.47 

19.47 

664.00 

JH.08 

$1167.52 

$ c. 

900.00 



$1064.54 



$ c. 
43.94 

88.30 

/TO 

$89^0 



PLANTING $ c. 

Digging out stumps from nursery, transport and 
planting . . . . . . 77.67 

COVER-CROPS 

Sowing mixture of Centrosema pubescens and Calo- 
pogonium at the rate of 4 Ibs. of each per acre 
cost of seeds and labour . . . .26.67 

DRAINING 

Digging deep water drains and deepening exist- 
ing drains and outlet drains . . . 217.96 

BUDDING $ c. 

Entwax .... 15.32 

Budding cloth . . . 42.90 

Budding labour 7627 stumps @ 
2 cents each . . . . 152.54 

Preparing cloth @ 50 per piece . 6.50 

Cutting budwood . . . 5.00 



OHAP. x OTHER ROOT AFFECTIONS 205 

Identification posts for clone num- $ c. 

bers 34.50 

Painting asphaltura . . . 3.67 

Bamboo shields for budded stumps 

infield .... 22.60 $ c. 

283.03 

FENCING 

With jungle timber posts 10 ft. apart and wire 

netting with a line barbed wire at top and bottom 94.17 
WEEDING 

One round @ $1.50 . . . . . 45.00 

TOTAL . . . $3509.18 



Cost per acre. ..... $116.97 



REFERENCES TO LITERATURE ON ROOT DISEASES 

USTULINA ZONATA 

BROOKS, F. T., 1914. "A Disease of Plantation Rubber caused by Ustulina 

zonata", New Phyt. xiv. p. 152; also in Bull. No. 22, Dept. of Agric. Fed. 

Malay States, 1915. 
SHARPL.ES, A., 1916. "Ustulina zonata, a Fungus affecting Hevea brasiliensis" , 

Bull. No. 25, Dept. of Agric. Fed. Malay States. 
SHARPLES, A., 1918. "Ustulina zonata (Lev.), Sacc. on Hevea brasiliensis" , 

Amis, of Appl. Biol. vol. iv. No. 4, March, p. 155. 
VAN OVEREEM, C., 1924. "Ueber Ustulina vulgaris, Tul. und V. zonata (Lev.), 

Sacc.", Bull. Jard. Bot. Buitenzorg, Ser. 3, vi. p. 256. 
FETCH, T., 1924. "Xylariaceae Zeyfanica", Amis. Roy. Bot. Gard. Peradeniya, 

vol. viii., May. 
HARRIS-STOUGHTON, R. H., 1925. "A Preliminary Report on a Method of 

Treatment for Ustulimi Collar Rot", Fourth Quar. Circ. Rubber Res. 

Scheme (Ceylon), p. 10. 
TAYLOR, R. A., 1930. "The Replanting and Rejuvenation of Old Rubber 

Areas", Trop. Agric. Ixxiv. pp. 207-215. 
SHARFLES, A., and GUNNERY, H., 1933. "Callus Formation in Hibiscus rosa- 

sinensis, L., and Hevea brasilietisis, Mull. Arg.", Anns, of Bot. vol. xlvii. 

No. CLXXXIII., Oct. 
WILKINS, W. H., 1934. "Studies in the Genus Ustulina with special reference 

to Parasitism: (1) Introduction, Survey of Previous Literature and Host 

Index", Trans. Brit. Myc. Soc. vol. xviii. Part IV, April, p. 320. 

SPHABROSTILBE REPENS 

BROOKS, F. T., 1914. "A Root Disease of Para Rubber, caused by Sphaero- 

stilbe repens", Agr. Bull. Fed. Malay States", 3, p. 40. 
SMALL, W., and BERTUS, L. S., 1929. "On the Parasitism of Sphaerostilbe 

repens, B. & Br.", Anns. Roy. Bot. Gard. Peradeniya, vol. xi. Part 2, p. 189. 



206 DISEASES AND PESTS OF THE RUBBER TREE PART in 

FOMES LIGNOSUS 

BBYCE, G., 1922. "The Toxicity of Lime to Fomes lignosus, Klotzsch", Bull. 

No. 64, Dept. of Agric. Ceylon. 
VAN OVEKEEM, C., et WEESE, J., 1923. Icones Fungorum Malayensium, Heft 5: 

Polyporaceae, Rigidoporus microporus, Swartz. 
FETCH, T., 1928. "Tropical Root Disease Fungi", Trans. Brit. Myc. Soc. 

vol. xiii. p. 238, 

WEIR, J. H., 1928. Annual Report, Path. Div. Rub. Res. Inst. of Mai. p. 78. 
NAPPER, R. P. N., 1932. "Observations on the Root Disease of Rubber Trees 

caused by Fomes lignosus", Jour. Rub. Res. Inst. of Mai. vol. 4, No. 1, 

July, p. 5i 
NAPPER, R. P. N., 1932. "A Scheme of Treatment for the Control of Fomes 

lignosus in Young Rubber Areas", Jour. Rub. Res. Inst. of Mai. vol. 4, 

No. 1, July, p. 34. 
DE JONG, H. W., 1933. "Parasitism of Rigidoporus microporus (Swartz), van 

Overeem, syn. Fomes lignosus, Klotzsch", Arch, voor de Rubber cultuur, 

Jaargang xvii. Nos. 4-6, April-Juni. 

GANODERMA PSEUDOFERREUM 

BELGRAVE, W. N. C., 1916-17. "Root Diseases of Hevea and Clean Clearing", 

Ag. Bull. Fed. Mai. States, vol. v. Nos. 8 and 9, pp. 318-326. 
BELGRAVE, W. N. C., 1919. "A Wet-rot of Para Rubber", Bull. No. 28, Dept. 

of Agric. S.S. <fc F.M.S. 
VAN OVEREEM, C., 1925. "13. Ueber den Roten Wurzelpilz. Bei. Zur Pilzflora 

von Nederlandische Indien: II. (Nos. 10-13)", Bull. Jard. Buitzenzorg. 

Sec. Ill, vii. 4, pp. 436-446. 
SHARPLES, A., 1926. "Treatment of Wet-root Rot in Malaya, caused by 

Fomes pseudoferreus", Ag. Bull. Dept. of Agric. S.S. d> F.M.S. vol. xiv. 

No. 2, p. 32. 
SHARPLES, A., 1927. "Further Work on Treatment of Wet -root Rot", Ag. 

Bull. Dept. of Agric. S.S. & F.M.S. vol. xv. No. 2, p. 35. 
VON ZBORAY, E., 1930. "Red -root Rot in Young Hevea Plants in relation to 

Rejuvenation or Reclearing of Old Plantations", De Berg. No. 2, p. 34, 

Nov. 
CORNER, E. J. H., 1931-32. "The Identity of the Fungus causing Wet-root 

Rot of Rubber Trees in Malaya", Jour. Rub. Res. Inst. of Mai. vol. iii. 

No. 2, p. 120. 
SHARPLES, A., and SANDERSON, A. R., 1931. "The Root Disease Problem on 

Old Rubber Areas in Malaya", Bull. No. 3 (Nov.) Rub. Res. Inst. of Mai. 

FOMES NOXIUS 
SHARPLES, A., 1922. "Preliminary Account of Observations on the Fungus 

causing Brown-root Disease", Ag. Bull. Dept. of Agric. S.S. & F.M.S. 

vol. x. No. 7, p. 182. 

WEIR, J. H., 1928. Ann. Rept. Path. Div. Rub. Res. Inst. of Malaya, p. 79. 
CORNER, E. J. H., 1932. "The Identification of the Brown-root Fungus", 

Oards. Bull. S.S., June, vol. v. No. 12. 

RHIZOCTONIA BATATICOLA 

SMALL, W., 1927. "Recent Work on Root Disease of Economic and other 
Plants in Ceylon", Trap. Agr. Ixviii. pp. 201-210. 



CHAP, x OTHER ROOT AFFECTIONS 207 

SMALL, W., 1927. "Rhizoctonia bataticola and Root Disease", Trop. Agr. 

Ixviii. pp. 370-381. 
GADD, C. H., 1929. "Rhizoctonia bataticola arid Tea Root Diseases", Trans. 

Brit. Myc. Soc. vol. xiv. Parts I and II, pp. 99-109. 

MISCELLANEOUS 

VAN OVEREKM, C., 1924. "Itosellina sp. on Rubber", from Report of the Dir. 
of the (fen. Expt. Ma. A.V.R.O.8., and in Med. V.H. Aly. Proef station der 
A.V.R.O.8., Uen. Ser. No. 8, p. 47, July 1918-30th Juno 1919. 

MURRAY, R. K. S., 1930. Diseases of Rubber in Ceylon, issued by the Rub. 
Res. Scheme 1 (Ceylon). 

LEEFMANK, S., 1933. "Ziekten en Plagen der Cultuurgewassen in Nederlandseh 
Oost-lndie in 1930", Mcdetl. Inst. roor Planteuziekten, pp. 81-84; also 
abstract in Rer. of App. Myr. vol. 12, No. 7, p. 425, 1933. 



SECTION 2 
TAPPING PANEL AFFECTIONS 

CHAPTER XI 

MAJOR DISEASES 
Mouldy Rot Brown Bast 

INTRODUCTION 

AT the present date, four major diseases of the tapping panel are 
recognised and they are listed below in the order of their importance, 
in Malaya. 

Common Name Causal Fungus, 

(1) Mouldy Rot. Caused by Ceratostomella fimbriata (E. & 

H.), Elliot 

= Sphaeronema fimbriatum 
(E. & H.), Sacc. 

(2) Brown Bast. Cause, Physiological 

(3) Black Stripe. Caused by Phytophthora palmivora, Butler 

= Phytophthora faberi, Maubl . 

(4) Patch Canker. Caused by Pythium complectens, Braun. 

From 1912 to 1920, black stripe and patch canker were considered 
to be the most important panel diseases. Up till 1918, there was some 
confusion in respect of numbers (2), (3) and (4) owing to earlier obser- 
vations by Rutgers, who concluded that brown-bast symptoms were 
also caused by the fungus causing black stripe. Pratt, in Sumatra, was 
the first observer to register brown bast as an entirely separate 
disease. 

Despite Rutgers' assertions to the contrary, it may be taken as 
correct that, except for a slight outbreak of some bark affection in 
1910-11, rubber trees in Malaya were, as a whole, free from Phytoph- 
thora bark diseases till 1916. In the latter half of 1916, which was an 
unusually wet period, two serious outbreaks of panel disease occurred 
in widely separated localities: (a) black stripe in North Perak, (6) 
mouldy rot in Negri Sembilan. The former soon became generally 
distributed, but the latter remained for some considerable time 

208 



CHAP, xi MOULDY ROT 200 

closely confined to Negri Sembilan. During the last six to eight years, 
however, mouldy rot has spread practically throughout Malaya, and 
at the present time it is by far the most important panel disease in 
the country. 

Brown bast suddenly sprang into prominence during 1918, and from 
that year onwards till 1922 caused great alarm. About the year 1922, 
sufficient evidence had been collected to show that exhaustive tap- 
ping exercised a considerable influence on the causation and spread 
of the disease. In districts where daily tapping was the rule, the per- 
centage affection was often high, but on reverting to an alternate 
daily system, the number of brown-bast cases was greatly reduced. 

MOULDY ROT 

Caused by Ceratostomella fi mbriata (E. & H.), Elliot 
= SpJuieronema jimbriatum (E. & H.), Sacc. 

Mouldy rot disease was first definitely reported in Malaya in the 
latter part of the year 1916. An earlier record exists of a fungus 
growing over the surface of the tapped bark of some rubber trees on a 
plantation near Kuala Pilah in 1915, but it states that the fungus 
did not appear to be causing damage. As this district is not far 
separated from Serein ban, where mouldy rot first definitely appeared 
in 1917, and as there is considerable reason to believe that the fungus 
causing mouldy rot has increased in virulence with the passage of 
time, the 1915 note may very possibly have been the first actual 
record of the disease. In Java the disease was first found in 1920 and 
was reported to be ratlier virulent in Mid-Java. It has not yet been 
reported from Ceylon or India. 

Mouldy rot is by far the most serious tapping panel disease in 
Malaya. Up to date, there is no information to show how it originated. 
Its first occurrence in one definite and limited area suggests that the 
fungus may have been imported on another host plant and may have 
spread from it to the tapping panels of rubber trees. If the fungus was 
originally native to the peninsula, living on one or more different 
hosts, and if it had spread from these and become adapted to living 
as a wound parasite on the tapped bark of rubber trees, such adapta- 
tion would probably have occurred in more than one locality at about 
the same time. It is fairly certain, however, that the disease spread 
from the one originally infected area and was conveyed to other 
localities, mainly by human agency. 

The details with respect to the spread of mouldy rot throughout 
Malaya have been given for the years 1917-24 by South and Sharpies, 

p 



210 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

and in later years spread has been continuous, so that there are 
few rubber-growing districts to which it has not gained access. The 
writer has constantly pointed out its dangerous nature, more especi- 
ally in view of the possibility of a more virulent strain of the fungus 
developing. In 1925 attention was called to the fact that more 
virulent attacks might be anticipated, for while in 1916-17 the fungus 
was seldom seen within \ inch of the tapping cut, i.e. it took ten to 
twelve days to develop the typical visible symptoms, at the end of 
1918 disease spots appeared less than \ inch above the tapping cut, 
i.e. five days or even less had sufficed for the symptoms to become 
visible on the surface of the renewing bark. At the present date there 
is not the slightest doubt that, in certain districts, treatment which 
has been successfully employed since 1922 is not now keeping the 
fungus under control as formerly; and, as explained below, the fungus, 
in nature, now seldom produces the perithecial forms of fructifica- 
tion as it used to in 1917-20. The main fact which has adversely 
influenced the position is the lack of funds for disease work during the 
last two or three years of the last rubber slump. On Asiatic holdings, 
daily tapping has been carried out on infected trees without any 
attempt being made towards treatment, and even on European 
estates, European staff has been severely reduced and lack of 
essential supervision naturally follows. 

Symptoms. The earliest signs of an attack of mouldy rot are 
depressed spots or blotches from to 1 inch above the tapping cut 
which spread and join up to form an irregular, depressed band 
parallel to the cut. The diseased tissues rapidly darken and become 
covered with a thick, greyish mould easily visible at a considerable 
distance, say 30 to 40 yards, consisting of a mixture of fungi, chiefly 
mycelium and spores ofCeratostomellafimbriata (E. & H.), Elliot, and 
a Cephalosporium sp. This mould is the most characteristic feature of 
the disease, and once seen cannot be mistaken for anything else 
(Plate III and Fig. 26). In a later stage, small black bristles, about 
0-5 mm. long, may be found rising through the mould (this relates to 
the years 1916-21). These are the necks of the perithecia of the 
Ceratostomella shape, to which wax -like masses of spores are found 
attached. It is only comparatively recently that the spores of this 
fungus were found to be true ascus-spores with 8 spores in each ascus; 
the asci are very numerous and are enclosed in the flask-shaped peri- 
thecium which has a long beak and fimbriated opening (Fig. 29). 
Before extrusion the walls of the asci break down and the individual 
spores become free in the cavity of the perithecium; later they are 
extruded and remain attached to the fimbriated tips of the pycnidia 



MOULDY ROT 



211 



as the wax -like masses referred to above. 

Under favourable conditions, perithecia were produced in im- 
mense numbers in past years, many hundreds being found crowded 
together in a very small bark area. Their production was a constant 
feature up till 1920, for in this year Sanderson and Sutcliffe reported 
that "the pycnidium (perithecium) 
is quite characteristic and should 
always be looked for in supposed 
cases of mouldy rot". The peri- 
thecial fructifications have been 
seen but rarely during the last two 
years, and it appears that, in nature, 
peritheciai development is now in 
abeyance in Malaya. This feature 
was noticeable about 1925-26 and 
it has been confirmed over the last 
few years, for very few cases have 
been found in spite of intensive 
searching. 

In three to four weeks after in- 
fection the diseased tissues rot com- 
pletely, exposing diseased and dis- 
coloured wood and forming wounds 
similar to those produced by bad 
tapping (Fig. 27 a, 6). Penetration of 
the wood is slight and wood discolor- 
ation is rarely found at a depth ex- 
ceeding inch. It may be greenish - 
black in colour. The fungus has 
never been found to penetrate below 
the tapping cut, although narrow 
dark hair lines may run in the 
wood above and below the cut. 
They are both narrower and darker 
than the lines seen in black-stripe 
disease caused by Phytophthora, which also affects the tapped areas. 
Similar but shorter lines may not infrequently be found running from 
ordinary tapping wounds. 

While continuous rainfall or damp weather is essential for epidemic 
spread of mouldy rot, it appeared in 1916 that the disease could not 
develop seriously unless other conditions, either favourable to the 
fungus or unfavourable to the rubber trees, obtained. In recent years, 




FIG. 26. Mouldy rot. Photograph of 
tree showing surface mould on tap- 
ping panel. Tho two vertical lines 
on trunk are internal bark fissures 
(p. 260). 



212 DISEASES AND PESTS OF THE RUBBER TREE PART m 

however, it has been found that the disease may appear in virulent 
form on estates run on model lines. 

The Fungus. When the disease first appeared it was thought that 
some species of Phytophthora was the cause of the trouble; but 
this has never been found, and inoculation experiments showed that 
Ceratostomella fimbriata was capable of reproducing the disease. 




Fia. 27 a. Mouldy rot. Phtitdgrti^ which has been 

affected by mouldy rot for a long time and left untreated. 

C. fimbriata possesses three distinct spore forms: ascospores, borne 
in and extruded from flask-shaped perithecia; and two kinds of endo- 
spores one, hyaline and thin-walled, the other dark coloured and 
thick-walled. Following HaLstead and Fail-child, 1 these two types of 
eiidospores will be called hyaline endoconidia and macrospores 
respectively. 

1 Bull. No. 76, N. Jersey Agric. Station, p. 14. 



CHAP, xi MOULDY ROT 213 

The external mycelium of C. fimbriata is composed of septate, 
lightly coloured hyphae, 3-5/x broad, often containing oil-drops. 
Hyaline endoconidia are found in abundance in the surface mould on 
diseased bark and are cylindrical, and often loosely attached by 
their ends to form chains. They are variable in size from 16-31 x 8*0 
to 6-5/i, and average 20* 8 x 5-3/u, (Fig. 28). Their method of produc- 




Fio. 27 6. Mouldy rot. Photograph of tree in native holding which has been 
affected by mouldy rot for a long time and left untreated. 

tion can rarely be seen in such material, and is best seen in culture. 
Macrospores are also produced on the surface, but are few in number 
compared with the profusion of hyaline spores. They are continuous, 
generally spherical to elliptical, often with short stalk-like protrusions 
at one or both ends; a few aberrant forms may be cylindrical. They 
are generally olive-brown, and have well-marked, thick walls, and 
frequently two to three large oil-drops (Fig. 28, c). 



214 



DISEASES AND PESTS OF THE RUBBER TREE PART in 



In size they range from 13-6 to 22-2 x 12-2 to 13-8/x, with an average 
of 15-9 x 13-1/x. Perithecia are gregarious, black, with a thin, basal 




FIG. 2ft.Cerato8tomellafimbriata. (After Andrews and Hartor.) 

A-D, Olive-brown thick-walled conidia. x 1000. A and B indicate that the first abstrictcd spore is 
double walled; spores produced later from the same conidiophore arc single walled. 
K-L, Hyaline conidia. 

E, Conidiophore showing hyphal fusion at its base, x 666. 

F, Separation of the spore wall from the conidiophore end wall at a as a result of plasmolysis. N 1000 

G, Probably a remnant of the middle lamella a shown at base of recently abstricted spore, x 606. 
H, I, Germinated spores forming new endoconidia. x 666. 

J, Early stage in germination, x 666. 

K, L, Evacuation of spore contents after germination; contrast with H. x 666. 

A-D and F, from stained sections, others from live material. 

bulbous portion, about three parts immersed in the bark tissues. 
They vary from 300 to 500jit in length; diameter of the basal bulb 
50-100/4. The perithecial necks are long, about four times the dia- 



CHAP. XI 



MOULDY ROT 



215 



meter of the bulb, therefore varying in length from 200 to 400/z; 
width of neck 26/i, tapering to 15/x. Ascospores vary from 4-5 to 
8-7 x 3-5 to 4-7/z (Fig. 29). 

When grown in culture the necks of the perithecia appear to be 
even more variable in size. Dr. S. F. 
Ashby received cultures from Malaya 
and recorded measurements of 300-700/x; 
in another case they were up to 1 mm. in 
length, while the fungus, isolated from 
sweet-potato in Trinidad, produced peri- 
thecia with necks 400-800^ in length. 

When the fungus first came under ob- 
servation in the field, the slightly taper- 
ing perithecial necks looked just like a 
mass of bristles rising through a tangle of 
brown mycelium; the fimbriated openings 
were noticeable because of the hyaline 
hyphae there. 

The production of ascospores has 
been described. They are hyaline, thin- 
walled, and vary in shape from spherical 
to broadly ellipsoidal, often appearing 
polygonal from mutual pressure. Dr. 
Ashby informs me that a proportion of 
the ascospores formed in cultures were 
annulate. 

The measurements given were obtained 
during the investigations being carried 
through from 1910 to 1918. Since that 
period numerous investigations have been 
carried out on this fungus in other coun- 
tries, and in view of the various new 
features which have been demonstrated, 
it seems desirable that further investiga- 
tion is required into the life history of this 

fungus in Malaya. The writer commenced work to complete the 
picture of the life history in 1932, but pressure of other duties 
precluded much time being spent. There are two other species of 
Ceratostomella found on dead rubber twigs, and enquiries parallel 
to those on C. fimbriata will lead to more reliable information being 
obtained on the subject generally. 

The diseased tissues show microscopically no specially interesting 




FIG. 29. Mature perithecium. 

x 187. 
(After Andrews and Harter.) 



216 



DISEASES AND PESTS OF THE RUBBER TREE PART in 



feature. The hyphae in the bark and wood resemble those on the 
surface in being septate and branched; they are of a smoky-brown 


















* IG. 3U. Mouldy rot. Section through outer infected area, showing the 
macrospores developing in the outermost wood vessels, x 333. 

colour and intracellular, with no haustoria, and may pass from cell to 
cell either through pits or by the break-down of the cell walls. Macro- 



CHAP, xi MOULDY ROT 217 

spores are only rarely found in the tissues, but Fig. 30 shows these 
spores forming freely in the large wood-vessels at the periphery of the 
wood cylinder, and such a feature may account for the few refractory 
cases always met with when treatment is undertaken. 

In the wood, hyphae are most abundant in the medullary rays, but 
occur in all the other xylem elements. "Wound gum", dark in colour, 
is formed in the wood. 

Other fungi, chiefly Cephalosporium sp. and bacteria, invariably 
accompany G. fimbriata in diseased tissues. 

The dark lines running up and down from diseased patches of wood, 
and described above, are due to the deposition of dark "wound gum" 
in individual vessels. C. fimbriata has never been isolated from these 
lines, though they are doubtless due to a stimulus derived from its 
presence. A Cladosporium sp. has been obtained, but it was probably 
a secondary infection, and on inoculation did not reproduce black 
lines. 

Conditions which favour the Onset of the Disease. (1) Tapping on 
thin bark, virgin or renewed, where the formation of new healing 
tissues is slower and the liability to wound is greater. The danger of 
tapping on poor renewals was well demonstrated on one estate in 
1917. Tapping and general conditions were good, except on one patch 
of about ten acres, near the centre of the estate, where the bark was so 
thin that tapping should never have been allowed. About 50 per cent 
of trees were attacked by mouldy rot, while only a few individuals in 
neighbouring areas were affected. Soil conditions appeared to be 
uniform. 

(2) The system of tapping in favour on most of the attacked areas 
in 1917-18, viz. Chinese labour on contract, also lends itself to the 
spread of the disease. Naturally the contract tapper tends to work for 
maximum latex yield and taps deeply, wounding, on the whole, more 
than a Tamil or other worker on daily wages. The tapping on native 
holdings follows much the same opportunist policy with similar 
results. Exceptions can of course be found. One affected estate in 
1916-17 employed Tamil labour, while another conspicuously im- 
mune, though in the very worst infected area, was on Chinese 
contract. 

(3) Any factor maintaining high humidity around the tapping 
panels will encourage the disease. It has only recently been realised 
that the aerial mycelium of the fungus is very profoundly influenced 
by external humidity; certain test plots showing a 100 per cent infec- 
tion on December 24th, 1932, were found to have no visible external 
symptoms on December 27th, after three days' continuous dry 



218 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

weather. Thus, dense planting, forestry methods, allowing the 
"belukar" to develop without hindrance in ravines, will all encourage 
the growth and spread of the fungus to a degree much greater than 
has been suspected. On the particular estate where forestry methods 
were first carried out to the fullest extent, mouldy-rot disease 
developed on large numbers of trees in the areas where free develop- 
ment of the undergrowth had been allowed, and control of the disease 
could not be established until the heavy undergrowth had been cut 
back to ground-level. The bark damage done, while the fungus was 
active, was enormous and it proved irretrievable, so that there was no 
doubt that the fungus proved a limiting factor under the conditions 
provided. 

Spore Formation in Pure Culture. The fungus causing mouldy 
rot belongs to a small group which produce endospores. The 
formation of such spores has been mentioned earlier. As already 
stated, two kinds of endospores arc produced, one hyaline 
endoconidia, the other dark-coloured and thick-walled macrospores. 
On suitable culture media, and probably in nature,, there was, 
in 1916-17, a definite sequence in spore formation. Within three 
days of making sub-cultures, an abundance of the thin- walled 
hyaline endoconidia was produced on the surface of the medium, 
giving it a powdery appearance; this resembled the first stage 
appearing on a tapping surface recently infected. Many of the 
hyaline endoconidia germinate immediately with the formation of a 
second generation of similar spores. At this stage there is only little 
hyaline mycelium. About the third day, dark-coloured, short, lateral 
branches appear and the formation of dark, thick-walled macro- 
spores begins. The whole mycelium gradually darkens and the walls 
of the hyphae become slightly thicker. After two to three weeks, 
small black spots, made up of interwoven hyphae, may appear in 
culture, which develop, in five to seven days, into partially im- 
mersed perithecia. These may or may not produce spores. When 
present, the spores come to form waxy masses at the perithecial 
mouths, as in nature. 

The extrusion of hyaline endoconidia is much more rapid than that 
of macrospores. The former are pushed out about one every twenty 
minutes, while the latter appear at the rate of one in five to ten hours. 

The germination of the varied spore types only takes place freely 
in nutrient solutions or culture media. Hyaline endoconidia germinate 
within twenty-four hours of sowing; macrospores and ascospores ger- 
minate in twenty -four to forty-eight hours the latter after consider- 
able swelling by the production of a single germ -tube. Andrews and 



CHAP, xi MOULDY ROT 219 

Harter state that germination of macrospores appears to occur rarely. 
Once germinated, there is no constant difference between the three 
spore forms. Very soon after germination, sometimes before any 
branching has occurred, the production of hyaline endoconidia begins 
and two or three generations of such spores may be so produced before 
mycclial growth starts. 

The persistence of a fungus in nature depends to a large extent 
on the resistance of the spores to drying. The ascospores and hyaline 
endoconidia formed on agar slants have been observed to ger- 
minate five weeks after production; macrospores have survived for 
three months under the same conditions. Resistance to drying has 
been tested under very rigorous conditions, and while the ascospores 
and hyaline endoconidia lose their germinating power within twenty- 
four hours, macrospores resisted drying-out for a period of three 
weeks. Thus it is obvious that the production of macrospores enables 
the fungus to withstand very severe drought conditions, and this is 
the most important spore-form to be considered when discussing the 
question of control. 

When perithecia are present, they arise directly from masses of the 
dark-coloured mycelium which, with the black perithecia, give the 
infected surface a black appearance, about ten days after the first 
appearance of the white mould. As in nature, the long neck of the 
perithecium has a distinctly striated appearance due to the presence 
of thicker portions in the form of strands. At the apex, the strands 
split apart somewhat from the connective tissue, forming the 
fimbriated mouth through which the masses of ascospores are 
discharged. The specific name is derived from the fimbriated mouth. 

In cultures, development of perithecia and ascospores proceeds 
jiist as in nature. When these spores are liberated they adhere to the 
porithecial mouths as a white, more or less globular, sticky mass, 
which rapidly turns brown on drying. Eventually the mass of spores 
is pushed over the side and remains sticking to the outside of the 
neck, being followed in twenty -four hours or more by a second mass. 
The masses of ascospores are quickly affected by desiccation, and 
only a short time after their expulsion they may have lost the power 
of germination. 

Spread and Treatment of Mouldy Rot. Mouldy rot is a rubber tree 
disease, peculiar in the fact that its spread to areas far distant is not 
dependent on the usual atmospheric agencies: transport from one 
place to another is brought about mainly by human agency. A con- 
siderable body of evidence has been collected to support this state- 
ment and little doubt remains as to its correctness. Apart from the 



220 DISEASES AND PESTS OF THE RUBBER TREE PART in 

evidence as to human agency, it would be difficult to explain how an 
infection could appear at a place separated by nearly 200 miles 
from any known source of infection. It should be emphasised that 
only those spore-forms which are capable of extreme resistance to 
adverse conditions can be expected successfully to persist through 
the more or less extended dry period, during their transference to a 
non-infected area. The spores are carried chiefly on the clothes or 
tapping knives of coolies, and it seems evident that only the thick- 
walled macrospores will be able to persist through the adverse period. 
These are the only ones of the three forms which possess the requisite 
organisation. Localised spread only can be expected by the dissemina- 
tion of the wind-spread, thin- walled endospores and ascospores. The 
particular case is of such exceptional interest that a full description of 
the method of spread is extracted below, from Bull. No. 37, Dept. of 
Ag. S.8. & F.M.S. 

There is some reason for believing that C. fimbriata is not one of those 
fungi which occur commonly in the jungle in this country, but that it is 
more probable that it was imported in some way. In this respect it, differs 
from the majority of rubber diseases, Pink disease (Corticium salmoni- 
color) and probably even Black Stripe disease (Phytophthora sp.). These 
latter are all caused by fungi that occur on a number of different living 
or dead plants throughout Malaya and have adapted themselves to living 
on the rubber tree. Such diseases have naturally occurred fairly generally 
all over the peninsula at about the same time and are almost universally 
present, except in localities where certain of the surrounding conditions, 
especially low humidity, adversely influence their growth. These diseases, 
in any part of the country, spread to rubber trees, either from decaying 
jungle timber left on newly cleared estates, or from plants in the surround- 
ing jungle. It follows that the occurrence of any of these diseases on almost 
any estate is to be expected, and that a few cases of one or more of them 
can scarcely be avoided. Control measures under such conditions depend 
mostly on the removal of decaying timber and the prompt treatment of 
all cases found. 

In the case of Mouldy Rot, however, there is good ground for believing 
that the disease first made its appearance on one estate only and was 
conveyed from this to a few adjoining estates, probably by Chinese tappers. 
As has been shown in the previous section on the history of the disease, it 
spread gradually outward in successive years from the original centre of 
infection, appearing sporadically here and there in a steadily widening 
circle. In a number of instances too the new outbreaks have been associ- 
ated with the presence of tappers known to have been working recently 
in previously infected localities. Such behaviour is typical of a fungus 
introduced into the country, that has become adapted to living on the 
rubber tree. In this connection it may be emphasised that this fungus 
has never been found in Malaya on any host substance other than the 



CHAP, xi MOULDY ROT 221 

renewing bark of the rubber tree. Had the disease been due to a fungus 
widely distributed and growing on various living or dead plants in the 
jungle, it would almost certainly have adapted itself to rubber in different 
places at about the same time and, consequently, after appearing in 
several different localities almost simultaneously, would by now have 
become almost universally present on rubber estates in the same way as 
the root diseases and Pink disease have done. 

It seems apparent that the methods of spread of Mouldy Rot disease 
will differ from those of the majority of rubber diseases, since it does not 
use the jungle for its road as do the others. The question then arises how 
is it conveyed from place to place, so that it can jump suddenly to an 
area of rubber separated by many miles from the nearest infected estate 
without infecting any of the rubber in between. It is noteworthy that, 
when the disease first appeared at Padang Rengas, in Perak, in December 
1922, the affected area was separated by over 200 miles from any known 
source of infection. 

The answer is that in all such cases the disease is conveyed by human 
agency, tapping coolies carrying the spores of the fungus on their tapping 
knives, persons and clothes. The disease has been under careful observa- 
tion in the field for so long and the point is so well established that it 
seems desirable to give the evidence in some detail, since records of this 
nature are not numerous. 

During the years 1915 to 1917, when the disease first made its appear- 
ance and spread rapidly in the State of Negri Sernbilan, a number of the 
large, European-owned estates employed Chinese contractors to tap their 
trees; there was considerable competition for labour on account of which 
individual coolies moved about frequently, working first for one contractor 
and then for another on different estates. It was impossible under the cir- 
cumstances to keep a close watch on the movements of coolies most of 
whom were not known personally to the European managers. The con- 
ditions in Negri Sembilan were in contrast to those obtaining in other 
parts of the country, where each estate maintained its own comparatively 
stationary force of Tamil coolies, most of whom were known to the 
managers and whose movements, when they occurred, were better known 
and more easily traced, more especially as it was and is customary to en- 
quire of Tamil coolies recruited locally where they have been working 
recently. It is clear, therefore, that the labour conditions in the infected 
area in Negri Sembilan during these years were especially favourable to 
the spread of the disease by tapping coolies, while the incidence of these 
conditions corresponded so well with the somewhat rapid spread of the 
disease in these years from one European estate to another as to afford 
a clear indication that the movement of tapping coolies was an important 
factor in this spread. It is noteworthy also that in the first two years of its 
spread the disease occurred mainly on large European estates, though its 
subsequent spread was largely on small holdings on which the majority 
of the attacks occur at the present time. 

The impression, which had already been formed, that the disease was 
mainly spread by human agency was considerably strengthened when the 



222 DISEASES AND PESTS OF THE RUBBER TREE PART in 

outbreak occurred at Kuala Pilah towards the end of 1918, at a distance of 
20 miles from the nearest infected rubber which was separated from the 
Kuala Pilah area by a range of jungle -covered hills. 

Definite evidence of the presence of a tapper from an infected holding 
was obtained at Panchor in the Muar district of Johore, when a Malay 
officer of the Department, sent there to supervise the treatment and con- 
trol of the disease, recognised a Javanese coolie who had recently been 
working on an infected holding, belonging to the officer's uncle, in Kuala 
Pilah district. 

Further evidence was again obtained at Padang Rengas in Perak early 
in 1923. Here the nearest boundary of the large main block of infected 
holdings, found to be infected at the end of 1922, was about half a mile 
distant from the main road from Kuala Kangsar to Taiping, the inter- 
vening land being partly occupied by a large rubber estate and partly 
by padi land and fruit orchards. Early in 1923, a few infected holdings 
were found on the roadside at the 17th mile, a few others were found on 
the further side of the main road, while yet another infected area of about 
twenty acres was discovered adjoining an European-owned estate about 
two miles nearer Taiping. In every case one, or more, of the owners of 
land in these isolated areas also possessed land in the area first infected; 
or else, as was the case at the 17th mile, the isolated block of newly 
attacked trees was on land around the houses of tappers who were em- 
ployed in the originally infected areas. 

An important item in the successful treatment of the disease is the 
cessation of tapping on all infected small holdings for the period of three 
weeks, or a month, during which the trees are under treatment. A very 
large number of such holdings, from 1 to 10 acres in area, are not tapped 
by their owners, but by coolies of various nationalities, Chinese, Java- 
nese, Banjarese, Tamils or even Malays, who receive half the daily yield 
of rubber in payment for their work. When tapping is stopped on holdings 
so worked, the hired tappers immediately leave and go in search of work 
on other holdings elsewhere. The result is that the necessary measures for 
the local treatment of the disease are apt to result in its further distribu- 
tion. Thus, when it appeared at Bruas in December 1923, several Ban- 
jarese tappers, working on the infected holdings there, were recognised 
by the Department's Malay Inspecting Officers as having worked on an 
infected Chinese estate at Padang Rengas; a week or two later when further 
infected holdings were discovered at Sungei Rotan on the Bruas-Taiping 
road, a Banjarese and a Tamil were recognised as having moved on there 
from the infected holdings at Bruas. Again in September 1924, when the 
disease appeared at Selama on the Perak-Kedah boundary, a Banjarese 
family from the infected area at Bruas was found there. In November 
1924, two holdings, owned by one man, at Batu Kurau in Perak became 
infected and a Banjarese was found to be working there who was recog- 
nised as formerly employed on the Chinese holding where the disease 
was first discovered at Padang Rengas. 

A point which further supports the spread of this disease by human 
agency is that in the earlier years, 1915-1921, the spread of the disease 



CHAP, xi MOULDY ROT 223 

was into Johore and Pahang, localities where labour conditions were 
difficult and where in consequence the Chinese tapping forces were con- 
tinually changing. 

A further point is that in Malacca, where the disease is present over a 
large area of small holdings, only five large estates have so far been in- 
fected. In this Settlement resident Tamil labour forces are employed 
on most of the estates. These are settled and contented and are usually 
recruited with coolies brought direct from India. Consequently the coolies 
have not come in contact with infection and the estates have remained 
free from the disease. 

On one estate in Malacca, of which one division became infected, it 
was found that the infected tasks were tapped by Malays who tapped their 
own diseased trees in the afternoon. On an estate in Ferak a few trees 
became infected beside a path along which passed every day tappers who 
worked on infected small holdings beyond the estate. 

In many instances in recent years, when estates have been infected, 
the disease has been confined to trees near the boundaries of the estates, 
where the trees have been liable to be tapped, accidentally or purposely, 
by the tappers on adjoining infected small holdings. There is, however, 
in such cases always a possibility that the spores of the fungus may have 
been carried the few yards from the trees on an infected holding to those 
on the adjoining estate by wind, driving rain or insects. 

The treatment which was worked out in 1917 and amended later 
in 1922 was based on the fact that there was a definite sequence of 
spore formation in suitable culture media and therefore probably in 
nature. The weak point in the life history of the fungus is the thin- 
walled endospore stage, and if the fungus could be killed in the early 
stages, before the formation of thick-walled macrospores, it could be 
kept under adequate control. Thus, if a mouldy -rot infection could be 
"spotted" before a period often days had elapsed, it was very prob- 
able that, if treatment was undertaken promptly, all the hyaline 
endospores, which are very susceptible to injurious agencies, could be 
destroyed and the attack suppressed. 

In practice it was found that a 20 per cent solution of Agrisol, 20 
per cent solution of Brunolinum plantarium or a 3 per cent solution 
of Izal could be used successfully. But one application was not suffi- 
cient. The first application reduces the number of diseased cases 
considerably, but when the treated trees are examined ten days later, 
numerous cases can still be found, so that a second painting must be 
given. A second inspection ten days later will probably reveal a 
further reduction in number, but a few refractory cases will still show 
signs of the fungus, and so a third painting is necessary. The trees 
under treatment are put out of tapping for the time being. The 
following figures were obtained in our experimental work: 



224 DISEASES AND PESTS OF THE RUBBER TREE PAST m 

Diseased trees before first painting . . 948 

,, second ,, . . 592 

third .18 

It must be emphasised again that eradication, i.e. complete dis- 
appearance, of this disease cannot be hoped for, except at certain 
periods of the year when the weather is hot and dry for a few con- 
secutive days. The surface mould disappears very rapidly; two to 
three consecutive days of dry weather is sufficient. A longer period of 
dry weather may result in the death of the portion of the fungus 
growing in the host tissues, but this is mainly conjecture. The main 
point is that control, not eradication, is the only goal we can aim for, 
even if great care be exercised, and that the most successful method 
will always show a few refractory and persistent cases of disease. 

The method of control described is concisely stated below: 

(1) Diseased trees to be put out of tapping for one month. 

(2) Solutions of fungicidal disinfectants to be used as in White list 
given on p. 437. 

(3) Three paintings to be given at intervals of ten days. 

(4) Ten days to elapse after third painting before recommencing to 
tap. If the fungus is still showing, further paintings with periods of 
cessation from tapping must be given. 

The cost of controlling mouldy rot by this method over a period of 
eighteen months worked out, in 1922-23, at 10J cents per acre per 
month = $1.26 per acre per annum, and the treatment ensures the 
bark against injury. There was always a number of mouldy rot cases 
to be treated at any particular time, but as the number did not 
increase from month to month, it may be concluded that satisfactory 
control had been attained. 

Since 1929, the position with regard to treatment of mouldy rot 
cannot be considered to be satisfactory. Over the last three or four 
years, Asiatic small-holders have not been able to face the diminution 
in revenue which would result from the cessation of tapping, and for 
the same reason, daily tapping had to be undertaken. But all the 
blame cannot be laid at the door of Asiatic small-holders. On European 
estates, where satisfactory control has been maintained for many 
years, the management in their quest for economy require the cheapest 
form of fungicide, and disinfectants with fungicidal properties of 
proved reliability are superseded by cheaper articles. Further, the 
European estates which adopt uncontrolled forestry methods will 
certainly provide encouragement for the mouldy-rot disease. A com- 
bination of forest conditions with a period when climate favours the 



CHAP, xi MOULDY ROT 225 

vigorous development of the fungus would result in rapid and very 
serious damage being done to the bark reserves of the trees. Under 
forestry conditions, whether controlled or uncontrolled, the greatest 
care is necessary once this disease makes its appearance. When it 
becomes apparent, all undergrowth should be cut back to soil-level 
and kept low as long as cases of mouldy rot persist. 

Another point must be referred to here. The protagonist of forestry 
methods developed a scheme for control of mouldy rot disease by 
covering infected bark areas with ordinary whitewash. The explana- 
tion given for using an ordinary whitewash was that the use of the 
alkaline solution would increase the^H value (presumably of the bark 
areas covered by the solution), and that spores of the fungus causing 
mouldy rot could not germinate on an alkaline medium. The value of 
this method of control can be judged from the fact that, on the 
infected areas so treated, a complete cessation of tapping was ordered 
by the visiting agent, because bark reserves were practically non- 
existent. It is evident that whitewash will hide a multitude of defects 
and, temporarily perhaps make the trees look more decorative, but it 
has nothing else to recommend it. This matter would not have been 
referred to here but for the fact that whitewash treatment has been 
recommended again recently, and it is considered advisable that the 
planting community should be advised of the results likely to 
eventuate. 

The present general tendency may lead to very dangerous 
ground. Evidence has been given above for considering that a 
variant of the former mouldy rot fungus has developed which is more 
dangerous than the parent form. Further, if tapping, either daily or 
alternate daily, is continuous, it is exceedingly difficult to check the 
development of the fungus, and at the present time little attention is 
paid to any advice which would mean resting diseased trees from 
tapping for a period of one month. Tests on blocks of trees showing 
100 per cent infection have shown that, on trees tapped and painted 
daily with a water-miscible fungicide, the fungus usually appears to 
be under control after about ten to twelve daily paintings (Diagram 
VI). But if painting is stopped at this point, the fungus will re- 
appear in about five to seven days* time and painting must be 
resumed. But if a single painting is done every five to seven days 
after the twelve daily consecutive paintings, it is found that, in a 
large number of cases, little or no damage is done to the affected bark. 
Such a method of treatment is expensive on account of the amount of 
disinfectant used, but as an offset to this there is the amount of latex 
which is obtained by continuous tapping. The great drawback to 

Q 



226 



DISEASES AND PESTS OF THE RUBBER TREE PAKT in 



continuous tapping is that affected trees are seldom free from the 
fungus except during dry- weather periods, and with the slightest 
degree of carelessness during a period favouring the growth and 
development of the fungus, an enormous amount of bark damage may 



DISINFECTANT I in 5O. 
_. DISINFECTANT 1 in 25. 

STANDARD PREPARATION A. 
STANDARD PREPARATION 5. 




(O 



12 



3 A- 5 6 7 8 q 
DAYS OF TREATMENT 

DlAGBAM VI 

Curves show results of daily paintings with suitable disinfectant solutions. The 
number of mouldy rot cases decreases rapidly until the 8th-9th day, when only a 
small number of barely noticeable cases can be found. 

be the result. Although bark damage may be reduced to a minimum 
while tapping is continued yet control of the disease can never be 
obtained. 

Systems of tapping, involving a period of rest during the year, may 
be utilised for the purpose of controlling mouldy rot. Thus, in A B C 
tapping, one-third of the estate is not tapped during four months of 



CHAP, xi MOULDY ROT 227 

the year. Estates using this system of tapping, which are contiguous 
to badly infected native holdings, should select their blocks in such a 
manner that the trees nearest the boundaries and most likely to be 
infected from the diseased holdings will form the block which will be 
rested from tapping during the bad mouldy rot months, i.e. from 
September to December. Very favourable reports have been received 
from estates adopting this practice. 

Precautions of a similar nature may be taken on infected estates 
where the disease is definitely localised. In such cases a band of 
healthy trees, 6-12 rows wide or even wider, is formed around the 
diseased area, and the tapping panels of all the trees in this band are 
painted with the disinfectant solution in the same manner as the 
diseased trees, as soon as possible after the latex has been collected. 

Dyes such as Methylene Blue and Fuchsin are recommended for 
colouring the disinfectant solutions with a view to aiding supervision. 
Red Ochre is often used in various parts of Malaya. The writer is not 
an ardent supporter of adding dyes to the fungicidal solutions, for if 
essential supervision is being given it is not difficult to spot whether a 
tree has been painted or not. 

Another point which is often raised, not only by the layman but by 
trained agricultural officers, is the liability of a water-miscible fungi- 
cide to be washed off by rain. I am in full agreement with Steinmann 
on this point (page 437). The modits operandi of a water-miscible fungi- 
cide is firstly, that the external mycelium and spores should be killed 
immediately. Secondly, that enough fungicide should be absorbed by 
the cortical cells infected by the fungus hyphae as to kill all that may 
be present. This is a matter of a short time only, if the application is 
done before the development of the thick-walled macrospores. But 
if the latter are already in process of formation, numerous paintings 
are required before they can be killed. 

In ordinary circumstances, therefore, the external mycelium and 
spores are killed almost immediately, and if rain follows, the washing- 
off of surface fungicide is entirely immaterial. The fungicide absorbed 
by the cortical cells which are penetrated by the fungus hyphae will 
be held so tightly that considerable force must be exerted to dissolve 
this out from the interior of the infected cells, and only an immediate 
heavy rainstorm would be successful in bringing this about. But most 
rubber growers are sensible enough to realise that it would be ex- 
tremely foolish and waste of time and of money if they painted their 
trees when a rainstorm might be expected soon after painting. The 
washing-off of surface fungicide should not be considered of ultimate 
importance, and far too much weight is given to this feature. It has 



228 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

been shown clearly that repeated applications of the fungicide results 
in the fungus being overcome fairly rapidly in ten to fourteen days, 
in spite of daily wet weather which is favourable for the growth of the 
fungus, and this can only be ascribed to the fungicide being absorbed 
and strongly held by the affected cortical cells. 

Andrews and Harter have recently published a paper on the 
morphology of reproduction in C. fimbriata. The most important 
portion of this paper is the method of production of the asci and 
ascospores in the perithecium. This is of little general interest to non- 
technical readers, and interested readers can probably consult the 
reference given. Some details on asexual reproduction are given 
which are reproduced below, and Fig. 28 is reproduced from their 
article. 

The process whereby the conidia of C. fimbriata are abstracted within 
the sheath of the conidiophore has been discussed at some length by Hal- 
sted and Fairchild, and more recently Lehman has contributed some ad- 
ditional facts. The asexual spores of C. fimbriata are of two types, oval 
spores of olive-brown pigmentation and hyaline spores that are mostly 
linear in shape and extremely variable in size. 

Lehman presented evidence to show that the walls of the endoconidia 
were generated anew by the protoplast and were not the result of longi- 
tudinal splitting of the conidiophore wall as claimed by Brierley for the 
endoconidia of Thielavia basicola (B. and Br.), Zopf. 1 Additional evidence 
of this fact is adduced here from the frequent presence of an intercalary 
element between newly formed endoconidia. The structure shown at (a) 
in Fig. 28 G may consist of lamellar substance that has adhered to the 
base of the newly abstricted spore. Lehman further contended that the 
thick-walled olive conidia were in no case formed endosporously, since 
the protoplast is distended from the ruptured tip before the conidium is 
abstricted (Fig. 28 C, a). In material with olive conidia formed in great 
abundance, a considerable number of spores can be found with two dis- 
tinct walls, the inner wall appearing to be that of an endospore (B). 
In A, the outer wall of the spore is shown to be continuous with the 
sheath of the conidiophore, with the line of rupture just visible. 

Germination of the thick-walled olive conidia (D) figure by Harter 
and Weimer, appears to occur rarely. Hyaline conidia (Fig. 28, E to L) 
are capable of germinating as soon as they are discharged from the sporo- 
phore, and water mounts from any area of a colony on agar media will 
usually show large numbers of germinated and germinating spores which 
disintegrate after having formed a chain of smaller endoconidia. There 
is normally no evacuation of spore contents as appears in Fig. 28, K, L. 
The one or more germ tubes form at a characteristic angle to the conidium 
(H to L), and may proceed at once to the formation of new endo- 
conidia (H). 

1 Threlaviopisis basicola (Berk.), Ferr, according to information received from 
Mr S. F. Ashby, is the correct name for the endoconidial fungus. 



PLATE III 




lirown Bast Cortex 

A, Note slight brownish discoloration of the cortical tissues situated internally, not far distant from 
the cambium. 

B, Note brownish discoloration becoming more generally dispersed through the cortical tissues 
and generally more prominent. 

C, Typical appearance of cortical tissue showing advanced stage of Brown Bast attack. 




Mouldy Rot 

Tapping panel of rubber tree attacked by Mouldy Rot. 

Note white surface mould and upper lino of old wounds running parallel to tap- 
ping out. 



CHAP, xi BROWN BAST 229 

In Petri-dish cultures and on sweet-potato roots in moist chambers, 
the aerial chains of conidia collapse and become suspended in droplets of 
water which condense among the aerial hyphae. Under these conditions 
large numbers of the hyaline spores germinate and the germ tubes grow 
downward to the surface of the medium. Conidia discharged beneath 
the surface of the agar germinate and grow upward, discharging new en- 
doconidia above the surface of the medium. Germinating conidiospores 
very frequently fuse with one another and with neighbouring hyphae, 
forming an irregular entanglement of aerial mycelium having considerable 
rigidity. 

BROWN BAST 

Cause Physiological 

This tapping panel disease caused great alarm about 1917-23, but 
now the particular nature of the affection and the important factors 
which influence its appearance and spread are much better known, 
there does not appear any valid reason for serious apprehension. 
The investigations of the writer (together with Lambourne) led to 
the conclusion that the disease was entirely physiological in origin 
and not bacterial as was held strongly by Keuchenius. This conclusion 
has not been controverted, and our physiological explanation for 
the appearance of brown-bast symptoms has received strong support 
from the physiological work recently published (1933) by Frey- 
Wisselinghe. 

The disease has been known to exist in Java since about 1912, 
though it was confused with other panel diseases. * 'Burred" trees 
were common in 1912, when the writer first went to Malaya, and as 
"burrs" usually appear as a result of neglected attacks of brown bast, 
the disease was probably present in Malaya before that date. But it 
is obvious from the following statements that, in Malaya, both 
Gallagher in 1909, and Bateson in 1913, had noticed the symptoms 
which later became known as typical for brown bast, and the former 
made a shrewd guess as to the physiological origin of brown bast 
symptoms. Gallagher says: 

The growths commonly called " warts" or "peas" are to be found on 
nearly all trees. Tapping does not appear to induce them as they are found 
on untapped trees of three years and older; I believe they are dormant 
buds. They should be taken out when quite young; this is easily done by a 
tap from a hammer or with a strong knife. The wound soon heals over 
completely. The practice of many planters having their old trees examined 
systematically at periodical intervals for these excrescences is worthy of 
wider application. The rough outgrowths, often several square inches or 
even square feet in area, which usually begin at the bottom on trees where 
the early tapping has been bad, seems to be a disease not due to any 



230 DISEASES AND PESTS OF THE RUBBER TREE PART in 

parasitic organism but to some derangement in the internal economy of the 
tree induced perhaps by severe tapping. 

Bateson says: 

Up to the present (1913) bark canker has not been recorded from the 
F.M.S., and the absence of this troublesome disease is a point on which 
planters may well congratulate themselves. There is another disease affect- 
ing occasional trees on some estates which is sometimes mistaken for 
canker, but beyond the fact that the bark is slightly discoloured and either 
ceases to give latex or yields a diminished amount, the characteristic 
symptoms of canker are lacking. 

The slight discoloration, with diminishing or complete lack of 
yields, are characteristic symptoms of the early stages of brown bast 
attack. It has been recorded from Borneo and Ceylon and is probably 
present in all rubber-growing countries of the Middle East. 

Symptoms. The only certain macroscopic symptoms are the cessa- 
tion or falling-off in latex yield, with the affected cortical tissues 
becoming somewhat succulent, i.e. waterlogged, and taking on a 
definite discoloration, ranging from blackish-grey or greyish-brown 
to a sepia colour (Plate III c). The earliest and most usual indication 
of brown bast is a slight discoloration of the bark in the tapping cut, 
which appears in small brownish patches or spots. Most writers 
emphasise the drying-out of a portion of the cut as a sure sign of 
approaching brown bast, but in many cases there is a preliminary 
substantial increase in latex-flow. Ultimately, however, the latex- 
flow ceases as the disease progresses, and the tree is said to go "dry". 
If a tree has been a normal yielder in full foliage and not otherwise 
diseased, a sudden increase or decrease in latex-flow is practically a 
sure indication that a brown bast attack is imminent. During the 
wintering months in Malaya, the drying-out of the cut alone cannot 
be accepted as a symptom, as during this period a number of trees 
become partly or altogether dry. Various investigators believe that 
the earliest macroscopic symptoms are antedated by microscopic 
changes in the affected tissues, and that trees liable to an early attack 
of brown bast can be detected by a microscopic examination. The 
writer is not prepared to subscribe to this view but supports 
Keuchenius, who states that brown bast cannot be diagnosed with 
certainty unless the macroscopic symptoms are well marked. The 
point is not one of major significance, for, with sufficient experience, 
brown bast can be detected, in most cases, quickly enough to allow of 
recovery, if the f trees are rested from tapping for a period of three 
weeks. 

Cases of brown bast on untapped trees have been reported from 



CHAP, xi BROWN BAST 231 

Java and Malaya, but these are merely of academic interest. The 
initiation of the affection on the tapping cut is the only type of brown 
bast which needs serious consideration. 

It has been definitely proved by numerous tapping experiments 
that overtapping, which results in the extraction of more latex from 
the tree than can be permitted if normal physiological relationships 
are to remain in a balanced state, is the primary cause of the disease. 
The term overtapping should not be misunderstood. The trees in a 
mixed stand vary considerably in their capacity for yielding latex, 
and a system of tapping which may result in brown bast developing 
in one tree may not be anywhere near the limit of safety for its 
neighbours. It is obvious, therefore, that for individual trees the term 
overtapping must be allowed considerable elasticity, i.e. a system of 
tapping such as the J spiral cut daily, may result in brown bast 
appearing in some trees, but would not have this effect in others. 
Further, with regard to the excessive withdrawal of latex, it is very 
probable that the liquid portion, rather than the solid constituents of 
the latex, is of primary importance. This hypothesis, first stated by the 
writer in 1924, has been strongly supported by recent physiological 
work. While it is difficult to obtain absolute proof, the evidence for it 
is so strong that practically all investigators who have worked on the 
problem are in agreement, and believe the cause to be a physiological 
one. Keuchenius is the only investigator who may still hold the theory 
of bacterial origin, but he has not made any reply since 1924 to the 
writer's criticism of his work. 

In our experimental work, a prominent feature was a sudden 
increase in number of brown-bast cases during certain months of the 
year. Thus, heavy tapping on an experimental plot showed no brown- 
bast cases from April to September; in this latter month 45 trees 
developed brown bast. Another quiescent period followed until 
December; in this month a further 57 cases were found. These quies- 
cent periods between sudden rises in the number of cases are quite 
typical for heavy tapping systems, but it is unlikely they will show up 
prominently under normal systems. 

The fact that over-extraction of latex was closely related to the 
incidence of brown bast was shown where a heavily tapped test plot 
remained free from brown bast over an eleven-months tapping period, 
when a sudden increase in number of brown-bast cases was definitely 
correlated with a sudden increase in yield. 

During these experiments it was noted that the extension of brown 
bast down the tree was often stopped at the places where old 
"opening-up" marks were evident. It was further noted that, if 



232 DISEASES AND PESTS OF THE RUBBER TREE PAKT in 

"spotted" in the earliest stages, brown bast in a large percentage of 
cases does not extend much below the tapping cut, but in about 14 per 
cent of cases the affection spreads to the base of the trees after heavy 
tapping, in spite of resting. These two points are of some practical 
importance with regard to the method of treatment recommended by 
Keuchenius and also offer a probable explanation of a problem which 
has been remarked npon by many authorities. In the early days of the 
rubber industry, when large numbers of superimposed cuts were put 
up the trees to a height of 10-15 ft., brown bast was apparently 
unknown. Harmsen has collected evidence (vide Rands) showing that 
with two superimposed cuts, brown bast makes its appearance first 
on the top cut in 80 per cent of cases. It is probable that in these early 
days the top cuts became affected with brown bast, but each tapping 
area below acted as an isolation barrier preventing the appearance of 
the affection in the lower panels. Little care, moreover, was taken in 
the matter of bark excision, and it is possible that affected bark was 
removed almost as rapidly as it appeared, in many cases. At the 
present time, however, it is fairly obvious from the burred condition 
of the tapping panels of old trees that they have commonly suffered 
from brown bast. 

There is no definite connection between rainfall and brown-bast 
development, beyond the fact that sufficient rain must fall if good 
yields are to be maintained. Heavy brown-bast infections coincide 
with dry periods, if yield continues high over the dry period. 

If extraction of latex is a feature of primary importance in initi- 
ating brown-bast symptoms, then a priori, good-yielding trees will be 
more readily attacked than poor-yielding trees. Experience and ex- 
periment both strongly support the statement. But it is wrong to 
assume that poor-yielding trees are more immune. It is a purely 
general statement with no real relation to susceptibility and im- 
munity, for we have definitely shown that lower -yielding trees often 
develop brown bast earlier than higher-yielding ones. One fact was 
prominent, i.e. that if a high-yielding tree maintained its yielding 
capacity without big fluctuations, such trees did not suffer from an 
early attack of brown bast. 

In the present stage of our knowledge it does not seem necessary 
to go into details of microscopic changes in the tissues or the symp- 
toms in advanced cases, for on estates showing an abnormal number 
of brown-bast cases, the only economic method of control is to change 
the tapping system so as to reduce the output. However, if the disease 
is not detected early, the discoloration in the portion of bark which is 
drying-out may appear as a definite pale-brown line on the tapping 



CHAP, xr BROWN BAST 233 

cut near the cambium (Plate III A). Between the brown line and the 
cambium the cortex may still be laticiferous and, if pricked down to 
the wood, will still yield latex. The more seriously affected areas are 
sharply defined by the difference in colour of the cortical tissue as 
compared with normal cortex. In advanced cases, the outer bark is 
frequently characterised by long or short longitudinal splits or cracks, 
a preliminary to scaling. This is more common when the disease 
commences about two feet above ground-level, and spreads down- 
wards to the collar. Such cracks are most frequent from a point just 
above the collar (below an old cut), spreading along a lateral root. 

The most distinctive microscopic feature, according to Sanderson 
and Sutcliffe, is the presence of meristematic tissues in brown-bast 
cortex, almost invariably in the vicinity of latex vessels, the latex in 
the enclosed vessels in the meristem tissues usually being coagulated. 
The remaining characteristics of brown-bast cortex, e.g. the deposi- 
tion of tannins, calcium oxalate, excessive quantity of sclereides at 
an unusual depth, often very deep-seated, depletion of starch, etc., 
are considered to be secondary symptoms arising directly as a result 
of meristem activity. The disease is diagnosed by its secondary 
symptoms, which give the characteristic appearance of brown-bast 
cortex. 

Treatment. Two lines of treatment have to be considered: (a) Pre- 
ventive; (6) Curative. 

It is now generally accepted that the over-extraction of latex is the 
fundamental cause of the affection as it appears on the tapping cut. 
Exceptional cases of brown bast in untapped trees have been reported 
and there are authentic cases of brown bast appearing in places where 
wounding has taken place. 

PREVENTIVE TREATMENT. The obvious line of treatment is a 
change of tapping system which will decrease the output of latex, or 
in the case of individual trees, cessation from tapping. At the present 
time, it may be stated that cessation of tapping is the only treatment 
being carried out, and if the affection is detected in the early stages, 
three to four weeks' rest from tapping will result in the disappearance 
of the typical symptoms, when tapping can be resumed. 

If a large number of brown-bast cases are continuously being found 
and it is considered undesirable to change the tapping system, 
inspecting coolies should be specially trained to note the symptoms 
and report suspected cases. An intelligent coolie can become very 
adept and, after some time, complete reliance may be placed upon 
him if a good choice has been made. If the disease is noted when the 
first few discoloured spots appear on the tapping cut and tapping is 



234 DISEASES AND PESTS OF THE RUBBER TREE PART in 

stopped immediately, there is seldom any extensive spread into 
untapped bark below. 

CURATIVE TREATMENT. Prominence has been given in past years 
to several methods of curative treatment, but as stated, these 
methods are not much in evidence at the present date. It may be of 
interest to briefly note these various methods. They are as follows: 

(1) Planing method. 

(2) Peeling or stripping method. 

(3) Harmsen's tarring method. 

(4) The method of Keuchenius. 

The Planing Method has been in common use in Java and is carried 
out in the following manner. First of all the borders of the diseased 
patch are determined, after which the bark and diseased cortex is 
planed off or scraped away with a tool consisting of a bent and 
sharpened piece of hoop iron with a wooden grip at either end. All 
discoloured tissue must be removed until healthy bark tissue is 
reached. It is said that in mild cases this method has been used with 
satisfactory results. The planed surface is covered with paraffin wax 
or grafting wax after it has dried. 

The obvious danger in this method is that in many deep-seated 
cases of brown bast, the affected tissue lies so close to the cambium' 
that it is practically impossible to scrape away all the diseased tissue 
without seriously wounding this important meristematic layer. If 
any diseased tissue remains behind after scraping, brown bast will 
reappear at a later date. 

The Peeling or Stripping Method. This method was first practised 
by Pratt, while later, Sanderson and Sut cliff e strongly supported it 
in Malaya. The borders of the diseased patch are determined in the 
usual manner, then a deep cut to the wood is made in healthy tissue 
all round the diseased patch. The edges of the area to be isolated are 
then gradually lifted and gentle leverage will bring away the whole of 
the diseased area. It is stated that the operation is made easier by 
first scraping away the outer bark layers. The exposed surface needs 
a cover to prevent it drying out by the sun. In Malaya the surface is 
shaded for twenty-four to forty-eight hours and then melted wax is 
sprayed over the surface with an ordinary garden hose. 

This method is expensive, but it has the great advantage in that all 
the diseased tissue is undoubtedly removed. On estates where this 
method has been applied, excellent bark renewals over the stripped 
surface have been obtained. The peeling method requires a fair 
amount of skill, and unless great care is taken, severe damage may 



CHAP, xi BROWN BAST 235 

be done. It is seldom, if ever, put into operation at the present 
date. 

The Tarring Method. Usually known as Harmsen's treatment, as 
it was first introduced by this investigator in Java. It has been used 
fairly commonly in Java but was not taken up to any extent in 
Malaya. In this method the area of diseased cortex is delimited as 
before; it is then isolated by deep vertical and horizontal cuts, but 
these should not be so deep as to penetrate to the wood. The bark is 
then scraped off to half its thickness and hot tar is painted on. The 
tar has to be heated until it starts bubbling. The writer cannot recom- 
mend the tar method, as many objections could be made against it. 
As it is now more or less inoperative, no good purpose will be served 
by pointing out the drawbacks and dangers. 

The Method of Keuchenius. The basis of this method is the isola- 
tion of the diseased tissue by means of deep cuts to the wood. The 
affected tissues are delimited in the usual manner, then a surface cut 
is made in healthy tissue surrounding the diseased patch, by a tapping 
knife. Following this, a deep isolation cut to the wood is made with a 
thin-bladed knife, along the channel cut by the tapping knife. When 
only small areas of bark are affected no further treatment is necessary, 
but if bark areas larger than 2-3 ins. are opened up, the outer cortical 
layers are scraped off. The latest recommendations issued in 1931 by 
the A.V.R.O.S. experimental station, Sumatra, are as follows: 

In the case of small infections the practice of scraping the bark can be 
discontinued and instead of discontinuing tapping of treated trees, it is 
recommended for the future that such trees be kept in tapping but with 
a shortened cut. 

Summarising, the treatment is now as follows: 

Trees running dry and with discoloration on parts of the tapping cut 
are either reported by the tappers and tcapping manclors, or treated by a 
special disease gang. 

In the latter case it is desirable that all cuts be inspected twice per 
month, or, once per month when being tapped on alternate days. Im- 
mediately after cutting, the latex is scraped from the tapping cut toward 
the spout with a stick of hard wood. 

The infections, if any are found, are treated in the afternoon. 

Infections with a diameter of less than 10 cm. are considered small. 
(The diameter of a latex cup is about 10 cm.) 

The boundary of the infection is accurately ascertained by means of a 
bent knife or a tapping knife. 

An isolation groove is made right to the wood at a distance of a few 
centimetres outside the edge of the infection around the diseased part. 
This is done by cutting a groove to a depth of about half the bark thick- 
ness with a tapping knife, and in the middle of this groove a cut is made 



236 DISEASES AND PESTS OF THE RUBBER TREE PART in 

down to the wood with a sharp knife, which can be made from an old 
tapping knife. 

The bark is not scraped off, and tapping of such trees is continued over 
the diseased part. 

If the diameter of the infection exceeds 10 cm. (i.e. when the infection 
cannot be covered by a cup), the infection is considered as a large case, 
and is treated as follows: 

The edge of the infection is ascertained and an isolation groove made, 
as indicated above for small infections. Subsequently the outer bark 
layer is scraped off with a bent knife. 

The scraped part is not tapped. 

The tapping cut is shortened. If tapping had been carried out over \ of 
the circumference, the cut is shortened to J, if a J cut had been used, 
it is shortened to J of the circumference. 

Tapping of the tree is not discontinued, but continued with the shortened 
cut, if necessary under the isolation cut or on the next tapping panel. 
Subsequently the tree is always tapped with the shortened cut, also on 
later panels, for the shortened cut prolongs the cycle for bark renewal so 
much, that discontinuation of tapping is no longer necessary. 

As a measure of saving on costs for brown-bast treatment, it is recom- 
mended, in times of low rubber prices, that infected trees, which normally 
yield less than 20 c.c. of latex per tapping, should not be treated, but 
should be taken out of tapping. 

It is also recommended that the treated trees be inspected every three 
months as to the formation of wood burrs, and to remove burrs which 
may have formed. 

Recently, owing to the fact that in numerous cases brown bast 
has been found passing across the isolation cuts, the recommenda- 
tion to isolate diseased tissue by deep tapping cuts has been with- 
drawn. The writer called attention to this feature in 1924 when 14 to 
20 per cent of brown-bast cases passed across the isolation cuts, if 
tapping was continued. 

Brown bast does not call for much attention in Malaya at the pre- 
sent time, but as its origin in any tree is purely a question of excessive 
yields, it may prove in the future to be of great significance in high- 
yielding areas developed by bud-grafting or seed selection. The 
writer does not think, however, that much reliance can be placed on 
preventive measures. Cessation of tapping, or reduction in length of 
tapping cut, will prove of major importance as they are at the present 
date. 

In dealing above with the subject of brown bast the author has 
purposely jettisoned the numberless inspired journalistic efforts 
printed in local publications. Two articles need further mention. In 
addition to Keuchenius, an organic cause was mentioned by Belgrave 
in the very early stages of the investigations, and he wrote at the 



CHAP, xi BROWN BAST 237 

time, "Inoculation experiments have not yet been carried out, but 
the mode of occurrence leaves little doubt that the fungus is the cause 
of the disease". The organism was first considered to be a Spongospora 
species. In a footnote he states that this identification was probably 
wrong and that the organism seen might come to be identified as 
one of the lower forms of Algae. He quickly rejected this opinion and 
was one of the first observers to suggest a physiological cause of the 
disease. 

In 1921 Home described symptoms of "Phloem Necrosis" in the 
bark of //. brasiliensis affected by brown bast. The breakdown of 
sieve-tubes in the case of a physiological disease of potato had 
attained prominence from Quanjers' work in 1913, and the present 
writer made careful observations on these lines early in 1920. This 
line of work, however, was relinquished early in 1921, because of 
extremely variable results which were obtained when brown-bast 
cortex in the earliest stages were examined. The results obtained in 
the first half of 1920 would have supported the explanation put for- 
ward by Home, but, as was shown by later work, phloem necrosis 
could not be accepted as the immediate cause of brown bast. The 
morphological effects in the cortical tissues caused by the operation of 
tapping are but little understood even at the present date, and any 
suggestions based on the examination of pickled specimens should be 
supported by examinations of living material. Most investigators who 
have had the opportunity of working in the East are accepting the 
physiological explanation put forward in this section. 



CHAPTER XII 

MAJOR DISEASES (contd.) 

Panel Diseases caused by Phytophthora and Pythium spp. Black Stripe 
Patch Canker. 

PANEL DISEASES CAUSED BY PHYTOPHTHORA AND PYTHIUM SPP. 

Reproduction. In a previous section attention has been called to 
the reproduction of the fungi included in these groups by means of 
free -swimming spores. The orders Phytophthoraceae and Pythiaceae 
are closely related and species of each order are concerned in the causa- 
tion of panel diseases of H. brasiliensis . 

In species of Phytophthora and Pythium the vegetative portion of 
the fungus, i.e. the mycelium, is composed of hyphae which resemble 
a hollow tube, for the hyphae are not broken up into individual cells 
by the formation of cross walls. The fungus causing black stripe in 
Malaya lives almost exclusively in the diseased tissue, the hyphae 
growing in between the cells, i.e. intercellularly, but they also pene- 
trate through the cell walls and continue development in the interior 
of the cell, i.e. intracellular development. After a time the reproduc- 
tive phase ensues and a sparse aerial development may take place; 
on these aerial branches small, pear-shaped structures, i.e. asexual 
sporangia, are borne. In Malayan black stripe the aerial sporangia are 
not often seen in nature, even though this was the only reproductive 
element formed in pure cultures in the earlier investigations. Other 
Phytophthora species produce different forms of reproductive organs 
which are formed in or amongst the cells of the invaded tissues. These 
are known as (a) Chlamydospores, (b) Oospores. The former are 
asexual spores; the latter are sexual reproductive organs, and result 
from the union of a male and female element. Thus, we may have three 
different reproductive structures in a species of Phytophthora, two of 
which are asexual. In Malayan black stripe, oospores or chlamydo- 
spores were not found in the original investigations, neither in nature 
nor in pure culture. In Java, sporangia and chlamydospores are 
reported by Steinmann, while there is no definite record from 
Ceylon. The above remarks refer only to pure cultures and not to the 
mixed cultures which have been so intensively studied in recent years. 
A description of the three spore types of Phytophthora palmivora, 
Butl., is given below. 

238 



CHAP, xii MAJOR DISEASES 239 

Sporangia or Zoosporangia. The free-swimming spores which 
emerge from the sporangium are known as zoospores, hence the term 
zoosporangium. The asexual sporangia are thin-walled structures 
densely filled with finely granular protoplasm, with a less dense 
central vacuole. They vary from spherical to pear-shaped, with 
prominent and characteristic blunt-ended, thickened, hyaline papillae. 
They are very variable in size; Thompson gives the range for P. palmi- 
vora as 36 x 75ju, in length and 21-36/x broad. The normal development 
of the sporangium is for the protoplasm to break up into a number, 
10-35 (most often 15-20), of smaller portions of protoplasm, which 
finally separate and are actively motile. These are the zoospores 
which escape through a hole in the wall formed by the disappearance 
of the papillae. The zoospores vary in outline from circular to pear- 
shaped and in size from 7 to lip. They are usually flattened on one 
side, and provided with two cilia of unequal length. They swim about 
freely at first but later on they become quiescent, rounded-off and 
finally germinate as an ordinary conidium. But often there is no 
development of the zoospore stage and the sporangium puts out a 
germ -tube and germinates in the manner of an ordinary conidium. 

Chlamydospores, or Resting Spores. These spores are round, 
23 x 50ju, in diameter. At first the walls are thin but later thicken up 
and may become as much as 3 x 4/t thick. In water, the chlamydo- 
spores germinate within twenty-four hours and form a greatly rami- 
fied mycelium, there being no production of zoospores. Steinmann 
reports that while the presence of light is favourable to the formation of 
sporangia, the generation of chlamydospores is favoured by darkness. 
Chlamydospores are considered to be modified sporangia and rarely de- 
velop on the surface; they are usually found buried in the substratum. 

Oospores. These are sexual reproductive bodies resulting from 
fertilisation. The oospores of Phytophthora palmivora, Butl., have not 
yet been described from pure culture but only from mixed cultures. 
Mixed cultures are those in which two different strains of Phyto- 
phthora obtained from different host plants are put into a culture tube 
and allowed to grow together. At the "spots" where the hyphae of 
the two strains meet, oospores are often developed. The female organs, 
i.e. Oogonia, are 28 x 34/i in diameter, and have a thick brown-yellow 
wall; the male organs, i.e. Antheridia, have a thin wall and are colour- 
less, 10 x 16/z long and 13 x 17/i broad; they are attached to the base of 
the oogonium. The oospore resulting from the fecundated oogonium 
measures 21 x 28/i, is round and colourless and has a thick wall 1 x 2ft 
thick. The oospores are formed inside the substratum. Germination 
is by means of a germ tube as in an ordinary conidium. 



240 DISEASES AND PESTS OF THE RUBBER TREE PART in 




FIG. 31. Geranium stemrot. 

A, a-h t Stages in formation and germination of zoospores. 

B, Three stages in early growth of sexual bodies. 

C, Fertilisation: a. Beginning of oosphere contraction; b, passage of antheridial contents into 
subjacent oosphere through hole in fused walls: c, oosphere rounding up; d, e, and /, exospore wall 
formation by clear band extending around oosphere periphery. The clear band in e and / is drawn at 
twice actual width, to render it visible at scale of reproduction. 

D, Oospores, showing attachment on slender stalk and relation to an them! him. 

Fig. 31 illustrates the reproductive structures produced by the 
fungus Pythium complectens, Braun, and this illustration is repro- 



CHAP, xii BLACK STRIPE 241 

duced from Braun's article. The production of zoospores, their ger- 
mination and the various stages in the development of sexual 
reproductive organs, Oogonia and Antheridia, are detailed in the 
caption to the illustration. 

The above is a very generalised account of the structural details of 
the type of fungus causing black stripe and patch canker diseases. 
The detailed morphological differences which would involve the con- 
sideration of statistical data regarding size of spores, mixed cultures, 
etc., is likely to prove too intricate for the majority of readers and 
the exact position is still by no means clear. 



BLACK STRIPE 
Commonest cause in Malaya = Pkytophthora palmivora. Butl. 

This panel disease has figured under many common names such as 
black thread, black stripe, black line canker, bark rot, decay of the 
renewing bark, cambium rot and stripe canker. Fetch remarks that 
the names black thread or black stripe are perhaps the most appropri- 
ate, and he utilises the designation black thread; the name black 
stripe is generally used in Malaya at the present time. 

In Ceylon a disease resembling black stripe was first noticed in 
1909, and in the following years it became prominent in Java and 
Sumatra. Black-stripe disease was reported in Malaya for the first 
time in 1916. 

Symptoms. Natural infection, which always takes place on the 
tapping cut, produces symptoms which are by no means obvious; 
short, vertical linear, shallow depressions about inch above the 
cut being the only external signs of attack for a considerable time 
(Fig. 32). If the bark is pared off, dark lines are found beneath the 
depression together with other lines which do not appear on the 
surface. 

In Malaya, the black lines extend into the wood, widening as they 
go into stripes or bands, and it was quite common to find stripes 
inch broad and |-J inch deep in the wood at very early stages of 
infection (Fig. 33). This very early and rapid, radial and deep penetra- 
tion into the wood was most noteworthy during the investigations in 
1916 in Malaya, and up to that time other investigators had not 
emphasised this particular feature. Fetch states: "The effect of Black 
Thread extends into the wood and black lines may be found there 
running up and down the stem for some distance. ... It has not yet 
been demonstrated that the causal fungus is present in these streaks." 



242 DISEASES AND PESTS OF THE RUBBER TREE PART m 




FIG. 32. Typical appearance of a black stripe affection on a tree growing under 

dense shade. 

Note. Vertical, depressed stripes, and darker area about midway along the cut, which represents a 
rotted bark area where several stripes have coalesced. 




FIG. 33. Cortical tissues stripped away to expose wood surface and black stripes 
therein. (From Bull. No. 31, Dept. of Ag. S.S. & F.M.S.) 



CHAP, xii BLACK STRIPE 243 

On this basis he argues that there is no necessity to cut out these lines 
or to cut out any wood. While this statement has been supported by 
experience in Malaya, the writer reported in 1917 that, as far as black 
stripe was concerned, the fungus had been isolated from diseased wood 
taken at a depth of f inch in the stem. There is no doubt that in Malaya 
the fungus is active at a considerable depth in the discoloured wood 
tissues. Dastur states that it seldom runs below the tapping cut in 
Burma, but Fetch and Rutgers record instances where the decay 
travelled downwards to involve the untapped bark. These cases, 
however, appeared to be exceptional, whereas in the Malayan out- 
break in 1916, the decay in the wood was often found one or two inches 
below the tapping cut, while rare cases of extensions exceeding six 
inches have been met with. Considerable variation exists. In many 
cases the disease is more superficial and wood penetration is slight or 
absent; in others there is rapid coalescence of stripes and rotting of 
the tissues, although tapping may have been stopped at the earliest 
signs of the disease. These variations may be due to the fact that 
several strains of Phytophthorae have been found causing black stripe, 
and these closely related but different strains may show varying 
degrees of virulence. 

The fungus is seldom visible externally except on wet mornings, 
when a delicate white "bloom" may be seen just above the diseased 
tapping cut. This bloom consists of the mycelium of a species of 
Phytophthora, and a very limited number of sporangia of that fungus 
mixed with the mycelium and spores of a Fusarium sp. Bacteria are 
also present in abundance. 

In all cases in which a causative agent of black stripe has been 
determined, the fungus has proved to be a species of Phytophthora. 
Thompson, in his comprehensive work in Malaya, isolated three 
different species of Phytophthora from naturally occurring cases of 
black stripe. The three species are: 

P. palmivora, Butl. 
P. meadii, McRae 
P. heveae, Thompson 

In the earlier work on black-stripe disease, the name of the causal 
fungus has been generally accepted as Phytophthora faberi, Maubl. 
This is now considered to be the same species as Phytophthora palmi- 
vora, Butl., and on the ground of priority this name must be used. 
This is the commonest causative agent of black-stripe disease in 
Malaya. 

The disease has now been recorded from all rubber-growing 



244 DISEASES AND PESTS OF THE RUBBER TREE PART in 

countries in the Middle East, i.e. Burma, Ceylon, Java, Malaya, 
South India and Sumatra. 

Factors affecting the Intensity and Spread of Black Stripe. As 
stated above, only thin-walled sporangia were found in the early 
investigations from 1916 to 1920; chlamydospores and oospores were 
not found, either in culture or in nature. This raised a difficult 
problem for which no explanation could be found at the time, In the 
absence of resting-spores, i.e. chlamydospores and oospores, it was 
difficult to see how the fungus causing Malayan black stripe could 
tide over unfavourable seasons. But now that we are aware that 
several different strains of Phytophthora are concerned in black stripe, 
the problem is not so difficult. Further, Thompson has shown that 
two strains of Phytophthora isolated from tissues suffering from black- 
stripe disease produce numerous chlamydospores in culture. These 
thick-walled spores are capable of resisting drought conditions for 
some considerable time, and so unfavourable periods for development 
and growth of the fungus may be lived through safely. 

But various factors arise for consideration. Survival through un- 
favourable periods may be facilitated through the presence of one or 
more native host plants not yet recorded; or there may be a slight 
unnoticed amount of leaf- fall with corresponding "die-back" of the 
branches allowing the fungus to "winter" in the latter. Recently we 
have gained new light on such factors. Reydon has recorded out- 
breaks of black stripe on mature rubber, the species of Phytophthora 
causing which had spread from small seedling plants of rubber grow- 
ing under a thick cover of Centrosema] and in another case the leaves 
and stems of the seedling rubber plants were found to be diseased 
with a species of Phytophthora prominent on and within the diseased 
areas. It is pointed out, when describing patch canker, that Pythium 
complectens, Braun, has been isolated from diseased rubber seedlings, 
and as this fungus is closely related to species of Phytophthora and is 
evidently a common soil-inhabiting fungus in rubber plantations in 
Malaya, it is not stretching the point too far when it is suggested that 
the situation reported from Java might arise in the near future in 
Malaya. This possibility may influence the question of establishing 
"forestry conditions" in rubber areas, for rubber seedlings are 
recommended for extensive use in this connection. 

But, given the fungus, the main factor in epidemic spread and 
intensity of infection is moisture. Without high humidity, external 
mycelium does not grow and sporangia do not germinate, while zoo- 
spore formation takes place only in the presence of water. 

Epidemics of black-stripe disease have attained their greatest 



CHAP, xii BLACK STRIPE 245 

intensity in Burma and South India during the S.W. monsoon, when 
daily rain falls persistently from June to September, with the result 
that atmospheric humidity is constantly high. The opinion was 
expressed that the evenly distributed rainfall in Malaya might be as 
favourable to the growth of the fungi causing bark diseases as the 
alternating wet and dry periods in other countries which are definitely 
affected by the S.W. monsoon. This has proved not to be the case, and 
intensive epidemics in Malaya are strictly localised to districts where 
the lie of the land results in a persistent high humidity during the 
period of greatest rainfall, viz. from October to December. Rubber 
plantations situated in valleys between high hills are most subject, 
and the sudden spread of the disease after the first cases appear is 
often very alarming. But on the great majority of Malayan estates 
which have suffered owing to outbreaks of black stripe, a 10 per cent 
infection would be considered a high figure. From the pathological 
standpoint, especially in Malaya, it should not be forgotten that 
records showing total daily rainfall may be misleading, for the greater 
part of the rain (estimated at two -thirds) falls during afternoon 
thunderstorms, while the mornings are usually hot and dry and un- 
favourable to fungus growth. There seems no reason to doubt that the 
comparative freedom from black stripe enjoyed by Malayan rubber 
plantations may be cogently argued from this feature, for even during 
the heaviest rainy periods, daily bursts of sunshine may be expected. 

After rainfall, atmospheric humidity profoundly influences the 
development of the fungi associated with black-stripe disease. Here 
again, average returns of atmospheric humidity are useless. It has 
been shown that the fungus will not grow on agar smears when the 
relative humidity falls below 90 per cent, so it appears that an ordinary 
Malayan day would check the spread of the disease, for on rainless 
days the relative humidity falls from circa 90-98 per cent at night to 
82-86 per cent at 10 A.M., and to 60-75 per cent for the rest of the 
day. Of course, the onset of rain will raise the atmospheric humidity, 
but it is not necessary that heavy rain should fall to bring about a 
high relative humidity. Little or no rain may fall, but heavy overcast 
weather may bring about a succession of mornings with high relative 
humidity, and it is during such periods that the spread of black stripe 
reaches its peak. Such periods are to be feared more than those when 
rain falls several mornings in succession; if rain supervenes early in 
the morning, tapping is stopped and then there is less chance of 
infection. 

Tests made by Pratt and others appear to indicate that tapping 
cuts near the ground are more liable to infection than cuts a consider- 



246 DISEASES AND PESTS OF THE RUBBER TREE PART in 

able distance away. The evidence seems hardly conclusive and the 
writer agrees with Fetch on this point. The enormous fall in percent- 
age number of cases between cuts at five inches high with a 30 per 
cent infection, and those at eighteen inches high with a 3 per cent 
infection can hardly be accounted for by atmospheric differences, 
and it seems probable that some factor other than the height of the 
cut was operative. Harmsen furnishes figures which support those of 
Pratt, but in any case the matter seems one for further investigation. 

Other factors which might be expected to influence the incidence 
of black stripe are depth of tapping, mode of tapping, daily or alter- 
nate daily, etc., and slope of cut. The effect of tapping systems in 
general has been discussed in a previous section. Harmsen has main- 
tained that the percentage infection was much higher for deep cuts 
than for shallow cuts, but results obtained from tests carried out in 
Malaya do not support this view. Results on lightly tapped and deeply 
tapped bark show no appreciable difference in percentage infection 
while attacks could be discovered earlier on the deeply tapped trees 
an important consideration in control methods. 

Treatment of Black Stripe. The attacks of black stripe in Malaya 
in 1916 were noteworthy for virulence; coalescence was rapid and the 
area of bark rotted was large, while wood penetration was much 
deeper than that described in other countries. During the last few 
years, however, few reports of outbreaks of this disease have been 
sent in, and there does not appear to be any good reason for antici- 
pating epidemic outbreaks except under abnormal weather condi- 
tions. 

In 1916, and for a few years afterwards, various treatments were 
tried. Pratt first showed that excellent results could be obtained by 
using weak solutions of proprietary disinfectants with fungicidai 
properties. It should be understood, of course, that the prosperity 
prevailing in Malaya and other rubber-growing countries prior to 
1920 would largely influence the recommendations for disease treat- 
ment. For instance, scrap rubber from the tapping cut is an article 
of value if the price of rubber is high, and in the years 1916-17 the 
possible deterioration of the scrap rubber through the application of 
fungicidai fluids had to be considered. This problem is of no importance 
at the present time, for little trouble is taken even to collect scrap 
rubber from the tapping cuts. 

It does not now seem necessary to consider all the various treat- 
ments which have been recommended. The fungicidai fluids most 
commonly used in Malaya have been Agrisol in 20 per cent solution, 
Brunolinum Plantarium in 20 per cent solution, Izal in 3 per cent 



CHAP, xii BLACK STRIPE 247 

solution. Any of the fungicidal fluids listed in another section could 
probably be usefully employed. If the infected trees are taken out of 
the tapping round, the diseased areas are painted over with the solu- 
tions of strength given above, followed by a second painting four to 
five days later. This is usually sufficient except in neglected and re- 
fractory cases, when a longer rest and further applications of the 
fungicidal solution may be necessary. If tapping is continued, more 
frequent applications may be necessary, and painting after every 
tapping may have to be undertaken. 

The disinfection of tapping knives has been recommended, but it 
has been shown that preventive painting alone will control the 
disease, so that disinfecting the tapping knives, while theoretically 
an advantage, would merely be over-elaboration. 

Murray reports a disease of young bud-shoots caused by Phyto- 
phthora palmivora, Butl., and the following quotation is given for the 
sake of completeness, though the disease has not yet been reported 
from Malaya: 

Economic Importance. The disease has not, up to the present, proved 
a serious factor in retarding the development of young buddings in Ceylon, 
and has only been reported from three estates. As is indicated above, the 
progress of the disease is largely dependent on wet weather conditions, as 
would be expected from the zoosporangial method of reproduction of the 
fungus. The chief danger would appear to lie in the outbreak of the disease 
in a bud-wood nursery in wet weather. If the bud-shoots were very young 
they might quickly he killed back to the stock and a supply of valuable 
material might thereby be lost. It is unlikely that older shoots with several 
growth increments would be completely killed, since inoculations have 
shown that the fungus does not readily attack or spread to the more 
mature portions of the shoots. There is the possibility, however, that 
Diplodia and other secondary fungi might gain entrance to the diseased 
shoot and cause a complete die-back. 

Occurrence in other Countries. The disease is known in East and West 
Java but is stated to occur only when the atmospheric conditions are 
wet. The fungus causing the disease is apparently the same strain as that 
isolated in Coy Ion. In Sumatra a severe attack of Phytophthora faberi 
(P. palmivord) in bud-wood nurseries is reported by d'Angremond, but 
it is not known whether this disease was caused by the same strain. In 
Malaya, Weir describes a disease which attacks the young bud-shoot at 
its extremity and mentions a Phytophthora as a possible causal agent. 

PATCH CANKER OR CLARET-COLOURED BARK CANKER 
Commonest cause in Malaya=P//Mtww complecten^, Braun. 
This disease was first discovered on Hevea, in Ceylon, about 1903. 
It has since been reported in Java, Sumatra and Fiji, but it has never 



248 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

been found to be of common occurrence in Malaya. Recently it has 
been reported to be common in Kedah, and has been found to be 
associated with damage by lightning on numerous estates in other 
parts of Malaya. 

Causal Fungus. Steinmann reports that, according to the investi- 
gations of Rutgers and Vischer, this disease of the tapping panel is 
caused by the same species of Phytophthora which causes black-stripe 
canker. Fetch states: "The Phytophthora which causes claret-coloured 
bark canker is identical with that which causes the similarly coloured 
canker in Cacao". Recent work in Malaya showed the constant 
association of a Pythium sp. with patch canker following on lightning 
damage, while Thompson isolated two species of Phytophthora and 
one species of Pythium from naturally occurring patch canker in 
Malaya. Steinmann points out that Hartley in an unpublished paper, 
had stated that the differences between the various Phytophthorae 
which cause patch canker in cacao and black stripe and patch canker 
in Hevea are comparatively small, and that they should not be 
considered separate species. This question of the identity of the .fungi 
causing canker in cacao and Hevea is not as important in Malaya as 
in Ceylon and the Dutch East Indies. In the latter countries mixed 
plantings of cacao and rubber have been a fairly common feature in> 
past years, and the intermixture of these two crops, both susceptible 
to attack by the same fungi, has probably resulted in more intense 
attacks of patch canker being experienced on Hevea than has been 
the case in Malaya. 

Thompson records the fungi isolated from naturally occurring 
cases of patch canker in Malaya as under: 

Phytophthora palmivora, Butl. (rubber group) 

Phytophthora sp. (undetermined) 

Pythium sp. (probably P. complectens, Braun) 

In connection with the fungi listed above, the writer submitted 
two cultures for examination to Dr. S. F. Ashby, Mycologist, Imperial 
Mycological Institute, one of which (a) was a Pythium sp. associated 
with lightning damage on rubber trees, the other (b), being isolated 
from a diseased rubber seedling. His report was as follows: 

Both of the isolations yielded a similar fine silky, radial growth on 
maize extract agar, the hyphal characters being also much alike. 

Transfers to water from a young growth on bean agar of (a), after two 
days at 23 C. numerous, spherical sporangia, borne as a rule on lateral 
branches, were produced; zoospores were developed freely after the culture 
was brought into the cooler room. The contents of the sporangium passed 



CHAP, xii PATCH CANKER 249 

into a vesicle, in which, after about 10 minutes at 21 C., zoospores had 
differentiated and had begun to swim away. 

The evacuation tube was short (J to \ the diameter of the sporangium). 
Sexual organs were scanty on the mycelium growing into the water from 
the inoculum after a further 2-3 days. Conidia (sporangia) were formed 
abundantly on bean agar and sexual organs fairly freely. The antheridium 
was applied laterally to the oogonium, clasping it frequently ovar half its 
surface as in Pythium complectens, Braun. In sporangia and size of sexual 
organs, the strain agrees very closely with that described by A. Thompson 
from patch-canker of Hevea rubber (Malayan Agric. Jour. xiii. 139, 1925) 
and is doubtless the same species. Like the earlier isolation from patch - 
canker, it can be considered a strain of P. complectens, although not quite 
identical with Braun 's strain. 

The form (6) produced sporangia less freely and tardily in water; they 
were quite similar, however, in size, evacuation tube, and vesicle. Sexual 
organs were produced more freely in water; they were quite similar to 
those of the other strain. Sexual organs were formed freely on maize -meal 
agar but sporangia were very scanty on bean, maize, and quaker-oats 
agars. This strain differs from the other apparently only in the more 
pronounced degree of the sexual over the asexual reproduction, It was 
a pure culture, but the culture (a) carried a bacterium which seemed to 
have no inhibiting effect on vegetative growth and might have promoted 
asexual reproduction. Both strains produced an abundant aerial mycelium 
on the agars. 

In 1928, Weir reported that he had made many soil isolations, and 
commonly obtained a Pythium sp. in culture. This species would 
almost certainly prove to be P. complectens, and the microphotographs 
illustrating the sexual organs of the fungus -causing patch-canker 
were taken by Mr. R. M. Richards, and are quite typical for P. 
complectem (Fig. 34 , 6). This fungus is obviously the most frequent 
species found closely associated with affections of the rubber tree, and 
may reasonably be considered the commonest cause of patch-canker 
in Malaya. Details of reproductive structures produced by this fungus 
are given in Fig. 31. 

Before proceeding to the description of the symptoms of patch- 
canker it will be of interest to state shortly the characters of the 
cortex of a healthy tree as it appears when carefully scraped away. 
Healthy Hevea cortex, if not previously tapped, has a thin green layer 
underlying the outer, brown corky layer. Beneath this green layer, 
the cortex is yellowish, becoming whiter as the cambium is ap- 
proached. In renewed bark, the green layer is never prominent and is 
usually absent, and the outer living layers of the cortex are, in part, 
a clear red. Frequently this red coloration runs in a narrow zone, just 
within the cortex. This clear red coloration is a normal appearance 
which may persist in the renewed bark for many years. 



250 DISEASES AND PESTS OF THE RUBBER TREE PART in 




FIG. 34 a. Pythium complectens. Sporangia and Oogonia of P. complectenft 
developed in pure culture. (Photograph by Mr. R. M. Richards.) 




Fia. 346. Enlarged photograph of above to show a single sexual 
reproductive body. (Photograph by Mr. R. M. Richards.) 

Note. A male organ Antheridium, clear and devoid of protoplasm which has passed into 
female organ Oogouium, with dense protoplasm. 



CHAP, xii PATCH CANKER 251 

Symptoms. In the early stages of patch-canker there is little out- 
ward indication of the disease. If the tree has acquired a thick, outer 
brown bark it is only by scraping away the outer tissues that the 
diseased areas become visible. From the diseased areas a reddish or 
purplish liquid may exude in many cases and this dries on the surface 
in small streaks. In very wet weather, this may occur when only a 
small patch of bark is diseased, but more usually it only happens 
after a fairly large area has become affected. But when the disease has 
reached an advanced stage, the decaying bark attracts boring beetles; 
frequently it is not until this stage is reached that any trouble is 
noted. In some instances an attacked tree ceases to yield latex; but 




Fio. 35 a. Tree affected by patrh ank. r following on lightning strike. Corky bark 
lightly scraped away to OXJIOM- r \tornal surface of diseased cortical tissue. 
Note dark discoloration of cortical tissue. 



this is not a certain symptom of the disease, as it is in the case of 
brown bast. 

If the outer bark layers of a tree suffering from patch-canker are 
scraped lightly so as to expose the diseased tissue, a thin black layer 
is first met with, and the cortex beneath this is moist and discoloured 
(Fig. 35 a). When recently attacked it is greyish or yellowish-grey 
with a well-defined black border, but in advanced cases it becomes 
claret-coloured or purple-red. Frequently the diseased cortex is dirty 
red when cut, but soon darkens to purplish -red on exposure. It is 
hardly possible, to confuse this usually muddy looking, discoloured 
tissue with the clear, translucent red zone characteristic of healthy 
cortex of renewed bark, and the discoloured areas are always clearly 
marked oil by a black line from the surrounding healthy tissues. 



252 DISEASES AND PESTS OF THE RUBBER TREE PART in 

The disease pursues its course by infecting the external cortical 
layers; it then works inwards towards the cambium, spreading out at 
the same time more or less equally in all directions. This indicates 
that all the cortical tissues are indiscriminately attacked in turn and 
that the fungus does not confine its activities primarily to any par- 
ticular type of tissue system, such as the medullary rays. Thus, the 
black-stripe fungus utilises the medullary rays for rapid radial spread 
into the wood, and because of this we get the characteristic symptoms. 
In most cases, a patch-canker infection would be detected before it 
has fully penetrated through the cortex to the cambium, but if left 
alone it will kill the cortex right down to the cambium and spread 




FIG. 35 b. Patch canker. Affected bark seen in Fig. 35 a stripped away from wood 
to show inner surface of cortex which was in contact with the wood. (Figs. 
35 a arid b from Annals of Applied Biology, vol. xx. No. 1, p. 1.) 

A'ntc.- The corticjil tissues arc diseased throughout its thickness. White areas show where latex haa 
exuded from diseased areas to coagulate in spaces between wood and cortex formed by shrinkage of 

diseased cortical tissue. 

laterally as long as growth conditions are favourable to the fungus 
(Fig. 35 b). It may thus extend over large areas of bark, and ulti- 
mately kill the tree, without producing any open wound or giving 
any outward indication except the bleeding already mentioned. When 
dry weather sets in, however, the disease is generally checked, and 
the affected cortex then dries up and forms a scale which ultimately 
falls off. The most serious cases of patch-canker are those in which the 
tree is attacked at the collar (Fig. 36). The disease may then run 
rapidly round the base of the tree and kill it in a few weeks. In Malaya 
this type of collar infection is met with most commonly as an after- 
effect following lightning damage. It will be dealt with in detail in a 
later chapter, but it may be stated here that Rutgers and La Rue 
mention a cherry-coloured or purple discoloration of bark and cam- 



CHAP, xii PATCH CANKER 253 

bium in cases of lightning wounds. They state this discoloration 
remains visible for a short time and can only be seen in cases which 
are diagnosed at once. 

If the primary infection takes place on the tapping cut so that the 
recently tapped, renewing bark is involved, the diseased tissue often 
remains yellowish -grey in colour, i.e. does not assume the character- 
istic claret colour. But where it extends into the untapped aijea under 
the tapping cut, as usually happens, the diseased tissue assumes the 
typical claret colour. There should not be any confusion between 
black stripe and patch-canker, for the typical colour of patch-canker 
is quite distinct and it spread*s uniformly in all directions from the 
point of infection as a continuous sheet of diseased tissue with no 
tendency to form lines or stripes, which at a later stage may fuse 




FIG. 36. Showing wounds at base of tree caused by an attack of patch canker at 
the collar. (Photograph by Mr. A. Thompson.) 

together. During the dry seasons experienced in Java and Ceylon the 
disease automatically ceased to spread, or only spread very slowly. 
Under a protracted dry- weather period, the affected bark patches dry 
out and are scaled off by the action of the undamaged cambium 
beneath. 

Treatment. As stated above, under ordinary circumstances, patch- 
canker is not a common disease in Malaya; this remark needs some 
reservation perhaps, for the situation seems worthy of further review 
in the Kedah and North Perak districts. 

The recognised treatment for patch -canker is to strip off the 
diseased bark area in one piece; but if this is not possible, to take out 
the diseased tissue in convenient lumps, treatment which could only 
go astray through sheer carelessness. The first operation is to paint 
over and about the diseased area with a strong fungicidal solution, 
such as Izal, in 5 per cent solution, so as to kill any aerial mycelium 



254 DISEASES AND PESTS OF THE RUBBER TREE PART in 

on the surface. A little time is allowed to elapse and then the diseased 
area is delimited by very light scraping. The clearly defined edges of 
the diseased bark are usually easily traced out; when this has been 
done a cut down to the wood is made, including about one inch of 
healthy cortical tissue within the area isolated by the cut, together 
with the whole of the diseased tissue. The knife is then carefully 
inserted beneath the edges of the isolated area, and is gradually 
worked right round to loosen the diseased patch at the edges. This 
operation demands care but, if not hurried, little difficulty is to be 
expected. When the edges are loosened, the knife is carefully inserted 
and gentle force applied to lever out the diseased patch. Undue haste 
will only result in disappointment. When removed, the diseased patch 
should be burnt as quickly as possible; it is useful to immerse the 
diseased patches immediately in solar oil, a receptacle containing 
which should be carried round by the coolies undertaking the work. 
The stripped surface is then protected by a wound-cover to prevent 
the entrance of boring beetles; tar is recommended in Ceylon, while 
in Malaya asphaltum -kerosene or asphaltum -solar oil mixture is 
generally used. 

If a serious attack is experienced and large numbers of trees need 
treatment in the vicinity of the tapping cut, it may be best to adopt 
the scraping method, but the gravest precautions must be taken to 
prevent small pieces falling to the base of the tree and causing infec- 
tion at the collar. Scraping can only be recommended with safety for 
treatment during periods of dry weather, when the diseased part may 
then be scraped away so as to remove most of the cankered bark, the 
scraping being continued until latex begins to issue from the inner 
cortical layers in minute drops. This is a sign that the limit of the 
diseased part is being reached as cankered bark does not yield latex. 
The remainder of the diseased cortex is then left to dry up and scale 
out. If the disease has penetrated to the wood, the whole of the 
cankered cortex has to be cut out. According to Malayan experience 
of the scraping treatment, when the operation has been carried 
out at some height above ground-level, an attack of patch- canker at 
the collar follows later. As stated above, this is the most dangerous 
form of the disease. 

The following is a summary of the treatment required for patch- 
canker: 

(1) Paint infected area with a solution of 5 per cent Izal to kill aerial 
mycelium or sporangia. 

(2) Allow 30 minutes to elapse, then delimit diseased area by very light 
scraping. 



CHAP, xii PATCH CANKER 265 

(3) A cut down to the wood is then made with a sharp knife to include 
one inch of healthy cortical tissue with the diseased area. 

(4) The bark area isolated by the cut is then carefully "stripped" off 
as indicated above. 

(5) When the stripping has been carried out, the exposed wood surface 
must be protected by painting over with tar or covering with 
asphaltum-solar oil mixture. 



CHAPTER XIII 

MINOR PANEL AFFECTIONS 

Marasmius palmivorus, Sharpies Internal Bark Fissures Drying-out of the 
Tapping Panel Squirrel Damage Acanthopsyche snelleni. 

MARASMIUS PALMIVORUS, SHARPLES 

ABOUT the end of 1922 and the beginning of 1923, Thompson reported 
that the renewing bark of rubber trees had been recently damaged by 
a fungus similar to one which formerly was observed to grow super- 
ficially on young bark at the top corner of a tapping panel. The 
fungus, which was referred to the genus Marasmius, had not been 
observed to penetrate through the bark into living cortical ceils before 
the 1922 outbreak, and it disappeared normally by natural scaling of 
the bark. But in 1922 slight penetration through the bark on the 
tapping panel was noted in a few instances. Recently (June 1933), 
numerous cases of this disease have been reported from one estate and 
there cannot be the least doubt that the fungus is actively parasitic, 
rotting the bark and cortical tissues of the newly tapped surface down 
to the wood. 

Symptoms. During the last year two outbreaks of Marasmius bark 
rot have been observed. These developed normally as described by 
Thompson, who says: "Trees which were opened up for tapping on 
January 1st showed the disease after three weeks daily tapping". 
Both cases in 1933 showed about two to three inches of bark removed 
by tapping, and both were newly opened-up panels for test tapping on 
trees, some seven years of age. On estate A, the trees were first tapped 
on April 1st, 1933, and on June 5th a visit of inspection was made. 
The tapping system was spiral, alternate daily, opened up at a 
height of 22 inches. The affection was spread over about 200 acres 
of closely planted rubber, and by the middle of June, over 400 trees 
showed the external strands of the fungus growing over the tapping 
panel. 

As stated by Thompson, the plates of mycelium are found in one or 
all the corners of the tapping panel, but they are most commonly 
found in the upper corners. The reason for this has been recently 
discovered. 

In the last case examined in 1933, the affection occurred on an 

256 



CHAP, xm MINOR PANEL AFFECTIONS 257 

area similarly closely planted and the infection was a heavy one. The 
fungus not only grew over the surface of the tapping panel but grew 
out and covered the vertical channel which leads the latex to the 
latex-cup. In both cases the virgin bark was noticeably more scaly 
than usual, and the external fungal strands appeared to be running 
from beneath the bark scales on the upper boundary of the tapping 
panel and then on to the tapping panel itself, growing downwards 
towards the tapping cut. If the right conclusion is drawn from this 
appearance, it is very probable that the fungus strands filling the 
vertical channel would be growing out horizontally across the channel 
and not passing upwards or downwards. This proved to be the case. 
The fungus strands were growing out from the pre-infected bark 
scales which had been cut through by the tapping knife when the 
channel was made. 

Thus, the scaly bark found before tapping is a diseased condition, 
the scaliness being brought about by the development of circular 
cork-cambia around patches of diseased outer cortical tissue, which 
later dry up and scale off. This is plainly seen when the bark is 
examined microscopically. When tapping is started in virgin bark, 
the fungus does not make its appearance from underneath the scales 
on the upper boundary of the tapping panel until two to three inches 
of bark have been excised by the tapping operation. The fungus 
cannot appear from underneath the bark scales below the tapping 
cut as long as tapping is continued, but since the fungus strands grow 
downwards to cover the tapped bark more quickly than the tapping 
operation opens new areas of freshly tapped bark, the tapping panel 
may become wholly covered by the fine, silky, mycelial threads. The 
cases seen this year show that the fungus can actively penetrate 
through the thin, recently tapped, renewing bark, completely 
passing through the cortical tissues to the wood, and causing a 
definite rotting of the bark. The newly developing cortical tissues are 
rotted down to the wood in a band running parallel to the tapping 
cut about {- inch broad and several inches in length, the rest of the 
renewing bark being covered with surface mycelium only, for the 
tissues immediately underneath the outer bark layers appear quite 
fresh and green. 

Thompson says that one of the first signs of attack is the appear- 
ance of a small fan of white mycelium J-f inch above the tapping cut, 
later forming a small plate of white mycelium, with a mycelial fan 
at the edges. A number of these plates may be formed; they are 
commonly found in one or all the corners of the tapping panel. Later 
some of these plates may fuse together into several patches which may 



258 DISEASES AND PESTS OF THE RUBBER TREE PART in 

be from 6 to 8 ins. diameter. In the latest outbreak (1933) the whole 
of the tapped surfaces were covered with fine, silky strands of 
mycelium, giving a silvery white, external appearance in advanced 
cases. The diseased bark areas are quite conspicuous, on account of 
their covering of whitish-grey mycelium, which is white at the edges 
(Fig. 38). The mycelial plates and strands resemble those produced 
by species of Marasmius, and when fructifications are found they 
will probably belong to this group. (This has since been found to be 
correct.) Figs. 37 and 39 show the habit of growth of the fructifica- 




FlG. 37. Fructifications of M. palmivorus (?) growing in situ (natural size), 
developed in laboratory. 

tions. These will need further study as they show features very 
similar to those of Marasmius palmivorus, described by the writer 
from coconut and oil palms. The following is the description given 
for this fungus, which is regarded as a species new to science: 

MARASMIUS PALMIVORUS, SP. NOV. Under Dry Conditions. Pileus 
^f inch across; umbonate; smooth, slightly striated. Upper surface 
Eosine Pink when young, Shrimp Pink later (Ridge way), glabrous. 
Margin incurved when young. Gills pure white; attached when young 
but in old specimens becoming slightly detached from stalk; no cross 
veins; thick, distant. Stalk |-f inch high. White, glabrous, solid, 
slightly bulbous at base; the bulbous base often shows same colour as 




FIG. 38. Mycelium of M . palmivorus ( ?) on panel of rubber tree and in vertical tapping 
channel. Mycelium on panel has not yet spread actually on to the tapping cut. 











Fia. 39. Marasmius palmivorus. 
A = Upper Surface of Pileus. B = Under Surface showing Kills. 

Note. Great variability in size of fructifications. The illustrations are natural size and the small 
ones represent the fructifications as seen in the field. The large type arc developed in the laboratory 
in the presence of constant supplies of moisture. 



260 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

upper surface of young pileus. Single or caespitose. Spores hyaline, 
10 x 5-5jLt. Slightly beaked when mature. 

Under Moist Conditions. Pileus white and transparent; when 
young shows traces only of brownish-red colour, 2-3 ins. across. Much 
convoluted with upturned edges. Stalk 1-2 ins. high. Bulbous base 
usually retains traces of pink colour. 

Hab. On tapping panels of rubber trees, and on leaf bases of 
coconut and oil palms. 

Treatment. There is no reason to suppose that this disease will not 
prove amenable to treatment if proper precautions are taken. No 
fruiting bodies have been found in nature up to date, and the only 
source from which fresh infections can originate is the sterile my- 
celium, portions of which may be carried from one tree to another on 
the tapping knife. If tapping is stopped for a fortnight, one painting 
with a strong fungicidal solution, or two paintings with a weaker 
solution, should be sufficient to kill out the fungus. A summary of 
treatment follows: 

(1) Cease tapping for two weeks. 

(2) Paint once with a 20 per cent solution of Agrisol, Brunolinum 
Plantarium or 5 per cent solution of Izal. 

Or (3) as an alternative to (2), paint first with a 10-15 per cent 
solution of Agrisol or Brunolinum Plantarium, or a 3 per cent solu- 
tion of Izal, to be followed by a second painting seven days later; 
tapping may be recommenced seven days later. Before reopening the 
tapping cuts, the scaly bark above the tapping panel and beneath 
the tapping cut should be scraped away, so as to remove the primary 
cause of infection. 

INTERNAL BARK FISSURES 

Sutcliffe, in 1930, first reported in Malaya these abnormal develop- 
ments in Hevea cortex. The bark fissures show up externally as 
vertical lines on the tapping panel and at a casual glance might be 
mistaken for an unusual form of black-stripe disease (Fig. 40). On 
closer examination it will be found that the symptoms are quite 
different from those of black stripe, for the stripes do not spread 
irregularly and no fusion takes place. The lines are distinct and quite 
separate, usually slightly inclined to the vertical. 

Sut cliff e reported on the first cases examined, that the tapping 
system was a single cut on a quarter of the tree on virgin bark and the 
cut was about forty inches above ground-level. He does not specially 
comment upon this feature, but it is obvious that, as tapping in 
ordinary cases is seldom started at a height of more than three feet, 



CHAP, xrii MINOR PANEL AFFECTIONS 261 

and as the trees were twenty-one years old, tapping had been com- 
menced on a panel of virgin bark above the old renewed panels. 

In 1931-32, numerous estates with fields of old rubber had reached 
a position which was not too reassuring in respect of bark reserves. 
Yields were diminishing if tapping was continued on the old re- 




FIG. 40. Tapping panel of old tree showing typical external appearance of internal 
bark fissures, running across the whole of the tapped area, slightly inclined to 
the vertical. 

newed bark panels, so, in an attempt to keep yields at a normal 
level, tapping was started at a height of forty-eight inches, or even 
sixty inches, in virgin bark above the old renewed panels. In most, if 
not in all cases, the black lines now known as internal cortical fissures 
appeared in the tapping area opened up in the manner depicted, and 
the writer has never observed them except in these particular 
circumstances. 



262 DISEASES AND PESTS OF THE RUBBER TREE PABT m 

In most cases the lines run from the top of the tapping panel to the 
tapping cut (Fig. 39). In other cases, the lines begin half-way down 
the panel and continue down to the cut. In still other cases, the lines 
which completely cross the tapping panel may be followed upwards, 
running beneath the surface of the untapped virgin bark, while at the 
lower end the lines continue to run for some distance below the 
tapping cut. The number of lines on a tapping panel varies from one to 
eight; they are not truly parallel to one another but are slightly wider 
apart at the lower ends, being inclined from the vertical, to the 
right. Sutcliffe says the fissures follow approximately the course of 
the latex vessels. 

No fungus or other organism has ever been found associated with 
these lines. Bobilioff described similar fissures from Java in 1927. In 
one case he found as many as 113 fissures on one tree. 

The cause of the formation of the fissures is unknown but Bobilioff 
suggests that trees growing on poor soils exhibit an intense develop- 
ment of stone cells. The result thereof is the formation of a very hard 
bark, while the soft bark is thin. When growth sets in the hard bark 
is not sufficiently elastic, so the soft bark tears and the fissures 
mentioned are formed. In the meantime, the latex vessels are 
damaged, so that the fissures become filled with latex. The fissures 
are immediately bounded by a cambium, and by its activity new 
cells are formed, and it is for this reason that not only latex but cells 
also are found in the fissures. They are mostly parenchyma cells 
which have been transformed into stone cells. 

The writer has not had the opportunity of making a careful micro-* 
scopical examination of these fissures. The explanation given above 
does not appear to be very convincing, and judgment must be 
suspended until further work can be carried out upon this aspect of 
the trouble. 

DRYING-OUT OF THE TAPPING PANEL 

Steinmann remarks that this disease is often mistaken for mouldy 
rot, but this is an erroneous impression, as it is a purely physiological 
phenomenon. It is uncommon in Malaya, as it is said to occur in the 
dry season only, chiefly on weak trees, or those which have been too 
deeply tapped; overtapped trees with poor bark renewal as a result of 
growing on poor soils often show the symptoms typical of this wound 
reaction. The patch of dry discoloured bark does not follow the line 
of the tapping cut as do the diseased areas in a mouldy rot attack, so 
there should be no difficulty in diagnosis. 



CHAP, xiii MINOR PANEL AFFECTIONS 263 

PANEL DAMAGE CAUSED BY SQUIRRELS 

Large open wounds on recently tapped bark are often caused by 
squirrels, which eat the soft renewing bark away to expose the wood. 
Further reference to squirrel damage will be made in a later chapter 
(Fig. 69). 

PANEL DAMAGE CAUSED BY LARVAE OF PSYCHE 

(ACANTHOPSYCHE) SNELLENI, HEYL. 

The larvae of one or more species of Psychid moths occasionally 
appear in large numbers and begin to feed on the recently renewed 
bark in close proximity to the tapping cut. Further remarks with 
reference to this insect will be found later (Fig. 62). 



REFERENCES TO LITERATURE ON TAPPING PANEL 
DISEASES 

MOULDY ROT 

SHARPLES, A., BELGRAVE, W. N. C., NORRIS, F., DE LA MARE, and ELLIS, 

A. G. G., 1920. "Black Stripe and Mouldy Rot of Hevea brctdiliensis" , 

Bull. No. 31, Dept. of Ag. S.S. & F.M.S. 
SANDERSON, A. R., and SUTCLIFFE, H., 1920. "Sphaeronenm sp. (Mouldy Rot 

of the Tapped Surface)", Anns, of App. Biol. vol. vii. p. 56. 
BALLY, W., 1920. "Mouldy Rot", Arch. v. d. Rubber cultuur. Gen. Sor. No. 8. 
SHARPLES, A., 1921. "Treatment of Mouldy Rot Disease by Application of 

Agrisol", Ag. Bull. Dept. of Ag. 8.S. & F.M.S. vol. 9, No. 3, p. 184. 
SHARPLES, A., 1921. "Estate Treatment of Mouldy Rot", Ag. Bull. Dept. oj 

Ag. S.S. rf? F.M.S. vol. 9, No. 4, p. 277. 
SHARPLES, A., 1923. "Final Report on Treatment of Mouldy Rot Disease with 

Agrisol", Mai. Ag. Jour. vol. 11, No. 2, p. 36. 
ELLIOTT, J. A., 1925. "A Cytological Study of Ceratostomella finibriata (E. & 

H.), Elliott", Phytopathology, xv. 417. 
SOUTH, F. W., and SHARPLES, A., 1925. "The Mouldy Rot Disease of Hevea 

brasillensis in Malaya", Bull. No. 37, Dept. of Ag. S.S. cfc F.M.S. 
ANDRUS, C. F., and HARTER, L. L., 1933. "Morphology of Reproduction in 

Ceratostomella fimbriata" . Jour, of Agric. Res. vol. 46, No. 12, p. 1059. 

BROWN BAST 

GALLAGHER, W. J., 1909. "Field Notes", Ag. Bull. S.S. & F.M.S. No. 3, 

March, p. 107. 
BATESON, E., 1913. "Bark-Canker of Hevea in Java", Ag. Bull. F.M.S. , 

March, No. 8, vol. 1, p. 299. 
PRATT, H. C., 1917. "Brown Bast on Rubber Trees its Cause and Spread", 

Malayan Tin and Rubber Journal, vol. 6. 
HARMSEN, J. R., 1919. Bruine Binnenbastziekte. Ruggrok & Co., Batavia. 



264 DISEASES AND PESTS OF THE RUBBER TREE PART in 

SANDERSON, A. R., and SUTCLIFFE, H., 1921. Brown Bast. Rubber Growers' 

Association, 38 Eastcheap, London, E.G. 3. 
RANDS, R. D., 1921. "Brown Bast Disease of Plantation Rubber. Its Cause 

and Prevention", Arch. v. d. Rubbercultuur en Nederlandsch. -Indie, 5, 

C. Jaargang, No. 5, Mei, p. 223. 
KEUCHENIUS, P. E., 1921. "Die Rindenbraune der Hevea brasiliensis" , Eine 

Kritische Untersuchung, Abdruck aus dem Centralblatt fur Bact. Para- 

sitenkunde & Infektions krankheiten: Zweite Abteilung, Bd. 55, Heft 1/4. 
FARMER, J. B., and HORNE, A. S., 1921. "On Brown Bast and its immediate 

Cause", India-Rubber Jour. vol. Ixi., June, p. 25. 
HORNE, ARTHUR S., 1921. "Phloem Necrosis (Brown Bast Disease) in Hevea 

brasiliensis" , Anns, of Bot. vol. xxxv. p. 458. 
SHARPLES, A., 1922. "A Consideration of Recent Work on the Brown Bast 

Problem", Mai. Ag. Jour. vol. x., June, No. 6, p. 155. 
SHARPLES, A., and LAMBOURNE, J., 1924. "Field Experiments relating to 

Brown Bast Disease of Hevea", Mai. Ag. Jour. vol. xii. Nos. 9 and 10, 

p. 290. 
FREY-WYSSELING, A., 1932. "Investigations on. the Dilution Reactions and 

the Movement of the Latex of Hevea brasiliensis during Tapping", 

Archief. v. d. Rubbercultuur, 16. e Jaargang, No. 3, Moi- June, p. 1. 

BLACK STRIPE DISEASE 

RUTGERS, A. A. L., 1912. "Hevea Ranker", Meded. v. d. Afdeeling Voor. 

Plantenziekten, No. 2. 
DASTUR, J. F., 1916. "Black Thread Disease of Hevea in Burma", Bull. 

No. 14, Dept. of Ag. Burma. 
DASTUR, J. F., 1916. "Phytophthora sp. on Hevea brasiliensis", Memoirs of 

the Dept. of Ag. in India, vol. viii. No. 5, p. 217. 
SHARPLES, A., 1917. "Bark Canker in Hevea brasiliensis, and the Significance 

of Diseases in the Economy of Malayan Rubber Plantations", Kew. 

Bull. No. 6. 
PRATT, H. C., 1917. "Preventive Measures against Black Thread", Ag. Bull: 

F.M.S. p. 180. 
PRATT, H. C., 1917. "Apparent Relation between Height of Tapping Cut 

and Black Thread Attacks (Phytophthora faberi, Maubl.)", Trop. Agri- 
culturist, vol. xlix. p. 7. 
HARMSEN, J. R., 1918. "De bestrijding van streepjeskanker en proefnemingrn 

dienaangaande", Nederlandsche Indisch-Rubbertijdschrift, June 1st. 
SHARPLES, A., and BELGRAVE, W. N. C., et al., 1920. "Black Stripe and Mouldy 

Rot of Hevea brasiliensis", Butt. No. 31, Dept. of Ag. 8.8. & F.M.8. 
D'ANGREMOND, A., 1929. "Annual Report of the Director of the Gen. Expt. 

Station of the A.V.R.O.S., July 1st, 1928. 
THOMPSON, A., 1929. "Phytophthora Species in Malaya", Mai. Ag. Jour. 

vol. xvii. Nos. 3-4. 
WEIR, J. R., 1929. "A Blight of Young Buddings", Quar. Jour. Rub. Res. 

Inst. of Malaya, vol. i. Nos. 1 and 2. 
MURRAY, R. K. S., 1930. "A Disease of Young Bud-shoots caused by Phyto- 

phthora palmivora, Butler", Trop. Ag. Ixxiv. p. 216. 

PATCH CANKER 

RUTGERS, A. A. L., 1919. "Lightning Damage of Rubber", Arch. v. d. Rubber- 
cultuur, vol. 8, No. 4, p. 163. 



CHAP, xin MINOR PANEL AFFECTIONS 265 

LA RUE, C. D., 1922. "Lightning Injury to H evea brasiliensis" , Phytophthology, 

vol. xii. p. 386. 
VISCHER, W., 1923. "Some Notes on Three Diseases of the Tapping Surface 

Drying up, Striped Canker, and Mouldy Rot", Archie} v. d. Rubber- 

cultuur, vol. 7, No. 1, p. 28 (with English summary). 
THOMPSON, A., 1929. "Phytophthora Species in Malaya", Mai. Ag. Jour. 

vol. xvii. Nos. 3 and 4. 

MARASMIUS BARK ROT 

THOMPSON, A., 1924. U A Preliminary Note on a New Bark Disease of Hevea", 

Mai. Ag. Jour. vol. xii. p. 161. 
SHARPLES, A., 1928. "Palm Diseases in Malaya", Mai. Ag. Jour. vol. xvi. 

Nos. 9 and 10, p. 313. 

INTERNAL BARK FISSURES 

BOBILIOFF, W., 1927. "Ondczook over het Voorkomeii van invendige spleton 
in de bast van Hcvea", Arch. v. d. Rubbercultuur, No. 7, July. 

SUTCLIFFE, H., 1930. "Internal Fissures in Hovea Cortex", Quart. Jour. 
R.R.L of Malaya, vol. 2, No. 1, March. 



SECTION 3 
STEM DISEASES 

CHAPTER XIV 

MAJOR AND MINOR STEM DISEASES 

Pink Disease (Corticiutn salmonicolor) Die -back in Rubber Trees- Stem Ustulina 
White Thread Blight Horse-hair Blight Ring-Rot Mistletoes (Loranthus 
spp.) on Rubber Trees. 

INTRODUCTION 
FETCH mentions the following in his chapter on stem diseases: 

(1) Pink Disease 

(2) Ustulina zonata 

(3) Death of Green Twigs 

(4) Die-back 

(5) Fusicladium Stem Disease 

(6) Mouldy Rot of Tapped Surface 

(7) Thread Blight 

(8) White Stem Blight 

(9) Horse-hair Blight 

(10) Top Canker 

(11) Pestalozzia disease of seedlings 

(12) Loranthus 

Of this list Nos. (1), (2), (6), (7), (9) and (12) are found in Malaya; 
No. (6) (Mouldy Rot) has been described in a previous section. 

Nos. (5), (8) and (11) have not been recorded definitely in Malaya, 
while Nos. (3), (4) and (10) may possibly be considered as arising from 
similar causes, for as far as Malayan experience goes, the symptoms, 
as described by Fetch, would now be ascribed to lightning injury or 
die-back following on scorching. The only important stem diseases in 
Malaya are pink disease, Stem Ustulina as it is termed, and die-back 
caused by a Diplodia sp., which fungus always appears rapidly after 
scorching. 

266 



PLATE IV 




Pink Disease 

N = Neeator pustules on xppt'r surface of attacked branches. 

O.W. = ()pen wound characteristic of pink disease. 

P. I. = Pink incrustation. 

C.F.=- Cobweb form of fungus KrmviiiK out from cd^e of pink incrustation. 

N.S. = Ne\v shoots from dormant buds in healthy areas of stem, still free from the fungus attack. 



CHAP, xtv PINK DISEASE 267 

PINK DISEASE 
Caused by Corticium salmonicolor y B. & Br. 

The cause of pink disease, Corticium salmonicolor, B. & Br., is a 
widely distributed fungus. It is reported to be of economic importance 
in other countries on different crops. In Java, coffee and cinchona are 
seriously affected by it and in Ceylon it causes a serious disease of tea. 
In the West Indies, a pink fungus on cacao, known for a long period 
as Corticium lilacino-fuscum, B. & C., owing to a misidentification, has 
been proved to be C. salmonicolor . West Indian records show that 
pink disease occurs in Porto Rico, Dominica, St. Lucia and Trinidad 
on cacao, and it has also been found there growing on other host 
plants. 

C. salmonicolor is not only a widely distributed fungus, but it is 
also practically omnivorous for it has been found on so many species 
and genera of plants, widely separated. Rant mentions that it has 
been found on no less than 141 species of plants belonging to 104 
genera and many different families. The fungus has been recorded on 
gymnosperms and dicotyledons but has not yet been recorded on 
monocotyledons. In Malaya, the following host plants have been 
listed: 

Common Name Scientific Name 

Para rubber Hevea brasiliensis, Mull.-Arg. 

Cocoa Theobroma cacao, L. 

Coffee Coffea robusta, R. Br. 

Gardenia sp. 

Hibiscus Hibiscus rosa-sinensis, L. 

Camphor Cinnamomum camphora, T. Nees & Eberm. 

Cassia sp. 

Horse mango Mangifera foetida, Jour. 

Langsat Lansium domesticum, Jack 

Lime Citrus medica, L. var. acida 

Durian Durio zibethinus, Murr. 

Jak Artocarpus integri folia, L. 

Belimbing Averrhoa belimbi, L. 

Mango Mangifera indica, L. 

(Tepkrosia hooker iana, W. & A. 

Bush covers llndigofera arrecta, Benth. 

\Clitoria caganifolia, Benth. 

C. salmonicolor is probably native in most of the countries in which 
it has been recorded. Many of the plants found attacked by the fungus 



268 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

in Java are indigenous and some of the plants found affected in 
Malaya are indigenous also. The fungus has probably spread from 
native hosts to plants that have been introduced, such as rubber, tea, 
coffee and cinchona. There is presumptive evidence that the fungus 
does grow on jungle trees in Malaya but there is no definite record 
up to date, and in any event it seems unlikely that pink disease 
wo.uld cause serious damage to forest trees. Unfortunately, this fungus 
has shown a great partiality for H. brasiliensis in certain localities, 
and as far as Malaya is concerned, this host is by far the most 
frequent. 

Distribution. In 1914 the chief centres of distribution of pink 
disease in the Federated Malay States were Southern Perak and the 
Northern part of Selangor, the district round Telok Anson, near 
Kajang, and in Kuala Selangor. At the present date every state 
growing rubber trees of a susceptible age has reported attacks of pink 
disease but it is only in certain localities, where climatic conditions 
favourably affect the growth and spread of the fungus, that they are 
serious. It is still most abundant in the districts of heaviest rainfall in 
the proximity of the mountain range or high hills or where large tracts 
of jungle still remain intact. In Malaya, it might be said that all 
estates where serious pink-disease attacks are met with are situated 
in the neighbourhood of large jungle reserves, and in the writer's 
opinion this is the most important feature. A line drawing (Diagram 
VII) is given; this is copied from an official map, which illustrates 
the type of situation where serious pink-disease centres are found, 
if the rubber areas carry trees from two to nine years of age. Estate 
A, recorded at the close of the company's financial year in 1933, that 
on an area of 132| acres, carrying a total of 17,551 trees, 10,417 
were treated and 18,513 prunings were made in the systematic 
treatment of pink disease. 

Pink disease attacks rubber trees of all ages, once the woody parts 
are definitely developed; a few cases may be found on trees less than 
two years old, but it is uncommon until after the second year has 
passed. From this point onwards, pink-disease attacks will, in favour- 
able localities, increase in severity until the eighth or ninth year, even 
though systematic treatment may be carried on continuously. But if 
treatment is maintained, the disease incidence will begin to fall 
rapidly between the seventh and tenth year, and after the peak is 
passed the disease should not cause much further trouble. But if 
treatment at any stage is neglected there is no doubt that the disease 
can persist in a destructive manner up to the fifteenth or twentieth 
year. In such areas it may attack the main stem of twenty-year-old 



CHAP. XIV 



PINK DISEASE 



269 



trees and "ring" them at a height of ten to twenty feet from the 
ground. Cases of this type usually die. 




J^^l &UB5ER. ESTATES. W/fr, FOREST RESERVES. 

1IIIIIIHII MALAY RESERVES. 

DlAGBAM VII 

The following table gives actual figures obtained of the number of 
pink disease cases requiring treatment over the first ten years on 
one estate: 



270 



DISEASES AND PESTS OF THE RUBBER TREE PART in 



TABLE IV 

NUMBER OF CASES OF PINK DISEASE TREATED FROM 1923 TO 1932 





Planting Years 


1923 


1924 


1925 


1926 


1927 
8524 


1928 


1929 


1930 


1931 


1932 


No. of trees 
treated 
No. of trees 
cut out 
Annual rain- 
fall 






255 


889 


14,298 


7846 
1816 


9203 
2074 
140" 


20,604 
684 
157" 


2272 
133" 





























Symptoms. The external symptoms of pink disease are very 
variable. Four distinct forms of the fungus can be distinguished, and 
all four forms may be found together on diseased bark areas at the 
same time; or, there may be only the commonest form present, i.e. 
the pink incrustation, which gives the popular name to the disease. 

Pink disease is so called because the fungus causes a pink incrusta- 
tion on the branches or main stem and it is usually better developed 
on the under or shady side of the branches. When fresh, this pink 
incrustation is very striking and cannot be confused with any other 
disease of rubber trees (Plate IV). The bright pink colour fades away 
rapidly to a dingy white, especially if a short, dry spell supervenes, 
while the incrustation cracks irregularly. 

The three forms, other than the common pink incrustation, are 
known as under: 



Malaya 

(a) Cobweb form 
(6) Pustular form 
(c) Necator decretus, Mass. 



Java and Sumatra 
Spinnegewebe form 
Hockerchen form 
Necator decretus, Mass. 



Plate IV illustrates three forms exhibited by C. salmonicolor, when 
the fungus attacks a rubber tree. If the pink incrustation is fresh and 
prominent, the other two forms depicted (a) and (c), will very often 
be found present; (a) the cobweb form growing out from the edges of 
the pink incrustation as white or pale-pink strands of a cobweb- 
like nature which run irregularly over the surface, the strands some- 
times being so delicate that they are easily overlooked; (c) the Necator 
stage consisting of orange -red (not pink) pustules, about J of an inch 
in diameter ; this form is usually found on the upper side of an 
attacked branch which is exposed to the brighter light. 

In Malaya, the pustular form is not commonly found except when 



CHAP, xiv PINK DISEASE 271 

the fungus attack has been continued for some time and the pink 
incrustation has lost its fresh pink colour. The pustules are minute in 
size, are pale-pink or white in colour and are situated in small cracks 
in the bark arranged more or less in parallel lines. This is sometimes 
the only form of the disease which can be seen externally; in such a 
case, it is not a simple matter to diagnose the attack correctly, with- 
out careful examination. 

Method of Attack. In Hevea the disease appears generally to 
originate at the fork of a tree or where several branches arise at the 
same level from the main stem. Different observers have different 
views as to the first signs noticeable after the fungus has successfully 
established itself. Fetch says the first indication is usually the appear- 
ance of a pink incrustation of interwoven hyphae over the bark. If 
this statement may be interpreted as the appearance of the loose 
cobweb form of the fungus, it would then be in agreement with experi- 
ence in Malaya. The pink patch gradually extends and may ulti- 
mately cover the whole circumference of the stem and the bases of the 
adjacent branches for a length of several feet. Such vigorous infections 
are seldom met with in Malaya except on estates where treatment is 
neglected, for the disease is practically concentrated in the side 
branches. Under the central part of a diseased patch the bark has 
usually been killed by the fungus and is brown and dry, but towards 
the margin it may still be alive and laticiferous. This is explained by 
the fact that the fungus travels over the surface of the bark more 
rapidly than within it, hence, although the bark is permeated by the 
fungus over the greater part of the patch, the advancing margin is 
generally superficial. The dead bark usually dries up and cracks and 
splits away from the wood, leaving an open wound (Plate IV). The 
fungus penetrates into the wood or xylem and destroys the continuity 
of the functional water-vessels which are situated in the peripheral 
region of the woody cylinder. As a result of the leaves of attacked 
branches being deprived of water, they shrivel up and die. Tyloses in 
the woody vessels are a constant feature when H. brasiliensis is 
attacked by pink disease, but these bladder-like ingrowths are com- 
monly met with wherever branches or stems of Hevea are wounded. 
Another common feature in the early stages of infection is the exuda- 
tion of latex from the affected parts which often serves to indicate 
the presence of pink disease to the planter. 

The main seat of attack on young trees commonly lies on the stem 
at the places where the branches originate, and the response made by 
plants attacked is very typical, owing to the upward passage of the 
water stream being seriously interfered with. The dormant buds in 



272 



DISEASES AND PESTS OF THE RUBBER TREE PABT in 



the healthy cortex below the attacked stem areas, are stimulated to 
activity, and numerous, healthy, adventitious branches are usually 
produced. Such cases can be treated very simply and effectively by 
pruning or pollarding the young trees below the diseased areas and 
removing all adventitious shoots excepting one or two which show 




FIG. 41 a. Pink disease. General features, showing pink incrustation, open 
wound, and new shoots from dormant buds in healthy cortical tissue. 

vigorous growth. Plate IV and Figs. 41 a and b show these typical 
features. 

Spores. The different forms of pink disease can be subdivided into 
sporing and non-sporing types. The cobweb and pustular forms are 
non-sporing, i.e. are infertile; they are merely mycelial aggregates in 
and on the bark and though they do not bear reproductive spores 
they may aid in the spread of the disease since dead bark scales 
carrying viable portions of the fungus frequently flake off. This is in 



CHAP. XIV 



PINK DISEASE 



273 



fact one of the least appreciated items in control, for it can be said 
with a fair measure of certainty that when control operations are 
being undertaken, insufficient attention is given to preventing small 
portions of diseased bark being distributed about the plantations. This 
commonly happens when diseased branches are carelessly pruned. 




FIG. 41 6. Pink disease. Severe attack of pink disease on main stem of young 
tree; showing numerous new shoots arising from dormant buds. 

The common pink incrustation is considered to be a spore pro- 
ducing type of C. salmonicolor ', but the exact systematic position of 
the fungus in Malaya needs further investigation. Authorities in other 
countries accept the basidial spore production in this fungus as 
normal for the genus Corticium, but in our investigations in 1914, this 
did not seem to meet the case. The writer has never had opportunity 
of looking into this question since that year, and the point requires 
investigation. Great difficulty was experienced in finding basidio- 



274 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

spores in the 1914 investigations, but this may only be a question of 
striking the correct developmental conditions, as is instanced in the 
case of Fomes lignosus, noted earlier in this book. In Malaya, the 
pink incrustation which carries basidiospores is noticeably thicker, 
has a more homogenous surface, and when dry, cracks into larger pieces 
than the sterile incrustation. The basidia, as seen in the investiga- 
tions mentioned above, are scattered and irregularly arranged. 

The Necator stage was formerly considered to be a separate fungus, 
and was named Necator decretus by Massee; it is now known to be a 
stage in the life-history of C. salmonicolor. 

The name N. decretus was given in 1897 to a fungus which was 
associated with a disease of coffee in Selangor. On rubber the Necator 
stage is found in the form of orange-red pustules, each pustule being 
a mass of spores which serve to propagate the disease. The individual 
spores are irregular in shape and are hyaline when seen individually 
under the microscope. Each spore-mass is waxy in consistency and it 
is probable that the spores become separated from one another only 
in wet weather, when they are washed apart. When a Necator pustule 
is about to be formed, the mycelium aggregates beneath the outer- 
most cortical layers, forming a kind of stroma, which by growth 
ruptures the tissues of the host. The whole of this stromatic mass 
becomes converted into spores by the separation of the cells one from 
another. The irregularity in size and shape of the spores is due to this 
peculiar method of spore formation. The dimensions of the spores are 
14-20/Ltx8-10/i. 

The first record of pink disease was probably the one made in 1897; 
when Massee misidentified it as due to Necator decretus. But at later 
dates the fungus has been designated Corticium calceum, Corticium 
javanicum and Corticium zimmermani\ as stated above, similar con- 
fusion existed in the West Indies, where the fungus was misidentified 
as C. lilacino-fuscum. 

The Necator spore form of the fungus is much more commonly 
formed than the basidial stage, and it is very probable that it takes a 
more active part than the latter in the dissemination of the disease. 

Spread. The chief agent of distribution is the wind, for diseased 
bark, carrying each or any of the various forms of the fungus, easily 
breaks into small flakes which are blown about. The pink incrustation 
and the pustular forms of the fungus retain their vitality for an ap- 
preciable length of time after being detached from a diseased tree. 
It is also possible that red ants and other insects which visit rubber 
trees might carry spores and infective material from diseased to 
healthy trees. 



CHAP, xiv PINK DISEASE 275 

Control of Pink Disease on Rubber Plantations. Experiments were 
carried out in Malaya in 1914 with a view to utilising Bordeaux 
Mixture in the control of pink disease. The conclusion drawn from 
this experiment was that, in this country, the difficulties attendant on 
spraying tall trees with power sprayers were too great and alternative 
methods had to be sought. Promising results were obtained by 
painting over the diseased surfaces with tar, and continuing the paint- 
ing two feet above and two feet below the external, visible symptoms. 
One month later the treated trees were examined again and, if pink 
disease symptoms were still evident, a second painting with tar was 
given. In later years, tar 80 per cent was mixed with 20 per cent crude 
oil, because it was claimed that the mixture could be applied more 
easily. These methods were generally adopted and if the monthly 
round was adhered to, results were satisfactory. 

The frequency of treatment, of course, depends on the amount of 
money available and during the last few years of necessary economies, 
estates have not paid sufficient attention to the monthly examination 
and treatment. Adequate control can be maintained only if this pro- 
gramme is carried out. The position has not improved at the time of 
writing, and the disease has assumed more serious proportions on 
some estates than would otherwise have been the case. 

Treatment by tar painting has defects owing to the variability in 
different shipments of tar, and when a "dud" consignment comes on 
the market, there are numerous complaints of serious damage due to 
bark burning. There is a very indifferent brand of tar being sold at 
the present date (1933), and during the last two months the en- 
quiries with reference to treatment of pink disease have trebled. The 
trouble is nearly always the same, bark burning following on tar 
treatment. Other complaints have been made, even with the best- 
known brands; some are difficult to apply while others do not adhere 
properly to the infected surfaces. Tar of an unknown composition 
is a dangerous substance in the hands of coolies, and if bark burning 
is to be prevented, it is advisable to use an asphalt um -kerosene mix- 
ture, which has a known composition and can be brought to any 
desired consistency. The question of cost again arises, but the mixture 
recommended is only slightly more expensive than tar, and if solar 
oil is used in place of kerosene, the mixture is then slightly cheaper. 

In a fair percentage of intractable cases the tar treatment has to be 
supplemented by pruning away diseased branches and destroying 
them by fire. Absolute reliance cannot be placed on any method of 
painting and as Fetch suggested in his 1921 edition, a combination 
of painting and pruning would probably be the better course. Experi- 



276 DISEASES AND PESTS OF THE RUBBER TREE PART in 

ence has proved this to be the case, but cutting-out must be carefully 
performed. As little as possible should be done in wet weather be- 
cause of the great difficulty attached to the adequate disposal of 
diseased tissues. A judicious combination of pruning during dry 
weather and painting only during wet weather has been found to be 
the best plan in Malaya. The following schedule is recommended at 
the present date: 

(1) During wet weather periods, a monthly round must be kept 
up. Diseased bark areas must be painted over with the asphaltum- 
kerosene mixture or asphaltum-solar oil mixture recommended 
below. Pruning to be suspended as far as possible. * 

(2) During dry weather periods the disease gang should be in- 
creased for the time being; so that a fortnightly or three -weekly 
round can be worked to. The branches which show symptoms of pink 
disease should have the diseased areas painted over with a strong 
antiseptic solution; a 5 per cent solution of Izal is recommended. 
The branch should then be cut out and destroyed by fire as quickly as 
possible. A strong antiseptic solution should be painted over the 
diseased areas in all cases before pruning in order to kill all external 
parts of the fungus, so that even if small flakes of diseased bark are 
allowed to blow about as a result of careless work, they will be harm- 
less. This is a most important point which is often neglected. 

It will no doubt be realised that modifications of the above treat- 
ment will have to be considered for individual cases, more especially 
if the main stem or large branches are involved, when cutting-out 
would result in serious loss of leaf canopy. But this must be left to the 
discretion of the planters who are directing the control work. 

The mixture which is now generally recommended for painting 
treatment is as follows: 

Asphaltum, (DX) brand . . . .40 Ibs. 

Kerosene or Solar Oil . . . .4 gallons 

Brunolinum, Noxo or Solignum . . 2 pints 

The method of mixing is detailed on page 442, where attention is 
drawn to the various precautions which must be observed. 

Good results have also been obtained in control of pink disease 
by using a 20 per cent solution of Agrisol or Brunolinum Plantarium 
for painting over diseased areas. This treatment is simpler as there is 
no complicated mixing to be done, but it is more expensive. 

Butler reports that Bordeaux Mixture has been used very suc- 
cessfully to prevent new infections in young rubber trees. It is certain 
the attack is due to spores, whether from jungle trees or from dis- 



CHAP, xiv DIE-BACK 277 

eased rubber trees. Hence, if the parts of the tree most susceptible 
to attack, such as the forks of the branches, can be coated with 
Bordeaux Mixture before the onset of a rainy period, the spores lodg- 
ing in these places would be killed. If the mixture can be made to 
stick on a tree during heavy rains, considerable advantages would be 
gained. This was done by the addition of resin adhesive to a Bordeaux 
Mixture of 6 Ibs. copper sulphate, 4 Ibs. quicklime and 45 gallons of 
water. The mixture was kept well stirred and applied with a brush 
round the forks and for a foot or two down the stem and up the 
branches. The result was a reduction of the disease by 50 to 75 per 
cent. Some of the trees had three applications, some two, some only 
one. Such, in broad outline, are the results obtained in South India 
but, as the methods described have proved satisfactory in Malaya, 
no work has been carried out on these lines by the writer. Bancroft, 
in 1912-13, however, reports a case on one Malayan estate where 
spraying with Bordeaux Mixture on an area carrying trees five to six 
years old was undertaken. The area sprayed covered 33 acres and the 
spraying was confined to the forks and branches of the trees for the 
reason explained above. The cost of spraying materials and labour 
was 1-05 dollars per acre, to which the cost of the machine, 150 dollars, 
must be added. The results of the treatment were not recorded. 

DIE-BACK IN RUBBER TREES 
Caused by Diplodia sp. 

This disease is commonly known in Malaya as " Diplodia Die- 
back", and was recognised very early in the history of the rubber 
plantations in this country. It was specially investigated by Bancroft 
in 1911. It is found in all the rubber-growing countries of the Middle 
East. 

Though the die-back disease has been under scrutiny for such a 
long period, much confusion still surrounds the life-history of the 
causal fungus, and there is still doubt regarding the exact status of 
the fungus as a parasite on H . brasiliensis . 

Spore Forms of the Carnal Diplodia sp. In 1911 Bancroft con- 
cluded from his investigations that three different spore forms are 
included in the life-history of the fungus; firstly, a Diplodia sp. which 
appears to be the form destined for rapid reproduction and the para- 
sitic form; secondly, a Cytospora sp. which develops on the plant some 
time after it has died, and thirdly, an ascigerous fructification, which 
he named Thyridaria tarda\ the latter form appears later and can 
infect the living plant with subsequent production of the Diplodia 



278 DISEASES AND PESTS OF THE RUBBER TREE PART in 

form. No supporting observations for these views were forthcoming 
until 1929, when Tunstall, working on die-back of Tea in India, found 
a few specimens of an ascigerous fungus associated with a die -back 
disease of tea bushes. According to Tunstall the fructifications found 
agreed with the description given by Bancroft for Thyridaria tar da, 
Bane. Ascospores from these fructifications were germinated and 
grown in pure culture and produced pycnidia, typical of Diplodia. In 
a later paragraph, Tunstall says, "This form (Thyridaria) has not been 
produced in culture, but immature pycnidia, typical of the Diplodia 
fungus, have been obtained from cultures of the ascospores obtained 
from two specimens". The supporting evidence obtained by Tunstall 
cannot be considered entirely satisfactory, for an element of doubt 
must still remain until mature pycnidia are produced in pure culture. 
Another point that may be noted is that Tunstall mentions only the 
Diplodia and Thyridaria stages of the fungus, while the Cytospora 
stage described by Bancroft is not referred to. (Since writing the 
above in 1933, information has been obtained which suggests that 
Tunstall's observations must be treated with reserve, and it will 
therefore avoid confusion if the Hevea fungus is still referred to as 
the Diplodia sp.) This is another example of the difficulties en- 
countered in tracing the sequence of spore forms and getting exact 
systematic names, even for the most common disease-causing fungi 
in the Middle East. 

Inoculation Experiments. During the last six to eight years many 
interesting observations have been made which indicate that this 
fungus is a selective parasite and that its destructive work can only 
be initiated under certain conditions. If these conditions are pro- 
vided, infection takes place and when the conditions favour the 
growth of the fungus, i.e. if the attacked trees are not too vigorous, 
it spreads down the branches and stems in the characteristic way 
conveyed in the term "Die-back". The Diplodia die-back fungus, 
while definitely exhibiting parasitic tendencies, can easily maintain 
a saprophytic existence on various kinds of rotting materials. In 
fact it is so common as a saprophyte on many different kinds of plant 
material, that it would be impossible to suggest any feasible cleaning- 
up measures if the fungus caused more serious damage than it does. 

Bancroft reports successful inoculations made through wounds on 
seedling plants five to twelve months old. Efforts to inoculate un- 
wounded seedlings were unsuccessful. Further inoculations were 
made, but beyond endeavouring to inoculate the tapping surface 
of trees seven to nine years old, he did not carry out experiments on 
mature trees. 



CHAP, xiv DIE-BACK 279 

Ward, in 1926, working under the writer's direction, performed 
some inoculation experiments which indicated the precise nature of 
the conditions governing infection. It was shown fairly conclusively 
that the Diplodia fungus responsible for producing die-back symptoms 
in rubber trees will readily infect a tree only if localised areas of 
cortical tissue have been sufficiently heated or scorched. The fungus 
readily penetrates the scorched tissue and enters the wood, through 
which it makes progress both upwards and downwards. 

This species of Diplodia does not appear to be an ordinary wound 
parasite as is commonly believed to be the case, but is rather a special 
type of parasite which rapidly follows any damage done by scorching. 
In Malaya, the "die-back" fungus is always prominent in the follow- 
ing affections: 

(a) Lightning damage, both on old and young trees. 

(/>) Sun-scorch of exposed lateral roots. 

(c) Seedlings affected by excessive ground heat at the collar. 

(d) Die-back in large snags after the budding operation is done. 

(e) Spear-head wounds at junction of scion and stock. 

A description of the affections listed above will be given in a fol- 
lowing chapter. 

The evidence obtained in Malaya is strongly supported by the 
description of "die-back" attacks given in other works of reference, 
and in the writer's opinion there seems little doubt that the Diplodia 
die-back fungus is practically harmless to vigorous rubber trees if 
scorching of the cortical tissues is prevented. 

Symptoms. The progress of the fungus is marked by a typical 
ashy-grey discoloration of the wood tissues. If a section of the 
diseased wood tissue is studied microscopically, dark-brown hyphae 
can be seen running through all the tissue elements. But the hyphae 
extend beyond the limits of the discoloured tissue for a distance of 
many inches, for they are hyaline at first and only later take on 
the distinctive colour (Fig. 42). 

Fetch describes the symptoms of die-back as follows: 

In the typical case described above, B. theobromae enters the stem at 
the top through a dead green shoot. The shoot may have died from one or 
many causes, but in general, the fungus appears to enter through shoots 
which have been killed by Oloeosporium alborubrum or Phyllosticta rami- 
cola. The fungus then grows down the stem, both in the wood and the bark 
but rather more rapidly in the former, and as it descends to the level of 
the branches it kills them, either by attacking them or by cutting off the 
supply of water. The wood is blackened and the cambium, with the inner- 
most layers of the cortex, becomes a black film on the surface of the wood . 



DREE PART in 



280 DISEASES AND PESTS OF 

Further, he states: 
The trees are generally attacked in groups, sometimes of about a dozen; 



one or two of these are usually killed but the others are generally in the 
early stages of the disease and can be saved by pruning off the dead tops. 

This last quotation is an exact description for lightning damage 
on young rubber trees as seen in Malaya and dozens of cases have been 




FIG. 42. Section of woody tissue of rubber branch, showing thorn permeated with 
the dark-coloured hyphae characteristic of the Diplodia sp. causing die-back 
disease. 

inspected this year (1933), which has been remarkable for the large 
amount of damage done by lightning in many different districts. 
The fungi mentioned above, 0. alborubrum and P. ramicola, are not 
prominent, although one case recently examined showed Gloeo- 
sporium heveae, Fetch, in abundance. 

The only form of die-back which can be described as typical in 
Malaya is that found on steeply sloping, hilly areas which have 



CHAP, xiv DIE-BACK 281 

suffered badly from erosion, or on rubber-growing areas which have 
been neglected in other ways. This type of die -back is of some im- 
portance as there is a considerable acreage of such rubber scattered 
throughout the country. In 1926 an enquiry was made to ascertain 
whether the Diplodia fungus was the most prominent one to be seen in 
this particular type of die-back. Sun-scorch was suspected since the 
trees had their branches almost devoid of leaves, and overheating of 
the bare branches by the sun, could not be avoided. A random sample 
of 105 branches of H. brasiliensis, suffering from die-back was 
gathered; these were examined by splitting them open, and the re- 
sults obtained are given below: 

Typical Diplodia die-back cases . . . .11 

Diplodia sp. present along with other fungi or insects 22 
No Diplodia present . . . . .72 

The fructifications of many fungi are found on such die-back 
branches and these are included in the list of fungi which is published 
in this work. The collections were made by Weir and Baker. One of 
the fungi found most frequently on branches or woody tissue suffer- 
ing from overheating, is Polystictus hirsutus, Fr. 

Fructifications. The following description of the Diplodia and 
Thyridaria fructifications is taken from Tunstall's paper: 

The common (Diplodia) type of fructification is the black, spherical 
bodies (pycnidia), either half embedded in the bark or produced in clusters, 
in a stroma on the exterior of the bark. The pycnidia are globose or sub- 
globose, ostiolate and dark-brown to black in colour. In some cases, the 
pycnidia are covered with hairs. The pycnospores are oval or ovoid, densely 
granular, often very thick- walled. They are at first hyaline and continuous 
but afterwards they take on a yellowish -brown tinge and ultimately 
become dark- brown in colour and uniseptate. The dark- brown and uni- 
septate spores have longitudinal striations. They measure 29-5/z by 
14-75/x. The spores are borne on short conidiophores and are liberated in 
threads through the ostiole of the pycnidium. These threads are at first 
white but afterwards become black. Paraphyses are present. 

The only comment necessary is that in the above description, a 
printer's error appears to have escaped notice. The 14-75/z given for 
the spore measurement should probably be 14-15/ut, which figure 
is approximately correct. The figures given by Tunstall, with this 
correction, agree well when compared with Bancroft's figures, given 
many years earlier. 

The other form of fructification, (Thyridaria form. A. S.) the perfect 
stage of the fungus, is found on the stems and exposed portion of the root 



282 DISEASES AND PESTS OF THE RUBBER TRKK I'.MIT 

(of the tea bush. A. S.). It has so far been found on four occasions. The 
perithecia are immersed with the mouth projecting. The asci are cyliridric 
clavate, either sessile, or with a very short stalk and contain 8 spores. 
The ascospores are arranged in irregular rows, they are oblong, triseptate, 
slightly constricted at the septa, and of a dark-brown colour. The asci 
measure 115-150/x x 18-26/z, the ascospores measure 26-28-5/Lt x 64-9/x, 
and the paraphyses are 130 to 450/i in length. 

In a preceding paragraph it is remarked that Tunstall does not 
mention the Cytospora stage recorded by Bancroft. He points out, 
however, that sometimes the black spots on the bark, which mark 




FIG. 43. Section showing Diplodia pycn'utia produced on stroma, 
and containing spores. 

the position of the pycnidia, are fringed with a white, chalky powder, 
and that this is commonly the case when the bushes are growing in 
a heavy, stiff clay soil. This white substance, he states, is the my- 
celium and chains of spores of another fungus, possibly parasitic 
on Thyridaria tarda. Petch makes a similar record as occurring on the 
tea-bush in Ceylon. He says the white fringe which appears round 
small clumps of hyphae or extruded spores on the roots consists of 
masses of minute, globose, hyaline spores, 1/x in diameter with hya- 
line hyphae 1 to 2/x in diameter, on which conidia are borne laterally 
or on finer lateral branches. Whether this is a stage of the Diplodia sp. 
or a hyphomycete parasitic on the latter, has not been determined. 
For the purpose of completeness, Bancroft's description of the 
Cytospora sp. recorded by him is given: 



CHAP, xiv DIE-BACK 283 

Cytospora. Pycnidiis submembranaceis, atris, ovatis, stromate atro 
ruguloso immersis, ostiolo prominulo (30 microns la to), donatis, 200- 
250x180-200 microns; sterigmatibus copiosis, 22-24x3 microns; sporis 
ellipticis, hyalinis, 3-4 x 1-5-2/z. 

Reference to a recent paper by Shear must now be made. He 
reports that Saccardo, in his Sylloge Fungorum, gives Diplodia as the 
pycnidial form of species of Cucurbitaria, Massaria, Otthia, Mel- 
anomma, Pleospora, Tkyridaria and Gibberidia, and remarks this 
is not a complete list and probably other genera could be given. 
He further states that his studies show that at least such highly de- 
veloped forms as those usually referred to Diplodia may occur in 
such widely separated genera as Tryblidiella, Physalospora and 
Cucurbitaria^ and that parallelism of this sort evidently occurs in 
other cases. The mention of the genus Tryblidiella is interesting to 
investigators in Malaya, for the writer has occasionally found a 
species of this genus on dead branches, while Ridley records Try- 
blidiella rufula, Sacc., being found on dead branches in Singapore. 
While some uncertainty exists as to whether the records from Malaya 
refer to dead branches of rubber trees, there is no doubt as to Try- 
blidiella leprieurii (Mont.), Sacc., occurring as a saprophyte on dead 
branches of Hevea, in Ceylon. This appears to afford a convenient 
starting-point for a further investigation in respect of the Diplodia 
complex. 

Distribution. The fungus responsible for Diplodia die-back is 
very widely distributed and has been recorded from almost every 
country in the tropics. Fetch remarks that owing to the incomplete- 
ness of description and the highly variable nature of the fungus, it has 
received an extraordinarily large number of names. A list of synonyms 
is appended: 

Botryodiplodia theobromae, Pat. 
MacropJwma vestita, Prill, and Del. 
Diplodia cacaoicola. P. Henn. 
iMsiodiplodia nigra, Appel and Laubert 
Lasiodiplodia theobromae, Griff, and Maubl. 
Botryodiplodia elaMiceae, Petch 
Diplodia rapax, Massee 
Chaetodiplodia grisea, Petch 

Treatment. The only treatment which can be recommended is to 
cut out and burn the diseased tissues. The cut must be made through 
healthy tissue, nine to twelve inches beyond the limits of obviously 
diseased tissue. In young plants, one to three years old, suffering 



284 DISEASES AND PESTS OF THE RUBBER TREE PART in 

from lightning damage, the limit of diseased tissue is usually indi- 
cated by the shooting of lateral buds and the trees can be pruned or 
pollarded at the level indicated by these buds just as in the case of 
treatment of pink disease on young trees, where the same feature is 
commonly met with. 

STEM USTULINA 

The root diseases caused by U. zonata first gained prominence in 
Malaya in 1914-16, and a full description of symptoms, growth and 
the structure of the fungus is given in the section devoted to root 
diseases. In those days it was noted that this fungus could function 
as a wound parasite in any part of the tree system, particular atten- 
tion being called to a case of "stag's-head" in a rubber tree, in which 
fructifications of U. zonata were found developing luxuriously on 
small wood branches not more than half an inch in diameter. Stag's- 
head in rubber trees is usually attributed to an attack of the common 
die-back fungus, Botryodiplodia theobromae. While the position was 
clearly established in 1917, South, in 1927, directed attention to the 
increased prevalence of U. zonata on the stems and main branches of 
rubber trees on several of the older rubber estates, especially in the 
coastal districts of Selangor. 

In such cases as the above, where the stem or main branches arc 
affected, the attack usually commences at a spot where a wounded 
surface is present, owing either to the careless pruning of a lateral 
branch, to damage caused by wind, or by an accident such as the 
falling of one tree against another when thinning-out is in progress. 

Stem attacks by this fungus in Malaya, may (a) follow on attacks 
by boring beetles, or (b) enter the stem tissues through large wounds 
caused by the breaking of the main branches which results in the 
exposure of a large, rough wood surface. Collar attacks might come 
under the category of stem attacks, for there is little doubt that the 
starting-point of many collar attacks is behind the pad of old, oxi- 
dised rubber which commonly accumulates at the base of old trees. 

Boring Beetles and U. zonata. The association of U. zonata with 
attacks by boring beetles is dealt with later, where it is pointed 
out that the food of the larvae is a fungus growing upon the walls 
of the burrows of the adult beetles, and that the fungus develops 
from spores carried in the stomach of the female. In 1916 the 
writer isolated U. zonata from boreholes made by these insects, and 
attention was directed to fructifications found in the conidial stage, 
the upper flat surfaces of which showed undoubted insect tracings. 
These observations are of some interest as indicating the possibility 



CHAP, xiv STEM USTULINA 285 

of U. zonata being a fungus commonly carried by the so-called 
"ambrosia" beetles. 

Method of Attack. In the writer's experience, the favourite seat 
of infection is a large, uneven surface of exposed woody tissue such 
as a wound on a main stem where a large branch is broken away by 
wind. But Fetch points out that, in Ceylon, it is very noticeable that 
attacks by Ustulina usually occur on diseased or damaged areas on 
which the previously damaged bark has remained more or less in situ, 
i.e. has not fallen off and exposed the wood. This is very probable, 
for as pointed out above, a common starting-point of an attack at the 
collar is beneath or in close proximity to pads of coagulated rubber 
which have accumulated at the base of the stem. The cortical layers 
covered by these pads of rubber cannot function normally, and owing 
to their unhealthy condition, probably form very suitable places for 
infection by U. zonata. 

When stem infection takes place through a wound formed by the 
breaking of a large branch, there is after a time a copious exudation 
of latex which coagulates on the bark around and beneath the wound. 
These large pads of coagulated latex are the most prominent feature 
in this type of infection, when conditions favour the rapid growth and 
development of the fungus. The fructifications of the fungus often 
develop prolific-ally in stern attacks; cases have been met with where 
the fructifications extended in a continuous sheet for a distance of 
over two feet, the plate being about nine inches to fourteen inches 
wide (Fig. 9c). 

When large branches are attacked they should be cut out as early 
as possible. The first cuts should always be made on the under side 
close to the trunk or larger branch from which it is being removed 
and should penetrate to about one-third of its thickness. The branch 
should then be cut through from the upper side at a point a few 
inches further out than the cut on the under-side. As a heavy branch 
nearly always falls before it is cut completely through, this method 
prevents it from tearing a strip of bark and wood out of the trunk or 
larger branch to which it was attached. No "hat pegs" should be left, 
but all branches or stubs of large branches cut off in the manner de- 
scribed above should be removed at their junction with another 
branch or with the main trunk, and the wounded surface should be 
smoothed with a sharp instrument and be thoroughly tarred or 
covered with an ashphaltum mixture at once. Further dressings of the 
exposed surface with these preparations may be given at intervals. 
Wounds caused by winds or accidents should also be smoothed off 
with a sharp instrument and care should be taken to leave no hollows 



286 DISEASES AND PESTS OF THE RUBBER TREE PART in 

in which water can collect. Such wounds should also be dressed 
at intervals with the wound covers. 



WHITE THREAD BLIGHT 

White Thread Blight is of common occurrence on cultivated trees 
other than rubber. As the name implies, the external appearance of 
the fungus is very similar to strands of coarse thread, white in colour, 
running over and closely adhering to the surface of attacked 
branches, ascending the leaf-stalks and frilling out to finer threads 
on the surfaces of the leaves, which become as a result closely matted 
together. 

These white threads are mycelial or rhizomorphic strands, and they 
represent the vegetative phase of the fungus. The mycelial strands 
vary considerably in size and may run long distances over the 
branches. When the fungus reaches the smaller twigs and leaves, 
the latter die as they become matted together, and the mass of dead 
leaves and twigs stands out prominently. 

Brooks states that the white thread blight is very variable in 
character and it is possible that more than one species of fungus is 
involved. Largely because the fungus has never caused any serious 
damage to rubber trees in Malaya, no critical work on this particular 
line has been accomplished, so the position has not yet been clarified 
up to date. 

Bancroft described the white thread blight of Para rubber and 
Camphor in 1911; since that time only one record of a fruiting stage 
has been made. A notable feature of most thread blights is that fruc- 
tifications are but rarely produced and the single collection in Malaya 
was made by Richards, who forwarded it to England for identifica- 
tion. It was named Cyphella heveae by Massee. Further fructifications 
should be examined before the name is considered finally settled. 

In Northern India, tea-bushes are attacked by a thread blight, 
while it has been reported on rubber from all Eastern rubber -growing 
countries. 

The thread blight growing on rubber trees is spread through the 
plantations by diseased leaves carrying portions of the mycelium 
being blown about and coming to rest amongst the branches or 
foliage of healthy trees. Fetch states that cases can often be found 
where a dead leaf, or the remains of it, are seen adhering to the stem 
at the point where the thread starts. If trees are so closely planted 
that their leaves are in contact, it is obvious that the fungus could 
very easily pass from a diseased to a healthy tree. It is in such over- 



CHAP, xiv MINOR STEM DISEASES 287 

crowded situations that the fungus could cause a certain amount of 
damage. A case was recently examined in which trees, two years of 
age, were covered with a thread-blight fungus at the base, extending 
from ground-level up the stem to about six to nine inches in height. 
In this instance the threads were more silky than usual, and the 
fungus formed a prominent white, silky layer over the whole circum- 
ference of the stem. A close examination was necessary to make cer- 
tain the strands were not those of Forms lignosus. 

Treatment. Cut out and burn diseased leaves and branches. 



HORSE-HAIR BLIGHT 
Caused by Marasmius equicrinis, Mull. 

This fungus is only rarely met with in Malaya. It takes the form 
of rnycelial cords, black in colour, which resemble black horse-hair in 
appearance. The name, horse-hair blight, includes the mycelia of 
many different species of fungi, in the same manner as thread blight. 
The mycelial cords found on rubber trees are round, smooth and more 
or less polished. They do not adhere closely to the branch along their 
whole length as described for the mycelial cords of white thread 
blight, but are attached only at certain points by small brown pads of 
mycelium. It does not always pass from the branch to the leaves via 
the leafstalk; it may pass across from stem to leaf, or from one branch 
to another by means of long, free cords, and large numbers of twigs 
and leaves may become involved. 

Fetch states that this fungus is common on tea-bushes in Ceylon, 
and is frequently found on rubber trees interplanted with tea, more 
especially at the base of the stem up to a height of one foot from the 
ground. It is not parasitic, but lives on the dead brown bark scales. 

The writer has not found the fructifications on rubber trees in 
Malaya, but Fetch states that it is a small, mushroom-like fungus 
named Marasmius equicrinis, and that it is rare on the mycelium 
which overruns the higher parts of a plant but is frequently present 
on the black cords at the base of rubber trees. It is more common 
on rotting Herea fruits which have fallen to the ground, in Malaya. 

RING ROT 

This curious disease was first described by Keuchenius, in Sumatra. 
In Malaya, the writer has seen only a few cases. The affection is 
characterised by the drying-up and peeling-off of concentric black 
zones or rings (Fig. 44). It is reported that in the dry season the 



288 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

disease is usually dormant and will recur when the rainy season sets 
in. When in the active state, if the outer cork layer is carefully re- 
moved, the bark shows a sepia-coloured discoloration outside the 
ring-like pattern. The discoloration is only superficial and has not 
been found to reach the cambium. It may reach a depth of about half 




FIG. 44. Tree affected by ring-rot. External scaly bark scraped away to show 
typical concentric rings. 

the bark thickness and some latex containing bark may be spoiled 
thereby. 

The causal agent of the disease has not yet been determined. If 
affected trees are found, the discoloured bark should be scraped away. 

MISTLETOES (LORANTHUS SPP.) ON RUBBER TREES 

The semi -parasitic plants of the mistletoe type are well represented 
in Malaya, and are commonly seen growing on all types of dicoty- 
ledonous plants. Only a few species are recorded from rubber trees. 



CHAP, xiv MINOR STEM DISEASES 289 

Occurrence. In 1911 Bateson recorded the occurrence of a species 
of Loranthus growing on rubber trees in Pahang, whilst in 1914 
Brooks gave an account of two species of Loranthus attacking rubber 
trees in Negri Sembilan. The latter investigator mentions that one 
of these mistletoe species was also found growing on a common 
melastomaceous plant, presumably Melastoma malabathricum, L. 
( =Kedudok.). In 1924 Sands described the five species of mistletoe 
which are the chief pests of cultivated trees in Malaya. These are: 

(1) Loranthus ferrugineus, Roxb. 

(2) Loranthus pentandrus, L. 

(3) Loranthus grandifrons, King 

(4) Loranthus pentapetalus , Roxb. 

(5) Elytranthe globosa, G. Don. 

Of the above list, (2) and (5) are commonly found on rubber trees 
in Malaya; (1) rarely so, while (3) and (4) have not been recorded 
as growing on rubber trees up to date. Recently, two new records 
of mistletoes growing on rubber trees have been made: 

(6) Loranthus crassipetalus, King 

(7) Loranthus casuarineae, Ridl. 

L. crassipetalus is a somewhat uncommon species, while L. casua- 
rineae is usually confined to Casuarina trees, which are commonly 
grown in Malaya. 

Mistletoes are green-leaved, evergreen, shrubby plants with a 
special seed mechanism which enables them to become attached and 
to grow on woody, dicotyledonous trees; they are seldom found on 
monocotyledonous trees such as bamboos and palms. They are 
parasitic in that they are dependent on the host plant for the pro- 
vision of water and nutrients from the soil, but they are not com- 
pletely parasitic since they possess green leaves, and are able to per- 
form their own function of converting water and carbon dioxide into 
organic food materials, i.e. carbohydrates, by means of the energy 
derived from light. Owing to the fact that they can manufacture their 
own carbohydrates they do not make such serious demands on the 
host plant as would otherwise be the case. Hence these semi-para- 
sitic plants do not usually destroy their hosts rapidly unless the 
latter are in extremely poor condition, when the infestation may be a 
very heavy one. 

The sticky fruits are one-seeded, succulent berries usually bright 
coloured or white, with a fleshy exterior and a mucilaginous interior. 
The seed has a very sticky, gelatinous coat, which enables it to 

TT 



290 DISEASES AND PESTS OF THE RUBBER TREE PAKT in 

adhere closely to any surface with which it comes in contact. This 
gelatinous covering can absorb water from rain, mist or dew, so that 
the seed does not perish rapidly under unfavourable conditions. 
Further, it is the only means by which the seed, on germination, 
obtains the water necessary for growth until the haustorium or 
sucker has penetrated into the water- conducting tissues of the host 
plant. 

It is practically certain that birds which feed on the berries are the 
chief means by which the seed is disseminated. Observations in other 
countries have shown that birds, after feeding on the pulp of the 
berries, wipe their beaks against the branches of trees in order to 
rid them of the sticky seed, which is distasteful ;<they may also void 
on to branches with their excrement any seed swallowed. Other 
possible agencies for dispersal are (a) heavy rain which beats down 
the fruit, (6) high winds and the natural fall of ripe berries from 
higher to lower levels of the host trees. 

Method of Attack. The seed on germination puts out a short, 
stout cylindrical root-like body, the hypocotyl, which, on coming 
into contact with the bark of the host plant, swells out at its free end 
into a disc and forms what is known as a holdfast. From the central 
or lower portion of this the haustorium or sucker develops, which is 
capable of penetrating to a considerable depth into the tissues of the 
host by means of solvent ferments and the pressure resulting from 
growth. After the supply of water and food has been made secure by 
the haustorium, the young shoot develops rapidly. 

The haustorium in forcing its way through the bark destroys this 
during its passage, and eventually penetrates the wodd and forms ( a 
close organic connection between the wood vessels of the host so that 
water and raw food materials can be readily obtained. 

As growth proceeds, a rounded, swollen mass of tissue forms over 
the place where the holdfast was attached to the host plant. The 
swellings may be small but are sometimes very large. In the species 
L. pentrandus, occurring on rubber trees, large masses of hyper- 
trophied tissue occur at points where the primary and secondary 
haustoria enter the host and they become knobby and warty with age 
(Fig. 45 6); in E. globosa, the primary and secondary swellings where 
haustoria enter the host are small or absent, and in L. ferrugineus, 
the swollen masses are small in size. 

Secondary haustoria are mentioned above. In all species of Lor- 
anthus and Elytranihe, secondary branches arise at the original point 
of infection, also secondary branching roots, or runners, which travel 
for considerable distances along and around the infested branch in 



CHAP. XIV 



MINOR STEM DISEASES 



291 



different directions (Fig. 45 a). At frequent intervals, haustoria are 
formed along the side of the root-runner nearest the branch; on large 
branches they are formed about every 1| inches or more, on smaller 
twigs about every J of an inch, and they enter the host-branch almost 




. 45. () 
ners" of 
formed 
the host 



General view of mistletoe on branch of rubber tree. Note the "run- 
the mistletoe plant. (6) Showing large masses of hypertrophiod tissue 
on rubber branches where haustoria of Loranthus pentrandus enter 



directly below the place of formation. In this way, a tree deficient 
in vitality may become heavily infested from a single seed. 

The haustoria continue to expand and multiply as growth pro- 
ceeds. Eventually, the end of the branch of the host is killed as a 
result of the continued withdrawal of water and inorganic food 
materials by the parasite. In cases where the attack is a very heavy 
one, the whole tree may be so weakened that it dies outright. 



292 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

Sands reports that certain of the local species of mistletoe can 
parasitise each other; for example, L. ferrugineus has been found 
growing on L. pentandrus, E. globosa, E. barnesii and Viscum 
articulatum, while V. articulatum has been frequently observed on 
L. pentandrus, L. ferrugineus, E. globosa and E. barnesii. But the 
most unusual case was one in which a durian tree (Durio zibethinus) 
was attacked by E. barnesii', on this mistletoe V. articulatum had 
attached itself, while L. ferrugineus was growing on V. articulatum. 

Generally speaking, the parasites are found on the higher and outer 
branches of the trees they attack; that is, in places where they obtain 
plenty of light. They do not, as a rule, thrive under dense shade, 
hence cultivated trees which are in poor condition suffer more 
severely than those in good health. Vigorous mistletoe attacks on 
rubber trees in Malaya have been found only in neglected fields of 
rubber. Brook's specimens, obtained in 1914, were reported as having 
been obtained from neglected rubber fields. In recent years, rubber 
estates on the east coast of Malaya, which were severely affected by 
the unprecedented floods of 1926, have been attacked by these semi- 
parasitic growths and they are quite commonly found on estates in 
Kelantan. 

Treatment. Branches supporting the semi-parasitic bushes should 
be cut away, and an attempt should be made to reinvigorate the 
trees by improving soil conditions. It is obvious that simply cutting 
away diseased branches from debilitated trees will not improve the 
position to any great extent, unless due attention is given to the 
necessity of increasing the vigour of the plants so that they may 
withstand further reinfection. 



REFERENCES TO LITERATURE ON STEM DISEASES 
PINK DISEASE 

MASSEE, G., 1898. "Fungi Exotici", Kew Butt. p. 119. 

RANT, A., 1912. "t)ber die Djamoer-oepas Krankheit, und iiber das Corticium 

javanicum" , Zimm. Bull, de Jard. de Buitenzorg, Series 2, No. 4. 
BANCROFT, C. K., 1912-13. "Miscellaneous Botanical Notes", Agr. Bull. 

F.M.S. vol. i. p. 218. 
BROOKS, F. T., and SHARPLES, A., 1914. "Pink Disease", Bull. No. 21, Dept. 

of Agr. F.M.S., and Anns, of App. Biol. t 1915-16, vol. ii. 
BROOKS, F. T., 1916. "Observations on some Diseases of Plantation Rubber in 

Malaya", Anns, of App. Biol. vol. ii. No. 4. 
BAKER, C. F., 1919. "Hevea versus Fungi", Qards. Bull. vol. ii. No. 4, p. 109. 



CHAP, xiv MAJOR AND MINOR STEM DISEASES 293 

DIE -BACK 

BANCROFT, C. K., 1911. "The Die-back Fungus of Para Rubber and of Cacao 

(Thyridaria tarda, n.s.)", Bull. No. 9, Dept. of Agr. F.M.S. 
BANCROFT, C. K., 1911. "The Die-back Disease of Para Rubber, and a Note 

on the Leaf Diseases of Para Rubber", Bull. No. 14, Dept. of Agr. F.M.S. 
CHIPP, F. T., 1921. "A List of the Fungi of the Malay Peninsula", Gard. Bull. 

S.S. vol. ii. Nos. 9, 10 and 11. 
WARD, F. S., 1926. "Inoculation Experiments in relation to 'Sun-scorch' on 

exposed Lateral Roots of Hevea brasiliensis" , Mai. Agr. Jour. vol. xiv. 

p. 286. 
WEIR, J. R., 1928. Annual Report of Pathological Division (including initial 

period), p. 70. 
TUNSTALL, A. C., 1929. "Vegetable Parasites of the Tea Plant (cont.): Blights 

on the Root", Quar. Jour. Ind. Tea Ass. Part I. p. 68. 
SHEAR, C. L., 1933. "Life History of Tryblidiella Species", Mycologia, vol. 25, 

No. 4. 

STEM USTULTNA 

SOUTH, F. W., 1927. "Ustulina zonata, Sacc. a Warning Note", Mai. Agr. 
Jour. vol. xv. p. 446. 

WHITE THREAD BLIGHT 

BANCROFT, C. K., 1911. "A Thread Blight on Para Rubber and Camphor", 

Agr. Bull. S.S. c- F.M.S. vol. x. 
RICHARDS, R. M., 1914. Mycologists* Report for 1912-13, Malaya Peninsula 

Agr. Ass. 
BROOKS, F. T., 1916. "Observations on some Diseases of Plantation Rubber in 

Malaya", Anns, of A pp. Biol. vol. ii. No. 4. 

MISTLETOES 

BATKSON, E., 1911. "Loranthus as a Parasite on Hevea brasiliensis", Agr. Bull. 

S.S. <fc F.M.S. 
BROOKS, F. T., 1914. "Parasitic Flowering Plants on Rubber Trees", Agr. Bull. 

F.M.S. vol. ii. No. 7, p. 165. 
BROOKS, F. T., 1914. "Species of Loranthus on Rubber Trees", Agr. Bull. 

F.M.S. vol. iii. No. 1, p. 7. 
SANDS, W. N., 1924. "Mistletoes attacking Cultivated Trees in Malaya", 

Mai. Agr. Jour. vol. xii. No. 3, p. 64. 



SECTION 4 
LEAF DISEASES 

CHAPTER XV 

MAJOR AND MINOR LEAF DISEASES 

Loaf -fall caused by Oidium heveae South American Leaf Disease; Abnormal Leaf- 
fall in Burma, South India and Ceylon; Gloeosporium spp. Bird's-eye Spot 
Shot-hole Leaf Disease; Rim Blights Loaf Spotting Sooty Moulds Diseases 
of Green Twigs Phyllosticta ramicola and Gloeosporium alborubrum. 

INTRODUCTION 

NUMEROUS fungi have been reported as causing a certain amount of 
damage on the leaves of both seedling and mature rubber trees, 
but only three serious leaf diseases have occurred throughout the 
world. These three diseases are known as: 

(a) South American Leaf Disease, caused by Melanopsammopsis 
ulei (Henn.), Stahel. 

(b) Leaf-fall caused by Phytophtkora meadii, McRae. 

(c) Leaf-fall caused by Oidium heveae, Steinmann. 

The South American leaf disease is confined to the Western Tropics, 
having been reported from Brazil, Peru, British Guiana, Surinam an4 
Trinidad. It has not yet been reported from the rubber plantations 
of the Middle East. 

The abnormal leaf- fall, (6) above, has been reported from Ceylon, 
South India, Burma and Java, according to Fetch; Steinmann says, 
however, that leaf-fall caused by attacks of P. meadii have not been 
found in Java; neither has it been reported from Malaya, up to date. 

Oidium leaf-fall has been reported from Ceylon, Malaya, Java 
and Sumatra, but not from the rubber-growing districts of India and 
Burma. 

Leaf-fall caused by O. heveae is the only leaf disease of importance 
in Malaya, but the other two cause serious losses in the countries 
where they are present, the South American leaf disease being so 
severe that it prohibits the profitable development of rubber planta- 
tions. For this reason, a short account of the two leaf-fall diseases 
not yet reported in Malaya will be given. 

294 



CHAP, xv MAJOR AND MINOR LEAF DISEASES 295 

In addition, there is a fairly long list of rather indefinite leaf 
affections known as leaf spottings and rim blights. The following list 
is compiled from Fetch's last edition with small alterations: 

Common Name Reported Casual Fungus 

(a) Mite attack Associated with Oloeosporium albo- 

rubrum, Fetch, or Gloeosporium 
heveae, Fetch 

(b) Bird's-eye spot Helminthosporium heveae, Fetch 

(c) Shot-hole leaf disease Several fungi are found associated 

with this type of affection 

(d) Listed from S. America Catacauma huberi, P. Henn. 

(e) Rim blight Ascochyta heveae, Fetch 
(/) ,, ,, Sphaerella heveae, Fetch 
(g) ,, ,, Guignardia heveae, Syd. 

(h) Disease caused by the Cephaleuros mycoidea, Karst. 

Alga 
(i) Sooty moulds Species of Capnodiae 

Colletotrichum heveae, Phyllosticta heveae and Pestalozzia palmar um 
have also been recorded growing on leaves of Hevea. Of the above list, 
only (a) and (b) can be considered of economic interest in Malaya. 
With reference to the remainder, only short notes will be made in 
this section, for the position in Malaya in relation to these fungi is 
so ill-defined that they can be considered only of slight interest. 
The association between the spider attack and Gloeosporium and 
Helminthosporium species of fungi is dealt with under Oidium Leaf- 
fall. 

LEAF-FALL CAUSED BY OIDIUM HEVEAE, STEINMANN 

The first recorded appearance of this disease was made in the 
Malang district of West Java by Arens in 1918. In 1925 Oidium leaf- 
fall was reported from Ceylon, and in the same year the writer first 
recorded the disease in Malaya. 

In all these countries the Oidium leaf-fall disease has assumed 
serious proportions, requiring active combative measures on a large 
scale and at considerable cost. Between 1925 and 1929 there were 
no records of Oidium leaf- fall in Malaya, but in 1929 the disease be- 
came apparent in many districts, and from that year annual out- 
breaks have been reported, that for 1930-31 being most virulent. 
The virulence of the disease is largely dependent on climatic factors 
and so the intensity varies accordingly; if the climatic conditions 



296 DISEASES AND PESTS OF THE RUBBER TREE PART in 

favour the spread and growth of the fungus, or happen to be such as 
to cause a slow refoliation after wintering, a serious outbreak will be 
the outcome. In the same way, soil conditions may be such that the 
trees are lacking in vigour and, as a result, a slow refoliation takes 
place; more serious outbreaks occur on these places than on areas where 
soil conditions are normal. Thus, when making a comparative statement 
in any particular year full allowance must be made for the influence of 
climatic and soil factors. For instance, Sanderson stated in 1930 that 
"the appearance of the Oidium mildew on Hevea in Ceylon was first 
noted in 1925 and since then the area and intensity of attack have 
both steadily increased", but Murray, in Ceylon, says in 1931, "Oidium 
attack has not increased to any serious extent since the disease was 
first reported in Ceylon in 1925". This statement suggests, as will be 
shown later actually to be the case, that the limiting factors for 
spread and virulence are very definite. The correct attitude to take up 
is to realise that once the fungus has become established, it only 
needs favourable conditions for a virulent attack to ensue and vice 
versa. There is little doubt that in Malaya there is a tendency to- 
wards a considerable spread in the affected area between the years in 
which virulent attacks occur. The fact that the Oidium leaf- fall fungus 
is well established in Malaya and can carry on from one season to 
another until a favourable season supervenes, is, to say the least, dis- 
concerting. 

Causal Fungus. Oidium heveae, Stein., belongs to the group 
known as the "powdery mildews" (Erysiphaceae); this group con- 
tains many species which are obligate parasites and cause many de- 
structive diseases. 0. heveae is an obligate parasite, and the delicate, 
hyaline, cob web -like mycelium usually develops on the surface of 
leaves, forming a more or less superficial covering. This statement is 
made by Steiiimann, but in Malaya, a complete covering is uncom- 
mon. Beeley has successfully photographed an extraordinary dense 
growth of the Oidium fungus on the midrib of the leaf (where the 
conidiophores and chains of conidia were so dense as to be in contact 
with each other), and yet to the naked eye the growth was only 
visible when observed in certain angles of light, A slight, glistening, 
furry surface could then be distinguished on an otherwise smooth 
leaf (Fig. 46 (a and &)). This finding differs from certain advanced 
cases reported from the N.E. Indies and Ceylon, where the fungus spots 
on the leaves resemble "whitewash" spots. But in the Kalutara 
district of Ceylon, Murray reports that the leaf symptoms are similar 
to those in Malaya, where the fungus is not easily visible, and occurs 
generally in spots on, or in close proximity to, the leaf veins, the 



CHAP. XV 



OIDIUM 



favourite position being on the midrib on the under surface of the 
leaf. Being found chiefly on the under-side of the leaf, the fungus is 
always shaded from the midday sun. 



l^^ 
^ 

' ' 





FIG. 46. (a) Showing dense growth of O. heveae on leaf vein, with a spore germin- 
ating in situ, x 300. (6) Illustrating the spore chains produced by O. heveae on 
infected leaves, x 300. Note top spore of chain germinating in situ. 

When the spores germinate on the leaf, they first form attachment 
organs, the appressoria. Later they produce a surface mycelium. 
Branches of the surface hyphae penetrate the cuticle and special 
haustoria or absorbing organs grow into the epidermal cells. These 
bladder-like haustoria are confined to the epidermal cells, and 



298 DISEASES AND PESTS OF THE RUBBER TREE PART in 

draw the food-supplies of the fungus from the cell contents of this 
layer. 

Spores (conidia) are usually produced in abundance on short, erect 
conidiophores, and they are chiefly responsible for the character- 
istic powdery appearance. The spores are distributed by wind, 
insects or other agency, but are short-lived, so that if conditions 
are unfavourable for spread, the disease is soon checked. 

Symptoms. The attack of mildew in mature rubber is always 
most pronounced on young leaves, during and immediately after 
the wintering season. The young leaves in the bronze, greeny bronze, 
and later, pale-green stage, are particularly liable to attack. Young 
rubber or seedlings in nursery beds had not been reported as being 
attacked in Malaya, by this fungus, until 1933, although Reydon 
reported in 1925 that in East Java the mildew has appeared on the 
budding beds or nurseries of 17 per cent of the estates reporting 
attacks. 

In the case of young foliage the leaves become more or less dull 
in appearance, as contrasted with the shining appearance of healthy 
leaves, crinkled from the tip, and later, a portion, commencing at the 
tip, becomes bluish or purplish-black in colour. 

These changes apply to the leaves both in the bronze and early 
green stages. The leaflets soon fall to the ground and become shrivelled 
in appearance. The mycelium and spores can be best seen near the 
midrib on the under-sides of the leaves. In cases of severe attack 
the ground may be covered with a carpet of decaying leaves, and 
the retention of the more or less bare leaf-stalks on the trees, almost 
denuded of leaflets, is a striking characteristic. The next flush qf 
leaves may be attacked in the same way and fall to the ground long 
before they are mature. It is obvious that several repetitions of such a 
leaf -fall during any one season may have serious consequences. 
Attacks on mature leaves have not been very noticeable in Malaya, 
and Beeley reports that "the mildew fungus usually attacks only 
young leaves half an inch to two inches long". However, investi- 
gators in Ceylon and the Netherlands East Indies report attacks on 
mature leaves which are not very severe as compared with attacks 
on young leaves, and attacked mature leaves frequently remain 
attached to the leaf-stalks. The exact nature of the stimulus which 
brings about the leaf-fall response to the fungus attack may prob- 
ably be explained as follows. The attack by 0. heveae results in the 
destruction of the cuticle and epidermal cells. As a result the water - 
regulating mechanism is seriously interfered with and comparatively 
large quantities of water vapour are lost through the diseased leaves. 



CHAP, xv OIDIUM LEAF-FALL 299 

In order to prevent greatly increased losses of water, the leaves are 
disarticulated and fall to the ground. 

In Malaya the attack of mildew on the flowers is of considerable 
interest. An active, sporulating growth of the fungus can usually be 
found occurring on the flowers and flower-stalks even when, owing 
to recent rains, there is considerable difficulty in demonstrating the 
actively sporulating stage of the fungus on the leaves. It may be pre- 
sumed that the natural hirsute condition of the flowers affords a 
means of protection from the elements, and incidentally a means of 
carrying over infection from one flush of new leaves to the next, 
despite occasional heavy showers of rain in the meantime. The ulti- 
mate effect of a severe floral attack is a huge reduction in the amount 
of matured seed. In one case, not a single young fruit could be seen 
during a prolonged tour in the infested areas, and last year (1932) an 
approximate estimate of the reduction in seed harvest was attempted 
on estates where sulphur dusting with power machines was in opera- 
tion. The estimate indicated a reduction from 100 to 4 per cent. Few 
inflorescences remain on a tree when there is a severe floral attack, 
and even if they do remain attached, very few open to maturity. 
Further, early wintering trees may fail to set any fruit at all, while 
later wintering trees, though bearing a heavy flush of flowers, may 
be so heavily infected that few if any ripened seeds are finally pro- 
duced from the flowers. One of the main effects of a mildew attack lies 
in the seed harvest and lack of seed for future planting programmes 
is a matter of some consequence. 

Leaf Damage confused with Oidium Leaf -fall. During 1933, in 
answer to a questionnaire, a large number of estates reported Oidium 
leaf- fall and sent in specimens for examination. Of these specimens, 
25 per cent could not be diagnosed as Oidium; for the damage was 
done by an insect and resulted in the production of malformed leaves, 
very similar in appearance to those attacked by 0. heveae. The 
damage was caused by a small, very quick-moving "Attid" spider, 
which weaves a web round the triplets of very young leaves. Leaves 
so bound together in triplets form between them an ideal damp 
chamber for the development of leaf-spotting fungi of the Hel- 
minthosporium and Gloeosporium types. These fungi cause the death 
of the leaf- tips, which later are torn apart by the wind and appear 
very ragged as a result. Leaves damaged in this way are usually 
malformed, the tips discoloured and badly torn, while even healthy 
parts may be eaten away and badly spotted. 

Other leaf-eating insects are also fond of the shelter provided by 
the bound leaves, and are responsible for further damage. A weevil. 



300 DISEASES AND PESTS OF THE RUBBER TREE PAKT in 

Phytoscaphus leporinus, Faust. (Fam. Anculionidae), is the most 
commonly found in such cases, while the common mite, Tarsonemus 
transluscens, Green, is also frequently observed within the sheltered 
leaf chamber. 

This spider pest has been active particularly in young, immature 
rubber, one to six years of age, in Selangor, Perak, South Kedah and 
South Johore. It seems to prefer a rainy season, but is much less de- 
pendent on climatic conditions than is 0. heveae. 

Mites and Oidium Leaf -fall. Sanderson reports that mites have 
been found on some occasions in association with Oidium attacks, 
but it by no means follows that the attack by the fungus must be 
preceded by mite attack. At a later date, Beeley points out that 
mites were present only in advanced stages of the disease, when the 
mildew fungus was difficult to find and when decomposition had set 
in. Apparently healthy, young, green leaves and also flowers were 
observed to be heavily infected with the fungus, while mites were 
entirely absent. As O. heveae is an obligate parasite, its requirements 
for successful growth and development are but the cell conditions 
of the host plant as regards turgidity and the necessary climatic 
conditions. It is possible that the association of these insects and the 
fungus is met with merely because they both show their greatest 
development under similar conditions. It may further be mentioned 
that the most effective treatment for mildew is also the chief means 
of combating mite attack. 

Gadd reports from Ceylon that another fungus has been found 
on many of the older Hevea leaves examined for the presence of 
Oidium, namely, a species of Cicinnobilis which is parasitic on the 
Oidium. This fungus has oval, usually stalked, brown or yellow- 
brown, cellular pycnidia, measuring 34-4(y x 24-28^; the spores are 
hyaline, oblong oval, 6-8/x x 3-4/x. On such leaves the Cicinnobolis 
is more easily found than the Oidium, and no doubt it helps to keep 
the latter in check. Cincinnobolus has not yet been recorded from 
Malaya. It is also interesting to note that the fungus causing the 
South American leaf disease is commonly parasitised by another 
fungus, a species of Botrytis. 

Factors affecting Spread. As a result of laboratory experiments, 
Beeley believes that under Malayan conditions an Oidium spore, 
when freed, must quickly alight upon a suitable host-substratum, 
germinate and become attached to its host, in as short a time as 
possible, if it is to survive and multiply so as to produce a disease of 
epidemic nature. Extreme conditions, high or low temperature, dry 
or wet atmosphere, cannot be favourable to an epidemic spread of the 



CHAP, xv OIDIUM LEAF-FALL 301 

disease. It has been found that for the optimum growth of the fungus 
and optimum production and germination of spores the following 
conditions are necessary: 

(1) A temperature not lower than 56 F. and not higher than 62 F. 

(2) A percentage humidity of 75 to 80 per cent. 

(3) Suitable living tissues on which to grow. 

Observations show that fresh young rubber leaves, two to three 
inches long, the turgidity of whose cells are such as to afford the most 
easy ingress of the feeding organs of the surface mycelium, are most 
suitable. 

It has been generally understood that the amount of rainfall has 
some considerable influence on the incidence and spread of this 
disease, but reference to the rainfall figures in certain infected dis- 
tricts in Ceylon and Malaya shows that the differences in rainfall 
totals are not so great as would cause such a vast difference in amount 
of disease and leaf- fall. This point regarding total annual rainfall and 
total atmospheric humidity has been referred to previously when dis- 
cussing black-stripe disease. It is the nature of the rainfall which 
seems of most importance. In the case of Oidium leaf- fall frequent 
light showers may have no appreciable effect on the spread of the 
fungus, while infrequent heavy rains definitely retard the rate of 
growth and spread of the fungus. 

Heavy rains may influence the course of the disease in many ways: 

( 1 ) By causing the fall to the ground of ripe spores which may have 
developed during the interval between storms. 

(2) By stimulating a more rapid growth of the buds and young 
leaves of the trees, so that the latter rapidly assume a condition of 
turgidity and maturity, unfavourable to the penetration of the 
fungus. 

(3) By reducing the range of temperature changes; a more moder- 
ate day temperature being experienced during a period of heavy 
rains, while in dry weather the temperature ranges are greater, and 
high day temperature with comparatively low night temperatures are 
the rule. 

(4) By reducing the humidity range for a few hours following the 
storm. Showery weather will, however, maintain this condition over 
longer periods, and hence humidity conditions more favourable to 
the fungus obtain. 

Two definite effects of rainfall can be deduced from the statements 
made above, viz.: 

(a) That rainfall may influence directly the conditions which favour 
the growth of the fungus. 



302 DISEASES AND PESTS OF THE RUBBER TREE PAKT ni 

(6) That rainfall directly influences the growth of the host tissues, 
more especially in the matter of rapid refoliation. 

Field observations in Malaya definitely show that (6) is of the 
greater importance, in that the induced rapid refoliation consider- 
ably reduces the period of time over which the leaves are susceptible 
to attack. In this respect, O. heveae resembles the fungus causing 
South American leaf disease, for Stahel reports that young leaves 
lose their susceptibility to infection seven days after bursting from 
the bud. 

An example of the manner in which rainfall influences the inci- 
dence of the disease may be interesting. The Uva district of Ceylon, 
in April 1920, registered only 4-25 inches of rain, with nineteen wet 
days, an average of 0-22 inch per wet day. These light rains produced 
a slow growth of young leaves, and by preventing high midday tem- 
peratures favoured the growth of the mildew fungus; consequently a 
bad outbreak ofOidium leaf- fall was experienced. In the same month 
of the same year, twenty wet days in Kuala Lumpur yielded 10-01 
inches of rain, an average of 0-5 inch per wet day. The heavy rains 
in Kuala Lumpur district probably prevented an epidemic spread of 
the disease by inducing a rapid growth of the young leaves to 
maturity, thus reducing the period of time during which the leaves 
are subject to infection. In 1933 the great majority of reports of the 
occurrence of the disease came from estates having three to six 
inches of rain in February and between three to six inches in the 
first half of March. Normally there is a large increase in the rainfall 
in Malaya in the month of April, and the result of sufficient supplies 
of rain water to the soil is a rapid renewal and growth of leaf, so that 
the mildew fungus has but little opportunity of causing fresh in- 
fections. The April rainfall figures for many years past show that the 
heavy rains during this month tend to prevent any further consider- 
able activity on the part of the fungus; the spread of the disease 
ceases although the active fungus can always be found on some of the 
more immature leaves and flowers. It may be that the growth of the 
leaves during wet weather is so rapid that the mildew fungus has 
little chance of striking the optimum conditions necessary for growth, 
development and spread. The fact that the rainfall has a far greater 
effect on the rate of growth of the leaves is of greater importance 
than the actual influence of the rainfall on the mildew fungus itself. 
Other factors affecting the retention of moisture in the soil will also 
have some influence. 

The two meteorological factors of temperature and humidity are 
those which are chiefly responsible for the absence in Malaya of any 



CHAP, xv OIDIUM LEAF-FALL 303 

serious epidemic of this disease. This country normally experiences 
a very dry midday period and a damp night period, although the 
water-vapour pressure in the atmosphere remains more or less con- 
stant in the rubber-growing districts of Selangor. This is due to the 
tremendous difference between day and night temperatures, viz. 
91 F-70 F. As already mentioned, laboratory tests have shown 
that the fungus is subject to rather definite limits of tempera- 
ture and humidity for the optimum germination and growth of the 
spores. 

In the Malay States the temperature is at all times usually above 
what is considered the maximum limit for optimum growth. This 
assumes even more importance when considered in conjunction with 
the figure showing the hourly changes in humidity for the respective 
states, which indicates that for only about one hour in the morning, 
9 to 10 A.M., and for less than two hours in the afternoon, 4 to 6 P.M., 
is the humidity value suitable for optimum activity of the fungus. 

Alor Star, in Kedah, has the lowest rainfall of all Malayan record- 
ing stations in the months of January and February, the total rain- 
fall being only about 0-5 inch during these months. According to pre- 
conceived ideas, this district should be more subject to Oidium leaf- 
fall than any other. The rubber trees are often without leaves for 
several weeks during this intensely dry period, yet no reports of 
Oidium leaf- fall have so far been reported. Reference to the tempera- 
ture and humidity records offer the most reasonable explanation for 
this. Both these factors show big variations in the twenty-four-hour 
period, with the result that temperature is always unsuitable, while 
humidity is favourable to the growth of the fungus for only one hour 
in the morning, 8 to 9 A.M., and about one hour, 7 to 8 P.M., in the 
evening, the actual period varying slightly according to the period 
of the day during which rain falls. 

Thus there are three factors in Malaya which will largely ensure 
rubber trees remaining comparatively free from attacks of O. heveae. 
They are: 

(a) Unsuitable temperature conditions. 

(b) Unsuitable humidity conditions. 

(c) Advent of heavy rains in April which ensures a rapid growth of 
young leaves during the refoliation period. 

The rubber districts in Malacca have suffered more from Oidium 
leaf-fall than those in other parts of Malaya. In general, the soils 
in the Malacca area are in poor condition, considerable areas now 
carrying rubber trees having been opened up on old "lallang" (Im- 
perata arundinaceae) and tapioca areas. The soils are now in an 



304 DISEASES AND PESTS OF THE RUBBER TREE PART in 

exhausted condition and the trees look poor and definitely lacking in 
vigour, with the result that they cannot renew their leaves as quickly 
as those in other districts where the soil is in better condition. A 
similar statement has been put forward regarding the upland rubber 
districts of Ceylon, where tea has been grown for many years previ- 
ously, in many cases the tea having been interplanted with the 
rubber. Malayan experience has shown that rubber trees on virgin 
soils well preserved from soil wash recover their new leaves more 
rapidly than those on land previously heavily cropped, where the 
soil is. now poor as a result of erosion. In 1933 the whole of the Malacca 
territory suffered more severely than others with the exception of the 
inland district around Batang Malaka, though Chabau near by had 
quite an appreciable attack. Further, at the end of August some of 
the estates in Malacca reported a second Oidium attack. An inspection 
showed that the disease was present only in those trees which were 
wholly or partially refoliating. There is usually an appreciable num- 
ber of trees which do not winter during the usual Malayan wintering 
period, February-March, but do so in the second drought period of 
the year, August-September. It has already been mentioned that 
the recognised time for wintering in Java is August. Observation has 
shown that in particular years 15 per cent of the trees in a mature 
clearing do not winter or only partially winter at the recognised time 
in March. This second outbreak, at the time of writing (1933), ap- 
peared to be prevalent only in the districts of Malacca and North 
Johore, and was confined chiefly to trees close to small clearings 
caused by elimination of trees suffering from root disease. 

The optimum conditions for growth and germination of the 
spores of Oidium heveae, i.e. for epidemic spread, are: 

(a) Suitable young plant tissues. 

(6) Rainfall not too heavy during the refoliation period. 

(c) Atmospheric temperature around 60 F. 

(d) Atmospheric humidity in the neighbourhood of 75-80 per cent. 
The climates of the high level rubber-growing districts of Ceylon, 

Java and Sumatra more nearly approach these optimum conditions 
than does that of Malaya, where most of the rubber is grown only 
at comparatively low altitudes and hitherto has remained com- 
paratively free from the disease. With regard to Java, attention has 
been directed to the correspondence which has passed between the 
Rubber Research Institute of Malaya and the Director, Proefstation, 
West Java. 

The outbreak of Oidium leaf- fall in both Ceylon and Malaya in the 
same year (1925) is of some interest. No special comments are offered 



CHAP, xv OIDIUM LEAF-FALL 305 

on the outbreak in Malaya, but Gadd's remarks may be given for 
Ceylon. He states: 

It is a point of some importance that the disease in Ceylon occurred 
almost simultaneously in most of the rubber growing districts at points 
widely separated. This would indicate that the fungus was already widely 
distributed here on some unknown host plant, and that it was not a recent 
introduction from abroad. If recently introduced, the disease would have 
spread from definite centres, places to which the disease had been brought 
with introduced plants. Usually a species of Oidium parasitic to plant life 
is unable to live saprophytically, so that one must look for mildews on 
other plants, particularly allied plants, as the probable source of infection 
for Hevea. 

Fetch has published (Anns. Perad. VI. pp. 243-244) a list of thirty-one 
plants on which species of Oidium have been found in Ceylon, and it is 
possible that the fungus from one or more of these has adapted itself to a 
new host. When the attack of Oidium was first reported on Hevea from 
Java, he tried to infect Hevea seedlings with the mildews from Euphorbia 
hirta, Linn., and Phyllanthus niruri, Linn., two common weeds belonging 
to the same natural order as Hevea, but without success. This line of en- 
quiry, however, is worthy of further investigation. 

Normally, at the time when Hevea is putting forth its new leaf, weather 
conditions in Ceylon are dry, and are not favourable for fungus growth. In 
1925 there was more rain and the number of wet days was greater than 
usual during February and March in the rubber districts, and it is probable 
that these wetter conditions favoured the fungus and helped the process of 
adaptation to its new host. If so, given normal climatic conditions at the 
time new leaves are next produced, it is unlikely that the trees will be 
severely attacked, as what infectious material has persisted on the old 
leaves will be shed with them on wintering. If reinfection then occurs, it 
must happen under unfavourable conditions and from an external source 
unless the fungus proves itself able to overwinter on the Hevea twigs. 
Consequently, given dry climatic conditions at the time of production of 
new leaves it is not expected that the disease will recur to any serious ex- 
tent. But as the fungus belongs to a genus which contains a number of 
species causing very serious plant diseases, a careful watch should be kept 
for the recurrence of this mildew on Hevea. 

The position in Ceylon is evidently very similar to that in Malaya. 

Control of Oidium Leaf-fall. Sulphur dusting by means of power 
dusters is regarded as the most suitable means of control for Oidium 
leaf -fall. The application of sulphur dust depends mainly on the 
weather, i.e. it can only be done successfully when it is dry. Four 
types of machine have been used in Malaya for sulphur-dusting pur- 
poses. These machines are included in the following list: 

(1) Bjorklund power duster. 

(2) Carl Schlieper Handel mij Holder Motor Duster Sulphia III. 

x 



306 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

(3) Drake and Fletcher's Dustejecta. 

(4) Craven and Co.'s New Tornado power dry sprayer. 

It has been emphasised that really heavy rain or complete lack of 
rain prevents the disease assuming an epidemic form. The fungus ap- 
pears to be so dependent upon young leaf tissue that little benefit can 
be expected from dusting before the new, young leaves begin to 
appear. Having efficiently dusted the buds and young leaves the 
sulphur may be expected to provide a prophylactic effect for a period 
of about seven to ten days, if there is no fall of heavy rain during that 
period. It is of little advantage to dust during wet weather, for not 
only is it difficult to apply the sulphur powder, but having done so, 
it will be washed off by the rain in a few hours leaving the leaves un- 
protected. 

Dusting should be commenced only when the young leaves are in 
the earliest stages of attack. A severe wintering will most likely indi- 
cate a rapid and more uniform refoliation, in which case only a brief 
and intense attack need be expected, and two or three rounds of 
dusting will probably give adequate control. A slow, desultory winter- 
ing indicates an indistinct season, showers of rain instead of definite 
drought, and then is the time to expect a heavy Oidium attack. 

The reasons for this are as follows: 

(a) Comparatively cool, moist conditions obtain for the growth of 
the fungus. 

(b) Slow wintering and slow refoliation gives time for its, spread 
and for its action upon the leaf. 

(c) Suitable young leaves are available over a long period. 

In most plantations it is noticeable that the older rubber suffers 
most, and even in such areas only patches of a few acres in extent 
may be affected sufficiently heavily to warrant dusting. Thus, only 
selective dusting of the worst areas need be attempted, such areas 
being singled out for dusting during the actual period of refoliation. 

The adoption of correct methods of cultivation in rubber planta- 
tions, so as to ensure the maintenance of vigour of the trees, must 
necessarily be a first item in the treatment of this disease. 

Recent experiments in Malaya, on sulphur dusting, indicate: 

(a) That more efficient control is obtained by dusting five pounds 
of sulphur at intervals of seven days than by dusting seven to ten 
pounds at intervals of ten days. The ten days' interval proved too 
long for this year's (1933) sudden, brief and intense attack. 

(6) Early and late season dusting is of little, if any advantage. 
It is necessary to dust during the refoliation period, when the mass 
of leaves are in the young stage. 



CHAP, xv OIDITJM LEAF-FALL 307 

(c) An economic area for treatment by one gang of labourers and 
one machine is about 2000 acres per season, when five rounds of 
treatment are carried through at the rate of five pounds per acre. 

At 1933 prices, the cost worked out at a little over two dollars per 
acre, including share of costs of machine and European supervision. 
Owing to a recent move which has been made there is a possibility 
of the price of sulphur being considerably reduced, and if this materi- 
alises the costs would not be more than about 1-50 dollars per acre. 
A detailed estimate of costs is given at page 311. 

Any recommendation for expensive treatment demands some con- 
sideration of the likely benefits to be derived therefrom. Repeated 
defoliations would certainly result in decreased latex yields, and 
sulphur dusting may be expected to prevent this to a certain extent. 
But the amount of decline to be expected in yield is a matter of 
conjecture and it is not possible to make an exact statement as 
to the exact increase in yield which will follow dusting. At present 
the only statement that can be made is that in some cases yields have 
improved slightly as a direct result of dusting. The results of ex- 
perimental dusting carried out in 1933, in Malaya, show that foliage 
and bark and slightly improved yields may be expected, while bene- 
fits from additional shade to the soil will result in a better soil flora, 
which in its turn will tend to benefit the trees. Murray, working in 
Ceylon, has published certain figures relative to dusted and undusted 
areas, and the comparison indicates a relative increase of 221 Ibs. 
per acre per annum in favour of the dusted field. He emphasises that, 
in this case, a strict comparison is not valid, but is of opinion that it 
is an increase of this order of magnitude. In a private communication 
Murray says that at a height of 2000 feet in Ceylon there is a 100 per 
cent defoliation in certain districts and, on such estates, fifteen pounds 
of sulphur per acre have had to be used as against the five pounds per 
acre recommended in Malaya. The estimation of the value of these 
factors is, however, very difficult and requires further investigation. 
However necessary dusting may be from a pathological point of 
view, it is not yet decided whether or not the operation is economi- 
cally sound at present commodity prices, i.e. before restriction. In 
many parts of Malaya, conditions are suitable to rapid growth of 
rubber trees throughout the year so that they may escape the disease 
or, when slightly infected, may themselves be able to overcome it 
and completely recover. In some parts of the country, however, 
e.g. certain districts of Negri Sembilan and Malacca, where condi- 
tions of soil and climate are not too favourable for the growth of 
rubber trees, it is well worth while considering dusting on a limited 



308 DISEASES AND PESTS OP THE RUBBER TREE PART in 

scale. Large estates could derive benefits from one machine each; 
smaller estates might combine and utilise one machine jointly, in 
each case the worst affected areas being selected for dusting. If the 
desired benefits are derived from this limited treatment it can, in 
future years, be extended as required or as further funds become 
available. 

All seed gardens and bud-wood multiplication nurseries should be 
dusted with sulphur as a routine practice so as to maintain continuous 
protection of such valuable material, not only from O. heveae, but 
from other fungi and insects capable of causing damage to rubber 
leaves, buds or flowers. 

The present-day power machines used in sulphur dusting, while 
tolerably effective, will no doubt be improved upon in the future. 
At the present time considerable care must be taken to prevent the 
finely divided sulphur becoming ignited, and the danger with a petrol 
engine is obvious. In tropical countries the operation of dusting, if 
efficacious, possesses so many advantages over spraying, especially 
in the case of tall trees, that the latter could not be recommended. 
The operation is, in no way, dependent upon the proximity of water 
supply, and as the material is easily transported labour costs are 
comparatively low. A fine, dry dust may remain suspended in the 
air for an appreciable time, and this is an important factor in dis- 
tribution (Fig. 47). 

A drawback to sulphur dusting is the action of the chemical on the 
eyes, but this does not appear to effect seriously the coolie labourers. 

For the carriage of the power dusters, the best type of suspension 
is shown (Fig. 48). With this type of slinging it has been found that 
the carriers can move about quite freely, even on steep hills. Four 
coolies carry the machine, while another six are engaged in carrying 
the sulphur powder to refill the machine as the dust is blown away. 
Tne dust-cloud will be carried to a distance of 100-150 yards by air 
'currents, and this drift determines the line of the return journey. 

The sulphur used in the dusting experiments is obtained through 
agents, from the Kawab Puteh Works, Java. Two grades are ex- 
ported; a very impure grade known as Mud Sulphur, containing 
about 65 per cent sulphur, and a purer grade known as Flotate 
Sulphur, containing 95 per cent sulphur. A form of sulphur, known 
under the trade name of Olite, has been put on the market by the 
Imperial Chemical Industries (Malaya), Ltd.; it contains a " spreader " 
(mellinite) which prevents agglomeration, and the machine is less 
likely to suffer from clogging. 

The real differences between the various sulphurs is found in their 



CHAP. XV 



OIDIUM LKAF-FALL 



309 




FIG. 47. Showing Bjorklund motor duster in action. Note drifting cloud of 
sulphur dust overhanging the tops of the trees. 

mechanical properties, i.e. water-absorbing properties, formation of 
hard agglomerates or pellets of sulphur, and lumping or caking during 
storage in the normal Malayan atmosphere. Olite sulphur, though it 



310 DISEASES AND PESTS OF THE RUBBER TRKH I-AKT in 

lumps slightly, does not form agglomerate particles to any great 
extent, and can be dusted, therefore, without being previously dried 
in the sun. Flotate sulphur is the next best and is quite as good as 
Olite, providing it can be dried for an hour or so in the sun before 
use. Mud sulphur is not appreciably worse than the other two, but it 
is essential to dry it before use, otherwise much of the sulphur is 




FIG. 48. Showing type of slinging found most suitable for transporting heavy 
machines over rough ground. 

wasted in the form of agglomerates or pellets which fall to the 
ground immediately after leaving the machine. 

The cost of the various sulphurs in past years has been of the 
order: Olite, 144 dollars per ton; Flotate sulphur, 107 dollars per 
ton; Mud sulphur, 90 dollars per ton. The large difference in prices 
almost prohibits the use of Olite, and as labour costs for drying the 
flotate or mud brands are comparatively small, about one dollar per 
ton, there does not seem to be much advantage to be gained by its use. 
It is in the lack of drying before use that Olite sulphur gains any 
advantage over the other brands mentioned, while it has a definite 
disadvantage in being liable to ignition and explosion. 



CHAP, xv OIDIUM LEAF-FALL 311 

Costs of Dusting. The following costs are computed on the basis 
of the maximum economical capacity of any one of the four machines 
named herein, i.e. the Tornado Power Dry Sprayer, the Bjorklund, 
the Holder Sulphia III and the Dustejecta, each having a similar 
capacity of 2000 acres per season, dusted five times at intervals of 
seven days: 

$ c. 

Oil, petrol 100 gals. @ 78 cents per gall. . . 78-00 

Lubricant 10 galls. @ 245 dolls, per gall. . . 24-50 

102-50 

Labour, 12 coolies for 36 days @ 40 cents per day . 172-80 
Depreciation, say 33 J of cost of machine . . 250-00 

European supervision . . . . .125-00 

Total . . . 649-30 

Rate per single dusting = 6-5 cents (approx.) 
Total cost of treatment = 6-5 times the number of dustings given 
plus cost of the weight of sulphur desired 
per acre in cents. 

Dusting five times at the rate of 7 Ibs. Flotate sulphur per acre. 
Price of sulphur 4 cents per Ib. will cost 6-5x5+4x7x5 cents, 
= 32 -5 + 140 cents 
= 1 -73 dolls, per acre 

Similarly 5 dustings at 5 Ibs. per acre will cost 1-32 dollars per 
acre, and 3 dustings at 7 Ibs. per acre will cost 1-05 dollars 
per acre. 

Costs will show slight variation according to local prices of com- 
modities and labour, while difficult land and unsuitable 
weather may also put up costs. 

Note. Provision must also be made for drying the sulphur 
say 1 dollar per ton. 

SOUTH AMERICAN LEAF DISEASE 

The fungus causing this disease, Melanopsammopsis ulei (Henn.), 
Stahel, occurs on wild species of Hevea in the forests of Brazil, Peru, 
British Guiana and Suriname. The history of the disease in rubber 
plantations is instructive as illustrating the difference between the 
incidence of disease on a single species when scattered in a natural 
way in the forest, and when collected together artificially as in rubber 
plantations. It shows also the advantage that may sometimes be 
gained by growing a crop plant away from its native country, out- 
side the range of its natural parasites, but it also indicates the 
dangers attendant on the introduction of rubber plants from outside 
countries. 



312 DISEASES AND PESTS OF THE RUBBER TREE PART in 

No\vell gives a short account, which is reproduced here, of the de- 
tailed investigations made by G. Stahel, in Suriname: 1 

The attack on the leaves begins when they are very young, and, as they 
develop, yellowish spots with a grey layer of conidia on the under side 
become apparent. 

The central part of the larger spots dries up and falls away leaving a 
ragged perforation. On fully grown leaves the surface becomes thickly sown 
with black dots, and on old leaves these have developed into rounded black 
slots interspersed with several or many ragged holes surrounded by a black 
ring. 

The fungus attacks the petioles and young internodes, but much less 
frequently than the leaves. On the petioles the check to growth on one side 
may cause curvature or spiral twisting; on the internodes swollen canker- 
like patches are produced. The inflorescences and fruit may also be in- 
fested. 

The Fungus. The causative fungus Melanopsammopsis ulei (Henn.), 
Stahel, has three forms of fructifications, viz. free conidiophores, pycnidia, 
and perithecia. The conidial form of the fungus was named Fusicladium 
macrosporium by Kuijper, and Pasaalora heveae by Massee; it was re- 
garded as pertaining to the genus Scolecotrichum by Griffon and Maublanc, 
a conclusion with which Stahel agrees. The conidiophores when young are 
short, unicellular, brown hyphae thickened at the base, penetrating the 
epidermis from subepidermal mycelium; this form appears on the young 
translucent leaves. On somewhat older leaves, the conidiophores are many- 
celled, elongated, and arise from a pseudo - parenchymatous base. The 
conidia are formed singly and terminally, measure 20-65/u, x8-12/z, norm- 
ally are divided into a wider basal cell and an elongated terminal cell, and 
are more or less bent or spirally twisted. 

The pycnidial form was first described as Aposphaeria ulei, Hennings. 
The pyncidia occur freely as small black dots on the surface of leaves, one 
to two months old, mostly on the upper side. They are roughly spherical, 
with an apical pore and little or no trace of a papilla. The pycnospores are 
5-10/it long, 2/x wide at the ends, narrowing to 1/u, in the middle. 

The perithecial form was described by Hennings as Dothidella ulei, but 
is placed by Stahel in the Sphaeriacea, in the new genus Melanopsammopsis. 
The perithecia begin to take the place of the pycnidia some two months 
after the leaves are full grown. They occur in rings of three to four milli- 
metres, or rounded groups of one to two millimetres in diameter, are 
smooth, carbonaceous, and closely resemble the pycnidia in form and size. 
The ascospores are hyaline, two celled (one larger than the other), con- 
stricted at the septum, 18-22/>t x 6-8/t. 

A species of Botrytis is common as a parasite of the fungus in all its 
stages. 

Infection. The conidia germinate in water in one and a half to two hours 
and cannot withstand more than fifteen to twenty hours' exposure in a 

1 Stahel, G., 1917, "De Zuid-amerikamsche Hevea Bladziekte", Bull. No. 34, Dept. 
Land, Suriname. 



CHAP, xv MAJOR LEAF DISEASES 313 

desiccator. Stahel found viable ascospores to be rare, and unable to with- 
stand more than four to six hours of desiccation. According to his observa- 
tions, the pycnospores germinate very weakly and appear to have no part 
whatever in the spreading of the disease, nor do the ascospores exhibit more 
than weak powers of infection. 

The conidia produce germ -tubes which penetrate the cuticle and give 
rise to a sub-cuticular hypha, from which branches pass between the cells 
of the epidermis and produce an intracellular mycelium. Infection takes 
place only in the very young and tender organs. Leaves are most sus- 
ceptible in the first four days after the opening of the buds, and lose their 
susceptibility after seven days' growth. The first sign of infection is a 
yellowish spot which appears in about five days, and one or two days later 
the conidial stage appears, followed by pycnidia ten to twelve days after 
infection. On the fully developed leaves the pycnidial fructifications at 
first predominate, succeeded later by the perithecia. 

Contrary to experience with most diseases, infections are most abundant 
in dry clear weather, and least in rainy weather, This is attributed by Stahel 
to the more favourable conditions for penetration provided by an all-night 
coating of dew than by intermittent wetting from rain, owing to the fact 
that the process requires some ten hours for its completion. 

Effects of the Disease. Severe infestation of the young leaves causes de- 
foliation of the trees, and infestation less severe, hinders the growth of the 
leaves and reduces their efficiency. The production of rubber is in con- 
sequence reduced, and should the defoliation, as frequently happens, be 
repeated, a severe die-back sets in, and the process may eventually result 
in the death of the top or of the whole tree. 

Control. No practicable means of control has been found. For spraying 
to be effective the young leaves would need to be coated at least twice 
during the first four days, which is more difficult to arrange for since the 
trees in a plantation come into leaf in a scattered way, and even different 
parts of the same tree do not come into leaf all at the same time. Moreover, 
the way the young leaves hang makes them difficult to cover. 

Stahel has proposed keeping the trees artificially bare of leaves for three 
or four weeks to prevent the formation and dissemination of conidia, and 
has also suggested the use of smoke clouds at night to prevent dew forma- 
tion, a method practised in vineyards against threatened frosts. 

ABNORMAL LEAF-FALL IN BURMA, SOUTH INDIA AND CEYLON 

Fetch suggests, in the 1921 edition of his book, that two species of 
Phytophthora, viz. P. faberi and P. meadii, can cause the abnormal 
leaf -fall which occurs in Burma, South India and Ceylon, and states 
that the most important difference between the two species from the 
economic point of view, lies in the effect of the fungus on the trees. 
If the leaf-fall is caused by P. faberi, the latex yield is not notably 
affected, but when the leaf-fall is caused by P. meadii the yield falls 
off enormously and it may not be worth while to tap. McRae finds 



314 DISEASES AND PESTS OF THE RUBBER TREE PART in 

that the Phytophthora which occurs on Hevea in South India is prob- 
ably the same fungus as that which is reported from Burma and has 
named it Phytophthora meadii\ it is said to be the cause of fruit-rot, 
leaf-fall, die-back and black thread, but apparently not the claret- 
coloured canker. Fetch discusses the systematy at some length, but 
the position seems still very indefinite in view of Thompson's find- 
ings that, in addition to P. faberi and P. meadii, two other species, 
P. heveae and a Pythium, have been isolated from naturally occurring 
pod-rot, in Malaya. 

This abnormal leaf-fall caused by a species of Phytophthora results 
in the fall of mature, fully formed leaves, though Fetch records that 
in 1917 and 1918 the first cases of leaf- fall occurred at the end of 
January, shortly after the new leaves appeared, and that in both these 
years heavy abnormal rains occurred at that time in some districts 
instead of the usual dry weather. The fall of mature leaves does not 
occur either in the South American leaf disease or in the leaf- fall 
caused by Oidium heveae', in both these diseases only young, newly 
developing leaves can be infected by the fungi concerned, and only 
young, immature leaves fall to the ground. As reported above, in the 
account of the South American leaf disease, the leaves are most sus- 
ceptible to infection by the fungus four days after the opening of the 
buds and lose their susceptibility after seven days' growth. 

Severe outbreaks of either pod-rot or abnormal leaf-fall have not 
been recorded in Malaya. Thompson records the isolation of more 
than one "Phytophthoraceous" fungus from naturally occurring 
pod-rot, and it is also .known that the fruits are very susceptible to 
infection in that country. When conducting artificial inoculations on 
the fruits of one tree in 1917, infection and spread took place so 
rapidly that, within ten days, three neighbouring trees showed every 
fructification more or less severely infected, and steps had to be 
taken to clear away at once all the diseased pods. This inoculation 
work on fruits was carried out by Belgrave. 

The following abstract is taken from Fetch's account of abnormal 
leaf-fall: 

In Ceylon the South-West Monsoon is supposed to burst in the latter 
half of May, and June and July should be months of heavy rainfall. If the 
rains of May and June are fairly continuous a second fall of leaf may set in 
about the beginning of July, and if the rains continue through July and 
August this leaf -fall is continued also. But should dry weather intervene, 
the leaf-fall ceases. Trees rarely lose all their leaves, but they may lose the 
greater portion of them so that the ground is thickly covered with dead 
leaves. 

This abnormal leaf -fall is known to occur in Ceylon, South India, Burma 



CHAP, xv MAJOR LEAF DISEASES 315 

and Java, It has been referred to as monsoon leaf -fall and second leaf -fall, 
but the term abnormal leaf-fall appears the most appropriate. In South 
India its incidence is similar to that in Ceylon, but a little later, in accord- 
ance with the later burst of the monsoon. According to McRae, the trees 
begin to shed their leaves about a fortnight after the monsoon has set in 
, steadily, and the leaf -fall is most noticeable from the middle of July to the 
middle of August, by which time the trees cease to shed their leaves to any 
appreciable extent. 

This disease is intimately associated with the fruit-rot, or pod disease, 
of Hevea. In all the countries in which abnormal leaf -fall occurs the cause of 
the principal abnormal leaf-fall is a Phytophthora, which in the general 
case, attacks the fruits first and then passes from them to the leaves and 
branches. 

The fruit rot which occurs in Ceylon was determined to be due to a 
Phytophthora sp. in 1905. In that year it threatened to destroy the whole 
fruit crop, but it was not associated with any marked leaf-fall. An abnor- 
mal leaf -fall occurred in Ceylon in 1909, but in August, after the seed had 
ripened. In 1912, leaf -fall and pod disease occurred together, and it was 
then determined that leaf-fall was also due to a species of Phytophthora. 
The dependence of the disease on climatic conditions during the time the fruits 
are ripening is very marked in Ceylon. 

Die-back of Shoots. After a severe outbreak of leaf -fall and pod disease, 
many of the green shoots are found to have died back, and, according to 
observations in South India, this dying-back may proceed further, along 
the larger branches, during the ensuing cold weather. McRae has demon- 
strated that this die- back is also caused by a species of Phytophthora, and 
that the mycelium of the fungus is present in the dead and the living tissues 
of the branch. On splitting open a dead branch, a dark- brown line is found 
separating the living from the dead part. The mycelium may be found on 
either side of this line, not only in the brittle dead portion, but also in the 
tough living tissues. It occurs in the bark, wood and pith. In some cases 
it extends only an inch or two along the living part, while in others it is 
found much further along, especially when fresh young shoots have de- 
veloped. It has been shown that the fungus invades the branch from the 
fruit-stalk or via the terminal bud. It can, however, attack the green shoot 
directly, and in the earlier stages of an attack of leaf-fall it is often possible 
to find blackened sunken areas on the green shoots, coincident with the 
appearance of the disease on the leaves and independent of diseased leaf- 
stalks. 

The mycelium of the fungus lives through the dry weather in the 
branches which have partly died back. According to McRae, the new shoots 
which are produced from the living part of these branches in the following 
spring may begin to wilt about a month later. The leaflets shrivel, dry up, 
and fall off; the lowest inch or so of the shoot becomes discoloured: and the 
shoot ultimately dies back to its parent branch. In many such cases the 
mycelium is not in the leaves but in the branch, and it would appear that it 
is the effect of the fungus within the branch which causes the new shoot 
to shed its leaves. 



316 DISEASES AND PESTS OF THE RUBBER TREE PART in 

It must be borne in mind that this form of die -back is only likely to occur 
during or after an attack of fruit disease and abnormal leaf -fall. There are 
many other causes of die-back of the green shoots of Hevea, and it is 
scarcely possible to distinguish between them without a microscopical ex- 
amination of the dead twigs. Shade is responsible for the death of many 
branches, especially in the lower part of the tree, while there is reason to 
suppose that too frequent forking, more especially on poor soils, may have 
the same effect. Of diseases, Gloeosporium alborubrum and Phyllosticta 
ramicola may cause die-back of the green shoots, and several other fungi 
are under suspicion. 

Preventive Measures against Abnormal Leaf -fall. The paragraphs 
following contain some observations by the writer, but as abnormal leaf- 
fall caused by a species of Phytophthora has not been found in Malaya, it is 
considered the better procedure to continue this section in close type. 

Fetch states that the principal cause of the rapid spread of the disease 
is the development of the fungus on the fruits. Once the disease has begun, 
the fruits serve as the main centres of propagation of the fungus and of 
distribution of the spores. Therefore any method of preventing fruit forma- 
tion or diminishing their numbers, would supply a check to the spread of 
the disease. 

The difficulties attendant on spraying tall rubber trees are well appreci- 
ated by all plant pathologists working on rubber. But Ashplant, working in 
South India, demonstrated that spraying with Bordeaux Mixture could Ic 
considered to be a practical estate measure. Such a statement depends 
entirely on the market price of the commodity for its validity. The costs of 
spraying, reported by Ashplant, varied between eight to seventeen rupees 
per acre; rupees may be considered the equivalent of Straits dollars in this 
connection. It would be totally impossible to consider such a large ex- 
penditure over the last three or four years, when low rubber prices hayc 
dictated economies along every possible line. 

Ashplant 's methods do not demand the use of power sprayers. Strongly 
constructed hand sprayers, with a spraying rod of about twelve feet long 
are used from movable platforms. The spraying is done in April or May 
before the burst of the South-West Monsoon. The results reported by Ash- 
plant were considered so good that some 4000 acres of from nine to twenty 
years, and 6000 acres of less mature rubber were sprayed in 1925. 

Ashplant also records that the results of preliminary experiments in the 
control of secondary leaf -fall by the application to the soil of synthetic urea 
are regarded as exceptionally promising, the trees in the treated plots 
developing 25 to 60 per cent more foliage than unmanured individuals. 
Satisfactory results were also obtained in February 1926, by the applica- 
tion of sodium nitrate and ammonium sulphate at the rate of two and 
three pounds per tree to two blocks which had received the same sub- 
stances at the rate of three and four pounds in December 1924. The trees 
in the manured blocks are calculated to bear 30 to 60 per cent more foliage 
than those in the untreated. 

The costs of these operations for control of secondary leaf-fall appear 
high at the present time, more especially when compared with the costs of 



CHAP, xv MAJOR LEAF DISEASES 317 

sulphur dusting as carried out for Oidium control. Five rounds of dusting 
with sulphur at the rate of five pounds per acre cost only about two dollars 
per acre in Malaya in 1933, and now suitable dusting machines are avail- 
able, the advisability of dusting with either Bordeaux or Sulphur powders, 
instead of with liquid mixtures, might be considered for control of abnormal 
leaf -fall caused by Phytophthora. The supply of clean water for the making 
of Bordeaux or Burgundy mixtures would be a difficult problem on most 
rubber estates in Malaya, which doubtless could be overcome in most 
cases, but only by a large increase in labour costs. 

Comparing spraying operations with hand-spraying and power-spraying 
machines, Ashplant states: "The maximum height that can be reached with 
a fine spray operated from the ground is from thirty to forty feet, is not much 
greater with a power than with a hand sprayer. With both, climbing has 
to be resorted to in order to reach the tops of the trees. It is this necessity 
for climbing that limits the possible task and takes so much time and 
labour. Could means be devised whereby the tops of seventy to one hun- 
dred feet Hevea trees could be reached by a ground operated spray or 
rather a battery of sprays, the full resources of power sprays would be 
capable of utilisation. The greater speed and labour saving then made 
possible would alter the position entirely to the advantage of power 
sprayers." 

R. H. Stoughton described the spraying apparatus found most useful in 
Ceylon and South India for control of leaf -fall caused by Phytophthora. 
The particular machine is known as the D.S.P. "HEADLAND" pump. This 
is a double -barrelled force pump, with a large inlet hose, with a strainer, 
a steel pressure chamber and two half-inch outlets with stop-cocks. The 
machine is sent out unmounted, but should be fixed to a small wooden 
platform with four projecting handles for carrying. Spares for the pump 
are supplied but may be usefully augmented. Two lengths of hose are re- 
quired, each seventy-five to one hundred and twenty feet long. If more 
than this length is used, undue wear and many bursts and other troubles 
are probable. The only hose that has so far proved capable of standing up 
to the rough usage is the "Armada" hose. To the end of each length of hose 
is attached either a bamboo "lance" (a long bamboo with a screwed metal 
pipe within it) or a light fifteen-foot steel pipe; to the end of this is at- 
tached a nozzle. Many types of nozzle have been tried but the most suc- 
cessful are the "Mistifier Junior" and the "Jumbo" nozzle. A new type 
of combined lance and adjustable nozzle has been put on the market at the 
instigation of Mr. Ashplant. This is called the Drake and Fletcher "Ar- 
mada" spray gun and Ashplant reports that exceedingly good results were 
obtained by its use. With this instrument the type of spray produced is 
varied by turning the stop -cock at the handle end. 

The labour requirements for each machine is best apportioned as under. 
It will be interesting to compare this with the labour requirements for 
sulphur dusting as given in the Oidium section. 

(1) Two coolies working the pump. 

(2) One coolie stirring Bordeaux Mixture and relieving pumpers in ro- 
tation. 



318 DISEASES AND PESTS OF THE RUBBER TREE PABT m 

(3) Four coolies spraying. 

(4) Two to six coolies carrying water and mixing the Bordeaux. 



GLOEOSPORIUM ALBORUBRUM, Fetch, AND 
GLOEOSPORTUM HEVEAE, Fetch 

These fungi and others are commonly found associated with mite 
attacks. In such attacks, the leaves become distorted as a result of 
asymmetrical growth, while complete defoliation of the young shoots 
may take place. 

The spore-bearing layers or acervuli of G. alborubrum appear as a 
pinkish spore-mass above the leaf surface, and when several acervuli 
are aggregated together they can be easily seen by the naked eye, 
more especially on or in close proximity to the midrib or veins. The 
single spores, as seen under the microscope, are hyaline. 

G. heveae has been recorded on rubber trees in Malaya on but few 
occasions and in each case they happened to be associated with light- 
ning damage. 

Fetch, Brooks and Arens all record that G. alborubrum has been 
the responsible agent in causing a leaf- fall in Ceylon and Java. The 
writer has no definite experience to record in connection with these 
fungi, excepting on a single occasion where an intense leaf- fall over 
some hundreds of acres took place. The rubber had been planted some 
three or four years and Gloeosporium alborubrum became quite promi- 
nent on large numbers of trees. The estate was situated in a low-lying 
coastal area and, a short time previous to the fall of leaf, the drains 
had been lowered rather hurriedly from a depth of four feet to six 
feet. The writer is of the opinion that the lowering of the water-table, 
as a result of the increased depth of the drains, was of greater im- 
portance in causing leaf-fall in this particular case than the fungus 
attack. 

Over the last three years, mites and Gloeosporium attacks have 
been quite common on the leaves of young bud-grafts during the 
heavy rain-falls of the months of April and May, and while in 1931 
they were particularly noticeable, in 1932 and 1933 the number of 
attacks were comparatively few. While the associated insect and 
fungus attack is more common in badly drained land, yet attacks 
have been inspected where the drainage certainly could not be con- 
sidered at fault. 

For successful control, drainage must be undertaken where neces- 
sary. The attacked leaves should also be dusted with powdered 
sulphur; four applications at five-day intervals have proved suitable. 



CHAP, xv MINOR LEAF DISEASES 319 

BIRD'S EYE SPOT 
Caused by Helminthoaporium heveae, Fetch 

This leaf affection is frequently found in nurseries and often on 
leaves of older trees growing under unfavourable conditions. The 
fungus first causes minute purple spots, which become white as they 
increase in size. The spots are generally circular with a narrow, 
purple-brown border and are very numerous on badly affected leaves, 
but the individual spots are never large, rarely exceeding 5 mm. in 
diameter. 

Helminthosporium heveae was described by Fetch, on Hevea 
brasiliensis, more than fifteen years ago. Bancroft, in 1911, stated 
that there was no record of its occurrence in the Federated Malay 
States. Butler, in 1918, says the disease occurs in Malaya, Ceylon, 
South India and Java. Both Fetch and Butler state that the fungus 
is confined to young rubber trees. This is usually true in Sumatra, 
but in 1919 La Rue found it on old trees on numerous estates. In 
some cases the leaves were riddled with spots and the injury must 
have been very considerable. The disease does not cause defoliation 
of the affected trees and where defoliation occurs it is usually found 
to be due to a simultaneous attack of mites. The fungus attacks the 
leaves and occasionally the bark of young twigs. Infection occurs just 
as the young leaves unfold, and the old leaves, either falling or still 
hanging on the trees are probably the source of the infecting spores. 
The fungus is easily grown in culture but is slow in producing fruits. 
The Sumatran form agrees with Fetch's description but the spores 
are rather smaller. 

This is the only leaf-spot which can be considered to do material 
damage in Malaya, and badly damaged nurseries need treatment. 
Feriodical dusting with sulphur has given satisfactory results and a 
small sulphur-dusting gun, which can be purchased for a few dollars, 
is quite efficient in dusting nursery plants. Dusting should be con- 
tinued at five-day intervals until the new leaves appear free from the 
fungus spottings. 

SHOT-HOLE LEAF DISEASE 

This is referred to because, in Malaya, spottings caused by Hel- 
minthosporium heveae lose their white centres quite commonly, 
giving the appearance of "shot-hole" leaves. Fetch reports that the 
spots resemble those caused by H. heveae, but that fungus is usually 



320 DISEASES AND PESTS OF THE RUBBER TREE PART in 

larger and in the case of the Helminthosporium the centre does not 
as a rule drop out. 

Various fungi have been found on these spots. The following are 
given by Fetch: Scolecotrichum heveae, Vincens; Fusarium heveae, 
Vincens; Aposphaeria ulei, F, Henn; Zygosporium paraense, Vincens. 

The first-named, viz. S. heveae, is considered by Vincens to be the 
principal agent in causing the disease. 

EIM BLIGHTS 

Rim blights are of common occurrence in Malaya, but usually only 
single trees are affected and the fungi found on the dead or diseased 
leaf -rims have never caused serious damage. The effect of these fungi 
is to produce a narrow, whitish or brownish zone, about 1 cm. wide, 
extending all round or partly round the leaf. Fetch records three 
different fungi as causing rim blight, and states that, without micro- 
scopical examination it is difficult to observe which fungus is re- 
sponsible. These three rim blights are caused by the following fungi; 
Ascochyta heveae, Fetch; Sphaerella heveae, Fetch; Guignardia 
heveae, Syd. 

It is unnecessary to give details of the structural features of the 
fungi concerned. Of the above, A. heveae and 8. heveae have been 
recorded in Malaya, 

LEAF SPOTTING 
Caused by Cephaleuros mycoidea, Karst. 

This organism, which is an alga and not a fungus, causes a purplish 
spotting on rubber leaves but rarely any material damage. It is much 
better known in connection with diseases of other crops, for on them 
it causes serious losses. It is the cause of the well known "red -rust" 
on Tea and is very troublesome in clove cultivation. It is one of the 
few algae which is capable of causing a plant disease. 

This parasite, named Cephaleuros mycoidea, Karst. (= Mycoidea 
parasitica, Cunningham), is seldom strongly developed on healthy 
rubber trees, and even on rubber growing under poor conditions it 
does not do conspicuous damage. It causes small, circular, purple 
spots on the actual leaf-tissue, but on the midrib and veins the spots 
may be more or less elongated. The fructifications of the alga are 
produced on the spots as minute, erect, yellow-looking hairs. Ridley 
describes them as fine, white hairs, topped with yellow, but when 
seen in mass, the yellow tips give the predominant colour. These 
hairs appear under the microscope as fine filaments, bearing at their 



CHAP, xv MINOR LEAF DISEASES 321 

ends a number of short arms, usually from three to nine in number, 
nearly equal in length. At the end of each arm, which is abruptly de- 
curved, is a yellow, rounded body, the zoosporangium. Zoospores are 
produced in the presence of sufficient supplies of moisture, in a manner 
similar to that seen in species of Phytophthora and they escape 
through a small hole when ripe and swim about by means of two 
cilia. 

Recently, the fructification of this parasitic alga has been found 
growing vigorously on the extrafloral nectaries of the leaves of un- 
thrifty rubber trees. 

Fetch reports that: l 

Cunningham named the species of Cephaleuros on Tea and other plants 
examined by him Mycoidea parasitica. There is not much doubt that he 
included more than one species under that name. Subsequently Hariot 
referred the superficial species described by Cunningham to Cephaleuros 
virescens, Kunze, a species collected in Cuba, and described in 1829. 
There is no type specimen of the latter, and the description is inadequate; 
consequently, Karsten (1891), in his paper on the Chroolepidae of Java, 
rejected Kunze's name and adopted the name Cephaleuros mycoidea. As 
Karsten's determinations are the first which can be definitely interpreted, 
they are followed here. 

SOOTY MOULDS 

Occasionally rubber leaves are found with a dense black covering, 
generally on the upper surface, the under surface remaining green. 
The black incrustation is caused by a fungus which belongs to a class 
usually known as Sooty Moulds (Capnodiae). 

These fungi are not parasitic, and any damage done is indirect in 
so far as the black incrustation prevents the leaf from functioning 
properly by cutting off part of the light which would reach it under 
normal conditions. 

The sooty moulds live on the sugary secretion of scale insects 
which are present on the leaves, and are especially plentiful along the 
veins. As the moulds cause no damage no treatment is necessary. 
The black incrustation usually disappears with the advent of rains. 

DISEASES OF GREEN TWIGS 

In relation to diseases of green twigs and leaves, both Brooks and 
Fetch refer to the action of Gloeosporium alborubrum and Phyllo- 
sticta ramicola. The latter fungus has been reported in Malaya on 
numerous occasions as occurring on leaves, and quite large patches of 

1 Fetch, T., 1923. Diseases of the Tea Bush. Macmillan and Co., Ltd. 

Y 



322 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

leaf tissue turn brown and die from the edge of the leaf, inwards. 
Both the above authors refer to the fact that the chief danger lies 
in the fact that shoots killed by these fungi may afford a point 
of entrance for the parasite causing die-back, i.e. Diplodia sp. But 
as pointed out in another section, it is extremely doubtful if the 
"die-back" fungus does function as has been thought in the past, 
at least as far as Malaya is concerned. The close association of 
the Diplodia die-back fungus with lightning damage is only just 
beginning to be realised, and descriptions given for attacks by 0. 
alborubrum and P. ramicola on green twigs are applicable in every 
detail to trees affected slightly by lightning. The writer, since taking 
up the problem of lightning damage on rubber trees, has not had 
time to work on this particular phase of the more general problem, 
but all previous writers, in considering the question of Diplodia die- 
back, remark on the trees being killed in groups, only a few in- 
dividuals of which are seriously affected. In general the descriptions 
tally, even to details, with lightning damage. The slightly affected 
trees in a group struck by lightning show many different symptoms, 
but one of the most common effects is a blackening of the green stem 
six to eight inches below the apex of the shoot. This is a symptom 
characteristic of P. ramicola, as will be seen in the description by 
Richards and others, given later. Recently an examination of speci- 
mens obtained from the slightly affected trees in a lightning group 
was made, and Gloeosporium heveae was present in abundance. 
Corner, working in Singapore, has had a similar experience. The 
writer cannot escape the feeling that the P. ramicola~G. alborubrum 
complex of past years is, in some fashion, connected with lightning 
injury. It is true that G. alborubrum plus mites can severely retard 
the growth of newly developing leaves of young trees but there is not 
much definite evidence to go beyond this. As the matter is still non- 
proven, it will be of advantage to give another investigator's account 
of the position. 

PHYLLOSTICTA RAMICOLA AND GLOEOSPORIUM ALBORUBRUM 

The following description was given by R. M. Richards, in 1917, 
when working as mycologist to the Malayan Planter's Association: 

For the purpose of this paper these two fungi may be dealt with together 
as they are frequently intimately mixed on the same affected branch or 
twig. The two fungi are parasitic and usually affect the uppermost twigs 
which still have a green epidermis or skin that is, where cork has not yet 
been formed. 



CHAP, xv MINOR LEAF DISEASES 323 

Phyllosticta generally makes its attack at a point six to eight inches 
below the apex of the shoot. When first noticed a brown patch may be ob- 
served which later spreads upwards and downwards, killing the twig. 
Usually the fungus spreads no further down than two to three feet below 
the apex. Gloeosporium has a similar mode of attack. It is usually im- 
mediately after wintering when the leaves are just unfolding that the 
attacks of these fungi occur most commonly. I have seen several thousand 
trees affected on one estate within a few weeks. Gloeosporium is frequently 
the cause of the fall of the young leaves before they are fully developed 
an effect of not uncommon occurrence. 

As far as these two fungi are alone concerned the attacks are not danger- 
ous. Dead twigs killed by the fungi are often found but the disease spreads 
no further. The real danger lies in the fact that their attacks afford oppor- 
tunity for the entrance of Botryodiplodia and for this reason affected 
branches should be removed and all diseased portions burned. 

More often than not, especially in flat lands, Botryodiplodia makes its 
entrance after the attacks of these fungi and, therefore, it is necessary that 
the utmost precautions should be taken to prevent a serious local epidemic 
of die-back. 

Since the above was written, a case with similar symptoms to 
those described by Richards has been noted. They became promi- 
nent on a group of about eighteen one-year-old, unbranched, budded 
plants. The earliest stages showed a brown patch of tissue appearing 
on the stem below the apex and in proximity to the second storey 
of leaves; in the majority of cases not more than four to six inches 
of stem tissue were involved. Spore development had not occurred 
on the discoloured areas, but a species of Gloeosporium and Phyllo- 
sticta ramicola were isolated from the diseased cortical tissue; there 
was no discoloration of tissues internal to the cortex. There was a 
discoloured brown patch of stem just above the second storey of 
leaves, the place being indicated by leaf stalks, the leaflets having 
fallen off. When looked at closely, it could be seen that some of tbe 
leaves in the topmost storey were torn and possessed shrivelled, dis- 
coloured tips. A later stage showed the discoloration of the stem 
tissues progressing upwards to reach the tip of the stem; the upper 
storey of leaves and leaf stalks have fallen completely, and new, 
leafy side branches were springing out from the axils of the leaves 
of the second storey of leaves and also from the stem region in close 
proximity. 

The primary seat of infection is the discoloured area of stem situ- 
ated just above the second storey of leaves. There is little downward 
progress to be noticed, but vertical progress is rapid, and the whole 
of the stem, up to the extreme tip, becomes involved. 

These specimens were brought in from the Experiment Station of 



324 DISEASES AND PESTS OF THE RUBBER TREE PART in 

the Rubber-Research Institute on October 14th, 1933. Enquiries 
through the Manager elicited the information that heavy lightning 
storms occurred in the near vicinity on September llth, 1933, and 
September 28th, 1933, the earlier one being the most severe. This 
particular case, while not providing incontestable evidence, supports 
the writer's views regarding the effects of Gloeosporium sp. and 
Phyllosticta ramicola in providing places of entry for the Diplodia 
die-back. Details of lightning effects will be given in the chapter 
following. 



REFERENCES TO LITERATURE ON LEAF DISEASES 

ABNORMAL LEAF -FALL IN SOUTH INDIA AND CEYLON 

McRAE, W., 1918. Phytophthora meadii, n. sp. on Hevea brasiliensis, Mem. of 

the Dept. of Agr. in India, vol. ix. No. 5. 
ASHPLANT, H., 1925. "Annual Report for 1924-1925", Rev. of App. Myc. 

vol. v. p. 53. 
ASHPLANT, H., 1926. "Rubber in South India", Bull. Rub. Growers' Ass. vol. 

viii. No. 9, p. 463; also abstract in Rev. of App. Myc. vol. vi., 1927, p. 117. 
STOUGHTON, R. H., 1926. Bull. R.O.A. vol. 8, No. 7, p. 333. 
ASHPLANT, H., 1927. The Planters' Chronicle, vol. xxii. No. 49, p. 745. 
THOMPSON, A., 1929. "Phytophthora species in Malaya", Mai. Ag. Jour. 

vol. xvii. Nos. 3 and 4. 

LEAF-FALL CAUSED BY OIDIUM HEVEAE 

ABENS, P., 1919. "Een nieuwe bladziekte van Hevea veroorzaakt door eeii 

Meeldauschimmel. (Oidium sp.)", Arch. v.d. Rubber cultuur, ii. 9. 
GADD, G. H., 1926. "Hevea Mildew", Year Book, Dept. of Agr. Ceylon, p. 22. 
SHABPLES, A., 1926. "Hevea Mildew in Ceylon and Malaya", Mai. Ag. Jour. 

xiv. No. 4, p. 88. 
MUBBAY, R. K. S., 1929. "On the Occurrence and Significance of Oidium Leaf 

Disease in Ceylon", Trop. Ag. Ixxiii. No. 2, p. 92. 
SANDEBSON, A. R., 1930. "Some Observations on the Mildew Leaf Disease of 

Hevea brasilienais due to Oidium heveae", Quar. Jour. R.R.I, of Malaya, 

vol. 2, No. 1, p. 16. 
BEELEY, F., 1930. "A Recent Outbreak of Secondary Leaf -fall due to Oidium 

heveae", Quar. Jour. R.R.I, of Malaya, vol. 2, No. 2, p. 61. 
BEELEY, F., 1930. "Cost of Sulphur Dusting for Oidium Loaf-fall Disease", 

Quar. Jour. R.R.I, of Malaya, vol. 2, No. 2, p. 66. 
MUBBAY, R. K. S., 1931. "The Influence of Oidium and Sulphur Dusting on 

Yield and Bark Renewal", Quar. Circ. R.R.I. (Ceylon), vol. 8, Pt. 4, p. 42. 
BEELEY, F., 1932. "Effect of Meteorological Factors on the Virulence of Oidium 

heveae in Malaya", Jour. R.R.I, of Malaya, vol. 4, No. 2, p. 104. 
BEELEY, F., 1933. "Oidium heveae: Report on 1933 Outbreak", Jour. R.R.I. 

of Malaya t vol. 5, No. 1, p. 5. 



CHAP, xv MINOR LEAF DISEASES 325 

MURRAY, R. K. S., 1933. "Further Yield Records in connection with Oidium 
heveae", Qwir. Circ. R.R.I. (Ceylon), vol. 10, Pt. 1, p. 1. 

HELMINTHOSPORIUM HEVEAE 

RUE, C. D. LA, 1922. "Helminthosporium heveae, Fetch, in Sumatra", Phyto- 
pathology, vol. xii. p. 60. 

DISEASES OF GREEN TWUJS 

RICHARDS, R. M., 1917. ''Diseases of the Leaves and Stems of Hcrea brasiliensis 
in the Malaya Peninsula*', Ag. Bull. F.M.S. vol. v. Nos. 8 and 9, p. 307. 



SECTION 5 

SCORCHING AND AFTER-EFFECTS, AND 
MISCELLANEOUS 



CHAPTER XVI 

SCORCHING AND AFTER-EFFECTS 

Lightning Damage Loaf Fires Sun-scorch of Exposed Lateral Roots Death of 
Seedling Plants caused by Excessive Ground Heat Die-back of Snags and 
Spear-head Wounds at Junction of Stock and Scion. 

INTRODUCTION 

THE close connection between scorching effects and the Diplodia 
species causing die-back in rubber trees has been referred to, and a 
list of affections is given on page 279 in which this fungus shows up 
prominently. In the headings to the present chapter the items in- 
cluded in the list are repeated, with one addition, viz. leaf fires, 
where the prominent fungus up to date has proved to be Ustulina 
zonata. A resume of the inoculation experiments which go to prove 
that the Diplodia die -back fungus will only penetrate readily into 
the tissues of H. brasiliensis under special conditions when local, 
areas of cortical tissue are scorched, is given in the section headed 
Sun-scorch of Exposed Lateral Roots. 

Lightning and leaf fires produce direct damage which is easily 
observable. The remaining four items listed, required very careful 
attention before substantial evidence was obtained which offered a 
rational explanation. 

LIGHTNING DAMAGE 

For many years the writer has been in close touch with the prob- 
lem presented by lightning damage in coconut plantations, and has 
stated his conclusion that lightning plays an extremely important 
role as the initiating cause of diseases of coconut palms in Malaya. As 
a result of the experience gained while investigating coconut diseases, 
careful attention has been directed towards estimating the amount of 
damage done by lightning in rubber plantations. Lightning damage 
has been noticed in rubber plantations in Malaya for many years 

326 



CHAP, xvi LIGHTNING DAMAGE 327 

past, but the year 1933 was outstanding in showing the serious dam- 
age which may accrue from this cause. Furthermore, the observations 
made during 1933 showed that the special features met with in coco- 
nut plantations are duplicated in rubber plantations, viz. numerous 
small patches of trees affected by lightning are frequently reported, 
and very occasionally large patches of trees, damaged in exactly the 
same fashion, are found. 

Weir summarises the general position as follows: 

The pernicious tendency of lightning to cause damage to plants has been 
well shown in rubber. Many cases have been investigated and talks with 
planters demonstrate the common occurrence of lightning injury to young 
rubber. The "die-back" of 4-12 months old trees wherein the tops wilt, 
the green bark turns black with the appearance later of three or four 
caulicolous fungi, finally resulting in death, is apparently attributable to 
lightning. The affected trees occur in patches and when cut back to stump 
height regenerate rapidly with a discontinuance of damage. 

The influence of lightning on the growth of trees, if the trees are not 
killed outright, usually takes the form of a modification of the developing 
wood cells of the season, so that the continuity of the normal structure of 
wood is broken and a "lightning ring" is formed. 

Most of the information detailed here is extracted from an article 
by the writer published in the Annah of Applied Biology in 1933. 

The observations on the effects of lightning on rubber trees can be 
most conveniently treated under two headings: 

(a) Lightning effects and die-back, usually found on young trees. 

(6) Lightning effects and claret-coloured bark canker at the collar, 
found on trees from four to twenty years of age. 

(a) The symptoms shown by young rubber trees affected by light- 
ning are well described in the quotation from Weir given above. 
The affected patches usually contain from eight to twenty trees, 
(Fig. 49), a few of which will be severely affected so that death super- 
venes quickly; the remainder will be slightly affected only and can 
be saved by pruning back to healthy wood. The important point is 
that few total losses occur, for young trees are seldom killed out- 
right and in those cut back to stump height, the cut being made 
through unaffected healthy tissues, regeneration is rapid, growth in 
length being continued by the shooting of lateral buds from un- 
affected tissues. A careful examination of the root systems of young 
trees affected by lightning is necessary to make certain that the 
symptoms shown are not the result of an attack of one of the fungi 
causing root disease, but only a single case, here and there, need 
be opened up. In fact, the various features are now so well established 



328 



DISEASES AND PESTS OF THE RUBBER TREE PAKT in 



that, except in very exceptional circumstances, a root examination 
can be dispensed with. 

The following is a record from an area recently affected by light- 
ning. The area was planted in 1928 and bud-grafted in December- 
January 1929-30. There were two areas affected: a large area situ- 
ated on an exposed hilltop and a small area on the side of a hill, one 
mile distant. 

The lightning storm, which occurred on November 3rd, 1931, 




FIG. 49. Photograph showing usual appearance of the individual trees in a group 
struck by lightning. Note leafless stem tops in trees affected. 



was a notably severe one. Nothing unusual was seen on the plantation 
until November llth, 1931, when over 100 trees were found showing 
the symptoms described above. The writer was notified on the date 
last mentioned and an inspection of the affected area was made on 
November 13th, 1931; on this visit a careful root examination was 
undertaken, and this showed the root systems to be perfectly healthy. 
In the larger area, 121 trees were treated; of this number, eight had 
to be cut out completely, the rest were treated successfully by pollard- 
ing. The number of treated trees in the smaller area was twenty, of 
which five were total losses. It should be noted in this case, that the 
date of the storm was November 3rd, and the first indication of 



CHAP, xvi LIGHTNING DAMAGE 320 

damage was seen on November llth, eight days afterwards. The 
period elapsing between date of storm and signs of lightning damage 
appearing on the trees varies between eight to fourteen days. 

A further unpublished record of a large area affected by lightning 
was made in 1933, in which 215 bud-grafted trees, two to three 
years of age, showed definite signs of damage. A plan is given (Dia- 
gram No. VIII). Two centres of affection show up in the plan, the 
first diffuse, with an ill-defined centre, lying between vertical rows 
8 and 20 and horizontal rows 7 and 17. The second is concentrated 
between vertical rows 15 and 26 and horizontal rows 25 and 33. In 
connection with this attack, the following paragraph was written 
in the official reply making recommendations: 

It is possible that the area affected will not spread to any great extent 
beyond the limits shown in the plan. In order to obtain a more precise 
conception of the manner in which the affection may spread, it will be 
advisable to make a second plan at the end of this week and a third at the 
end of next. Between the second and third inspections the rate of increase 
should be practically nil. If it shows signs of rising, then the lightning 
theory will have to be discarded. No treatment beyond pollarding is 
possible. 

In reply to this letter the manager reported that on the third 
examination no new infections could be discovered. In the majority 
of cases where a length of one to two feet of the scion was not affected 
by lightning or its after-effects, the buds were shooting with great 
vigour and the total losses numbered only twenty -eight. 

R. M. Richards described an outbreak of Diplodia die-back, in 
1917, in these words: 

On one estate I recall an occasion on which 150 trees seven years old 
were found affected in one group. A few of these trees, not more than six, 
were killed but many of the others had to be cut below the fork. Usually 
one tree is found killed and a group of trees in the immediate vicinity more 
or less seriously affected. 

The above seems an accurate description of a typical lightning 
strike. 

At this stage it may be of interest to give the gist of the general 
theory proposed by Dr. G. C. Simpson, which has a definite bearing 
on lightning in rubber and cocomit plantations in Malaya. He dis- 
tinguishes three types of electrical discharge, only two of which need 
concern us here, viz.: 

The discharge to the ground from a positive cloud. 
The discharge to the ground from a negative cloud. 



DIAGBAM OF TEES ON G ESWE AFFECTED BY LIGHTNING. 



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L LlGHTLV AFFCCTLD 60 

M MODERATELY AFFECTED 63. 

H HEAVILV AFFECTED 34. 

D SCION KILLED BACK TO UNION 26 

CD BOTH SCION AND STOCK KiLLED-2 

CD* 5EE SPECIAL NOTE IN TEXT I 

DIAGRAM VIII 




CHAP, xvi LIGHTNING DAMAGE 331 

The characteristics of the two types of discharge to the ground are 
very different. The discharge from a positive cloud starts high up 
in the atmosphere and branches out on its way to the earth. An 
earth-connected object may therefore be struck either by the main 
"trunk" or by one of its branches. On the other hand, a discharge 
from a negative cloud starts on an earth-connected object which 
takes the whole discharge. Thus the chances of being struck are much 
greater with a positive discharge than with a negative discharge. 

The theory leads to the conclusion that discharges from positively 
charged clouds would be frequent but weak, while discharges from 
negatively charged clouds would be infrequent but very strong. In 
both coconut and rubber plantations the feature of numerous slight 
discharges affecting six to twenty trees, and occasional heavier dis- 
charges affecting one hundred to three hundred plants is quite 
obvious. This year (1933), over thirty reports of lightning damage 
on rubber plantations have been received but the only serious case 
was the one illustrated by Diagram VIII. 

With reference to the prevalence of lightning in different countries, 
it is stated 1 that Java is the most intense spot in the world and 
apparently has more than twice as much lightning as any other 
part of the world. The close proximity of Malaya to Java is worthy 
of note. 

(b) Rubber trees, from four to twenty years of age or over, have 
been found affected by lightning discharges and they showed the 
unexpected feature of typical symptoms of claret-coloured bark 
canker, i.e. patch canker, developing in the region of the collar, at 
ground-level. The fungus, Pythium complectens, Braun, was isolated 
in every case and proved to be the active agent rotting the cortical 
tissues at the collar. 

The first case of lightning injury on trees four to five years of age 
was investigated in March 1931. The trees were planted on a hilly 
slope, on contours, and the ground was covered by a thick growth of 
the cover crop, Centrosema pnhescens. 

A lightning storm was noted in close proximity, five days before 
the affected trees were found. Trees on two contours were affected; 
on the lower contour two dead trees only were found, but on the 
upper, one dead tree and, in addition, seventeen neighbouring trees, 
all slightly affected at soil-level, were observed. 

The dead trees were taken out immediately. The seventeen trees, 
presumably affected by lightning, showed discoloured cortical tissues 
at ground-level. This discoloured tissue formed a patch about six 

1 Shipley, John F., 1933. "Lightning", in Distribution of Electricity, June, p. 1276. 



332 DISEASES AND PESTS OF THE RUBBER TREE PART in 

inches square and extended through the entire thickness of the cortex. 
The discoloured patches showed symptoms exactly similar to those 
described for the panel disease of Hevea, known as patch canker, and 
from them Pythium complectens was easily isolated. 

The important point in these findings was that if the trees show- 
ing the bark attack at the collar had remained unnoticed at the time 
the dead trees were taken out, and had been left untreated, there 
would have been a peculiar outbreak of root disease reported a few 
months later, for which it would have proved difficult to provide 
the correct explanation. 

The cases of claret-coloured bark canker recently found in Malaya 
associated with trees affected by lightning are invariably those in 
which the tree is attacked at the collar. The chief danger in such 
cases is that boring beetles, which are attracted by the smell of the 
affected tissues, may enter the tree and, if this happens, such trees 
succumb, in the majority of cases. 

With reference to the identity of the fungus causing the symptoms, 
the position was somewhat confused owing to the existence of several 
species of Pythium and Phytophthora which are known to be capable 
of producing disease symptoms in Hevea brasiliensis. Thompson has 
showed that two species of Phytophthora and one species of Pythium 
are direct causes of patch canker in Malaya; further, that seven other 
species of Phytophthora, isolated from host plants other than Hevea, 
are capable of causing patch canker symptoms if artificially inoculated 
into the bark of rubber trees. Thus it seems obvious that more than 
one species of Pythium or Phytophthora may be involved in the pro- 
duction of the diseased cortical tissues which are found at the collar 
of mature trees affected by lightning. However, the later work 
which led to the identification of Pythium complectens, as being 
the commonest cause of patch canker in Malaya, supports that of 
Thompson's. 

The most noteworthy occurrence of the association of lightning and 
claret-coloured bark canker at the collar can now be described. 
During the investigations on lightning effects the writer has noted 
the dates of lightning storms occurring in the vicinity of Kuala 
Lumpur. Two heavy thunderstorms were noted on November 18th 
and 19th, 1931; both took place between the hours of 1.30 and 
4.30 P.M. On December 2nd, 1931, a report of lightning damage 
was received from an estate only three miles from the Rubber 
Research Institute. A visit was made and several lightning patches 
were found on trees twenty years of age. There was no cover-crop 
present. 



CHAP, xvi LIGHTNING DAMAGE 333 

The affected patches were situated on a direct north-and-south 
line. The total number of trees found affected was 56. Of these, 
8 were killed outright and 48 were treated for claret-coloured bark 
canker or patch canker, at the collar. 

The symptoms shown by the affected trees could not be mistaken. 
The badly affected trees which had to be cut out were killed as a 
result of the scorched cortical tissues being rapidly invaded, both by 
boring beetles and the Diplodia fungus which causes die-back in 
rubber trees. This black, discoloured cortical tissue proves attractive 
to boring beetles, and the rapid penetration of these insects results 
in the quick death of the tree. The borer attack on badly affected trees 
is of importance when considering treatment of the slightly affected 
trees, showing typical symptoms of claret-coloured bark canker at 
the collar. Because patch canker tissues attract boring beetles, it is 
imperative to remove as quickly as possible not only the trees which 
must inevitably succumb, but also the affected tissue at the base of 
slightly affected trees to prevent penetration of the latter by these 
insects. 

The slightly affected trees all showed the typical symptoms of 
patch canker at ground-level in greater or lesser degree. Figs. 35 a 
and 6 show the appearance of an area of discoloured cortical tissue, 
ten inches by five inches, which was stripped from the wood at the 
collar of one tree. Fig. 35 a shows the extent of the discoloration of the 
affected area when the outer bark layers are scraped away. Fig. 35 6 
shows the appearance of the inner surface of the affected cortical 
tissues; this surface is directly in contact with the wood, and a re- 
flection of this appearance is found on the wood surface. The white 
patches are pads of rubber caused by coagulation of latex which has 
infiltrated from the attacked cortical tissues; in some way a cavity is 
formed by separation of wood and cortex at the cambial layer and 
the latex finds its way into this, finally becoming coagulated. 

The photographs illustrate an extreme case in which a compara- 
tively large bark area is affected, with the fungus penetrating to a 
slight depth into the wood beneath. The more numerous cases are 
those in which a smaller patch of cortical tissue is involved, and 
though the wood surface beneath is discoloured, there is no pene- 
tration of the woody tissues by the fungus. 

The treatment of the trees showing the small patches of diseased 
tissue at the collar is as recommended for patch canker. 

Steinmann reports that Rutgers and La Rue mention a cherry- 
coloured or purple discoloration of bark and cambium in cases of 
lightning wounds. According to these authorities this discoloration 



334 DISEASES AND PESTS OF THE RUBBER TREE PABT m 

remains visible for a short time and can only be seen in trees dis- 
covered quickly. 

Rutgers has investigated the effect of lightning on Hevea in Suma- 
tra, where injury due to this cause is by no means rare in some 
districts. He classifies the effects under four headings: 

(1) Single trees or groups of trees may be killed. In some instances one 
tree is killed, while the branches of the trees nearest to it are withered. 
In other cases, one or more trees are killed, and the tops of the neighbour- 
ing trees wither as in die-back. The bark may be killed in a longitudinal 
strip, sometimes running spirally down the stem, and the dead strip is 
soon attacked by borers. 

(2) Trees which have been struck by lightning but not killed may bear 
short, vertical wounds on the stem, sometimes arranged in a spiral line. 
These may be accompanied by wounds at the collar. 

(3) The exudation of latex from the upper branches is regarded as 
another form of injury caused by lightning. 

(4) The fourth type of injury is the scaling-off of the outer layers of the 
bark on the upper branches apparently somewhat similar to that known 
is ' Top- canker" in Ceylon. 

The mention of die-back in (1) and of wounds at the collar in 
(2) is of some significance in relation to the observations made in 
Malaya. 

La Rue's description of lightning injury to H. brasiliensis is also 
interesting in view of the observations made in Malaya, and there 
seems little doubt that his observations, made in Sumatra, parallel 
those described herein. La Rue states: 

The purple colour developed in the cambium which has been killed by 
lightning has already been sufficiently emphasised. This is of value in 
diagnosing lightning injury in Hevea trees as it is very rarely developed in 
cambium killed by other "agents. This colour often extends outwards into the 
bark nearly to the cork. 

After the bark is dead it is markedly different from bark killed in other 
ways. The bark of Hevea is always full of stone cells, and in bark killed by 
lightning all the other cells disintegrate within a remarkably short time 
leaving nothing but the stone cells with the strands of rubber which have 
coagulated in the latex vessels. The nature of the bark is a sufficient indica- 
tion of lightning injury in cases where it is too late to detect the char- 
acteristic discoloration. 

Without doubt a great many cases of die-back in the tops of Hevea trees 
are due to lightning but are erroneously attributed to Diplodia or some 
other organism. 

Rutgers states he has never seen branches or strips of wood and bark 
torn from Hevea trees injured by lightning. The writer (La Rue) has ob- 
served three cases of this type of injury, but it is extremely rare. 

The spread of the discoloration in the cambium and bark is curious and 



CHAP, xvi LIGHTNING DAMAGE 336 

closely resembles the progress of an infection. It appears that the path of 
the lightning is not on the surface of the tree as it usually appears to be in 
injuries to trees in Europe and America, but through the cambium. This 
tissue seems to offer the best path for the conduction of electricity. How- 
ever, it may be that the current passes mainly through the water in the 
vessels of the sap-wood and that the wood does not readily show the injury. 
The cambium which lies nearer the sap-wood than does the phloem or 
cortex shows evidence of derangement earlier than either. 

There is no doubt that lightning injury takes many peculiar forms. 
One of the features mentioned in the extract from La Rue's paper, 
where a large area of cortical tissue is stripped clean away from the 
wood and no other sign of injury is apparent, was noted in 1933. The 
area of bark affected was situated l|-2 feet above ground-level; at the 
lowest level the split between cortex and wood was complete and the 
cortical layers were lifted wholly from the wood for a distance of 
about twelve inches. In this case, only two trees were affected. 

During the year 1932, numerous cases of lightning damage plus 
claret -coloured bark canker at the collar were reported. During 1933, 
up to September, no cases of this particular affection have been re- 
ported although lightning injury plus Diplodia die-back has been 
extremely common on young plantations. 

Another point of general interest which has already been men- 
tioned is that the clone B.D.5 appears to be very susceptible to 
lightning damage in the first two years. The reason for this is prob- 
ably the habit of growth. Trees of this clone show very rapid growth 
in height with a late branching habit, so that tall, non-branched stems 
are produced which apparently attract lightning. At any rate it is 
found that young trees belonging to the particular clone, when grown 
in blocks contiguous with those of different clones, are always the 
ones to suffer most severely from lightning damage. This feature is 
shown in Diagram No. IX, in which a plan of the trees affected by a 
lightning strike is given; the area affected is carrying an inter- 
mixture of different clones, and while B.D.5 is more severely affected 
than the remainder in this case, it is run close in this respect by the 
trees of A.V.R.O.S.256. 

In conclusion, it may be of interest to place on record the writer's 
experience in 1933. It seemed probable that if lightning was an ex- 
tensive source of damage in rubber plantations, substantial evidence 
should be forthcoming if the dates of the severe lightning storms 
occurring in the vicinity of Kuala Lumpur were tabulated and com- 
pared with those of lightning damage reports received from planta- 
tions. When dealt with in this systematic fashion, all doubts regard- 



336 



DISEASES AND PESTS OF THE RUBBER TREE PART in 



ing the injurious influence of lightning storms on rubber plantations 
quickly vanished. In nearly 80 per cent of storms recorded, reports 




Half of the stem dead. 

Dead through out. 

o Dead on the top portion. 



BD. s. 


IT 


P B. 23. 


7 


P B. 156. 


6 


Av. 50. 





Av. 25d 


14 


sa. 9. 


11 


UN&UDDED. 


t 


TOTAL 


64 



DIAGRAM IX 



of damage to rubber trees were received from estates situated within 
fifteen miles of Kuala Lumpur, always within a period of ten to 
fourteen days. 



CHAP, xvi SCORCHING AND AFTER-EFFECTS 337 

LEAF FIRES 

During normal years when wintering is a more or less gradual 
affair, leaf fires are seldom numerous. There may be a localised district 
from which an occasional report may come, where a period of drought 
has brought about a heavy fall of leaves; in general, the wintering 
carries on during February into March, some trees being leafless, 
some have regained their new flush of leaves and some, estimated to 
be about 15 per cent, do not winter at all in the early season, but 
carry over till the later dry period about August, when there is a 
second, subsidiary wintering. 

During a season such as the wintering period of 1914-15, which 
proved to be a very regular one (i.e. more concentrated in time), the 
whole of the trees on many Malayan estates were quite devoid of 
leaves over short periods. A thick layer of dry leaves formed on the 
ground and such a carpet is very inflammable. Estates lying alongside 
the railway are very prone to leaf fires because the sparks from pass- 
ing engines are quite capable of igniting the carpet of dry leaves. 
Once started, the fire passes over large areas with amazing rapidity, 
scorching the trunks up to a height of ten feet. Usually the pass- 
age of the flames is so rapid that only the surface of the tree is 
scorched, and occasionally the burning of the deeper cortical tissues 
is avoided. 

If left untreated, boring beetles may be at work three days after 
the fire is extinguished. If immediate steps are not taken the insects 
multiply rapidly, and a large number of trees may be lost. Several 
estates lost four to eight acres of mature rubber in 1914-15 owing to 
neglect of treatment of the scorched trees after the leaf fires had been 
extinguished. 

The prominent fungus in cases of trees scorched by leaf fires proved 
to be Ustulina zonata, not the Diplodia die-back fungus, though the 
latter was present. U. zonaia is commonly found associated with 
attacks by boring beetles, and if neglected cases of trees scorched by 
a leaf fire are found heavily attacked by boring beetles, the wood will 
usually show the typical symptoms. 

Treatment of Trees scorched by Leaf Fires. For the purpose of 
treatment, trees scorched by leaf fires can be divided into two groups: 
(a) badly scorched, (b) slightly scorched. 

Treatment should commence as soon as the coolies can work in 
the burnt areas. All possible labour and supervision should be con- 
centrated on treating the lightly scorched trees rapidly; if the insects 
get well into the wood there is little hope of saving the trees. 

z 



338 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

The trees which show only the outer cortical tissues damaged by 
fire are those falling in the group (6). If treatment is carried out 
promptly all the trees in this group should fully recover. The treat- 
ment recommended is that all the scorched cortical tissue should be 
scraped away with an instrument such as a piece of hoop iron, until 
healthy tissues are exposed; the exposed surface should then be 
painted with a mixture of 80 per cent tar and 20 per cent crude oil. 
As a further measure of precaution a second painting might be given 
seven to ten days after the first. 

With reference to group (a), the cortical tissues may be so badly 
burnt that treatment involves the removal of the whole of the bark. 
Usually, in these cases, one side of the tree is more badly burnt than 
the other and the cortex on the more lightly scorched side may be 
saved by treatment as recommended for group (6). During prosper- 
ous times it might be well worth while to treat such trees, but at the 
present time it would probably be more economical to cut badly 
burnt trees right out. However, if badly burnt trees seem capable 
of proving amenable to treatment, and if it is proposed to let badly 
burnt trees remain, the following operations should be undertaken. 
The whole of the burnt tissue should be cut away and the exposed 
wood surfaces coated with the mixture of tar and crude oil in the 
proportions given above. A second coating should follow the first 
after a few days' interval and the trees should be inspected regularly, 
an extra coat being given as long as there are still signs of the beetle 
attack. 

Copious exudations of latex usually take place from bark tissues 
which have suffered severe burning. 

SUN-SCORCH OF EXPOSED LATERAL ROOTS 

In 1926 a lengthy dry period was experienced at the usual winter- 
ing time, February-March, and, as a consequence, the plantations 
in Malaya were practically leafless for a comparatively long period. 
As the usual wintering period in Malaya is somewhat uneven, there 
is usually fair amount of shade in the plantations. 

All the trees were leafless at the same time during the wintering 
period on estates in the vicinity of Kuala Lumpur, in 1926, and the 
daily temperatures were particularly high during the period. 

While the trees were leafless, attention was directed to an affection 
of exposed lateral roots, the symptoms of which suggested those of 
lightning damage or scorching. The disease or affection was first 
noted on a hilly estate and the lateral roots were well exposed, 



CHAP, xvi SCORCHING AND AFTER-EFFECTS 339 

probably due to loss of top-soil by erosion. On these exposed roots 
slight cracks appeared in the bark, which, on further examination, 
showed a much greater extension of apparently scorched, dead, 
dry tissue than the external cracks would indicate. Wounds, 
often two feet long, had to be made to clear away the dead woody 
tissue when the external cracks were not more than a few inches long. 
The affected woody tissue beneath the dead bark showed the typical 
greyish discoloration caused by the intrusion of the Diplodia die- 
back fungus. The wood was not penetrated to a depth of more than 
one inch, but was affected to a far greater extent than the limits of 
the dead bark. 

The fungus was making progress slowly through the wood but 
apparently making none, or very little, through the cortical tissues. 
A yellow discoloration was often to be seen on the inner boundary 
of the discoloured wood. 

No records of a similar outbreak could be found by the writer and 
the matter was somewhat disturbing for the following reasons. The 
percentage infection was about 10, a rather high figure. When trees 
are damaged by lightning, the progress of the die-back fungus is often 
very rapid, and death may ensue very quickly; further, there was no 
obvious explanation, for the fungus, when isolated in pure culture, 
proved to be the usual Diplodia die-back fungus. When this fungus 
was inoculated in fairly large quantities into wounded and unwounded 
roots, the results were negative. Similar results were obtained using 
large portions of diseased woody tissue as the inoculum. 

These negative inoculation results led to the conclusion that, 
except under exceptional circumstances, the disease was not likely 
to spread rapidly, and thus should escape boring beetles. Fortun- 
ately no indications of the presence of boring beetles were observed 
throughout the whole period. 

The problem of the apparent scorching was not easily solved. No 
fires had been reported; the position of the wounds and distribu- 
tion of the diseased trees precluded the explanation of lightning 
damage. After a careful study of the whole list of possible contribu- 
tory causes, the evidence obtained supported the explanation of 
"Sun-scorch". 

The distribution of the affected trees on the hilly slopes was such 
that moving east to west round the hill, no affected trees were found 
on the east side; then as the west side of the hill is approached, a few 
mild cases were found, while when the west side is finally reached, 
several trees in the same row were found severely affected. The same 
sequence is met with moving over the top of the hill from east to 



340 DISEASES AND PESTS OF THE RUBBER TREE PART in 

west, no cases on the east, a few isolated cases on the top, then a 
heavy infection on the west side. Further, on individual trees, show- 
ing a ring of exposed .lateral roots, those shaded by the trunk on the 
eastern side were unaffected or only slightly affected. Thus it appears 
fairly conclusive that the exposed lateral roots on the western slope 
were scorched because they encountered the full force of the direct rays 
of the hot afternoon sun, during a period when the trees were leafless 
and shade was absent. The scorched bark areas were next invaded by 
the Diplodia die-back fungus, which rots the bark to a comparatively 
small extent and penetrates slowly in the wood. 

Later, Ward obtained substantial evidence by means of inocula- 
tion experiments, which supports the explanation of sun-scorch as 
the cause. These inoculation experiments also strongly suggested 
that the Diplodia die-back fungus is not an ordinary wound parasite 
under normal conditions, but that it is a special type of wound 
parasite which can only gain entry into vigorous tissues with the 
greatest difficulty, but if a localised area of cortical tissue is killed 
by overheating, a strong infection follows and the fungus can then 
make rapid headway in the woody tissues of H. brasiliensis. 

This feature is of special importance in so far as several different 
affections of H. brasiliensis, in which the Diplodia die-back fungus 
figures prominently, can all be shown to be initiated originally by 
overheating of cortical tissues. A resume of Ward's inoculation ex- 
periments is given below: 

Expt. 1. It is necessary first to know whether the fungus found in roots 
affected by sun-scorch is capable of directly infecting healthy root-tissue, 
and whether it will function ordinarily as a wound parasite. 

Six wounds on six individual lateral roots were made; areas about four 
inches long and one inch wide were cut into the woody tissue of the roots. 
Coagulated latex produced at these wounded points was removed the 
following day and six pieces of fresh sun-scorched tissue, containing the 
fungus, of slightly less size than the wounds, were then placed on the 
wounds. Inoculations were wrapped in cotton- wool to prevent contamina- 
tion as far as possible. After fourteen days, the results were negative; they 
were still negative after five weeks. 

Expt. 2. Effects of scorching on inoculated and uninoculated lateral 
roots. Twelve leaf fires were made on twelve lateral roots. Six roots were 
inoculated with small pieces of sun-scorched tissue, and six were not in- 
oculated, but left merely scorched, The roots scorched and inoculated 
showed five out of six successfully inoculated, the tissues becoming well 
impregnated with the typical discoloration. The roots, which were scorched 
only, showed early symptoms of sun-scorch; the characteristic symptoms 
had only just penetrated slightly into the woody tissues. In no case did 
the discoloration proceed so far as in the roots scorched and inoculated, 



CHAP, xvi SCORCHING AND AFTER-EFFECTS 341 

although two cases, more advanced than the remaining four, were 
noticeable. 

Expt. 3. Eighteen roots were scorched by leaf fires and inoculated as 
follows: 

(a) Inoculated with the fungus grown in pure culture. 

(6) Inoculated with fresh sun-scorch tissue from diseased lateral roots. 

(c) Roots scorched but not inoculated. 

Three weeks later, all the specimens treated as in (a) and (b) showed 
the typical wood discoloration of sun-scorched tissue; in (c) the fungus 
had penetrated through the scorched tissue but had passed into the wood 
only to a very small extent as in Expt. 2. Two of the controls showed the 
fungus entering the cortical tissues well outside the scorched area. 

These inoculation results with both infected pieces of tissue and 
the fungus from pure cultures are quite positive and indicate the im- 
portant part played in the successful infection of the cortical tissue 
of H. brasiliensis by scorching. If scorching is not carried out, the 
results obtained are seldom positive even after a long period of time 
has elapsed. 

Further inoculation experiments were made to determine the 
amount or severity of scorching required for successful penetration 
of the fungus. The results were not clear-cut, but again the die-back 
fungus successfully penetrated through cortex scorched for thirty 
seconds with an iron bar. A few inoculations were made on branches, 
scorched in a similar manner for thirty seconds, with the addition 
of material from pure cultures of the Diplodia die-back fungus. After 
three weeks the fungus had penetrated well into the wood while the 
results obtained by inoculating branches with pure culture material 
without previous scorching were very different; in such cases the 
fungus had not penetrated into the wood after more than a six -weeks 
period. 

While the experiments quoted cannot be regarded as providing 
final proof, they offer strong indications of the main predisposing 
factor which favourably influences, and enables the Diplodia die- 
back fungus to make a successful entry into the tissues of H. brasili- 
ensis. This evidence, coupled with the prominence of the fungus in 
such affections as lightning injury, sun-scorch of lateral roots, die- 
back of seedlings owing to excessive ground heat, die-back of snags 
and the development of spear-head wounds at the junction of stock 
and scion, affords strong justification for proposing that all these 
troubles are initiated by the overheating of plant tissues in localised 
places. 

The treatment of lateral roots affected by sun-scorch is quite simple; 
all that is required is complete excision of the affected parts, the cuts 



342 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

being made well behind the discoloured wood tissue; the diseased 
parts cut out should be destroyed by fire. 



DEATH OF SEEDLING PLANTS CAUSED BY EXCESSIVE 
GROUND HEAT 

It has been reported, both from Java and Ceylon, that seedling 
rubber plants have been killed or damaged by excessive ground heat. 
Two cases have been observed in Malaya which might be attri- 
buted to a similar cause. In both cases, however, the Diplodia die- 
back fungus was prominent in the region of the collar, a feature 
which is not specially stressed in the cases reported from Java and 
Ceylon. Seedling plants in baskets were involved in both the out- 
breaks observed in Malaya (Fig. 50); the stems of the plants were 
about nine to twelve inches in height, and the outer cortical tissues 
for about one inch above ground-level became blackened. Later, the 
whole of the stem tissue in this area became involved, and the stem 
and head of leaves finally falls over. 

The description given by Fetch for Ceylon specimens corresponds 
closely with the symptoms observed in Malaya, but the causal fungus 
is given as Pestalozzia palmar um, Cke. While this fungus is exceed- 
ingly common in Malaya, it has never been reported as occurring in 
the affection under consideration. However, it is generally admitted 
that both the fungi mentioned are but weakly parasitic so that it is 
possible that P. palmarum might cause symptoms similar to those of 
Diplodia in Hevea, although the dark-coloured hyphae produced by 
the latter fungus could never be confused with those of Pestalozzia. 

The disease, in Ceylon, was found in nursery beds and, as Fetch 
points out, the same ground is often continuously used for nurseries, 
and consequently the soil becomes sour and quite unfit for use in 
nursery beds. Such conditions favour the development of weakly 
seedlings which are unable to resist the attacks of weakly parasitic 
fungi. 

In both cases observed in Malaya, the seedlings were in baskets so 
that the soil was used once only. Large, permanent, adjoining nur- 
series, containing ordinary seedlings for use as stumps, were free, 
or had only a few cases of the disease as compared with the basket 
seedlings. 

A careful inspection of the beds in which the basket seedlings were 
growing showed in one case only a heavy infection before planting. 
The remaining beds of basket seedlings in other situations were quite 
free. 



CHAP. XVI 



SCORCHING AND AFTER-EFFECTS 



343 



There seems little doubt that the heavy infection in certain beds 
was primarily due to the planting of seedlings obtained from a previ- 
ously infected bed. The writer holds the opinion, however, that a 
considerable number of seedlings first showed definite signs of infec- 
tion in the fields, and that considerations such as soil sourness en- 




Fio. 50. Showing typical appearance of seedlings affected by excessive ground 
heat, before bending to collapse finally. Note root development. 

B.C., Woody tissues exposed because cortex has fallen away. 

D.C., Showing discoloured stein areas before affected cortical areas have fallen away from the wood. 



abling a weakly parasitic fungus to attack weakly individuals will not 
account for the whole of the symptoms observed. 

Butler calls attention to a somewhat similar disease on Tea seed- 
lings, and though no parasite has been found in connection with the 
disease in India, yet in Java and Ceylon a fungus has been found on 
the diseased parts. Both in Java and India the original cause of this 



344 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

disease has been assigned to alternations of high humidity and great 
heat. The conditions were most closely examined in India and it was 
found that the disease, i.e. on Tea seedlings, occurred in a season in 
which there was first a long drought with considerable heat towards 
the end, then continuous, heavy rain for about a fortnight, followed 
by several extremely hot days. During these, the disease became 
evident. The trouble was attributed to climatic changes in India, but 
in Java and Ceylon the fungus present is considered to be the direct 
cause, Javan opinion holding, in addition, that abrupt climatic 
changes prepare the way for the attack. 

Steinmann has directed attention to this type of affection during 
dry- weather periods. He states that this disease symptom will often 
occur in nurseries sporadically, but that it is not of a serious nature. 

The symptoms he describes as follows: 

The leaves of the affected plants, already ten to fourteen inches in 
height, begin to pale, turn a dirty yellow and often drop off. At some dis- 
tance over the root-collar the plants also show a circular nick, one or two 
centimetres wide, the bark of which is discoloured and dries up completely. 
The young stem is thereby practically ringed so that below this spot the 
nutrient supply is broken. In a few cases only will the plants perish com- 
pletely; in most cases callus tissue grows from both sides and the dried-up 
belt is thus gradually overgrown. If this dried-up belt is situated on the 
stem above the root collar (which is usually the case), new roots are de- 
veloped from healthy stem tissues above it and the plant may thus be 
enabled to carry on. But sometimes when damage has been done to deeper 
living tissue, the stem dies off and falls over; new shoots will then, however, 
sprout again from below, but these new shoots may in turn become affected. 

In some cases the plants first affected show cracks running lengthwise 
down into the wood; later the tissue dies and the bark dries up completely 
in that spot. Fungus growth always occurs there. The fact that this dis- 
coloured belt is, with surprising regularity, found at the same height in all 
plants attacked, however, makes one suspect that another and primary 
cause has preceded the fungus infection. These fungi (chiefly Ph&ma, 
Colletotrichum and also Diplodia) all turn out to be of a very secondary 
character. 

The consensus of opinion appears to be that a purely physical 
cause is to be regarded as primary, viz. excessive heating by solar 
heat, and that the fungus is purely secondary and often superficial. 
While no definite work in the shape of isolations or inoculations was 
undertaken by the writer, it is agreed that the primary cause is 
scorching, but, in Malaya, it is only another case of the association 
of the Diplodia die-back fungus with overheating of cortical tissues. 

Swart observed a similar occurrence also on young basket plants, that 
at the start of the dry season had been transplanted from the nurseries 



CHAP, xvi SCORCHING AND AFTER-EFFECTS 345 

into the fields. In this ease, it is reported the early stages were sterile, 
whereas at advanced stages a fungus was found which, according to our 
experience in such cases, often occurs secondarily. The fact that the plants 
that were kept in the nurseries did not show this symptom of disease and 
that those plants that had been transplanted a few months earlier re- 
mained perfectly healthy, did not make it seem probable the disease was 
due to a parasitic fungus; everything seemed to indicate that it was due 
to a purely physical cause, viz. scorching by the heat of the sun. 

Steinmann suggests that the usual cause of the disease is that the 
seedlings have been planted too deep, so that the part of the stem that 
is still green and unprotected against external influence by a cork 
layer, comes into contact with the greatly heated soil surface and 
the hot layer of air immediately over it, and so gets burned. In most 
cases in which discoloration just over the ground occurs, the excessive 
reflected heat has first damaged the tissue of the stem, whilst wet 
weather following on the hot period stimulates the growth of fungi 
in these spots. 

Similar types of damage caused by overheating have been reported 
from temperate regions by Hartley. 

The disease, or affection, has never caused serious damage in 
Malaya, and removal and destruction of all the affected plants is all 
that is required. 

DIE-BACK OF SNAGS AND SPEAR-HEAD WOUNDS AT JUNCTION 
OF STOCK AND SCION 

These two affections can be treated under one heading. Both of 
them have to be considered as dependent upon and subsequent to 
the operation of budding, and in both cases, the ashy-grey dis- 
coloration typical in all woody tissues attacked by the Diplodia die- 
back fungus is conspicuous in the affected tissues. 

The budding operation should be undertaken preferably on young 
rubber trees from twelve to eighteen months old. It is desirable to 
carry out budding at as early an age as possible, so that when it has 
been successfully accomplished, and the stock finally pruned, only a 
comparatively small wood surface, from one to one and a half inches 
in diameter, is exposed. A wood surface of this small size is rapidly 
covered by the ingrowing callus. Healing may be completed in six to 
nine months' time and there is no special necessity to lay emphasis 
on the matter of a protective covering for the wood surface exposed 
by the final pruning. 

While it is generally recognised that young stumps or seedling 
stocks are most easily worked, there are numerous instances where 



346 DISEASES AND PESTS OF THE RUBBER TREE PART in 

obstacles have arisen to delay the budding programme and the plants 
attain the age of three to four years before the operation can take 
place. Cases are known where budding has been done on even older 
trees, and in these a very large wood surface is exposed at the final 
pruning, which must necessarily take a long time, even years, to heal 
over. 

The fundamental principles of disease treatment are all against 
leaving such large exposed wood surfaces unprotected. The usual 
treatment has been, in Malaya, to paint the exposed surface with a 
fungicidal solution of one of the usual proprietary coal-tar deriva- 
tives soon after cutting, and later to apply asphaltum -kerosene 
mixture. As long as the asphaltum layer remains unbroken, the scion 
tissues should not be penetrated. 

Trouble was soon experienced in the field, as a result of die-back fungi 
gaining entry to the stock tissues and causing the death of both bark 
and wood tissues. The favourite point of entry is on the side opposite 
to the bud patch; the reason for this is that the wood and cortical 
tissues in this region gradually begin to dry out because of the strong 
pull exerted on the water supplies by the rapidly developing scion. 
This die-back may, if neglected, develop and grow downwards into 
the scion tissue to a point well below the level of the bud patch, and 
occasional cases have been obtained where the die-back had pene- 
trated into the root system. Several fungi are prominent on such 
rotting scion tissues; two common ones &rsPolystictusoccidentalis,i\., 
and Lentinus lecomtai, Fr., while in almost every case the ashy grqy 
discoloration typical of the presence of the Diplodia die-back fungus 
is prominent. The percentage infection was often well over 30 per 
cent (Figs 51 a and 6). 

Anatomical investigations conducted on the tissues immediately 
covered by the asphaltum layer showed the pycnidia and spores of 
Diplodia developing quite normally, embedded in the interior of 
the asphaltum layer (Fig. 52). When the asphaltum layer was re- 
moved carefully from the wood surface, a distinct layer of Diplodia 
hyphae was found covering and growing downwards to penetrate 
into the woody tissues (Fig. 52). From these observations it was 
concluded, quite justifiably, that an asphaltum cover had many dis- 
advantages and a search was made for a better medium. 

Laboratory experiments indicated that a mixture of grafting- wax 
with 5 per cent of sulphur would be a great improvement. Twelve 
different covers were tried and the entwas-sulphur mixture, with 
reference to preventing entry of the Diplodia die-back fungus, was 
outstanding. Under the same conditions, stripped surfaces covered 



CHAP. XVI 



SCORCHING AND AFTER-EFFECTS 



347 




FIG. 51. (a) Showing ordinary appearance of snag die-back. (6) Showing one case 
of (a) split open. In this case there has boon some slight penetration of scion 
tissues, but this is comparatively small in amount compared with the penetra- 
tion of the fungi concerned, into the stock tissues. 



348 



DISEASES AND PESTS OF THE RUBBER TREE PART m 



with entwas-sulphur mixture were clear of invasion after six months' 
exposure, while those covered with home-made white lead paint, a 
mixture recommended for wound-dressing of orchard trees in 
England, were badly invaded after a period of three to five weeks. 
The wax-sulphur mixture was recommended for use in the field and 
the early results were very encouraging, for there was a notably rapid 
formation of the callus ring and there seemed no reason to suppose 
that the ingrowing callus would not continue to develop and finally 
enclose the exposed stock tissues. While the advantage provided by 




FIG. 52. Section through asphaltum layer, covering woody tissues which are exposed 
when the pruning is done, after budding has been performed successfully. 

Note numerous DiploiHa pyrnidia with spores, developing normally in the interior of the 
asphaltum layer. Discoloration of the medullary ray cells can be made, out if looked at carefully, 
and these are Diplodia hyphae which have entered and are penetrating through the woody tissues. 

complete and continuous shading was fully appreciated, the treat- 
ment sent up the costs to a considerable degree and, during a severe 
depressed period, insistence on the advantages of shade was not 
maintained. 

The ultimate results of field experience was just as bad as in the 
previous case with the protecting cover of asphalt. If not given shade, 
the wax is melted, probably daily, by the heat of the sun, and some 
of the melted wax runs over from the cut surface at the lower edge 
on to portions of the bark of the stock, on the side opposite to that on 
which the budding is done. These bark areas, which become covered 



CHAP. XVI 



SCORCHING AND AFTER-EFFECTS 



349 



with wax, were either burnt or smothered; in any case die-back set 
in again, and the position was by no means improved. 

Following this experience, attention was naturally directed to 
the question of overheating and its prevention by shade. It seemed 
desirable to enquire into the differences of temperature likely to arise 
between black and white surfaces, for it is well known that the former 
absorb while the latter reflect heat. For this purpose, large test-tubes 
containing water were provided with rubber corks, through which 




thermometers projected with the bulbs lying covered by the water. 
The outside of the tubes were coated with materials of various colours. 
The tube covered with the asphaltum-kerosene mixture represented 
the black surface, while a thick layer of whitewash on the outside 
of one of the tubes represented the white surface. The test-tubes, 
when prepared, were put out in the sun in an enamelled tray, lying 
on a thick pad of cotton- wool. 

The graph given in Diagram No. X shows the results obtained, 
and they were rather unexpected. The trays were placed in the open 
just after 8 A.M. and all showed the same temperature of 26 C. 



350 



DISEASES AND PESTS OF THE RUBBER TREE PART in 



Taking into consideration only the black and white test-tubes, the 
difference in hourly temperatures was as follows: 





Black Bulb 


White Bulb 


L>ifference 


9 A.M. . 


47-5 C. 


34-0 C. 


13-5 C, 


10 A.M. . 


54-0 C. 


36-0 C. 


18-0 C. 


11 A.M. . 


58-0 C. 


38-5 C. 


19-5C. 


12 NOON . 


60-0 C. 


40-5 C. 


19-5 C. 


1 P.M. 


61-0 C. 


41-0 C. 


20-0 C. 


2 P.M. 


61-5 C. 


41-0 C. 


20-5 C. 


3 P.M. 


60-5 C. 


39-5 C. 


21-0C. 



The results show that the difference in temperature after only two 
hours' exposure is 18 C. and thereafter a fairly constant difference of 
about 20 C. Converted into Fahrenheit, this difference is equivalent 
to 68 F. 

The large difference in temperature brings this particular type of 
decay into line with the other affections described in this chapter. 
The effect of overheating on the thin-walled, delicate cells composing 
the ingrowing callus ring cannot be ignored, and this is probably 
largely responsible for the presence and development of the Diplodia 
die-back fungus in the wood tissues of the stock. Enquiries have 
elicited the information that in French Indo-China the affection 
known as snag die-back has been very troublesome, largely because, 
in that country, a prolonged dry period is experienced during part of 
the year. The trouble is now no longer acute because budding is al* 
ways done on the side of the stock facing north-east or south-west, 
so that there is some measure of protection against the full force of 
the direct rays of the sun; this is supplemented by an annual paint- 
ing with whitewash, so as to completely cover the pruned surface, 
which had been previously treated with tar. Also seeds or cuttings 
of climbing legumes are planted at the base of the stock and allowed 
to grow up and over the wood surface exposed by the pruning, so as 
to provide shade; these climbing plants are prevented from growing 
over the developing scions. There seems little doubt therefore, that 
in these cases field-experience supports laboratory findings. 

A feature of some importance which has emerged from the work 
in the field is that the final pruning cuts should be made at a slope, 
not less than 45. Even a steeper slope seems to encourage the more 
rapid development of the callus. 

This is important because the die-back in the stock tissues may 
have progressed to a distance of five to six inches below the place 
where budding was done. In such cases, a very steep angled cut 



CHAP, xvi SCORCHING AND AFTER-EFFECTS 351 

would have to be made to cut out the diseased tissues efficiently: this 
can be done with safety, if there is no sign of diseased tissue in the 
vicinity of the bud patch. 

Protection of Pruned Surfaces in Budding Operations. (a) If 
budding is carried out on trees not older than 1 J-2 years of age, it 
is a matter of personal choice as to whether a protective layer should 
be used or not. Even if the pruned surface is not treated in any way, 
it is extremely unlikely that any damage would be done if the trees 
are vigorous and growing under normal conditions. 

(b) Buddings worked on large stocks should be treated as indicated 
above in the text. The final cut should be made at an angle of 
not less than 45 and an application of a disinfectant solution on 
the cut surface should be made the same day. On the day following, 
the cut should be covered with tar or an asphaltum mixture. It is 
stated by some estate managers that only the wood surface should 
be treated with the wound cover, while the cortical ring should be 
left untouched as far as possible. This may be good advice and is 
perhaps well worth trying, but the writer cannot speak from experi- 
ence. After a short time, more especially on the approach of dry- 
weather periods, the black surfaces should be given a coat of white- 
wash; once applied, this white surface should be maintained. Shade, 
provided in any suitable manner, will encourage the rapid develop- 
ment and early closing-over of the callus ring, It will be remembered 
that the use of whitewash as a fungicide for the control of mouldy rot 
was rather ridiculed in the section dealing with that disease, but if 
readers have followed the explanations given above, there should be 
no possible chance of confusing the issue. A whitewashed surface is 
less prone to excessive overheating by the direct rays of the sun. The 
point is an obvious one, but unless special mention is made here, it is 
possible that some attempt will be made to show that if whitewash 
proves of utility in one connection, there can be no absolute objection 
to its use in another. The point is that whitewash cannot be considered 
as a fungicide, or even as a disinfectant, and for mouldy-rot treat- 
ment in mature rubber areas it cannot possibly prove of permanent 
value. 

Treatment of Snags already suffering from Die-back. The only 
difference from the suggestions made above refers to the actual 
cutting-out of the diseased tissues. The angle of cut necessary to clear 
out all diseased tissue may be as steep as possible. In many cases, 
even a very steep -angled cut will not take out all the diseased tissue. 
If this is so, the diseased tissue should be allowed to remain and must 
on no account be chiselled out, more especially if it happens to be in 



352 DISEASES AND PESTS OF THE RUBBER TREE TART in 

close proximity to the point where the scion actually joins the stock. 
After the cut has been made, the instructions given above should be 
followed. 

Spear -head Wounds at Junction of Stock and Scion. This affection 
is merely a variant of snag die-back, in which not only the stock 




Fia. 53. Showing typical appearance of spear-head wounds. To obtain the necessary 
contrast for a photograph a coat of whitewash has been applied around the 
wound, on unaffected tissues. Note the lengthy discoloured wound formed in 
the scion tissues. 

tissues but the scion tissues become affected with the die-back fungi 
already mentioned. In so far as the scion is involved, this type of 
affection may have more serious consequences than the snag die- 
back, more especially as the black lines, characteristic of the presence 
of U. zonata, are usually present. The scion tissues involved are those 
on the side facing the stock, and if the tree is in vigorous health, the 
healthy cortical tissues commence to form a covering of callus tissue, 
which rolls in from both sides, forming a typically shaped spear-head 



CHAP, xvi SCORCHING AND AFTER-EFFECTS 353 

wound (Fig. 53). High -percentage affections have been recorded from 
a few estates and, at first, the writer was extremely pessimistic re- 
garding the number of likely recoveries. However, good natural 
recoveries have been made in practically all cases. 



REFERENCES TO LITERATURE 

LIGHTNING STORMS AND AFTER-EFFECTS 

RICHARDS, R. M., 1916-17. "Diseases of the Leaves and Stems of Hevea 
brasiliensis in the Malay Peninsula", Ag. Bull. F.M.S. vol. v. p. 311. 

RUTGERS, A. H. L., 1919. "Lightning damage of Rubber", Arch. v. d. Rubber- 
cuhuur, vol. 8, No. 4, p. 163. 

RUE, CARL D. LA, 1922. "Lightning Injury to Hevea brasiliensis", Phyto- 
pathology, vol. xii. p. 386. 

WEIR, J. R., 1928. Ann. Rept. Path. Div. Rub. Res. Inst. of Mai. p. 81. 

SIMPSON, G. C., 1929. "Lightning", Nature, No. 3134, Nov. 23rd; Twentieth 
Kelvin lecture, Inst. of Elec. Eng., April 25th. 

THOMPSON, A., 1929. " Phytophthora Species in Malaya", Mai. Ag. Jour. vol. 
xvii. Nos. 3 and 4. 

SHARPLES, A., 1933. "Lightning Storms and their Significance in relation to 
Diseases of (1). Cocos nucifera and (2) Hevea brasiliensis", Anns, of App. 
Biol. vol. xx. No. 1. p. 1. 

LEAF FIRES 

SHARPLES, A., 1926. "Scorched Trees and their Treatment", Ag. Bull. F.M.S. 
vol. v. No. 1, p. 1. 

SUN-SCORCH OF EXPOSED LATERAL ROOTS 

SHARPLES, A., 1926. "Sun-scorch of Exposed Lateral Roots of Hevea bras- 
iliensis", Mai. Ag. Jour. vol. xiv. No. 5, p. 116. 

WARD, F. S., 1926. "Inoculation Experiments in relation to 'Sun-scorch* on 
Exposed Lateral Roots of Hevea brasiliensis", Mai. Ag. Jour. vol. xiv. 
No. 9, p. 286. 

DEATH OF SEEDLING PLANTS THROUGH EXCESSIVE GROUND HEAT 

SWART, N. L., 1917. "Eenige opmerkingon naak aanleiding van ondernemings- 

bezoeken en de in 1916 door het Proef station uitgebrachte adviezen", 

Arch. v. d. Rubber cultuur, vol. 1. p. 47. 
HARTLEY, C., 1918. "Stem Lesions caused by Excessive Heat", Jour. Ag. 

Research, vol. 14, No. 13, p. 695. 
STEINMANN, A., 1923. "On a Disease of Hevea Seedlings in the Nurseries", 

Arch. v. d. Rubbercultuur, vol. 7, No. 10, p. 444. 
SHARPLES, A., 1925. "A Collar Disease of Rubber Seedlings", Mai. Ag. Jour. 

vol. xiii. p. 150. 



2A 



CHAPTER XVII 

MISCELLANEOUS 

Spot tings in Prepared Rubber Para -Nitro -Phenol as a Mould Preventive Rust 
Abnormalities Regeneration of Tissues after Wounding; Copper Compounds 
as Spraying Mixtures for Diseases of Rubber Trees. 

SPOTTINGS IN PREPARED RUBBER 

THE first problem the writer was called upon to deal with on arrival 
in Malaya was the outbreak of extensive epidemics of coloured spots 
in pale crepe and pale sheet rubber. These were the types of rubber 
commonly manufactured about 1912 and for several years afterwards. 
Later, the introduction of the present practice of smoking rubber 
rendered the problem a matter merely of academic importance. 

The main point of interest shown by the investigations of Bancroft 
and the writer was that the coloured spots were caused by the develop- 
ment of fungi within the substance of the prepared rubber. These 
fungi are commonly occurring ones, usually chromogenic organisms, 
and they find their way into the latex before coagulation. The spots 
were of various colours: red, black, blue-black, dark blue, yellow, 
violet; there were also transparent and opaque spots. As will now tye 
realised by readers, fungi will not develop in the absence of a sufficient 
degree of moisture, and delayed drying was shown to be the main 
cause of the trouble. Inefficient drying was closely associated with the 
ineffective design of the drying-sheds in the earlier days of the rubber 
plantation industry, for as often as not they were but temporary 
structures. 

Eaton gives the following probable reasons for slow drying: 

A badly ventilated drying-room. 

Excess of sodium bisulphite. 

Insufficiency of sodium bisulphite. 

Too thick a crepe. 

Storage in a damp place or on cement floors. 

It may be pointed out here that coloured spots may develop after 
drying and packing, while the rubber is in transit, on account of 
accidental wetting of the cases with rain, sea-water, or being stored 
in the damp hold of a ship. 

354 



CHAP. XVH MISCELLANEOUS 355 

The obvious remedy for preventing the development of these 
coloured spots is proper drying. There is no necessity to detail the 
methods which have been utilised for preventing the development of 
the spots by the addition to the latex of chemicals which are inimical 
to the development of fungi. 

1 part of formalin to 800 parts, or 1 pint to 100 gallons, of latex 
has been used successfully in spot prevention. * 

Chinosol has been recommended for use in 1 per cent solution, but 
this chemical is comparatively expensive. 

The following fungi have been mentioned as causal agents of these 
coloured spottings: 

Causal Fungi Colour of Spotting 

Monascus heterosporus (Schroet.) Red spotting 

Chromosporium crustaceum, Sharpies Black spottings 

Trichoderma koningi, Oudem. Blue-black spot on crepe 

Penicillium maculans. Sharpies Yellow spot on sheet 

Spondylocladium maculans, Bancroft Yellowish -red? or dark- 
green or almost black 
spot? 

Fusarium sp. Violet spots on sheet 

Botryodiplodia theobromae, Pat. Dark-blue spot 

Mycogone sp. Red flush on sheet 

Penicillium and Aspergillus spp. Transparent spots 

Eurotium candidum, Speg. Opaque spots 

After preparation, rubber of any description will develop mouldi- 
ness if stored under damp conditions, or if it conies in contact with 
water, either rain or sea- water, during shipment or transit. The moulds 
which develop are those commonly appearing on domestic articles 
when kept in a damp state in the tropics, such as the green moulds 
(Penicillium and Aspergillus spp.) which appear on damp shoes, or 
the yellow and black moulds (Sterigmatocystis sp.) which grow luxuri- 
antly on damp bread. There is only one satisfactory method of pre- 
venting mould development on pale rubber, and that is by keeping 
the rubber under conditions so dry that the growth of mould is im- 
possible. For the prevention of mould growths and "rust" on smoked 
sheet, the use of a solution of para-nitro-phenol has been found to be 
effective. Eaton recommends its use as follows: 

PARA-NITRO-PHENOL AS A MOULD PREVENTIVE 

Para-nitro-phenol has been found to be effective in preventing the 
development of mould growths and "rust" on smoked sheet. 



356 DISEASES AND PESTS OF THE RUBBER TREE PART in 

It is not recommended in the case of pale crepe, since pale crepe after 
treatment becomes discoloured on exposure to light. 

Methods of Application 

1. Addition to Latex. The substance is somewhat difficult to dissolve 
in water, and if it is desired to incorporate it with latex it may be mixed 
with the coagulant. A 1 per cent solution (i.e. 1 Ib. dissolved in 10 gallons 
of water) is recommended, in the proportion of 1 volume of the 1 per cent 
solution to 60 volumes of standardised latex (i.e. latex diluted to a dry 
rubber content of 1J-1J Ibs. per gallon). It can be used with acetic or 
formic acids or with sodium silico-fluoride. 

Owing to slight impurities in the commercial product, the solution 
should be filtered through a fine cloth in order to remove any insoluble 
impurities before it is added to the latex. 

2. Soaking method. An alternative method of application which is more 
economical and is recommended in preference to the direct application 
of the solution to the latex, is to soak the freshly-machined sheet in a solu- 
tion of the chemical. For this purpose 3| ozs. of the chemical are dissolved 
in 20 gallons of water (i.e. 1 part of the chemical in 1000 parts of water). 

The freshly-machined sheets are placed singly in the solution and all the 
sheets are allowed to soak for about half an hour. The sheets are then re- 
moved from the solution and allowed to drip for about two hours in a well- 
ventilated but a preferably shaded situation, before being placed in the 
smoke-house. 

In order to ensure complete immersion of all the sheets, a weight of some 
kind should be placed on the top of the sheets. The object of placing the 
sheets singly in the solution is to ensure that the whole surface of each 
sheet comes in contact with the chemical. If a mass of sheets is placed in 
the solution, the solution will not be absorbed by the sheets in the centre 
of the mass. 

The above quantity of solution is sufficient for the treatment of two 
batches of 100 Ibs. of sheet. If only one batch of sheet is soaked in the 
solution on one day, the solution may be kept for the treatment of another 
similar batch of sheets on the following day. The solution should then be 
discarded and a fresh solution used for the treatment of further quantities 
of sheet. 

Notes 

1. Para-nitro-phenol is usually shipped in drums and is in the form of a 
cake which contains a certain proportion of moisture. The most convenient 
method of handling it is to place the cake in any suitable vessel (e.g. a 
Shanghai jar) for about two days, after which it can be crushed easily into 
a powder. 

2. Samples of rubber treated with this chemical may be sent to the 
Institute for tests for mould development. The method of application of 
the chemical should be stated. 

3. The sheet should be packed as soon as possible after removal from the 
smoke-house, preferably after 10 A.M., when the atmosphere is warm and 
less damp than in the early morning. Sheet which is stored in the open 



CHAP, xvii MISCELLANEOUS 357 

absorbs moisture more rapidly and to a greater extent than sheet which 
is packed, and such moisture absorption increases the liability to mould 
development. All cases should be sun-dried before being packed and, after 
packing, should not be stored in direct contact with a cement floor. If 
sheet has to be stored on the estate and the store is badly sited, it may be 
necessary to adopt both methods of application of para-nitro-phenol. 



RUST 

This subject is referred to since Hellendoorn held the view that the 
deposition of a film of serum substances on sheet rubber causes 
"greasiness" and that rust is formed by the decomposition of this 
film by a micro-organism. The view held at the present time is stated 
by Eaton as follows: 

Rust is caused by the decomposition of serum, which exudes from the 
sheet during drying in the early stages of smoking. Rapid surface-drying, 
by hanging the sheets on racks in a well-ventilated place for about two 
hours before placing in the smoke-house, will usually remedy this defect. 
Soaking the freshly-machined sheet in a solution of para-nitro-phenol 
before smoking will also eliminate both "rust" and moulds. 

Weir, in his annual report for 1928, draws attention to many 
varied, miscellaneous matters. These are of minor importance but it 
is necessary, for the sake of completeness, to refer to them. The fol- 
lowing notes are largely copied from Weir's report: 

ABNORMALITIES 

Hevea is influenced by different growing conditions, and hereditary or 
inherent impulses may develop abnormalities of various kinds. 

(a) Fasciation. The flat band-like branches simulating ram or moose 
antlers are observed to be inherent in certain individual trees and are 
produced at successive intervals without the influence of outside agencies. 
A tree has been studied on which these fasciations had been pruned back 
to the parent stem. New shoots had developed at this point and these were 
fascia ted. The abnormal branches which had not been pruned but which 
had died back to the more cylindrical part of the branch, as they always 
do, had regenerated shoots below the dead parts. These also were fasciated. 
These observations imply an inherent force and not external agents as the 
cause. Fasciation has been artificially produced in Hevea by mechanically 
manipulating the terminal bud and by forcing growth into a single lateral 
bud. Seedlings with the tops heavily infested with mites occasionally 
produced bandlike terminal or lateral structures due to the concentration 
of the mites on one side of the shoots. 

(b) Warty Bark. In rare instances peculiar types of hypertrophies of the 
bark of Hevea are found. In one type the bark bears flat-topped, pyramidal, 



358 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

4- or 6-sided, laminated warts ranging in height from J to J an inch. These 
warts, which are composed almost entirely of cork, may be uniformly de- 
veloped over the entire surface of the older parts of the tree or may occur 
singly or in patches here and there. Trees having the above characteristics 
have been located and will be used for propagation purposes in a general 
study on disease resistance and inheritance. 

(c) Diseases of Catch Crops. The occurrence of some of the common 
root diseases of rubber on catch crops is of interest to planters but should 
not be considered in a serious light. A comprehensive system of control 
should take into consideration the fact that any condition which increases 
the amount of organic material, dead or living, in the soil may be expected 
to increase the incidence of root disease. The fact that the roots of catch 
and cover crops are attacked is an indication that there is more inoculum 
in the soil for a particular site than is desirable. This is a condition in most 
cases over which the planter may previously have had little control. This 
being the case, more attention should now be given to keeping the base of 
the trees free from disease. As stated elsewhere, the basic principle of root 
disease control is embodied in any scheme that will prevent infection of 
the basal parts of the tree. If this is done effectively much of the work on 
the inspection and elimination of lateral roots may be greatly reduced. 

The following fungi have been recorded on catch crops, viz. Fomes 
lignosus on Coffee, Tea, Tapioca, Oil Palm, Coconut Palm, Gambier and 
Kapok. Fomes lamaoensis on Coffee, Tea and Kapok. Ganoderma pseudo- 
ferreum on Oil Palms. 

(d) Cover Crop Diseases. What are probably the four principal fungous 
diseases of cover crops have been investigated in a preliminary study both 
under field conditions and under controlled experiments in pots. Sclerotium 
rolfsii, Sacc., has either been found in nature or inoculated on Vigna 
oligosperma (=Dolichos hosei), Calapogonium mucunoides, Centrosema 
pubescens, Centrosema plumieri, Pueraria javanica, Mimosa invisa, Crota- 
laria anagyroides, Crotalaria usaramoensis, Crotalaria striata, Tephrosia 
Candida, and Leucaena glauca. 

Rhizoctonia solani, Kuhn (Corticium vagum), B. et C. (=Hypochnus 
solani, P. et D.), attacks Vigna, Calapogonium, Tephrosia, Mimosa and 
Crotalaria. Pythium sp. has been found to cause a die-back of Centrosema, 
Indigofera and Vigna. These fungi either attack mature plants or cause 
a "damping-off" or wilting of seedlings. The effect in the field is to cause 
the cover to die off in patches which may or may not regenerate, depend- 
ing upon weather conditions. 

(e) Cover Crops: Relation to Disease in Rubber. Any condition that 
promotes a high moisture content around the base of the tree is favourable 
to root disease. Hence cover crops allowed to grow around the base of trees, 
especially young trees, are undesirable. The greater rapidity with which 
small jungle stumps decay when enveloped by a heavy growth of Cala- 
pogonium or Centrosema is a case in point. When covers are planted the 
base of the trees both large and small should be clean weeded. The fructi- 
fications and mycelial strands of Fomes lignosus, and the encrusting fruit- 
ing bodies and conidia- bearing hyphae of certain harmful fungi, have been 



CHAP, xvii MISCELLANEOUS 369 

found growing in early stages of infection abnormally high on trees sur- 
rounded by a dense growth of cover. 

Under a heavy mat of cover plants the strands of Fomes ramify over 
the surface of the soil and follow the tap-roots of the plants to their greatest 
depth, eventually causing their death. This condition has been studied in 
Calapogonium and Vigna and may be expected to occur with any cover. 

These are extreme conditions and may be explained by the fact that the 
fungi were in great abundance in the soil before the covers were planted. 
Ordinarily Vigna does not form a very dense cover except in rich, moist, 
exposed situations. 

That cover plants, whether herbaceous or shrubby, may be expected 
to afford an increase in nutrient substratum for mycelial development is 
by no means alarming. Plant cover plants by ail means on certain soil 
types if possible. Nitrogen fixation, aeration and prevention of erosion are 
desiderata which outweigh all other considerations on most soils. On 
level, porous soils where there is little or no erosion and where the rubber 
with increasing age is gradually developing a rich natural forest soil the 
planting of cover crops, it would seem, is quite unnecessary. 

Some remarks relative to cover plants and root diseases have been 
offered earlier, but a few comments may be added here on section (e), 
above. In view of the recent outbursts in respect of so-called "forestry 
methods" of cultivation, the remarks of a senior pathologist, with 
experience in many parts of the world, are of extreme interest. They 
show quite definitely that the essential principles of soil conservation 
are always kept well in mind by investigators working on patho- 
logical problems. They also show that controlled "forestry" methods 
are in no way antagonistic to the first principles underlying plant 
pathology. The date of their publication was in 1928, before the 
"forestry" method furore, which came about 1930 and has continued 
up to the present date. 

(/) Bark Hursts by formation of Rubber Pads. A peculiar feature noted 
in a field of nine-year-old bud-grafted rubber was a fair percentage of bark 
bursts which were caused by the formation of a large pad of rubber 
between the wood and the bark. Recent inspection has shown that in the 
great majority of cases the bursts originate in close proximity to the places 
where the ends of the wire cup-holders had been inserted into the bark. 

The bark was thin, and to attach the cup-holders firmly the ends of the 
wire had to be forced deeply into the cortical tissues. In many cases the 
cambium, or at least the rapidly developing inner cortical tissues, must have 
been badly injured. This was proved by the large number of trees which 
showed knobs or swellings of secondary tissue along the vertical line where 
the ends of the cup-holders had been inserted. 

The production of the large rubber pads (one measured 14 inches by 
4 inches and was 2 inches across at the thickest part) is difficult to ex- 
plain. As long as the latex remains sterile no coagulation will take place, 



360 DISEASES AND PESTS OF THE RUBBER TREE PART in 

so it may be possible that latex infiltrates for a considerable period until 
bacteria make an entry; when this happens, coagulation occurs, and, as a 
result of the great expansion brought about, the bark above is forced out- 
wards and ultimately bursts. 

It is not possible to give a satisfactory explanation for all cases 
when rubber pads are formed between the cortex and the wood along 
the line of the cambial layer. When there is direct injury of the cam- 
bial layer and the laticiferous vessels lying in close proximity above 
it, latex will naturally infiltrate into the cavities so formed. The 
cambial layer provides the line of easiest separation of cortex from 
the wood and it is quite conceivable therefore that latex will collect in 
this position, and when expansion on coagulation takes place, separa- 
tion between the wood and cortex would take place and gradually 
increase in size. The formation of rubber pads between the wood and 
cortex seems to be a common occurrence in patch canker, especially 
in those cases met with most commonly in Malaya, where untapped 
bark becomes affected following a lightning strike. The formation 
of rubber pads between cortex and wood are seldom seen in other 
panel diseases and are not likely to be found commonly in those 
which only affect recently renewed bark. South records that it has 
been proved by inoculations that the Phytophthora of black-stripe 
disease can produce blisters on the untapped bark at a height of about 
four to five feet up the stem. This statement refers to experiments 
carried out in Malaya. Fetch deals with this subject under the head; 
ing of Rubber Pads, and the following extract is taken from his book: 

Rubber Pads. This name is applied to lumps of rubber found between 
the wood and the cortex. They are usually circular and plano-convex, 
being flat on the side in contact with the wood and convex on the other. 
The bark over the pad may crack longitudinally and some latex may exude 
and run down the stem. Sometimes the overlying cortex decays, but it 
frequently remains healthy, especially when it has cracked, and forms two 
raised lips, or flaps, over the pad. 

No single cause can be assigned for these formations. It is probable that 
several agencies may induce this result, but a satisfactory explanation of 
the most general case has not yet been formulated, for it would appear 
that as a rule the overlying cortex is not diseased. It would, however, seem 
that one essential condition for their formation is that the cortex must 
separate from the wood before the pad is formed, The latex collects be- 
tween the wood and the cortex, and it would appear obvious that it cannot 
collect there before there is a cavity between them. 

Pads sometimes form beneath bark which has been killed by Claret- 
coloured Canker. If the dead bark separates from the wood, latex may 
collect behind it, presumably owing to the extension of the separation 



CHAP, xvn MISCELLANEOUS 361 

along the cambium into the surrounding healthy tissue, but this is not of 
universal occurrence in the case of this disease. According to the accounts 
of Black Thread in Burma and Malaya, rubber pads are frequently formed 
beneath the decayed bark in cases of that disease, but they are not com- 
mon under similar conditions in Ceylon. South states that it has been 
proved by inoculations that the Phytophthora of Black Thread disease 
can produce blisters on the untapped bark at a height of about four to 
five feet up the stem, the bark subsequently breaking up and disclosing 
a rubber pad underneath. 

Quite an epidemic of rubber pads occurred in Ceylon during the time 
the Northway tapping system with a rotating pricker was under trial. 
In the system in question the bark at the base of the stem was scraped up 
to a height of eighteen inches, and the pricker was run round the stem in 
horizontal lines, the latex being collected in a channel at the base. To assist 
the flow of latex the scraped part of the stem was syringed with water. 
In many instances, blisters with rubber pads beneath them were formed, 
and these were cited as damage caused by the pricker, but it was clear 
that, in general, they were in existence before the pricker was applied, 
as they bore the marks of the pricker on the outer surface and often con- 
tained fragments of bark which had been pushed into them by the instru- 
ment. In some cases these blisters were the result of Claret-coloured 
Canker, but in others, though the bark died, no disease was traceable. 
All that could be said was that they followed the scraping and syringing. 

An interesting case which probably has some bearing on the foregoing 
occurrence was noted during an attempt to infect Hevea stems with a 
possible parasitic fungus. A small patch on the stem was shaved flat, the 
fungus from a pure culture placed on damp cotton-wool, and this applied 
to the shaved patch and covered with a watch glass. As the weather turned 
dry, the cotton -wool pads were moistened daily. The inoculations were un- 
successful, but in several cases, both in the inoculations and the controls, a 
blister with a rubber pad behind it was formed, while the overlying cortex 
split longitudinally and latex ran down the stem. Thus the blisters and 
rubber pads were caused by keeping a small shaved patch of the stem 
continually moist. 



REGENERATION OF TISSUES AFTER WOUNDING 

This subject is one of considerable general importance and not 
only in a pathological sense. The operation of bud-grafting is ab- 
solutely dependent on regeneration of tissues, which can only be 
carried through successfully by vigorous plants. The subject has come 
into prominence recently as a result of researches carried out in the 
Rubber Research Institute of Malaya over the last two or three years 
and published by Sharpies and Gunnery in 1933. The recent work 
carried out over the same period by Napper on root diseases has led 
to conclusions which also have some relation to this subject. Napper 



362 DISEASES AND PESTS OF THE RUBBER TREE PART in 

maintains that the presence of wounds on a living root does not in- 
crease its susceptibility to those diseases caused by the Fames type 
of fungi, which are responsible for the most serious root diseases of 
rubber trees in Malaya. This view can be accepted without reserve. 
He points out: 

that entrance through a wound may be impossible, the reason being that 
in contrast to wound parasites like U. zonata, the root disease fungi are 
very sensitive to competition and may be easily crowded out and killed 
by the common saprophytic fungi and bacteria which colonise open wounds 
in the field. 

There may be supporting evidence for this, but it will be extremely 
difficult to provide convincing and final proof, especially in the case 
of root diseases, that saprophytic fungi and bacteria, which colonise 
wounds in Hevea roots, are capable of crowding out the important 
fungi causing root diseases. 

Several references have been made to the adequate repair mechan- 
ism possessed by Hevea brasiliensis. Most planters familiar with the 
"stripping" method, recommended in past years for the treatment of 
brown bast, could not fail to be impressed with the rapidity with 
which regeneration of new cortical tissues, to replace those "stripped" 
away, took place; further, when "stripping" was successfully accom- 
plished the renewed bark areas which ultimately developed appeared 
eminently satisfactory for purposes of tapping. 

It has always been assumed, until very recently, that successful 
regeneration of wounded tissues depended entirely on the successful 
functioning of the cambium. The researches mentioned above re- 
sulted in the discovery that, in the case of Hevea (and probably of 
numerous other woody plants), the cambium is not concerned in the 
regenerative process for quite an appreciable period of time after 
wounding has occurred; regeneration commences and is carried for- 
ward by a tissue system entirely different, and only at a comparatively 
late date does the cambium come into action. The subject is too 
technical to treat of in detail here, but it is undoubtedly one of funda- 
mental importance. The modus operandi may be stated for those 
readers who desire to know the main facts. The following account is a 
slightly modified form of the one published in the Annals of Botany. 

The regenerative process is practically the same in Hibiscus nosa- 
sinensis, L., and H. brasiliensis. The commencement can be more 
clearly observed, however, in the former, because tannin deposits, 
which interfere with clear definition of detail in Hevea, are absent. 
If a small bark area is stripped away from a vigorous plant signs of 
cell activity become manifest on the exposed wood surface two to 



CHAP. XVII 



MISCELLANEOUS 



363 



three days after stripping. In transverse sections it will be seen that 
the end cells of the medullary rays, which in Hibiscus are generally 
one to three cells wide, have become large, rounded, or oval-oblong 
with thin walls and sparse protoplasmic contents (Fig. 54). Between 
neighbouring medullary rays smaller cells of similar structure de- 
velop from wood parenchyma cells which normally would form 
xylem or wood elements. As a result of these activities the surface of 
the exposed wood becomes quickly covered with a layer of thin-walled 
cells, the most striking feature of which is their enormous size when 
contrasted with those from which they are derived. This proliferation 
of primary callus cells from the wood is accompanied by a similar 




FKJ. 54. Proliferation of end cells of the medullary rays in the early formation 
of wood callus. Note largo vessels of wood, V. x 200. 

development from the cut edges of the bark bounding the wounds 
occasioned by the stripping (Fig. 55). It is safe here to say that, as in 
the proliferation of callus cells from the exposed wood surface, the 
elements of the medullary rays give rise to the greater bulk of the 
callus cells proliferated from cortical elements, and it appears that 
no callus cells at all are derived from cambial elements. At this stage 
the entire wounded surface is covered with callus tissue, the base of 
the cavity being covered with callus derived from the medullary ray 
cells of the wood, the edges being covered with callus of bark origin, 
using the latter term to include the whole of the cortical tissues 
(Fig. 56). 

The proliferating phase above described is generally completed in 
about six days from the date of stripping, and at this early stage 
there is evidence of the downward extension of the phellogen or 



364 



DISEASES AND PESTS OF THE RUBBER TREE PART in 



cork-forming cambium, the continuity of which has been broken by 
the action of stripping. A further increase in thickness of callus tissue 
at the base of the cayity is brought about by normal cell division of 




FIG. 55. Later phase of callus formation, x 00. 

('.('., Showing radially disposed callus tissue developing from bark tissues. 
W.('., Callus developing on surface of wood. 

the cells composing the callus tissue. Repeated division results in a 
more or less radially disposed series of cell rows, which are loosely 
aggregated at first, but later become consolidated by mutual pressure 
into a large-celled parenchymatous cushion covering the surface of 




FIG. 66. Completed phellogen but incomplete cambium reconstruction, x 18. 

I.C., Unjoined ends of incompletely restored camblal cylinder. 
C.P., Complete phellogen layer. 

the wood. This cushion does not completely fill the cavity, the depth 
of which naturally varies according to the thickness of the bark. The 
phellogen, already developed in the bark callus mentioned above, 
now rapidly extends from the periphery inwards, just beneath the 
exposed surface of the callus cushion, the thin layer of cells thus cut 



CHAP, xvii MISCELLANEOUS 365 

off to the outside becoming suberised, i.e. corky, to form a protective 
layer to the delicate tissue beneath. (The term delicate refers only 
to the fact that such thin- walled cells rapidly lose moisture under dry 
conditions, and desiccation and resultant death would take place 
rapidly.) The pheliogen is completely restored in the way indicated, 
and with the complete formation of an outer suberised layer the 
dangers from desiccation are greatly reduced. 

The second phase of callus formation occupies fifteen to twenty 
days, and in the stripped area there is still a complete absence of any 
sign of normal activity in the zone where the wood and bast forming 
cambium would normally lie. It is not an exaggerated view to take 
that the operation of stripping appears to result in the removal of the 
wood and bast forming cambium in the stripped area. But during 
the callus formation over the stripped area the normal activities of 
those portions of the stem unaffected by the stripping proceed as 
usual, and an appreciable increase in diameter of the wood, owing to 
normal secondary thickening, takes place excepting in the stripped 
area, where cell activity is, for the time being, concerned entirely in 
callus formation. The ultimate result is that the callus cushion ap- 
pears to be sunk in the wood to a depth equivalent to the thickness of 
the woody tissue newly added since the stripping operation was 
performed. Coincident with the increase in thickness of the woody 
cylinder over the uninjured parts of the stem, the cambial ring appears 
to be carried outwards a similar distance, so that the severed ends 
of the cambial ring now impinge on the sides of the callus cushion 
some little distance from the original position at the time the bark 
was stripped. The last phase now ensues, viz. the development of a 
new cambial portion through the callus cushion to form a continuous 
cambial ring. The development proceeds from both sides at the 
points where the severed ends of the original cambium impinge on 
the sides of the callus in the cavity. The ends of the severed cambial 
ring grow towards each other through the callus cushion, sweeping 
across in the manner of a slowly closing diaphragm until the opposing 
ends meet and the cambial cylinder is thus fully restored. 

With the complete restoration of the cambial cylinder the sub- 
sequent history is merely one of normal cambial activity, secondary 
thickening proceeding in the usual way. But preceding this, the outer, 
protective, pheliogen layer is completed and the tissues of the callus 
cushion, in which the new cambial elements develop at a later stage, 
become adequately protected, so that the chances of the successful 
development of a continuous cambium across the callus cushion are 
greatly increased. If, as appears probable, the stripping results in the 



366 DISEASES AND PESTS OF THE RUBBER TREE PART in 

removal of the actual cambium, it is not difficult to visualise the 
necessity for the development of some type of "bridging" tissue 
which will remain in contact with the severed ends of the cambial 
ring on both sides while the latter is being carried outwards by the 
continuous secondary thickening. The development of the callus 
cushion as a bridging tissue allows for the formation of the cambial 
ring in the exact position it would have occupied if stripping had 
not taken place. 

Thus if an outer corky protective layer is formed across the callus 
cushion before the development of the cambium across it, the latter 
will seldom suffer injury. When a suberised corky layer is fully 
formed desiccation can affect the underlying cell layers only to a 
comparatively small degree, and as this proves the greatest danger 
during regenerative processes, little damage need be expected to take 
place to the actual cambial elements developing beneath in the callus 
cushion. Desiccation can affect only the large, thin-walled cells of 
which the callus tissue is composed, but in the presence of adequate 
supplies of moisture the callus cells developed by vigorous plants 
possess an inherent resistance to degenerative influences in the form 
of invading organisms, and therefore, while it may be possible, it is 
more likely improbable that saprophytic bacteria or fungi, or even 
parasitic forms, would cause any great interference with the re- 
generative processes going forward. 

All investigators who have undertaken artificial inoculations on 
the roots of mature rubber trees are well aware that they seldom' 
succeed, and in the writer's experience consistent success has only 
been obtained when Ustulina zonata has been inoculated into large 
wounds. There is little more to add beyond the remark that it 
seems preferable to rely on an explanation which has been demon- 
strated than on one for which it would be difficult to provide con- 
vincing proof. The suggestion of Napper's, therefore, viz. "that root 
disease fungi [of the Fames type] are very sensitive to competition 
and may be easily crowded out and killed by the common sapro- 
phytic fungi and bacteria which colonise open wounds [on rubber 
roots] in the field", does not appeal strongly to the writer. This 
matter is referred to only because a journalistic writer in a local 
Malayan paper has drawn special attention to this particular view 
stated by Napper, and draws far-reaching conclusions therefrom, 
which cannot be accepted by the writer, and probably would not be 
accepted by Napper himself. 



CHAP, xvn MISCELLANEOUS 367 

COPPER COMPOUNDS AS SPRAYING MIXTURES FOR DISEASES OF 
RUBBER TREES 

Most books dealing with plant diseases give details of the method 
of preparation of the standard copper and sulphur compounds which 
are commonly used in agricultural practice. The names Bordeaux 
Mixture, Burgundy Mixture and Lime-sulphur Mixture are familiar 
to all interested or engaged in agriculture; lime and copper are the 
fundamental components of the two first-named compounds. No 
special reference to details of component parts or the method of the 
preparation of these compounds will be given in this work, for it is 
obvious they now take a very minor place in the economy of rubber 
plantations. Spraying mixtures based upon a copper compound, 
usually copper sulphate, require mention, because it is well estab- 
lished that the presence of copper salts, or of particles of metallic 
copper in prepared rubber, induces tackiness. 

As copper spraying mixtures are never used in rubber plantations, 
it appears unnecessary to refer to the matter. But the use of Bordeaux 
Mixture, in the treatment of pink disease, was seriously considered 
around 1914, and it may be necessary to utilise spraying mixtures for 
the treatment of a rubber tree disease at some future date. It is 
advisable, therefore, to mention the work carried out in rubber- 
growing countries and the results obtained when Bordeaux Mixture 
has been used in such a manner as to ensure appreciable quantities 
being incorporated in the rubber after coagulation and preparation. 
This was performed by Brooks and the writer in 1914, and to make 
certain that Bordeaux Mixture had entered the latex, samples of 
rubber were prepared from latex into which the mixture was poured 
directly. The experimental rubber sheets were kept for nearly a 
twelve - months period, but no tackiness became apparent. Fetch 
deals with the subject shortly, and the copy of his paragraphs given 
below, indicates that similar results were obtained in Ceylon. As 
Fetch remarks, "the question of the employment of Bordeaux 
Mixture for diseases of rubber trees consequently remains open for 
further investigation", but it is not an urgent matter at the present 
date and is not likely to become one for a considerable time. Fetch's 
observations are headed 'The effect of Bordeaux Mixture on Rubber". 

It is well established that the presence of copper salts, such as copper 
sulphate, or of particles of metallic copper, in prepared rubber induces 
tackiness. If rubber is washed with a solution of copper sulphate it be- 
comes tacky, while if copper sulphate is added to the latex before coagula- 
tion, the resulting rubber changes into a resinous sticky mass when dry. 
Hence it is generally held that Bordeaux Mixture, which is the most 



368 DISEASES AND PESTS OF THE RUBBER TREE PT.III. 

efficacious fungicidal spray available for general use, cannot be employed 
in diseases of Hevea, because it is a copper compound, and if traces of it 
get into the latex the rubber will become tacky. 

The experiments which have been carried out to test this point have, 
however, not been attended by any such result. At Perideniya a row of 
twenty-five trees, tapped on alternate days, was well sprayed with Bor- 
deaux Mixture. The trees were tapped with two cuts a foot apart on one- 
third the circumference, and the mixture was applied to the tapping sur- 
face to a height of three feet in such quantity that it ran along the cuts 
and down the vertical channel. Heavy rain fell five days after the spray- 
ing, and the rubber of that day's tapping, when analysed, showed 0-00016 
per cent of copper in the biscuit, and 0-003 per cent in the scrap. For six 
months from the date of spraying, the rubber, which was all prepared in 
biscuit form, was kept under observation, but no case of tackiness was 
observed. The experiment has been repeated with similar results in Java 
and Malaya. 

The question of the employment of Bordeaux Mixture for diseases of 
rubber trees consequently remains open for further investigation. It is 
possible that the conflicting results obtained in the experiments quoted 
depend upon the state of the copper in Bordeaux Mixture as opposed to 
that in copper sulphate. Before the adoption of Bordeaux Mixture can be 
recommended, research is required not only into its action on raw rubber 
but also into the behaviour of the rubber during vulcanisation and manu- 
facture. 

REFERENCES TO LITERATURE 

BANCBOFT, C. K., 1911. "Occurrence and Nature of Spots on Shoot Rubber 

and Crepe", Ag. Bull. Straits & F.M.S. X. p. 319. 
SHABPLES, A., 1914. "The Spotting of Prepared Plantation Rubber", Bull. 

No. 19, Dept. of Ag. F.M.S. 
HELLENDOOBN, H. J., 1919. "Over hot ontstaan Van mistiness bij sheet 

rubber", Arch. v. d. Rubber cultuur, Jahrg. 3, No. 9, pp. 419-436. 
EATON, B. J., 1928. "Guide to the Preparation of Plantation Rubber", Plant- 
ing Manual, Rub. Res. Inst. of Mai. No. 1, p. 21. 
WEIR, J. R., 1928. Annual Report, including Initial Period, Rub. Res. Inst. of 

Mai. pp. 61-95. 
SHABPLES, A., and GTJNNEBY, H., 1933. "Callus Formation in Hibiscus rosa- 

sinensis, L., & Hevea brasiliensis, Mull, Arg.", Anns. of. Bot. vol. xlvii. 

No. CLXXXVIII., Oct., pp. 827-838. 



SECTION 6 
PESTS 

CHAPTER XVIII 

INSECT PESTS 

White Ants (Coptotermes curvignathus) Boring Beetles (Xyleboms parvulus) 
Cockchafer Grubs (Psilopholis grandis) Geometrid Moth (Hemithea costi- 
punctata) Limocodid Moth (Thosea sinensis) Lymantrid Moth (Orygia 
turbata) Caterpillar and Noctuiid Moth (Spodoptera sp. and Tiracola plagiata) 
Psychid Moth (Psyche (Acanthopsyche) snelleni) Scale Insects (Lecanium 
niyrum, Pulvenaria sp.) -Rubber Leaf Mite (Tarsonemus iranslucens) Short- 
horned Grasshopper (C yrtacanthacris (Valenga) nigricornis) Crickets (Brachy- 
trupes portentosus) Rhinosceros Beetles (Xlyotrupes gideon) Eumeces squamo- 
su8 Batocora rubra. 

INTRODUCTION 

THE animal pests of all plantation crops are largely comprised in the 
order Insecta. A very striking feature of the pest and disease situation 
in relation to rubber cultivation is the fact that, apart from the 
ravages caused by white ants, there are no major problems to be 
dealt with. This statement should be perhaps modified, because the 
cockchafer grub plague, though at present circumscribed in area, is 
described by interested parties as a potential menace to the industry. 
The writer, however, does not subscribe to this view. 

The following insect pests have been recorded as causing damage 
to rubber trees: 

Common Name Scientific Name 

White Ants ^Coptotermes curvignathus, Holmgr. 

= Coptotermes (Termes) gestroi, Wasm. 

Boring Beetles = Xyleborus parvulm, Eichh. 

Cockchafer Grub = Psilopholis grandis, Cast. 

Geometrid Moth = Hemithea costipunctata, Moore 

Limacodid Moth = Thosea sinensis, Walk. 

Lymantrid Moth = Orygia turbata, Butler 

Noctuiid Moth = Tiracola plagiata , Walk. 

Caterpillars = Spodoptera Sp. 

Bag Worms = Psyche (Acanthopsyche) snelleni, Heyl. 

369 2B 



370 DISEASES AND PESTS OF THE RUBBER TREE PART in 

Scale Insects (Lecanium nigrum, Nietn. 

and =-! 

Mealy Bugs [Pulvinaria Sp. 

Mites =Tarsonemus transluscens, Green 

Grasshoppers =Cyrtacanthacris (Valenga) nigricornis, 

Burn. 

Crickets ** Brachytrupes portentosus, Licht. 

Rhinosceros Beetles = Xylotrupes gideon, L. 
Weevil Eumeces squamosus 

Longicorn Beetle =Batocera rubra 

A large number of insects have been recorded as occurring on and 
perhaps damaging H. brasiliensis. The list given above contains 
those which have been found causing definite damage in Malaya. But 
insects may also cause losses in indirect ways, more especially on 
plantations where a cover crop or a mixed natural cover is allowed to 
develop. There are several recorded cases of the caterpillars of Thosea 
sinensis, Walk., a Limacodid moth infesting fields of rubber where 
certain types of grass have become established. These caterpillars 
feed on the grasses originally. They have tufts of irritating hairs on 
the upper surface of the body, and when these tufts of hair make 
direct contact with the skin great irritation is set up which may last 
for hours. It is extremely difficult to get the coolies to work in in- 
fested fields and, in the cases noted, tapping had to be stopped until 
the attack subsided. As the caterpillar stage of this insect may per- 
sist for about a month, 8J per cent of the yearly crop is lost over in- 
fested areas from the commencement of the attack. Attacks may be 
recurrent and it is obvious that a large percentage of crop may be lost 
in any one year if further generations develop after the adult stage 
has once been terminated. 



WHITE ANTS 

Coptotermes curvignathus, Holmgr. 
= Coptoterme8 gestroi, Wasm. ( = Termes gestroi) 

Pratt wrote in 1914: 

The plantation rubber industry which developed with phenomenal 
rapidity in the Malaya Peninsula has not been threatened with any serious 
insect pests. Before any considerable acreage had been planted it was 
generally considered that Termes gestroi would prove a menace to the 
industry and it was decided to offer the sum of 5000 for an adequate 
remedy against its attacks upon the Para rubber tree. 



CHAP, xvin WHITE ANTS 371 

There is no doubt that at that time there was a good deal of justification 
for the alarm caused by this insect. Many plantations, especially those on 
low-lying lands, were losing a very considerable number of trees apparently 
through the attacks of T. gestroi. One estate lost on one occasion approxi- 
mately 2000 trees of 4 and 6 years of age in the course of 15 minutes (i.e. 
blown over), the majority of which were found to be hollowed by T. gestroi. 

The above describes the position in Malaya and Java, but Fetch 
says that the white ant is not a pest on rubber in Ceylon and South 
India, because T. gestroi is not found in these countries. But as far 
as Malaya is concerned the white ant problem has never been suc- 
cessfully tackled and the position to-day (1932) is not materially 
altered from that of 1910-12. In the days when rubber was very 
profitable, clean clearing and following-up the runs made by the 
insects with a view to finding and destroying the nest, might have 
been an economical proposition, but such control methods are im- 
possible with present-day prices, unless other important factors, i.e. 
treatment of root disease in young areas, are taken into considera- 
tion at the same time. 

Our knowledge of the life history and control of the insect is still 
unsatisfactory, but a comprehensive series of control measures is 
being tried out in Malaya at the present time by Beeley. The results 
of this work are given at the end of this section. 

Termites, which are popularly known as white ants, form a separ- 
ate order of insects, the Isoptera, and are of considerable interest on 
account of their habit of living in communities much in the same 
manner as do certain species of bees and ants. The nest is known as 
the termitarium and contains numbers of individuals belonging to 
different castes, the members of each caste serving the rest of the 
community in their own particular manner. 

The winged forms, which are only too familiar at the lights of 
houses in Malaya during certain periods of the year, comprise normal 
males and females. A male and female, or rather "king" and "queen", 
establish a colony and, from the ova produced by the queen, in- 
dividuals are produced in which the sexual organs are aborted. The 
majority of these sexless termites are "workers" whose function is to 
construct and attend to the termitarium, feed the royal pair and the 
immature forms (nymphs), and, in certain species, to cultivate the 
fungus gardens. The workers are soft-bodied creatures and are quite 
blind, having to rely entirely on the "soldiers" for their protection. 
The latter have prominent hard heads and are equipped with powerful 
mandibles; their primary function is to keep off invaders whilst the 
workers repair any breach in the walls of the termitarium. 



372 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

Once a colony is established, the queen produces ova at a prodigi- 
ous rate; the abdominal segments of her body become greatly dis- 
tended and she often attains an enormous size. The queen remains 
imprisoned in a cell with the king and the sole function of the latter 
is to fertilise the queen. The eggs are oval or cylindrical in shape and 
round at each end. As soon as they are laid they are taken charge of 
by the workers, who clean them and carry them to special nurseries 
where they are tended until the young nymphs hatch out and are 
sufficiently developed to take their allotted place in the nest. The 
development from the egg to the adult stage is gradual, that is to say, 
there is no definite larval and pupal stage as in the true ants; so that 
when they emerge from the egg they resemble in general form a ter- 
mite rather than a grub, and it is through undergoing several skin 
moults that they attain the adult stage. 

At certain periods of the year the sexed wing forms are produced in 
large numbers and, when certain climatic conditions obtain, they 
leave the termitarium at dusk, and those that escape destruction 
establish new termitaria. 

About eighty species of termites are known to occur in the Malay 
Peninsula and doubtless others await discovery. Many of the species 
are very similar in appearance and their identification is often a 
matter of difficulty, and this, coupled with the paucity of literature 
on the subject, has led to confusion, and remarkably little detailed in- 
formation is available concerning any but the two or three commonest 
species. 

There are two closely related species of termites about which some 
confusion has arisen. One is Coptotermes gestroi Wasm. (=-Termes 
gestroi) the other Coptotermes curvignaihus, Holmgr. In connection 
with this, Mr. H. M. Pendlebury, of the Selangor Museum, Kuala 
Lumpur, informed the writer in a private communication that: 

much confusion has arisen over the identifications of Coptotermes gestroi, 
Wasm., and C. curvignathus, Holmgr. Wasmann's original description 
was not entirely adequate, and Haviland (1897), by misidentification, 
regarded C. gestroi as being one of the commonest pests on rubber trees, 
and several authors followed him uncritically. It was only when Holmgren 
(Kungl. Sven. Vet. Akad. Handlingar, Band 50, 1913, p. 77) examined 
Wasmann's type that he found the species which had been treated as 
gestroi (Auctt. nee Wasmann) was distinct in certain structural details; 
this he denominated curvignathus. The fontanelle is present in all castes 
of the Mesotermitidae, to which the genus Coptotermes belongs. 

It appears therefore that C. curvignathus, Holmgr., is probably the 
most important species of termite as far as the rubber-grower in 



CHAP, xvin WHITE ANTS 373 

Malaya is concerned. The soldier of C. curvignathus is somewhat larger 
than that of C. gestroi, 7-5-8-5 mm. as against 6-6-5 mm., and has a 
less oval head; the mandibles are more curved and the pronotum is 
1 mm. wide against 0-65 mm. with C. gestroi. A small orifice is situ- 
ated at the front of the head from which a milky white fluid is dis- 
charged. This is the fontanelle mentioned in the preceding para- 
graph. 

The following observations were made undoubtedly on C. curvig- 
nathus] this should be noted, for it is difficult to decide which species 
Pratt was dealing with in his observations on Termes gestroi, for they 
do not tally with those offered here for attacks by duly authenticated 
C. curvignathus. Termites have often rightly been recorded in Malaya 
as causing damage to living rubber trees, though there appears to be 
a general impression that they confine their attention to diseased 
trees. Pratt says, with reference to T. gestroi, "that the original 
trouble is due in nearly every instance to fungus or bad drainage 
causing root-rot may be taken as an established fact". It may be 
stated quite definitely that there is no justification for the belief that 
healthy trees are immune from attack by C. curvignathus. This 
species appears to be common in Malaya in suitable situations, show- 
ing a strong preference for damp, low -lying land where moist soil 
conditions obtain; the rubber trees planted on peaty areas which carry 
quantities of buried timber are usually very seriously attacked. It has 
been found attacking young rubber showing no signs of disease, and 
if left undisturbed can inflict fatal injury within three or four weeks. 
During recent observations in Malaya, only young rubber was found 
attacked, but it is not suggested that this termite cannot infest 
mature trees. 

On young rubber little variation is shown in the method of attack. 
First a mud tunnel is constructed on the trunk upwards for a distance 
of several feet (Figs. 57 a and 6), and this tunnel is gradually ex- 
tended laterally until the whole of the lower portion of the trunk is 
encased with mud. Repeated examinations of the lower termination 
of the tunnel, which usually stops abruptly about one or two inches 
above the surface of the soil, failed to give any indication of the point 
at which the termites emerged from the soil. 

Once the mud wall has been completed the bark is attacked sim- 
ultaneously at a number of points, but most strongly near the base 
of the trunk. The exudation of latex does not appear to deter the 
invaders, and the attack is usually continued until the whole of the 
lower part of the trunk is denuded of bark. Then the wood is pene- 
trated and numbers of long vertical tunnels are constructed; this is 



374 



DISEASES AND PESTS OF THE RUBBER TREE PART in 



followed by an attack on the root system, by which time the tree is 
injured beyond recovery (Fig. 58). 

Fetch, writing of attacks by Termes gestroi, says : 

T. gestroi usually attacks a tree below ground-level. Like the majority 
of termites, it travels underground by means of narrow galleries, and when 
one of these galleries happens to meet a root of a rubber tree the insects 




FIG. 57 a, Showing mud tunnel, or covering, which extends upwards for several feet 
and covers a large portion of the lower part of the stem. After first appearance 
of the cover at ground level, the mud casing is built up very rapidly, reaching 
the height of several feet in a few days. Mud cover broken away for purposes of 
photography. 6, Photograph to show where the strongest attack is made by 
White Ants, at base of trunk. 

attack it. Lateral roots may be immediately attacked, or the insects may 
tunnel a gallery underneath the lateral until the tap-root is reached, into 
which they penetrate. Once inside the tap-root, the termites eat out 
galleries in the wood and advance upwards into the stem. The wood of the 
tree is hollowed out, and the cavity is filled with a comb which is built of 
the excreta of the insects, and is, in fact, the remains of the wood of the 
tree after it has passed through their bodies. Ultimately the tap-root is 
destroyed, the laterals hollowed out and the interior of the stem becomes 



CHAP, xvni WHITE ANTS 375 

a termites' nest. The affected trees may then blow over, or fall over during 
rainy weather owing to the extra weight of the wet foliage. 

When young bud-grafted trees are subjected to attacks by C. 
curvignaihus , the upper limit of the mud wall may not extend beyond 
the point of union of stock and scion and the termites may concen- 
trate their attack upon the snag. When, as is frequently the case, 
there is a good growth of cover it is very difficult to detect trees which 
are being attacked until severe injury has been done. From direct 




Fiu. 58. Showing the wood of a mature rubber tree hollowed out by White Ants. 
Photograph from a specimen in possession of the Imperial Mycological Institute. 

observation, C. curvignathus can kill three -year-old trees within a 
month, and moreover, if treatment is not applied within a fortnight 
of the first appearance of the pests it is unlikely to be of any avail 
later. 

It seems probable that these attacks are made from a central 
nest which may be situated some distance underground. The fact 



376 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

that the large numbers of soldiers which are found in the early stages 
of an attack give place subsequently to a preponderance of workers 
indicates that communications are maintained between the termites 
on the tree and those in a central termitarium. The queens of C. 
curvignaihus have been found but rarely, and there does not seem to 
be any evidence to indicate that this species makes permanent nests 
in young rubber trees. Pratt also states that there is no doubt that 
the queen of T. gestroi is extremely rare. 

A further record of an attack on old rubber by a different species of 
termite was obtained in August 1932. The species concerned was 
Eutermes (Hirtitermes) hirtiventris, Holmgr. As far as could be ascer- 
tained by inspection, the method of attack is very similar to that em- 
ployed by C. curvignaihus, a mud wall being constructed over the 
bark some three or four feet from the ground and access to the wood is 
obtained under this cover. On this occasion about a dozen trees were 
being attacked simultaneously in a very small area and the attack 
was evidently in an initial stage. In a few instances the mud cover- 
ing had been partially removed, presumably by tapping coolies, and 
this had sufficed to drive off the invaders. The mud covering was 
thin and brittle and presented a different appearance to that made by 
C. curvignathus, but this difference may be more apparent than real 
and attributable to different soil conditions. 

In June 1911 a white ant attack by Termes carbonarius was re- 
ported which was stated to be killing newly planted stumps by 
stripping them of their bark. At that date attacks by this species of 
white ant were only noticed on rubber estates which were opened up 
on land previously under tapioca. No recent records of damage done 
by this species have been obtained. The correct name for Termes 
carbonarius is Macrotermes carbonarius, Hagen, which has reference 
to the comparatively large size and sooty colouring of the soldiers. 

White Ant Control. On certain rubber areas where conditions are 
exceptionally favourable to white ants, such as low-lying, peaty 
areas with much heavy, hard-wood timber submerged two to three 
feet deep in the soil, it is practically impossible to visualise any form 
of economic control. On such places the only method of control 
worth considering is the removal of all the submerged timber. Such 
an undertaking would involve deep digging to a depth of three feet, 
and this on any type of soil would be very expensive. On light, easily 
worked soil the cost of digging over to a depth of 3 ft. was $450 per 
acre in 1930, while another block of 3 acres dug over to three feet in 
1931 cost $300 per acre. On heavy clay soils the cost would be ap- 
preciably higher. 



CHAP, xviii WHITE ANTS 377 

At this stage a quotation from Pratt might be given: 

Gestroi is an insect which in its native state may be called comparatively 
rare and springs up as a pest owing to the exceptional advantages that are 
afforded it when a new clearing is made. Although very persistent in 
localised areas it is unable to maintain for many years, and it certainly 
cannot increase, the high position which it eventually occupies in regard 
to the number of individuals that are produced in these exceptionally 
favourable circumstances; for, however suitable the rubber tree may be as 
a food for this insect, it is impossible for fresh colonies to be continually 
and successfully established on the living tree, which would be necessary 
for the continuance or the increase of the high standard of multiplication 
that has been reached. There must inevitably result from these gradually 
changed conditions a steady diminution of gestroi among the older rubber, 
arid this slow but steady decline is frequently asserted to be due to per- 
severance in repelling their attacks on rubber trees. This latter fact may 
have some influence in aiding the decline of gestroi, but the inadequacy of 
the systems which have been employed, and for various other reasons, 
I am inclined to believe that the gradual abatement of gestroi as a pest on 
medium-aged clearings originally planted with rubber is mainly due to the 
altered and less favourable conditions rendering it impossible for this 
insect to maintain the same rate of increase which it has reached in cir- 
cumstances known to be favourable for its multiplication. Were this not so, 
those rubber trees on existing plantations would, in a few years, be com- 
pletely destroyed. It would nevertheless be most unwise to allow gestroi 
to have full sway on a young clearing, and await the decline of the pest, 
which would take something like 12 years, perhaps more. During this 
period it has ample opportunity to cause great harm to the trees. 

Pratt 's statements have been borne out by experience. In certain 
areas very favourable for the insect, economic control, no matter 
what the price of the commodity might be, is practically impossible. 
In the writer's experience, the number of areas worth clearing is 
small and such areas are seldom large in extent. On rubber planta- 
tions planted upon "lallang" (Imperata arundinaceae, Cyrillo) areas, 
no trouble is experienced from attacks by white ants, and they are 
not very prominent on undulating land, which forms the major portion 
of the area planted with rubber in Malaya. But the coastal alluvial 
areas usually show a heavy incidence of white ant attacks, and 
systematic treatment, which may be only repellent and not eradica- 
tory, will help the young trees to attain the age when the danger 
zone is passed, i.e. when the conditions for the insects become less and 
less favourable for attack with time. On the alluvial, coastal or 
riverine areas, Towgood states that he found termitaria exclusively in 
Kumpas (Koompa-ssia malaccaensis) and Meranti (Shorea sp. 1 ) logs 

1 The local Malayan timber trade includes under this name almost all the softer 
Diptorocarps and many other unrelated timbers. 



378 DISEASES AND PESTS OF THE RUBBER TREE PART in 

and roots, and chiefly in kumpas. Other timbers in which white ant 
nests have been found are given below: 

Kayu Api = ? 

Merbau =Intsia sp. & Dialium laurinum, Baker 

Pataling ^Ochanostachys amentaceae, Masters 

Jelutong = Dyer a sp. 

Nibong Palm = Oncosperma filimentosa, Bl. 

The method of control proposed in the early days was to follow 
up the underground runways or galleries from the tree attacked to 
the log in which the principal nest was situated, and then to destroy 
the termites in the log by fumigating with arsenic-sulphur fumes 
(page 384) pumped from the Universal Ant Exterminator. Later, 
certain modifications were introduced, but these methods were not 
really successful and were very expensive. Certain subsidiary 
measures, such as (a) collection of queens, (b) flooding badly attacked 
areas, (c) selective removal of timber, have all been suggested. 

At the present time the general control of white ants is based on 
the fact that conditions grow less and less favourable for the insects 
as the plantations reach maturity. Leaving out of consideration the 
hopelessly attacked areas, can an economic method be devised, 
possibly only repellent, which will give some assurance that mild 
attacks only are likely to develop? This leads to the consideration 
of the chemicals which have been tried in this connection. 

A 0-5 per cent of mercuric chloride has been in common use for 
many years, and in some cases satisfactory results have been ob- 
tained. But in 1931 numerous complaints of the inadequacy, non- 
permanency and expensiveness of the treatment were raised. 

For this reason it was suggested that Paris Green 1 powder, which 
had been used successfully against white ant attacks on Ceylon tea 
estates, should be experimented with in Malaya. In general, the use 
of this substance in Malaya has proved a decided improvement on 
solutions of mercuric chloride. If too large amounts of the paris green 
powder are used in heavy clay soils, which retain water tenaciously, 
there is a tendency towards bark-scorching and a subsequent develop- 
ment of the root disease caused by Sphaerostilbe repens. This combina- 
tion caused serious damage on one estate which practised the paris 
green treatment and later flooded the area for ten days. But, as pointed 
out when describing this root disease in an earlier section, Sphaerostilbe 
repens is the usual fungus which causes damage to the root systems 

1 Report of Insect Pests in Ceylon during 1929, Dept, of Agriculture, Sept. 1930, 
pp. 10-11. 



CHAP, xvin WHITE ANTS 379 

after flooding. Experiments with mixtures of 50 per cent paris green 
and 50 per cent lime show that this mixture gives passable results; a 
mixture of wood ashes 30 per cent, lime 30 per cent and paris green 
40 per cent may also be suggested as a possible white ant repellent. 
But all these mixtures and other methods are in the experimental 
stage and final results cannot be expected for some time. 

Of the subsidiary measures mentioned above, planters are re- 
minded that the termites which build mounds in which ' 'queens" 
are commonly found are quite harmless to rubber trees. As queens 
of C. curvignathus ( C. gestroi) are rarely found and then only 
in timber, care should be exercised in accepting large numbers of 
so-called "queens" for compensation when gathered by members 
of the labour force. "Queen" -collecting will probably not have much 
practical value in the matter of keeping down the numbers of in- 
dividuals. Richards discovered, moreover, that the removal of the 
queen was no guarantee that the colony would cease to exist, and his 
researches showed that substitution queens were provided by the 
ants to replace the parent queen. He says: 

Should the queen of a colony be killed, a number of substitutes are 
quickly provided to take up her duties. These substitution queens are 
easily recognisable from a normal queen by the fact that they have never 
developed wings. The wings of a normal -sexed individual are shed along a 
definite suture and the bases persist throughout life as small triangular 
stumps on the back of the thorax. The absence of these wing-stumps 
readily determines the substitution queens. 

Flooding attacked areas has been mentioned above. This treatment 
is commonly used in areas of coconut palms attacked by white ants 
without any apparent damage being done. But flooded rubber areas, 
apart from paris green treatment, are very liable to suffer severe 
damage owing to the Sphaerostilbe root disease, and, in the writer's 
opinion, flooding should be strongly condemned. Selective removal of 
timber promises well, but unfortunately the identification of timbers 
which are sought out by white ants for constructing termitaria is 
very difficult for the practical planter. 

For the period 1917-28 the white ant problem was not particu- 
larly serious because most of the plantations were mature. Now that 
large bud-grafted areas have been opened up, the position is different. 
Once undoubtedly successful results in the matter of high yields have 
been attained, there will be a fairly general move towards opening 
up new reserve areas, and replanting old areas on which latex yields 
are diminishing, so that in the future the problem is likely to be even 



380 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

more serious. The present experimental programme on white ant 
control has been envisaged to meet forthcoming requirements. 

Richards in 1917 argued strongly that clean clearing was the only 
sound method of combating attacks, especially in view of the fact that 
this would also help in the control of various root diseases which 
were becoming prominent at that time. In this view he is supported 
by Corbett in a recent publication, who declares that: 

it has been definitely established that the only satisfactory measure for 
eradicating white ants on both rubber and coconut estates consists in the 
destruction of all timber in which they can make their nests. 

This statement is perfectly true, but the economic facts as to rubber 
plantations must be faced, and the "destruction of all timber", with 
the commodity at present-day prices, would prove ruinous. But the 
basic idea is sound, and taken into consideration together with the 
suggestions given for root disease treatment, there is not the slightest 
doubt that white ant damage on newly planted areas would be re- 
duced to a minimum. 

The most recent work on white ant control has been done by Beeley 
in Malaya. The following has been abstracted from an article re- 
cently published by him: 

Two common type of termites are often found on badly infected areas, 
one being Coptotermes curvignaihus, Holmgr., the other being a species of 
Capritermes, probably C. dolichocephalus, 0. John. 

The termite C. curvignaihus appears to be the only offender which at- 
tacks the rubber tree. It is of common occurrence in low-lying soils and 
shows a strong preference for damp sheltered situations such as obtains 
under a heavy growth of cover crop. 

Though one must admit that an attack of root disease predisposes a 
tree to termite attack, nevertheless there is ample proof that C. cur- 
vignathus will attack apparently healthy young rubber trees and, if left 
undisturbed, can inflict fatal injury within three or four weeks' time. 

The seat of attack varies considerably and may be at a point a few 
inches above ground or at any point below ground-level. The most usual 
point of entry is at a fork of the tap-root or near some hollow malforma- 
tion of the tap-root at about 9" below soil-level. As the attack is extended 
upwards above ground-level a mud wall or casing is built round the trunk 
to protect the colony from other insects, birds and heat. Beneath this mud 
casing the bark is attacked almost at once at many points, causing exu- 
dation of latex which mixes and coagulates with the attached mud, form- 
ing a rubbery mass, which can only be cleaned off with some difficulty 
when treatment is undertaken. 

Once an entry is gained, the insects commence mining vigorously in the 
wood of the tap-root, causing numerous long, radially-flattened galleries. 



CHAP. XVIII 



WHITE ANTS 



381 



These galleries are extensively interconnected and in time so weaken the 
tree that it is blown over by the slightest wind. 

In the case of buddings being attacked by white ants the upper limits 
of the mud wall may not extend beyond the union, the attack being con- 
centrated on the snag. In heavy cover, infested trees may easily be over- 
looked until too late, when the trees are usually blown down. 

Various methods of control have been tried and the following list gives 
Beeley's opinion as to the probable order of merit. 

(1) Opening up of roots and applying insecticidal dusts. 

(2) Dibbling in around the bases of trees a small quantity of fumigant 
rubber jelly. 

(3) Castor Bran placed in a shallow trench round all attacked trees. 

(4) Using explosive gases to kill the termites by concussion. 

(5) Digging to eliminate buried timber and nests. 

It is pointed out that no method of treatment will quickly eradicate 
the termite pest and that a carefully planned campaign involving monthly 
inspection and treatment of affected areas must be carried out in order to 
effect a reasonable degree of freedom. It is not so much the type of in- 
secticide used which is of importance but rather the thoroughness with 
which the job is performed. 

Control of Termites in Young Rubber Trees using Insecticide Dusts. 
In view of the promising results obtained in these experiments, the follow- 
ing method of control of termites by using insecticide dusts is tentatively 
suggested for use on estates whose managers would like to assist in obtain- 
ing further experimental data. 

1. Mark out infested zones as indicated, Diagram XI, (a) supplies, (b) in- 
fested trees cut out and (c) present infested trees. Include also one ring of 
apparently healthy trees around the infested trees. 



O/ 



o 



X X 



> 



LJ Supply 

X Infested Trees 
t 

1..I Zone treated 
o Uninfested Trees 



Clean here 
thoroughly 



Diagram XI. 




9 inches to //oof 



2. If white ants are observed to be entering the tap-root at a lower 
level, open up the roots, as shown in the sketch, to a depth of 9 inches or 
more. Clean the exposed bole of the tree thoroughly and blow on to the 
bark a light dusting of insecticide powder. Clean off all mud walls or 
debris from the trunk above ground and blow more powder into the mass 



382 DISEASES AND PESTS OF THE RUBBER TREE PABT m 

of mud and termites so collected and also lightly dust the cleaned trunk 
up to the height reached by the termites. About to oz. of dust is 
sufficient for one tree. , 

3. The crater at the base of the tree is left open for four to five weeks, 
when a further treatment with insecticide dust is given, after which the 
crater may be filled in. 

4. Always attempt to trace up termite galleries to find and destroy nests. 

5. In view of the fact that termites can destroy a four-year-old tree 
within four or five weeks of the original attack, it is recommended that 
a small gang of coolies should patrol infested fields, so as to execute a 
complete round of treatment every four weeks. 

In heavily attacked fields having a flat peaty or alluvial soil it is ad- 
vantageous to treat all trees in the area at the first round of treatment. 

6. Suitable insecticide powders are as follows: 

Sodium silicon" uoride. 

Calcium arsenate. 

Cyanomag dust. 

Paris green (with lime if used in wet peaty soils). 

Suggested Method of controlling the Termite Pest of Young Rubber Trees 
by the Use of Fumigants. As illustrated, demarcate infested zones as 
indicated (a) by supplies, (b) infested trees cut out and (c) present infested 
trees. Include also one ring of apparently healthy trees around the in- 
fested trees. 

The tap-roots of all infested trees should then be opened up to a deptli 
of nine inches and the tree thoroughly cleaned of mud. Four pieces of 
impregnated rubber jelly the size of a walnut are then placed round the 
bole at a depth of about six inches below the surface level. Fill in the 
hole with soil, so that the level of soil slopes away from the tree, as the 
fumes penetrate better through the dry soil than through wet. 

Supplies and non-infested trees within the zone may have three or 
four similar pieces of impregnated rubber jelly dibbled in to a depth of six 
inches close around the tap-root. 

Always attempt to trace up termite galleries to find and destroy nests. 

As before, all known infested areas should be inspected once per month 
and fresh treatment given where necessary. 

The following fumigant liquids are suitable for use in this way: 

Or thodichlor benzene. 

Trichlorethylene . 

Mixtures of the above two and carbon bisulphide. 

The rubber jelly is made by treating small pieces of dry rubber clippings 
with the above fumigant liquids in the proportion of one pint of fluid to 
one pound of dry rubber. More of less fluid may be added according to the 
required viscosity of the jelly. The jelly should be kept in screw- capped 
vessels. It is advisable to keep records of trees treated, trees re- attacked 
after four and eight weeks or more, and costs of materials and labour used. 

Control of the Termite Pest of Young Rubber Trees. Results obtained in 



CHAP, xviii WHITE ANTS 383 

Routine Work on the Rubber Research Experiment Station, F.M.8. In 
his Report of Insect Peste in Ceylon during 1929 Mr. F. P. Jepson, De- 
partment of Agriculture, Ceylon, suggested a method of using paris 
green in control of the termite pest of tea. After a little experimentation 
the method was adapted to rubber and was used to some extent on the 
Experiment Station. Perchloride of mercury was also used on a similar 
number of trees for purposes of comparison. 

The method of treatment was the same as that which was recommended 
for estates, viz. that infested trees were opened up to a depth of nine 
inches, scraped clean of mud and latex and paris green powder lightly 
blown on to the roots and infested parts of the tree. The various fields were 
inspected periodically, usually at intervals of four to six months, and 
attacked trees duly treated. Observation, however, soon showed that it 
was possible for termites completely to kill a tree within four weeks of 
the commencement of attack. Trees were frequently not discovered 
until they were too far damaged to respond to treatment, so that the 
results summarised below under the heading "one treatment" are some- 
what disappointing. 

Treatment with perchloride of mercury consisted of opening up the 
roots in a similar way then spraying the trunk, roots and soil with one 
pint of a 2 per cent solution of the chemical or, better, 2 pints of a 1 per 
cent solution of the perchloride in water. 

During 1932 the following results were obtained: 

Degree of Control: 

(1) Paris Green 

(a) After one treatment 25% deaths, nil 

(b) After two treatments 70% deaths, nil 

(c) After three treatments 75% deaths, nil 

(2) Perchloride of Mercury 

(a) After one treatment 32% deaths, nil 

(b) After two treatments 55% deaths, 22% 

(c) After three treatments 58% deaths, 30% 

The large death-rate during 1932 is due chiefly to the activity of root 
disease fungi (Fomes) in conjunction with the white ants. In many cases 
the trees were too far gone with both disease and termite attack and should 
have been dug out at once. 

During 1933 paris green only was used until the end of September, 
when a change was made to Cyanomag on experimental grounds. 

Degree of control with paris green, Jan.-Sept. 1933: 

(a) After one treatment 42% deaths, 5% 

(b) After two treatments 63% deaths, 25% 

(c) After three treatments 66% deaths, 32% 

Omitting those trees which were obviously too weak to respond to 
treatment, it is found that the degree of control is as follows: 



384 DISEASES AND PESTS OF THE RUBBER TREE PART in 

(a) After one treatment 50% deaths, 2% 
(6) After two treatments 75% deaths, 13% 
(c) After three treatments 78% deaths, 20% 

Reference to the root disease records shows, further, that several trees 
were given up as lost before the white ants began to attack them. If these 
trees are also omitted from the total it is found that the degree of control 
after three treatments, using paris green, becomes 84 per cent and deaths 
14 per cent. 

This indicates that paris green has given excellent results under ordin- 
ary routine estate conditions. With regular monthly rounds of inspection 
it is almost certain that much better results would have been obtained. 

It should be noted that 25 per cent of the trees attacked by white ants 
had been for some time previously suffering from Fomes root disease. 
While admitting that attack by root disease fungi predisposes to attack 
by termites, observations show that the species Coptotermes curvignathus 
will attack well-grown, healthy trees of four or five years of age. 

It should be kept in mind that the work detailed above was purely 
experimental, but the results obtained obviously justify further extensive 
application of the method to overcome, if possible, any objectionable features 
which may be met with in field practice. It may be held that one un- 
fortunate episode should condemn the use of this chemical for white ant 
control, but the writer cannot subscribe to this view. The possibilities are 
obvious ; if anything like a 70-75 per cent control can be realised, the white 
ant problem assumes proportions which need not cause any alarm to 
planters; in the meantime, however, it will be advisable to emphasise the 
need for expert advice before utilising paris green for the purpose in- 
dicated. 

Sulphur Arsenic Mixture for Use in Universal Exterminator 

The approved mixture is Arsenious oxide = (White Arsenic) 7 

parts by weight. 

Sulphur (finely divided) = 1 part by weight. 

For the reaction to be complete, the charcoal in the brazier should 
contain sufficient red-hot charcoal to maintain the required tempera- 
ture. 

BOEING BEETLES 

Xyleborus parvulus, Eichh. 

Boring beetles belong to the family Scolytidae, which is naturally 
divided into two groups, one of which comprises the "shot-hole" 
borers or " Ambrosia" beetles. Anyone familiar with the work of the 
"shot-hole" borer on rubber trees is aware that this is a very appro- 
priate designation, for the effect resembles very closely that caused 
by firing small shot into wood. The galleries made by the shot-hole 



CHAP, xvin XYLEBORUS PARVULUS 385 

borer are of a uniform width for their whole length and all burrows 
are made by the adult beetle; there are no galleries made by the larvae, 
as in a closely related family. The burrows are usually carried right 
into the heart wood. The larvae do not eat any wood; their food con- 
sists of fungi growing on the wall of the burrow; these so-called 
"Ambrosia" fungi are cultivated by the female beetles, which carry 
the spores in the stomach. Each species cultivates its own particular 
4 'Ambrosia" fungus irrespective of the kind of tree in which it is 
boring. The eggs are deposited in the burrows, and the presence of the 
beetles at work is revealed by the ejected wood-dust, which some- 
times sticks together and projects from the entrance hole as a small 
funnel-like mass. 

The genus Xyleborus comprises the majority of species which 
attack cultivated plants, and a large number of species of this genus 
have been found in dead Hevea stems. Green enumerated twenty- 
three species in 1914, but according to Fetch the only two of im- 
portance on rubber are Xyleborus perforans, Woll., in Ceylon, and 
Xyleborus parvulus, Eichh., in Malaya. Xyleborus morstatti, Hag., in 
conjunction with the diplodia "die-back" fungus, causes a consider- 
able amount of damage in coffee plantations in Java. 

The males of the genus Xyleborus are unable to fly and in number 
and size they are greatly exceeded by the females. The boreholes 
made through the bark and into the wood are of small size, about one 
twenty-fifth of an inch in diameter. When the borers are actively at 
work the "frass" ejected from the holes often covers the exterior 
of the stem, and then the position appears somewhat alarming. 

In Malaya serious borer attacks are never found on healthy, 
vigorous trees, but it has been demonstrated conclusively that slight 
bark-scraping, which exposes the outer cortical tissues, is quite suffi- 
cient to allow entry to the shot-hole borer. But the position is not 
as stated by Green, who considers that it is doubtful if any of these 
small beetles can penetrate the healthy bark of the rubber tree with- 
out being hopelessly involved in the viscid latex. Fetch is inclined to 
the same opinion. If the bark of the rubber tree is scraped lightly so 
that there is no exudation of latex and a borer attack takes place on 
the exposed tissues, the insects bore through and, although there is 
a copious exudation of latex in which many of them are trapped, 
other individuals come along later and penetrate into the wood. The 
writer demonstrated this feature in 1916, and it appears that, as a 
result of light scraping, some external protective layer is removed. 
In Malaya leaf fires during the wintering season give the shot-hole 
borer the best opportunity of causing serious damage, for within four 

2o 



386 DISEASES AND PESTS OF THE RUBBER TREE PAKT in 

to six days after the fire the scorched bark areas will be found riddled 
with the characteristic holes, in fact, shot-hole borer is nearly always 
prominent wherever the bark tissue of the rubber tree has been 
scorched from any cause. Serious damage also follows on lightning 
injury on mature trees, while trees suffering from the Sphaerostilbe 
root disease are also often severely attacked. In former years, when 
bark-scraping to obtain increased yields was practised in certain 
districts, severe attacks of boring beetles were recorded on the tap- 
ping panels. It is obvious, moreover, that borer attacks are likely to 
become prominent during a thinning-out period, when falling trees 
must necessarily come into contact with standing trees, bruising them 
severely and scraping away much of the external protective tissues. 

Shot-hole Borer Attacks and Leaf Fires. The description of the 
important features to be noted when leaf fires occur, together with 
treatment, is given in Chapter XVI. A short repetition is given 
here. The wintering period in Malaya is usually somewhat irregular, 
and it is the exception rather than the rule to find a thick carpet 
of dried leaves during any particular year. But if a long dry spell, 
without the intervention of occasional storms or showers of rain, 
is experienced during the wintering period, then a thick mat of 
dried leaves is formed on the ground, and this readily catches fire. 
Large areas may be damaged by fire under the conditions depicted, 
since within four to five days after the fire shot -hole borers will 
inevitably be at work, and suitable precautions must be undertaken. 
The entry of the insect is often followed by the appearance of 'the 
typical symptoms of Ustulina zonata, and between the insect and 
fungus the trees often succumb rapidly. It is not known whether the 
insects carry the Ustulina spores amongst the trees; the writer, 
however, has isolated this fungus from the bore-holes made by this 
insect. But once the wood is thoroughly attacked by the fungus small 
portions of diseased tissue are transferred as the insect progresses 
from diseased to healthy tissues and scores of centres of fungus in- 
fection are set up, and the tree may thus be rapidly killed. 

Shot-hole Borer Attacks and Tissues scorched by Means other than 
Leaf Fires. The close relation between scorched tissues and the 
presence of the die-back fungus Diplodia sp. has been commented 
upon in another chapter. Sun-scorch is the commonest form, and 
boring beetles often gain entry to the interior of mature trees through 
sun-scorched bark. The only remedy in this case is to excise any roots 
or branches which may be affected by the sun's heat. 

Shot-hole Borer Attacks and Lightning Damage on Mature Trees. 
The association of patch canker disease at the collar of mature rubber 



CHAP, xviii PSILOPHOLIS GBANDIS 387 

trees which have suffered lightning damage has been fully discussed 
in Chapter XVI. As noted in the section on patch canker, affected 
bark evidently has a decided attraction for boring beetles. Treatment 
is as described, i.e. stripping out the diseased patches in large lumps; 
no scraping, other than to delimit the diseased area of bark, should be 
allowed. 

Shot-hole Borer Attacks in connection with Root Attacks by Sphaero- 
stilbe repens. In this combination it is usually impossible to re- 
commend any form of treatment, for the fungus disease is so far 
advanced that no hope can be entertained for the recovery of the 
attacked trees. The attacks of the insect undoubtedly hastens the 
death of the trees. The writer has seen sixteen acres of seventeen-year- 
old trees absolutely leafless and obviously approaching death which 
ten days previously were apparently healthy. 

Shot-hole Borer Attacks and Bark-scraping. About 1914-16 bark- 
scraping before opening the tapping panel was being practised by 
numerous estates; this procedure was based upon tapping results 
obtained by Fickendy, who reported an increased yield of 14 per 
cent. Shortly after this system of deep scraping was inaugurated the 
tapping panels showed symptoms very similar to those described for 
black stripe, and borers were penetrating through the diseased tissue 
into the interior of the affected trees. The only form of control was to 
cease scraping. 

COCKCHAFER GRUBS 
Psilopholis grandis y Cast. 

The grubs of various species of cockchafers or May beetles have 
long been known to cause severe damage to various crops. In Queens- 
land one species is considered to be the most dangerous pest to the 
sugar crop and the recommendations for control measures costs 
8-9 per acre per annum. Nowell, in 1915, reported that another 
species was occasionally destructive in Barbados canefields, and 
seemed confined to small and shifting areas, but in Mauritius, 
into which island it seems highly probable it was introduced in 
sugar-cane stools from Barbados, great and continuous damage is 
being caused over an ever- widening area. One or two species have 
been reported from Ceylon and Malaya as causing damage on young 
rubber plants, but an en masse attack on mature rubber areas had 
not been reported before 1930. Since that date two cases have come 
under the author's notice in Malaya. 

The true cockchafer beetles fall into two sub-families, the Rutdinae 
and the Melolonthinae\ the larvae of the latter are especially injurious 



388 DISEASES AND PESTS OF THE RUBBER TREE PART in 

in the larval stage, being root-eaters. The true melolonthine grubs 
always rest with their curved body on the back or side (Fig. 59 c) and 
only move with much difficulty on the surface of the soil. The species 
referred to above are listed below: 

On sugar-cane plantations in Queens- Lepidoderma albohir- 
land turn, Waterh., and 

several other species. 
On sugar-cane plantations in Bar- Phy talus smithii, 

bados and Mauritius Arrow. 

On young rubber in Ceylon . . Lepidiota pinguis, 

Burm., and Holotri- 
chia leucophthalntti, 
Wied. 

On young rubber in Malaya . . Tricholepis lactea? 

On mature rubber in Malaya . Psilopholis grandis, 

Cast. 

The cockchafer beetle under consideration has several synonyms 
as under: 

Psilopholis grandis, Cast = Tricholepis grandis = Holotrichia pub- 

erina = Lepidiota manilae. 

This beetle has been recorded from Sumatra, Java, Nias, Manila, 
Penang, Malacca and generally throughout the Federated Malay 
States. 

Lepidiota pinguis, Burm., is a closely related beetle, the grubs of 
which have been recorded damaging young rubber roots in Ceylon, 
and Lepidiota marginipennis, Moser., the grubs of which were also 
damaging rubber roots, has been recorded from Borneo. In the latter 
case it is not clear whether or not the trees were mature. Holotrichia 
leucophthalma, Weid., another related beetle whose grubs have been 
recorded from Java, was again found damaging young rubber roots. 

The cockchafer beetles in general are moderate -sized beetles with 
robust bodies, the elytra covering all but one spiracle, the legs only 
slightly broadened, and without horns or spines on head or pro- 
thorax. They are mostly dull-coloured insects, brown predominat- 
ing in the coloration, and they vary in length from a quarter of an 
inch upwards. P. grandis is about 1 ins. in length and -f in. in 
breadth. The antennae are short, with the knob composed of one 
more joint in the male than in the female; the leaflets are also longer 
in the male; the prothorax is small, the elytra generally smooth and 
fitting tightly to the abdomen; the legs are moderately long, fitted 
for walking and to a less degree for digging. 



CHAP, xvni PSILOPHOLIS GRANDIS 389 

The larvae of these beetles live in the soil and feed upon the roots 
of various plants. They are of a fleshy dingy- white colour, the body 
curved in an arch and the spiral segment large and smooth. There are 
many folds in the skin and three pairs of short- jointed legs. The 
larvae of P. grandis moves freely but slowly in the soil, but it is 
comparatively helpless on the surface, the curved body interfering 
with locomotion. When full-grown the grub makes a mud ceil and 
transforms to a pupa in the soil (Figs 59 a and 59 c). 

The imago flies by night; details with special reference to P. 
grandis will be given later. The fore-wings are not moved in flight; 
they are held rigidly and apparently serve for a parachute and as 
directors of flight. The food usually consists of vegetable matter 
leaves and flowers, and is eaten at night, the beetles hiding by day, 
but in the matter of food little is know of the habits of the adult 
insects in Malaya (Fig. 59 a). 

Economic Importance. Although not reported until July 1930, on 
one of the two heavily infested estates in Malaya, the grubs of the beetle 
have probably been present for at least five years (1928). No suspicion 
arose until the grubs were found in the soil in enormous numbers, and 
it is almost certain they had been present two or three years before 
the date of report. On one estate an attempt was made to improve 
the position by continuous digging and hand collection of the grubs. 
This field of rubber was 96 acres in extent and the trees were thirteen 
years of age. The grubs were ultimately found to be generally dis- 
tributed throughout the whole of this field, but large numbers were 
found over an area of 50 acres, and the worst affected area was about 
25-30 acres; the latter was dug over thirteen times. 

In May 1931 the following were collected in one day by 57 coolies: 
24,200 small grubs, 20 large grubs and 145 beetles. Even when such 
large numbers w r ere obtained by hand - collecting the number of 
grubs did not perceptibly diminish, and in view of the risk of injury 
to roots which might influence the grubs to invade them, a recom- 
mendation was made to stop digging. This particular area carried 
only a light undergrowth, and the ground was slightly undulating, 
being bounded on three sides by virgin jungle. The grubs are still 
confined to this particular field, neighbouring fields being still free 
on the date last examined (December 1933). 

The other badly infested area occurs on an estate situated in the 
foothills of the main range, and is bounded along its whole length by 
virgin jungle. The rubber trees on this estate have not been tapped 
for a period of years, and the land is hilly. In order to prevent soil- 
wash on the hilly slopes, a natural heavy undergrowth has been 



390 DISEASES AND PESTS OF THE RUBBER TREE PART in 

successfully established. The first indications of the presence of the 
grubs was on a steep hill-slope adjacent to the jungle, over an area of 
about one acre. In this area the undergrowth showed signs of dying off 
in patches and the soil appeared to be very spongy when walked over. 
The manager first suspected the presence of an oil spring until a 
strong wind passed over the estate, and the whole of the under- 
growth was laid low. An examination over the spongy area showed 
that the roots of the various species of plants comprising the under- 
growth had been eaten away, and slight disturbance of soil by digging 
soon revealed the typical cockchafer grubs. In such hilly estates, 
where the undergrowth must be encouraged to prevent soil erosion, 
much damage can be done by a massed attack, for the time taken to 
re-establish a good natural undergrowth is some two years or more, 
and much top-soil will necessarily be lost during this period. 

When the grub infestation was first brought to the writer's notice 
statements were made that a large reduction in the yield of rubber, 
amounting to 50 per cent, had been occasioned and that the latex was 
watery, i.e. had a low D.R.C. (Dry Rubber Content). This may very 
well have been the case, but when comparative D.R.C. tests were 
made in February 1932, on latex taken from affected and unaffected 
fields, the D.R.C. of the latex from the infested field was shown to be 
normal at 3 Ibs. 10 J ozs. to the gallon; two unaffected fields showed 
3 Ibs. 10 ozs. and 3 Ibs. 9| ozs. per gallon respectively. With regard 
to yields in pounds per acre per annum no exact figures have been 
obtained as yet (September 1933), but it may be possible to obtain 
figures at a later date. In the writer's opinion the yield of latex and 
rubber appears normal for the type of soil, and it is doubtful if any 
serious loss of yield has ever been experienced. 

A rough estimate of the amount of root damage done was made. 
The root systems of fifty-two trees growing in the worst infected area 
were exposed and it was found that seventeen had suffered root 
damage and thirty-five showed no signs of attack. But it has to be 
remembered that the soil of this area was dug over repeatedly and 
some root damage from this cause would be inevitable; further, 
various soil fumigants had been tried over the area, so it is difficult 
to apportion the damage correctly. The inference, of course, is that 
all the root damage cannot be attributed to the grub infestation. 

At the present time it is quite obvious that the tap-roots of young 
rubber seedlings are eaten through just below the surface of the soil, 
and that they form excellent food for the grubs. It seems probable 
that if the grubs cause damage to mature trees the portions likely to 
be attacked would be the small absorbing rootlets. As mentioned in 



CHAP, xviii PSILOPHOLIS GRAND1S 391 

preceding sections, the repair mechanism in the root system of H. 
brasiliensis is extremely efficient, and any damage done by the grubs 
to small rootlets would be quickly repaired by the outgrowth of ad- 
ventitious rootlets. It is, therefore, not reasonable to expect a big 
diminution in yield because of a massed infestation of the soil by the 
grubs of cockchafer beetles, but it would be quite impossible to pre- 
vent annihilation of the plants if a nursery bed of rubber seedlings 
became seriously infested. 

The grubs are practically polyphagous; all plants in a mixed under- 
growth are eaten indiscriminately. The wild fern, Gleichenia linearis, 
is a favourite food plant but nothing seems to come amiss; on one 
occasion grubs were found working through a neglected pineapple 
bed, and even the root systems of such a hardy plant were eaten 
clean away, and all the plants were leaning over at an angle. Of the 
usual cover crops, it has been shown that grubs will readily devour 
the roots of Mikania scandens, but slight feeding only was observed 
on the roots of Indigofera endecaphylla and Tephrosia Candida, and no 
feeding took place on Crotalaria anagyroides. At the present time it 
seems advisable to encourage the development of alternative food 
plants on which the grubs might prefer to feed and also to increase a 
fallen-leaf cover over the soil. 

Grubs are found in the jungle and appear to be slightly nearer the 
surface than in the infested areas. 

Little is known regarding the host plants of the adult beetle P. 
grandis in Malaya. It has been established that they will not feed on 
leaves of H. brasiliensis or Mikania scandens. They will feed on 
Mango, Mangosteen and Jambu (Eugenia sp.) leaves. 

Life Cycle. Detailed entomological observations on the life cycle 
of the insect in Malaya have not been made, but from the available 
data it appears that the life cycle is normal and agrees essentially 
with the details of related cockchafer beetles reported from other 
countries. The life cycle is completed in twelve months. The eggs 
are deposited during March and pupation begins in January. Adult 
beetles occur from January to April. The duration of life of the adult 
beetle under natural conditions is not known exactly but it seems 
likely that it is not less than three or four weeks. 

LIFE HISTORY. The eggs are white, ellipsoid bodies and are laid 
in the soil at a depth of one foot below the surface. They are de- 
posited in clusters of 11-34 ova (Fig. 59 a). 

LARVAE. On a visit made in the middle of March 1932, only one 
or two large grubs could be found. A number of very small grubs, 
however, were obtained, and as they are invariably found in small 



392 DISEASES AND PESTS OF THE RUBBER TREE PART in 

colonies it indicates that the grubs soon separate after hatching 
from the eggs. The grubs are for the most part confined to the first 
nine inches of soil but go deeper when the ground has been disturbed, 
occasionally to a depth of two feet. They are to be found in the soil 
during the whole of the year, but a decrease in numbers of full- 
grown grubs begins to occur in December and most pupae are found 
about the end of January (Figs. 59 a and 59 c). 

PUPAE. On the same date (supra) pupae were found every day by 
the digging coolies, but the numbers were diminishing daily. 

IMAGO. During the same visit adult beetles were fovind in the soil 
in large numbers. When the beetles first emerge from the pupal stage 
the wing-cases are soft and it seems probable that the beetles remain 
in the soil until the cases become hardened. One hundred beetles 
found in the soil on March 2nd 1932, were examined on that date 
and 33 per cent were found to have soft wing-cases; on March 14th 
the proportion of "soft" beetles was much smaller. The following 
approximates to the general life cycle in Malaya: Egg stage, 14 days. 
Larval stage, 311 days. Inactive larval stage, 7 days. Pupal stage, 
22 days. Inactive beetle stage, 11 days. One generation occurs in the 
year but there is considerable overlapping in the various stages. 

Normally no beetles are seen above ground during the daytime, 
but a few may rest on the under-side of the leaves of rubber trees 
and other shrubs. A report from Queensland states that several species 
of Ficus are favourite resting-places of the adult beetle Lepidoderma 
albohirtum, and it is recommended that groups of F. pilosa, Reinw. 
ex Blume, and F. benjamina, Linn., should be planted in the sugar- 
cane areas and that the beetles can be collected from them by shaking, 
which causes them to fall to the ground. As far as our observations 
have gone in Malaya, the great majority of the adult beetles spend the 
day underground. 

In the evening a very few beetles are active before 6.45-6.50 P.M. 
They must emerge from the ground and take wing immediately as 
none were seen crawling on the ground before 6.45 P.M., yet a few 
minutes later they were in full flight everywhere and the powerful 
droning noise can only be likened to that produced by a powerful 
fleet of aeroplanes overhead. The flight is very swift and, as far as 
could be judged in the darkness, not very high. Many beetles flew 
quite low and sometimes described circles over a small area. It is not 
known when the evening flight ceases. 

At 5.40 A.M. the field is quite silent and in total darkness. At a 
minute or so before 6 A.M. the beetles appear suddenly and there is 
a strong flight for a period of about twelve minutes. The number of 



CHAP, xviii PSILOPHOLIS GKANDIS 393 

beetles in flight, however, is probably only a quarter of that of the 
evening flight, and the insects are not so strong on the wing and 
possibly fly lower. By 6.15 A.M. the flight is over and the beetles fly 
(not drop) to the site of landing. On one day when observations were 
being made two or three beetles were seen to crawl under the nearest 
dead leaf and remain there. Another beetle crawled under a leaf and 
burrowed and it was not successfully recovered. Another beetle 
crawled into a hole in the soil at the base of a stump when it was 
seized by a scorpion. The four or five beetles of the morning flight 
which it was possible to examine proved to be males, and appeared to 
be in a state of exhaustion. 

The length of flight of the beetles, as determined by painting 600 
beetles, indicates that although they are strong on the wing the cir- 
cular movement employed during the flight prevents them moving 
to any great distance, half a mile perhaps would be the limit when 
flying among trees. No beetles have been found in copulation, but 
there is evidence which suggests this takes place during the evening 
flight. 

The food of the adult beetle is not definitely known. It seems as 
though it does not consist of rubber leaves or leaves from the neigh- 
bouring jungle, and the only conclusion which can be drawn at pre- 
sent is that it must be obtained from the soil. 

Biological Control by Natural Agencies. It is a well-known fact 
that cockchafer beetles are parasitised by various species of Scoliidae 
or "digger-wasps", and, in other countries, by an entomogenous 
fungus commonly named the "green muscardine" fungus ( =Metar- 
rhizium anisoplioe). Up to date, specimens of white grubs attacked 
by this fungus have not been found in Malaya. 

(a) SCOLIID WASPS. A wasp, Scolia manilae, was introduced into 
Hawaii in 1915 and 1916 to aid in the control of a grub attack on 
sugar-cane. This was successful, for the beetle (Anomala orientalis, 
Walent.) is now fully controlled by the wasp parasite. 

Two digger-wasp parasites of the grubs of P. grandis have been 
obtained in Malaya. These are Campsomeris pulchrivestita, Cam., and 
Campsomeris tristis, Sauss. ( =0. javana, Lep., or C. iris) (Fig. 59 a). 
On December 22nd both parasites were very conspicuous in the field, 
and on April 9th following there was no apparent decrease in the 
numbers of either species. 

Under normal conditions the wasp parasites have to burrow 
several inches below soil-level before reaching a suitable host, and 
several writers refer to a remarkable instinct the females possess for 
locating their victims. This has not been confirmed in our experience 



394 DISEASES AND PESTS OF THE RUBBER TREE PART in 

with P. grandis] numerous wasps have been followed into the soil 
with a trowel, but in no instance was a grub found, which suggests 
that the female enters the ground hoping to find a grub on which to 
oviposit and not because she knows that there is a grub under- 
ground. 

It will be of great interest to non-technical readers to have an 
account of the tactics adopted by the female wasp parasites when 
overpowering the grubs underground. This account is given by 
Illingworth: 

The wasp warily approaches the powerful jaws of its intended victim by 
clinging to its body and crawling with erratic movements until encounter- 
ing the legs of the alarmed grub, which, evidently aware of the impending 
danger, keeps squirming and pawing the air, threatening its enemy at the 
same time with widely opened mandibles. 

A few seconds are passed in this preliminary fencing, and then the wasp, 
making a sudden dive forward, seizes with caliper- shaped jaws one of the 
mandibles of the grub, and without loss of time drives its paralysing 
sting deeply into the throat of the unfortunate creature. The effect is al- 
most instantaneous, the rigid convulsive body becomes limp and unable 
to offer further resistance, as the parasite, now withdrawing its sting, 
plunges it deliberately several times into the mouth of its victim, between 
the maxillae, in order, presumably, to paralyse the mandibles. 

Sometimes, however, the tables are turned, and the venturesome 
parasite is seized and fatally crushed in the sharp jaws of its adversary, 
in which case it appears that the victorious grub does not rest until it has 
cut the wasp into little pieces. 

The digger-wasps may attack grubs working on or near the surface, 
and it has been observed that when this is done the wasps begin to 
dig the soil away in order to bury the body of the grub underground. 
This can be done in the relatively short period of twenty minutes. 

Pendlebury reports that C. javana was the dominant species in the 
Malayan outbreak. Under laboratory conditions the female wasp 
attacks and stings the grub with vigour, which rapidly becomes 
quiescent and paralysed. She then turns her prey on its back and 
appears to use her sting as a brush, and smears the ventral sur- 
face of the grub with it preparatory to oviposition. The egg is dropped 
on to one of the ventral somites, generally the fourth, though any one 
from the first to the fifth may be chosen, the position depending on 
which way the wasp was facing during the act of oviposition. The 
egg usually assumes an erect posture (Fig. 59 6). 

The egg stage lasts from two to three days, when the wasp grub 
hatches and commences to feed upon the beetle grub. The wasp grub 
continues to feed from five to six days before pupating; the pupal 



CHAP, xvni PSILOPHOLIS GRANDIS 395 

stage lasts from twenty-seven to twenty-nine days in the male, and 
from thirty to thirty-two days in the female. 

It has been found that, in the field, the wasp will not oviposit on 
other than nearly full-grown grubs. 

As regards (7. pulchrivestita the laboratory conditions have not 
appeared to favour its development. The mode of attack is similar to 
that described above. Though the fourth somite of the beetle grubs 
is the one usually chosen by the wasp for ovi position, any segment 
from the first to the seventh may be selected. The egg stage has been 
found to last three days, and the grub stage seven to eight days; the 
pupal stage in one case was forty -two days. 

As will be seen from Fig. 59 a, the male and female of these wasps 
species differ considerably in size and coloration, i.e. exhibit sexual 
dimorphism. The females are considerably larger than the males. 
Much confusion has arisen because of this sexual dimorphism, for the 
male and female of the same species have often been named as 
separate and distinct species. 

On a visit made last year males of C. javana constituted at least 
75 per cent of the total, females of both species being very little in 
evidence. Between 8 A.M. and 2 P.M. two or three females of C. javana 
may be seen each day and these are invariably being pursued by 
numbers of male wasps. Between 7 A.M. and 8 A.M., however, females 
are much more abundant and occur in about equal numbers with the 
males. The explanation appears to be that both sexes occur in ap- 
proximately equal numbers, but the females spend almost the whole 
time underground. 

Male wasps of both the above-mentioned species were found feed- 
ing on the flowers of a shrubby jungle plant Urophyllum strepto- 
podium, Wall. (Rubiacea); only three plants of this species were 
found and all were constantly visited by male wasps. 

A Bombylid fly, Hyperalonia tantalus, F., acted as a hyper-parasite 
and attacked several of the wasp grubs or pupae, but they did not 
occur in such quantities as to be a noticeable check. Other species 
of this family have been recorded as parasitic on mud-wasp grubs, 
or even mason bees. 

A composite illustration is given, Fig. 59 a, which shows character- 
istics of eggs, larvae or grubs, pupae and adults of P. grandis\ male 
and females of (7. Iris ( =javanica) and C. pulchrivestita\ and pupae 
and adult of Hyperalonia tantalum. 

(b) METARRHIZIUM ANISOPMOB (METSCH.), Son. The entomo- 
genous fungi are comprised in one genus, i.e. Cordyceps, and 
most of the individual species attack insects and only form perfect 




. , r )\}(i. Photograph of composite group of eggs, larvae (\\hitr gruhs), pupae, and 
adult booties of Psilopholis grandis, together with male and female specimens of 
"digger wasps", C. Iris (Javana) and C. pulchrivestita, which are parasitic on the 
"white grubs". Also specimens of Bombylid fly (Hyperalonia tantalus} and pupae 
thereof; this insect is predaceous on the two wasp species. (Set up by the Entomo- 
logical section, Dept. of Agriculture, S.S. & F.M.S., under the direction of the 
Govt. Entomologist, Mr. G. H. Corbett, B.Sc.) 





FIG. 59 c. Showing natu- 
ral, curved position of 
white grub in soil. 



FIG. 59 b. Showing white grub, with egg of digger 
wasp in the most usual position, standing verti- 
cally. Below, the illustration shows the develop- 
ing larvae of the wasps feeding on the body of 
the white grub. (After Dammermann.) 




FIG. 59 d. Showing chains 
of spores, as formed by 



OHAP. xvni PSILOPHOLIS GRANDIS 397 

fructifications on substrates rich in proteins. Gaumann says the 
genus includes about 200 species, but Gwynne, Vaughan and Barnes 
record that the group includes only about 60 species, which are 
mainly tropical parasites on insects, the bodies of which become 
transformed into sclerotia. 

As explained in a preliminary section, many fungi form two types 
of fructifications, the perfect and the imperfect, and that there is a 
vast group of fungi in which only imperfect fructifications are found. 
The fungus that will be dealt with in the present case falls in the latter 
class of Fungi imperfecti. According to Gaumann, the types of fructi- 
fications, as they appear on infected insects, are called "Muscardine", 
which name is transferred to the disease itself. With sufficient 
nourishment the spore-bearing filaments coalesce into graceful white 
or bright-coloured tufts (coremia) and they are classed in the im- 
perfect genus Isaria. Metarrhizium is a fungus belonging to the genus 
Isaria and the two names are often used interchangeably. This ex- 
planation may clear up the position, and as the fungus under con- 
sideration produces bright-green tufts of spores, it is commonly 
known as the "green muscardine" fungus. 

Metarrhizium anisoploae (Metsch.), Sor., has attracted much at- 
tention, and attempts have been made both in the West Indies and 
in Queensland, and probably other cane-growing countries, artificially 
to develop the fungus on a large scale with a view to its employment 
as an aid to natural control. 

The "green muscardine" fungus forms chains of spores (Fig. 59 d) 
in a very similar manner to the ordinary green Penicillium fungi; 
the latter become prominent on many domestic articles which are 
allowed to remain in damp situations; in fact, they can be considered 
related fungi. 

This fungus is not only of interest as destroying melolonthid grubs 
on sugar-cane in Queensland and other sugar-cane-growing countries. 
It has always been considered to be of great practical interest, as it 
has long been recognised as a most important natural enemy of 
Tomaspis saccharina, which is the well-known Frog-hopper pest of 
sugar-cane in the W. Indies. At times fairly favourable reports have 
been issued following on the artificial propagation and scattering of 
the spores over infested cane-fields, but the general opinion has been 
that artificial spreading of fungus spores is not followed by results 
which are proportionate to the expense and labour involved. A re- 
cent report by Pickles indicates, however, that the fungus M. 
anisoploae must still be regarded as an important factor in natural 
control of Frog-hopper. 



398 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

The appearance of the melolonthid grubs infected with this fungus 
is typical, for the body, instead of decomposing after death, retains 
its shape and, gradually hardening, turns at first whitish, and finally 
dull green owing to the production of the green spores. The internal 
organs and fluids of the victim are quickly absorbed, and replaced 
by vegetable tissue constituting the mycelium of the fungus, until, in 
the case of grubs of Lepidoderma albohirtum, in Queensland, the entire 
grub becomes as firm as a piece of hard cheese and can be easily 
broken to pieces. These hardened grub-cases filled with fungus hyphae 
are known as sclerotia. 

It seems obvious, from the point of view of control, that grubs 
parasitised by the fungus would be usefully employed. Such para- 
sitised grubs should either be left in the ground or broken into powder 
which can be mixed with the soil. 

Some Observations on control of Psilopholis grandis in Malaya. 
When making recommendations for the control of plant pests and 
diseases it must be remembered that the position is definitely gov- 
erned by the economics of the situation. In Queensland, control of 
melolonthid grubs in sugar-cane fields is now established by injecting 
into the soil either carbon bisulphide (CS 2 ) or paradichlor benzene. 
This method of control costs 8-9 per acre for each crop of treated 
cane. The position is such, however, that the sugar farmer gets 
a valuable return for his expenditure and labour, and from the 
economic view-point, the balance is not overloaded on one side 
or the other. 

The position in Malayan rubber plantations is exactly the op- 
posite. No large losses of crop have been reported; there is little 
damage done to the trees; the pest is confined to two areas covering 
about 100 acres each, and in one of these areas has not spread from 
the infected into neighbouring fields. Any control method which 
disturbs the soil cannot be recommended, because such disturb- 
ance makes the grubs burrow more deeply, and the soil cannot be 
mechanically furrowed by plough. With furrows produced by the 
plough it is comparatively easy to obtain good results from lethal 
gas injection. Thus for the present the only method that can be 
considered is to encourage natural control, more especially in the 
direction of increasing the number of predatory wasps. If simple and 
cheap methods were available to prevent the adult female beetle 
from ovipositing, these would be of great use in expediting control. 
As it has not been mentioned above it would be advisable to draw 
the attention of readers to parthenogenesis (viz. the laying of eggs by 
the female wasps without copulation). This has been proved to be a 



CHAP, xviii PSILOPHOLIS GRANDIS 399 

common occurrence in the "digger-wasp" family, and the larvae 
which develop from these eggs pass through a normal life history. 

Some of the restrictions in respect of control imposed by the par- 
ticular conditions existing in mature rubber plantations have been 
mentioned above; (a) soil disturbance of any description drives the 
grubs to burrow more deeply; (b) lethal gas injection cannot be re- 
commended when the distribution of the grubs is widely diffused. 
Other restrictions are: (c) the grubs do not appear to be parasitised 
by the Scoliid wasps before they are three-quarters grown, so they 
have a considerable period during which they may cause damage; 
(d) possible alternative food crops which will grow under shade have 
not yet been found. 

Poisoning the soil with sodium arsenite, paris green and lead arsen- 
ate has proved unsuccessful. Scent traps set up with eight different 
mixtures were useless, for after eight days only nine beetles were 
caught and these probably hit the traps by accident. Light traps were 
useless with Psilopholis grandis for the beetle actively avoided the 
light, though in Queensland it is reported that Lepidiota albohirtum is 
definitely attracted by this means. Pits filled with rich jungle soil or 
fresh bullock dung proved useless, as also did darkened boxes. While 
many birds would undoubtedly devour the grub if available and also 
the beetles, bird life is not unduly prominent round the infected 
areas in Malaya. 

Wild pigs visit the infested areas nightly and eat any beetles which 
are on the ground. They have not actually been seen eating the grubs, 
but, during the grub stage, wild pigs return night after night to the 
areas where the grubs are at work, and if a search is made, grubs can 
always be found in the soil areas disturbed by the pigs. It is highly 
probable, therefore, that wild pigs make an active search for the 
grubs during the hours of darkness. 

If wild pigs therefore are present in the vicinity they should be 
encouraged and all pig-shooting stopped. The domestic pig is use- 
less, for while they will eat the beetles if fed to them during the day 
they pay little attention to them at night. 

It is stated by authorities in Queensland that the adult beetles 
prefer to rest during the day on various Ficus species, such as F. 
pilosa and F. benjamina. The latter species grows well in Malaya, and 
clumps of these trees should be introduced into the infested areas. 

Further search is required into the feeding habits of the Scoliid 
predators in order to discover the jungle plants on which they feed. 
When found, the chosen plants should be spread around and about 
the areas where the chafer grubs are working in the soil. 



400 DISEASES AND PESTS OF THE RUBBER TREE PART in 

As far as our experience in Malaya will allow us to judge, the col- 
lection of grubs by digging, or of the adult beetles by nets, offers no 
hope of success. 

GEOMETRID MOTH 

Hemithea costipunctata, Moore 

This Geometrid moth was found in 1920 feeding on the inflores- 
cences of the rubber tree and was reported upon by Corbett and 
Ponniah in 1922. The eggs are laid usually singly, but occasionally in 
twos or threes one above the other on the flowers and stalks of the 
inflorescence. They hatch out in two to four days. 

The larva, emerging from the egg, is greenish in colour with three 
distinct lines running longitudinally along the body. It possesses three 
pairs of thoracic legs with only one pair of abdominal feet, placed 
on the ninth segment in addition to the anal pair, or claspers. The 
larva progresses by moving these two pairs of feet up to the thoracic 
legs so that the body is thrown into a large loop and they are hence 
called "loopers" or "geometers". The caterpillars generally rest 
during the daytime, reposing at an angle from the inflorescence by 
clasping a pedicel of a flower. In this position they look like the stalk of 
a rubber flower. The colour, resembling that of the environment, and 
the attitude of the larva when at rest, prevent it being readily de- 
tected and account presumably for this caterpillar not being observed 
before 1920. When full-grown the caterpillar is about 1 inch in length 
and attains this condition in seventeen to twenty-five days. 

The pupae are seen suspended by their anal ends among the in- 
florescences. They are about \ inch in length; the general colour at 
first is pale green, but later this changes to dark green with blackish 
spots. 

The moth emerges from the pupa in from eight to eleven days. It 
has a wing expanse of about f inch, the upper surface of the wing 
being cobalt green in colour with three white, silvery wavy lines. The 
under surface of the wings is silvery green in colour. The moth lays 
eggs four to five days after emergence from the pupae. 

The life cycle -occupies from twenty -eight to thirty-two days. 

The diseased branches and blossoms were first found on rubber 
trees nearly six years old. The insect hitherto has apparently only 
attacked the lowest branches, starting at the blossom and gradually 
working down to the branch, leaving a blackish discoloration. The 
leaves curl up, discolour slightly and eventually drop off. As the cater- 
pillars feed almost wholly on the inflorescences, the leaf effects are 



CHAP, xvin INSECT PESTS 401 

probably the result of some reaction due to the mechanical injury 
caused by caterpillars eating the flowers. 

Corbett and Ponniah, in conclusion, state that this pest is, at 
present, of no serious importance, but if seeds are required commerci- 
ally for the extraction of oil further observations as to its habits and 
control will be necessary. 

Attention may be directed here to the suggestion made in a previ- 
ous section with regard to the possible reaction to attacks of Oidium 
heveae (page 299) and to squirrel damage (page 299). A similar after- 
effect may develop if attacks by this moth on the inflorescences 
result in a diminution of the seed supply. 



LIMACODID MOTH 

Thosea sinensis, Walk. 

Fig. 60 illustrates the caterpillar of this insect, on which some 
remarks have already been made. In a recent outbreak, where it ap- 




FIG. 60. Caterpillar of Thosea sinensis. x 2. 

peared in a block of seventy acres of old rubber, the caterpillars were 
found definitely eating the leaves of young rubber seedlings. The area 
was under a cover of controlled grass and, in parts, Mikania scandens, 
and it was supplied with rubber seedlings twelve months before the 
outbreak. The caterpillar appears first to attack the grass, which was 
entirely eaten off in places. The rubber seedlings are next attacked, 
the caterpillar devouring the leaves. They were also found clustered 
on the tapping panels of the old trees, but visible signs of damage 
were not apparent in this position. This insect must now be included 
in the list of those which have been found causing direct damage on 
rubber plants. Its real significance is, of course, the indirect damage 
aforementioned. 

In the attacks recorded, the caterpillars practically disappeared 

2D 



402 



DISEASES AND PESTS OF THE RUBBER TREE PART in 



after one month, but a further attack soon appeared, but in a lesser 
degree, and this again subsided. At a later date the caterpillars ap- 
peared again but in much smaller numbers and were confined to one 
portion of the area originally infected. 



LYMANTKID MOTH 
Orygia turbata, Butler 

Orygia turbata, Butler, is a Lymantrid moth which normally 
pursues its life history in cover crops which are sown for the purpose 





FIG. 61 . Caterpillar of 
O. turbata. x 2\. 



FIG. 61 6. Winged Males of 0. tnrbata. 
(Natural size.) 



of ground shade and prevention of soil movement. A few reports 
have been made of the insect migrating from cover crops to rubber 
trees, where slight damage is done to the tender cortical tissues 
opened up by the tapping operation; small wounds are made which 
later come to resemble tapping wounds. In the majority of cases the 
caterpillars (Fig. 61 a) have been found on young or seedling rubber 
trees on the leaves of which egg masses have been laid, but Fig. Gl c 
shows a caterpillar at work on the tapping panel. While the damage 
done has never been serious, insect migrations from one crop to 
another must always be carefully considered from the entomological 



CHAP, xvni INSECT PESTS 403 

point of view, for there are numerous cases of very serious losses 
resulting from an insect gradually becoming attuned to feed and de- 
velop on a new plant very distinct from that on which it formerly 
lived. 

This insect shows a marked preference for Mimosa pudica, L., 
and also Centrosema plumieri, Benth. The latter is one of the most 
favoured cover crops grown on Malayan rubber plantations. 

The first outbreak of O. turbata in Malaya was recorded in 1926. 
The caterpillars originated in "belukar" bordering the estate at a 
certain point, spreading from there to the cover crop, C. plumieri, 




Fig. 61 c. Caterpillar of O. turbctia on tapping panel of Hevea. Note similarity of 

coloration. 

which they ate over a very large area; they also attacked the leaves 
of the rubber plants to some extent. As the migration of this moth is 
entirely dependent on the caterpillars (the females being wingless), 
it was advised that a poison barrier should be sprayed for a depth of 
about three yards beyond the limit of the last advance of the larva, 
and that all the stages of the insect found inside the area already 
attacked should be collected. These measures proved distinctly suc- 
cessful. In this outbreak O. turbata confined itself entirely to the 
Centrosema cover, Passiflora and Calapogonium being untouched; 
another outbreak was reported where rubber seedlings in a clearing 



404 DISEASES AND PESTS OF THE RUBBER TREE PABT in 

of about 260 acres were found to be badly damaged by swarming 
caterpillars. These, had apparently spread from the weeds surround- 
ing the area. The larvae, in this case, were polyphagous, feeding on 
Mimosa sp., Crotalaria sp., Melastoma sp., and other plants. 

These early recorded outbreaks of 0. turbata occurred on seedlings 
and young rubber plants, from which the various stages of this insect 
were easily collected and destroyed. The position might have been 
different if the caterpillars had migrated to mature trees, for in such 
cases control measures would have been considerably more difficult. 
It is possible also that the caterpillars might have become more de- 
finitely associated with older trees. Since 1930 the larvae of 0. 
turbata have been sent in each year from various estates. 

This insect appears chiefly to use the rubber plants for the purpose 
of pupating. It seems to be characteristic of the species that when 
fully fed the caterpillars move away from the original host plant, i.e. 
Mimosa sp., a distance of some six to ten feet to a taller plant on 
which to form the cocoons. These are usually spun in small groups, 
three to seven in number, on the under-side of rubber leaves, the 
three leaflets sometimes being bound together and the edges curled 
in, so that the group of cocoons becomes enclosed in a very open, 
irregular network of silk. Almost invariably the groups of cocoons 
contain both males and females; the male chrysalids are much smaller 
than the females and are easily distinguishable. 

Only the males fly (Fig. 61 6), the female being wingless and rarely 
moving more than one inch away from the original network. Usually 
they remain practically stationary after emergence. The eggs are 
laid in a mass, one layer deep, upon, or in close proximity to, the 
cocoon from which the female has emerged. Successive broods rarely 
appear more than ten feet away from the preceding one. This fact 
means that the spread in area is slow and is a point in favour of 
obtaining control reasonably quickly. Each mass generally contains 
from 250 to 300 eggs, but masses have been counted containing as 
many as 450 eggs. They are laid in regular rows, each egg being 
covered with short yellowish-coloured hairs. Each egg is about 0-75 
mm. in diameter, reticulated, the top slightly flattened and depressed. 
The centre of the depression is greenish-yellow in colour. 

The caterpillar of 0. turbata (Fig. 61 a) is blackish in colour with 
long branched hairs arising from various parts of the body, especially 
the sides. Just behind the head there are two tubercles which are 
usually red at the base, except in the last instar, from which pencils 
of long black hairs arise. The thoracic segments are marked with 
white. 



CHAP, xvin INSECT PESTS 405 

The first four segments of the abdomen bear tufts of hairs, which 
in the male caterpillar are generally yellow in colour, though the 
first two tufts are often black during the fourth instar of the female 
larvae. The fifth and sixth abdominal segments have white markings 
in the middle in the early stages and broad white lines near the sides 
in the later stages. 

The sixth and seventh segments have red tubercules in the middle 
which are known as eversible glands. Most of the caterpillars conform 
to this general description, except for differences in size and slight 
variation in colour. 

If more detailed observations on the coloration of the various in- 
stars is required, the reader should consult the article by Corbett and 
Dover. 

The life cycle is completed in about one month. The male moth has 
a wing spread of about one inch and is coloured a rusty brown; as 
mentioned above, the females are wingless. 

For control, Corbett and Dover recommend a poison barrier of lead 
arsenate as a means of confining the caterpillars to the area already 
occupied by them, as the insects can only spread by movements of 
the caterpillars. Lead arsenate (1 Ib. to 50 gallons of water) is sprayed 
on the leaves of Hevea and on any cover plants at the limits of the 
area infected with the caterpillars. If the cocoons and egg masses and 
caterpillars are to be found in profusion on young rubber plants, 
hand picking will help considerably towards a quick reduction. 

CATERPILLAR AND NOCTUIID MOTH 

Spodoptera Sp. and Tiracola plagiata, Walk. 

In 1918 Richards recorded a swarm of caterpillars in Malaya which 
devoured all the available grass and weeds and then attacked young 
rubber plants, stripping the leaves and eating the young green bark, 
over an area of several acres. This caterpillar was reported to be a 
species of Spodoptera. 

Another example of insects migrating from cover crops to rubber, 
is provided by the Noctuiid moth Tiracola plagiata, Walk., a major 
pest of the castor-oil plant in Malaya. An outbreak of caterpillars of 
this species occurred on castor-oil plants in 1923, causing considerable 
damage to the crop, from which they spread to rubber plants of about 
eighteen months old. Serious damage was done, and practically all the 
rubber plants were defoliated. The caterpillars of T. plagiata would 
seem to be strongly possessed with the migratory instinct, for on 
several occasions they have caused damage to rubber plants. 



406 DISEASES AND PESTS OF THE RUBBER TREE PART in 

PSYCHID MOTH 
Psyche (Acanthopsyche) snelleni, Heyl. 

The larvae of one or more species of psychid moths occasionally 
appear in large numbers and begin to feed on the recently renewed 
bark in close proximity to the tapping cut, making small wounds 
from which latex exudes. The larvae are enclosed in cases derived 
from old vegetable material such as dead leaves, and are better 
known as "case-moths". The cylindrical larval case of Psyche 
(Acanthopsyche) snelleni is about 1 J ins. in length and has been found 
on Hevea trunks in Malaya on several occasions; it is also a well- 
known pest of tea in Java. 

The female moth is wingless, so that it is during the comparatively 




FIG. 62. Bag Worms (Acanthopsyche snelleni} on tapping panel of Hevea. 
(fa natural size.) 

lengthy larval stage that any movement of the insect occurs. The 
male moths are not attracted by light and the most effective method 
of control is to destroy the larvae. Fig. 62 will show how these larval 
case-moths go to work when attacking rubber trees. 

Methods of Control: 

(a) Hand collection of the bags, whereby all the stages are de- 
stroyed except the winged males. 

(b) Painting or spraying the trunks with: 

(i) A 2 per cent Kerosene emulsion containing 0-5 per cent 

lead arsenate. 
(ii) A 2 per cent Izal solution. 



CHAP. XVIII 



INSECT PESTS 



407 



(iii) A 5 per cent Agrisol solution. 

(iv) A 5 per cent Brunolinum solution. 

If the "bag-worms" are present in small numbers only it is hardly 
worth while adopting any spraying methods of control as the damage 
done will be inappreciable. 



SCALE INSECTS 
Lecanium nigrum, Nietn., Pulvinaria sp. 

Two scale insects have been found on rubber in Malaya, viz. 
Lecanium nigrum, Nietn., and a Pulvinaria species. It is reported 
from Ceylon that Lecanium (Coccus) viride, 
Green, also causes damage to rubber. 

In Malaya damage by scale insects is 
seldom met with except in neglected stands 
of rubber. Lecanium nigrum is the common- 
est form. When this scale is found in Malaya 
on young rubber, it is usually in the para- 
sitised form, and closely resembles small, 
convex dark-brown to black blobs of latex 
about J- inch in length, f inch in breadth 
and J inch in height (Fig. 63). The actual 
scale insect is only about \ inch in length, 
and the pustular mass usually found is 
composed of the small dead insect en- 
veloped in a mass of fungal filaments. The 
fungus which most commonly parasitises 
Lecanium nigrum in Malaya is named Hypo- 
crella reineckiana and it grows over the scale 
in a hard cushion-like mass which is at first 
red-brown or yellow-brown but becomes 
black on ageing. These pustular masses 
may be found on the leaves, usually con- 
gregated about the veins and midrib, and 
they may also thickly encrust the terminal 
green stem. They are usually found on the 
leaves of the trees which are covered with the black "sooty moulds' ', 
i.e. Meliola sp. 

Fetch records a second fungus, Cephalosporium lecanii, which also 
attacks the commoner species of scale insects and kills them, sub- 
sequently growing out as a white fringe round each scale. 




FIG. 63. Parasitised scale 
insects (Lecanium nigrum) 
on green twigs of Hevea. 
(Natural size.) 



408 DISEASES AND PESTS OF THE RUBBER TREE PART in 

RUBBER LEAF MITE 
Common form =Tarsonemus translucens, Green 

This mite is commonly known as the yellow tea mite and does a con- 
siderable amount of damage on this crop. They are very minute and 
scarcely visible to the naked eye; they are about 0-2 mm. long, yellow 
in colour, with a dark stripe down the back. 

Richards reported in 1917 that small local attacks of this pest 
have been noted since 1914 in Malaya, mainly in nurseries. 

The rubber leaf mite is a pest which under certain conditions of 
soil and weather is capable of doing considerable damage to young 
rubber fields. It punctures the epidermis of the young leaves and 
sucks out the fluid contents of the cells. The response made by plants 
affected by mites is reflected in distortion of the leaves so that they 
become more or less curled, causing an asymmetrical growth, or 
there may be complete defoliation of the young shoots (Fig. 64). 
Serious mite attacks are frequently accompanied by attacks of leaf 
fungi; the most prominent fungus over the last few years has been 
Oloeosporium alborubrum, Fetch, with pinkish acervuli, but Gloeo- 
sporium heveae, Fetch, has also been recorded. 

It has been generally accepted that the serious mite attacks so 
far experienced in Malaya have only been found in places where 
soil conditions were not entirely favourable for growth. This may, be 
accepted as a general statement, but mite attacks have been met 
with during the last three years where there was little wrong with 
soil conditions. Drainage is undoubtedly one of the important factors, 
and serious mite attacks are seldom found on soils which are well 
drained. 

During 1931 and 1932 mite attacks were commonly reported, and 
the close association of the insect and the fungus 0. alborubrum or 
0. heveae was very noteworthy. The combination caused a notable 
amount of damage in several places. 

For successful control, drainage will have to be undertaken if 
necessary. The attacked leaves should also be dusted with powdered 
sulphur four applications at five-day intervals are recommended. 

From Java another but much larger mite is reported, being about 
1 mm. in length. This is the so-called grey mite and the leaves react 
to the attacks of the insect by becoming much elongated, and the 
edges curling inwards. 




Km. i'r-1. A. Young given loaves showing results of mite attack; note distorted 
leaves. B, C, Showing usual defoliation, B being only partially defoliated ; note 
that when leaves have fallen the leaf stalks still remain attached. D, Illustra- 
tions of the mite insect, Tarsonemus tranMuscens. x 200. 



410 DISEASES AND PESTS OF THE RUBBER TREE PART in 

SHORT-HORNED GRASSHOPPER 
Cyrtacanthacris (Valenga) nigricornis, Burn. 

As far as the writer is aware, no special work has been done in 
Malaya on the life history of this large grasshopper which is distri- 
buted from South India to Java and also occurs in the Philippines. 
The length amounts to 60-70 mm., the colour is greenish -grey, but 
later the insects become yellowish (Fig. 65), the fore-wings are 
darker towards the base, and the hind- wings have the base tinged 
reddish; there is a medium yellow line and pronotum. The species is 
distinguished by the black antennae and the femora of the hind legs 




FIG. 65. Cyrtacanthacris niyriformis, the short-horned grasshopper. (Natural si/o.) 

bearing two black cross bands. The nymphs are yellow, mottled all 
over with black. 

In Java Dammermann reports that this locust is found chiefly 
along the skirts of forests, especially teak forests, and in open local- 
ities within the forest. The female deposits eggs in masses of 70-100 
each or more, about 5-8 cm. deep in the ground. Oviposition occurs 
at the end of the rainy monsoon and the eggs lie dormant during the 
next dry period and do not hatch before the rains set in again, in 
November and December and even later. The young insects become 
full-grown in the course of the wet season, thus completing a one-year 
life cycle. The hoppers, when newly hatched, live at first on the 
ground but soon ascend the trees to feed on the foliage. When they 
are full-grown, the winged adults swarm from the original breeding- 
grounds to cultivated areas in the vicinity, but the species does not 
display any social or migratory instincts, each individual travelling 
by itself. 



CHAP, xvm INSECT PESTS 411 

It is reported from Java that usually only a small strip of land, a 
few kilometres wide, bordering on the forest, is attacked; further 
away the damage is unimportant. This is not so in Malaya, where the 
insect is generally distributed throughout any clearing of young 
rubber which possesses a dense cover crop. According to one authority 
teak is the most preferred food plant, the next being coco-nut and 
maize. The insects have been found attacking Castilloa, Hevea, 
Artocarpus, banana, coffee, dadap and many green -manure plants. 
Rice, as well as lallang and other grasses are free from attack. In 
Malaya attacks by this insect become conspicuous both on young 
coco-nut and rubber plantations if giant mimosa (Mimosa invisae) is 
used as a green cover crop. 

The chief damage now being done in Malaya by this insect is on 
young budded clearings of Hevea where the very young leaves, often 
before they are out of the bud stage, are eaten. If the leaves continue 
to develop they finally present a very ragged appearance and are 
usually found attacked by a leaf fungus and death is the result. The 
older fully -developed leaves are not usually attacked. 

An interesting case of varied susceptibility to attack was experi- 
enced in 1932, when three estates reported that on bud-grafted areas 
carrying a mixed planting of various clones, the clone A.V.R.O.S. 256 
was completely defoliated, while other different clones surrounding 
the defoliated plants escaped attack entirely. 

This grasshopper is not usually present in very large numbers and 
the usual method of control is hand-collecting by the small children 
of the labour force. If, however, they are very numerous and are 
causing material damage, the cover crops in which the insects are 
living should be sprayed with lead arsenate solution (2 Ibs. of lead 
arsenate paste or 1 Ib. of lead arsenate powder to 50 gallons of 
water). 

The use of poison baits has also proved successful. For this purpose 
4 ozs. of sodium arsenate is well mixed with 25 Ibs. rice bran and a 
little water, and small balls of the mixture are prepared. In the ab- 
sence of cover plants, the balls are broadcasted at the rate of 7 \ Ibs. 
per acre; where a cover is employed the poisoned balls are placed on 
the ground in small heaps in order to prevent any burning. 

Atractomorpha psittacina is the most common grasshopper found 
in the green cover plants in common use to-day and for purposes of 
comparison a line drawing of the insect is given (Fig. 66). It is much 
shorter than the short-horned grasshopper, attaining a length of only 
30-40 mm. as against 60-70 mm. It is characterised by a pointed 
conical head. 



412 DISEASES AND PESTS OF THE RUBBER TREK PART in 




FIG. 66. Atractomorpha psittacina. A small grasshopper found commonly in 
young rubber fields. (Natural size.) 



CRICKETS 

Brachytrupes portentosus, Licht. 

The large cricket B. portentosus (B. achatinus, Stoll) is reported to 
cause damage in nurseries by biting off the young plants one or two 
centimetres above ground-level. The writer has no record of this, 
but during the last two years several reports have been received to the 
effect that these insects have been seen and caught eating the new 
bark forming on the tapping panel \ inch above the tapping cut. 
There is no reason to doubt this statement, as the writer has seen the 
insects at work. 

The insects live in holes in the ground, where they remain during 
the day, emerging at night. Heavy rains drive them out of their 
holes, and for control it has been suggested that seed beds or nursery 
beds should be watered thoroughly or even inundated for a short 
time. Fetch suggests the use of poison baits, to be made by chopping 
up young maize plants and mixing a little treacle and 5 gms. of paris 
green or arsenic with each pound of the chopped plant. 

Pratt stated that a cricket was reported from Sumatra in 1906 as 
damaging young rubber seedlings. The insects saw through young 
plants at the base of the stems, leaving a stump one to three inches 
high. The attacks were circumvented by enclosing the young plants 
in a paper cylinder made from ordinary newspaper. A full sheet is 
rolled up into a cylinder the height of the paper and about six inches 
in diameter, and fastened with three pins. These are placed over the 
stumps and fixed in position by means of three thin stakes on the 
inside. 



CHAP, xvni INSECT PESTS 413 

RHINOSCEROS BEETLES 
Xylotrupes gideon, L. 

Fetch reports that Pratt has seen in Malaya an area of young 
rubber, 300 acres in extent, entirely devoid of leaves owing to the 
attacks of the insect commonly known as the Fork-horned Rhinos- 
ceros beetle. The stumps are attacked soon after planting out, as 
soon as the shoots appear. The young shoots are bitten off and the 
process may be repeated as often as new shoots appear, until the 
plants are worthless and have to be replaced. The same method of 
control as that given for crickets is recommended. 

The writer has not been able to verify Pratt's report, and damage 
by this insect has not come within his experience. 

WEEVIL 

Eu nieces squamosu^ 

Pratt reported about 1910 that this weevil was causing damage to 
young rubber trees by eating away the older leaves and young shoots. 
Collecting beetles by hand has proved effective in control. The beetle 
is practically omnivorous and, according to Pratt, is not likely to 
confine its attacks to rubber, but will continually appear and attack 
small areas of young rubber trees. A report of this insect by Wray, 
under the name of Astycits lateralis, may be found in Perak Museum 
Notes, vol. ii. pt. 1, p. 01. 

The writer has never seen this insect at work and over the last few 
years no specimens have been sent in. 

LONGIHORN BEETLE 

Bafocera ritira 

This longicorn beetle has been recorded from Ceylon as being found 
boring into the tap-root or the lower parts of the stem of Hevea 
plants. Only one case has been recorded from Malaya on Hevea. 



CHAPTER XIX 

ANIMAL AND OTHER PESTS 
Elephants Wild Doer Wild Pig Goats Rats Squirrels Spiders Slugs. 

INTRODUCTION 

FETCH states that all the common herbivorous animals show a 
partiality for H. brasiliensis and that horses and cattle devour the 
foliage greedily. The writer has not specially noted this, though 
bullocks have been commonly seen grazing under rubber trees with- 
out making any attempt to eat the foliage, which was within easy 
reach. The list of animals causing damage to rubber trees in Malaya 
are listed above and fall in the orders given below: 

MAMMALS . . Elephants 

Wild deer 

Wild pig 

Goats 
RODENTS . . Squirrels 

Rats 

ARANEAE . . Spiders 
MOLLITSCA . . Slugs 

ELEPHANTS 

Elephants have done and still do considerable damage in rubber 
plantations when they are present in large numbers in the neighbour- 
ing jungle. Even recently, the district planters' association in Pahang 
have had the item "damage by elephants" constantly on their agenda 
for discussion. It is only from a few localities, where elephants are 
plentiful, that damage has been reported. The huge beasts break down 
fencing which allows ingress of wild deer and pig, and these animals 
can do considerable damage in a short space of time. Elephants break 
off or uproot small trees, and they are said to eat the roots, the tap- 
root being particularly favoured. There is no systematised method 
of elephant-catching in Malaya, so this obvious method of reducing 
the numbers of these marauders is not employed. 

In 1914 a system of patrols was established in the Sungei Siput 
district in Perak. Contact was maintained with the destructive herds 

414 



CHAP, xix ANIMAL AND OTHER PESTS 415 

and their movements carefully noted. Paths through the forest were 
cut so that the patrols, armed with Chinese crackers and bombs, 
could move about freely, and if the animals showed any tendency to 
move in the direction of a planted area, they were turned in a fresh 
direction by firing the crackers and bombs. 

Another method of preventing elephant damage is to form what is 
called an elephant belt around the estate. The basis of the scheme is 
that a belt of jungle of varying width is felled and the trees are left 
lying all tangled up just as they fall. A passage through such a belt 
of felled jungle is not easily forced. In some cases the belt is made two 
chains wide, and is separated from the plantation by a number of 
strands of barbed wire. An elephant belt recently built on an estate 
has been made one chain wide, and through the maze of felled timber 
two strands of barbed wire have been run; on the wire, at about 
-chain intervals, kerosene tins filled about three-quarters full of 
loose stones have been fixed. It is reported that this particular belt 
has proved very successful in keeping out not only elephants but other 
wild animals which damage rubber trees, viz. wild deer and wild 
pig. Costs of establishing elephant belts will differ according to the 
district in which the estates are situated. The cost of one, for a belt 
two chains wide, was 13 dollars for five chains. 

WILD DEER 

This animal is the one which causes most damage in rubber planta- 
tions in Malaya, more especially if the trees are young and the estate 
is bounded by heavy jungle. They strip the bark from the wood from 
ground-level up to a height of four to six feet, and complete ringing 
of the stem is often brought about. 

Many repellent preparations have been tried but so far unsuccess- 
fully; most of the preparations tried are themselves positively 
dangerous and more damage has been done by their use than would 
have been done by the offending animals. Constant attention to 
fencing or the formation of an elephant belt on the lines described 
above are the only sure methods of preventing damage by deer. 

WILD PIG 

Similar remarks apply to these animals as to wild deer, except that 
in addition they injure the roots of rubber trees by grubbing up the 
soil during the feeding. Elephant belts will prevent wild pigs from 
entering rubber estates. 



416 DISEASES AND PESTS OF THE KUBBER TREE PART in 

GOATS 

Goats eat the leaves of young rubber plants freely and may do con- 
siderable damage in nurseries. 



RATS 

Certain herbivorous animals of the rodent order are classed as 
vermin because their activities are inimical to the growers of various 
crops. The rubber plantations in Malaya have not escaped entirely 
from damage by animals of this type. Squirrel damage has been 
known for many years, but damage by rats in young fields of rubber 
has only attracted attention since 1933. 

Damage. The enormous amount of damage done to- many crops 
by rats is too well known to need emphasis. In Malaya padi fields, 
oil palm and coco-nut plantations are often severely attacked, and in 
any event the annual losses, on the cultivations mentioned, is con- 
siderable. In other countries sugar-cane, cocoa and coffee are at- 
tacked by this pest. 

Pig. 67 depicts the typical signs of rat damage on young bud- 
grafted trees. In all cases examined in 1933 the opening of the runs 
through the cover crop have been quite conspicuous in the neighbour- 
hood of the attacked trees, and this fact alone should enable planters 
to spot the cause of the damage. It might be mentioned here that the 
new fields of young rubber which have been and are being started at 
the present time for the purpose of bud-grafting, are planted up as 
quickly as possible with cover plants, and a thick cover crop is 
usually found growing over these fields. 

There has been no record, in Malaya, of definite rat damage on 
Hevea plantations until 1933. In April scarring of the bark of a 
number of trees in certain fields of young budded rubber was first 
noted, and since that date up to the time treatment with poison baits 
was started, the number of trees attacked steadily increased. In all 
cases the infested areas carried a strong, thick growth of Cenirosema 
pubescens, the rubber trees being ring-weeded. The runs and rat- 
holes were frequently found at the edges of the rings formed when the 
cover crop was cut back. 

Two main areas were affected; the first, in a low-lying, poorly 
drained area, replanted in 1931 with budded trees, which were mostly 
stunted and of sickly appearance, averaging about five to six feet 
in height; the second area carried normal, well-grown budded trees, 
replanted in 1931, situated a few hundred yards away from the first 




Flo. 67. A, Showing scion stom of young buddcil rubber plant damaged by rats 
well above junction of stock and scion. B, Showing rat damage on scion near 
to junction and on stock below. C, Showing rat damage on both stock and 
scion of young budded plant directly about the junction. 



418 DISEASES AND PESTS OF THE RUBBER TREE PART in 

area. On the stunted trees in the first area, the scarred places caused 
by the animals extended from the union upwards to the commence- 
ment of the green -bark on the scion. The scars were mostly small, 
vertical, irregular oblongs and at the first glance one becomes suspici- 
ous of rodent damage. On many trees the scars are closely placed all 
round the stem and throughout the length of the harder, mature, 
brown bark portion, usually, though not invariably, leaving the more 
tender, recent growth at the top untouched. Sometimes the cambium 
and even a small portion of the wood beneath is removed. 

Scattered affections may be seen here and there in between and 
around each area. In the second area, with well-grown normal- 
budded trees, the animals appear to have a fondness for the corky 
bark of the stock below the union and for that of the scion immediately 
above the union. In many cases holes have been scooped out around 
the stock, and the trees may be completely ring-barked in conse- 
quence, but none have died up to date (1933). Here and there the 
cambium is damaged, but as a rule the wood is untouched, and on the 
larger trees it is rare that scarring occurs above a few inches from 
the ground. The severity of the wounding renders it doubtful whether 
the trees will ever regain perfect bark conditions, but in the writer's 
opinion, if further depredations by the rodents can be avoided, they 
should do. 

Control. For purposes of control, the Department of Agriculture, 
S.S. & F.M.S., which runs special rat campaigns in the large padi- 
growing areas in Malaya, was consulted. The Director of Agriculture 
very kindly approved the suggestion that the Rat Destruction 
Officer, Krian (R.D.O.K.), should visit one estate and give advice, 
which proved very successful. 

The R.D.O.K. decided to rely entirely on poison baits, for he 
thought Tamil coolies would not handle straight poison carefully 
enough or set steel traps properly without much supervision. Three 
small heaps of padi husk were placed at the entrance of each run in 
the ring-weeded spaces and, where occupied, holes were located and 
in the husk-pile three baits were placed. To make up the baits the 
articles listed below were well mixed together and the size varied 
from one-half to one inch in length and about one-quarter of an inch 
in diameter. 

The padi husk is locally known as "sekam" and proves very useful 
in laying baits because the smell of the padi encourages the rats to 
forage for and eat the baits; the material also stands weather well. 
They are easily seen and do not easily disintegrate. 

Two men are employed for bait-laying, one to lay the sekam and 



CHAP. XIX 



ANIMAL AND OTHER PESTS 



419 



the other to follow with the baits. Small scoops can be used to prevent 
undue handling, but if the operators rub their hands well at frequent 
intervals with a handful of sekam, the human element is masked to 
a large degree and scoops can be dispensed with. 

A change bait should be used once the rats become familiar with 
the sodium arsenite baits. Barium carbonate or strychnine may be 
used as alternative poisons for sodium arsenite, but the price will 
govern the situation as to which shall be most commonly used. 
When a change from poison baits becomes desirable in the rice- 
fields owing to the sagacity of the Krian rat, it is usually made by 
running a line of steel traps for a night or two, followed by poisoned 
grasshoppers. A return may then be made to the poisoned baits. 

The following articles are required for mixing in the baits recom- 
mended by the R.D.O.K.: 



VOLS. 

Rice polishings 4 

Tapioca flour . 2 

Tallow . . 1 

Palm oil . H 



Ozs. 

(approx.) 

46 

45 

4 

47 



VOLS. 

Water . . 1 
Salt . . 1 
Sodium arsenite 



Ozs. 

(approx.) 
24 
3 
IS 



The above ingredients are mixed thoroughly and then run through 
a mincing machine with a specially large delivery plate which turns 
out balls about the size of an ordinary marble, which is calculated 
to give approximately 0-696 grain of sodium arsenite to each ball. 
After being machined, the balls are dried and stored if not required 
for immediate use; they keep indefinitely. 

The results obtained by the use of poison baits were very success- 
ful. Working with Tamil coolies, poison baits were made up and 
placed in position. On inspection four days later, it was found that 
practically every heap had been disturbed, and it was estimated that 
at least 8 Ibs. (8000) out of the 10 Ibs. (10,000 baits) set had been 
taken, and only ten trees in the twenty-five acres treated had been 
freshly attacked. 

Dammermann gives two alternative formulae for making up 
poison baits for rat destruction, the poisonous ingredients being 
barium carbonate or strychnine. 

Barium Carbonate. This chemical is a most effective poison for 
killing rats and other rodents. It is not fatal to man, fowls or domestic 
animals, unless taken in fairly large quantities, about 1 gm. of pure 
barium carbonate being harmless to a chicken; a 4 gm. dose has 
proved fatal to man. 



420 DISEASES AND PESTS OF THE RUBBER TREE PART in 

The following formula is given by Pemberton for preparing 
barium carbonate cakes as a poison bait for rats: 

Mix together 1 part (by weight) of barium carbonate and 3 parts of 
flour, or preferably middlings, and add enough water to knead into a stiff 
dough which is rolled into sheets about \ cm. thick and cut into small 
cakes about 1 to 1-5 cm. in diameter. The cakes are dried thoroughly in an 
oven or by the sun and are then ready for use. A small portion of one cake 
is usually fatal to any rat. 

These cakes may be made rainproof by coating them, after they 
have dried and hardened, with a thin film of paraffin wax, which is 
best achieved by dumping them on to a tray in a pan of melted wax. 
The tray is then raised and the cakes are thrown through the air into 
a pan of water below. 

Cakes of this type, kept in dry storage for two years, were found to 
be as effective as fresh cakes. 

Strychnine. Strychnine is a deadly poison to man and the majority 
of vertebrates. It is only applied as a bait for controlling rats or birds 
and is made as follows. 

A mixture of 60 gms. each of powdered strychnine, powdered 
baking soda and salt, two teaspoons of saccharine and a cupful of 
laundry starch is placed in two litres of hot water and boiled slowly 
under continuous stirring until a fairly creamy paste is formed. This 
paste is poured over 25 kgms. of wheat maize or rice, all unhusked, in 
a wooden tub. The material is stirred until all the grains are covered 
with paste; it is then thoroughly dried and then becomes ready for 
use. 

The control of rats in young rubber fields by poison baits has been 
treated at length because of the potential menace which accompanies 
any sign of depredations done by these animals. A recent letter may 
be quoted in relation to control of rat damage in Malaya: 

Most of the sodium arsenite baits were taken and a decrease in the 
amount of new damage was observable. There still remained, however, a 
number of rats in the area causing fresh damage to the trees and it ap- 
peared the rats had become wise to the bait. 

A suggestion was made for a change of bait, and forty pounds of barium 
carbonate was procured and distributed in the affected area. This bait 
seemed less acceptable to the rats and, much of it was untouched. Sub- 
sequently, this poison was mixed up in powder form with cooked rice and 
distributed. Latest reports are that almost the whole of this has been 
taken; at the same time there is only very scattered and slight gnawing 
of the trees observable. 

While baits are being taken it is certain that a number of rats are still 
left in the area, and more poison is being obtained and will be distributed 



CHAP, xix ANIMAL AND OTHER PESTS 421 

by the last method. No estimate of the number of rats destroyed is ob- 
tainable as carcases are rarely found. The extent of damage is the only 
guide to the efficacy of the mixture. 



SQUIRRELS 

The Malay squirrel, Sciurus miiatus, Raffl., is a very important 
pest in coconut plantations, but does not often cause much damage 
in rubber plantations. There are certain periods, however, when re- 
ports of damage by squirrels become more frequent and it is probably 
during the season of the year when the rich, oily seeds cannot be 
found in the plantations. Thus as attacks of Oidium heveae may 
wholly prevent seed production in certain years, it might be expected 
that more squirrel damage will be reported from rubber plantations 
during the years when Oidium attacks are severe and extensive. 

The damage done is quite typical; the animals attack branches, 
usually about three to four inches in diameter, and eat out a narrow 
channel, half an inch in width, in the cortex; all the cortical tissue 
down to the wood is gnawed away on an ascending spiral (Fig. 68 c). 
This channel has serrated sides, for as the teeth bite into the tissue, 
little projections of cortical tissue remain untouched as would be ex- 
pected from the action of animals with prominent incisor teeth. 
The ascending, spiral channels, with serrated edges, found on the 
branches, soon become filled up with callus tissue and a prominent, 
raised ridge is formed (Fig. 68 a). It was puzzling to account for these 
raised ridges at first, for they closely resembled young stems of rubber 
plants up which climbing plants had been growing. Ultimately, 
specimens were observed in the very early stages which left no doubt 
as to the cause. There is no necessity to treat the wounds made on the 
branches, as good natural recoveries are usually made. 

There is a more serious type of damage done by squirrels than that 
described. This happens when the animals descend to the level of the 
tapping panel and commence to gnaw away the recently renewed 
bark of the tapping area. Large areas of tapping surface may thus 
be removed and a very ugly wound appears as a result (Fig. 68 6). 
When this type of damage is found, the open wounds should be 
covered in the usual manner with a dressing of asphalt or tar. 

Shooting or trapping the animals is the only satisfactory method of 
reducing the number of squirrels. Trapping is systematically carried 
out on many coconut plantations. 



422 DISEASES AND PESTS OF THE RUBBER TREE TAUT in 

^M^r>;G^' ;< ,'x^vK^:; ^'V*v^%U : '^>ff''^ ^Wi 1 ^ ^Iv 1 "^ ! " ] A ' r ^ .'" j -' - ' L "< f / u (l 

"; t; f ? "fi! M ^^#;!* J i,^^4^tt ,'' Ji^'f" "?' ' !^'!*^^ 




FIG. 68. a, Showing repair of squirrel damage on branches; note darker, raised 
ridges, formed by development of callus tissue. 6, Showing damage done on tap- 
ping panel by squirrels; note large, open wound on left, c, Squirrel damage 
on branches; note bark tissue eaten away down to the wood, forming a kind of 
channel, with typical serrated edges. 



SPIDERS 

Attention to spider damage has been directed on page 209. The 
following short remarks are but repetitions. 

During 1933 a certain amount of leaf- fall of newly refoliating leaves 
developed after wintering. This was initiated by a small spider, as yet 
unnamed. This insect is very quick in its movements and is very 
difficult to capture. Up to date, the spiders seen and captured are 
variable in colour and there may be more than one species concerned. 

This spider weaves its threads around the young pendant leaves 
in the very early stages of their development. In this way the leaves 



CHAP, xix ANIMAL AND OTHER PESTS 423 

are bound together in triplets and, as they grow and expand, the 
space between them forms an ideal damp chamber for the develop- 
ment of leaf -spotting fungi, viz. Helminthosporium and Gloeospvrium 
species. Excessive accumulation of moisture within the enclosed 
space causes death and rotting of the leaf -tips, which later are torn 
apart. Finally, the leaves appear malformed, the tips are badly dis- 
coloured and torn, while healthy parts of the leaves have been 
severely eaten away, and the remaining leaf tissue is attacked by 
leaf-spotting fungi. 

A leaf-eating weevil is also fond of the shelter provided by the 
bound leaves and is responsible for some damage. This insect has 
been identified as Phytoscaphus leporinus, Faust, fam. Cinculionadae, 
by Mr. H. M. Pendlebury, Curator, Selangor Museum. This pest has 
been reported from Selangor, Perak, South Kedah and South Johore, 
and is probably widespread in Malaya. It seems to prefer a wet 
wintering season. 

While defoliation occurs about the same period as Oidium leaf fall, 
the symptoms are quite distinct, for leaves which have fallen owing to 
attacks by this fungus have not the same ragged and torn appearance, 
although they may be malformed. 

Trees which suffer from attacks by this spider recover naturally as 
climatic conditions become more favourable to growth, but if treat- 
ment becomes necessary, sulphur dusting will have to be undertaken. 

SLUGS 

Damage by slugs was recorded in Malaya in 1905 and, in Ceylon, 
Green published an article on the subject in 191 1. Over the last decade 
there has been little damage done by these molluscs in Malaya. The 
following account is taken from Fetch's book: 

Early in the history of plantation rubber in the East it was found that 
slugs ascended the tree and drank the latex either as it ran down the 
tapping cut, on after it had collected in the cup. In Ceylon the species 
which acquired this habit is a brown slug, Mariaella dussumieri, Gray, 
while in Java, a different species, Parmarion reticulatus, Hass., has adopted 
the same practice. 

As long as these slugs confined themselves to drinking the latex their 
presence was disregarded. The chief result in the case of the Ceylon species 
was said to be a loss of scrap rubber. Keuchenius, however, has shown that 
where these slugs are abundant the loss of rubber, owing to their con- 
sumption of latex, may be fairly large. He calculates that if each slug 
drinks a cubic centimetre of latex per day, then ten thousand will cause a 
loss of 150 pounds of dry rubber per month; and he instances one case 
in which over 37,000 slugs were collected in a period of three weeks. 



424 DISEASES AND PESTS OF THE RUBBER TREE PART in 

In young rubber trees slugs have caused great damage by an entirely 
different method of feeding. During a spell of dry weather, caterpillars, 
snails and slugs commonly leave their accustomed haunts and feed upon 
any succulent tissue which attracts them. They climb up the stems during 
the night and eat off the terminal bud. New buds then develop and these 
in turn are bitten off. On the shoot in the centre, the apex is clubbed and 
consists of a number of arrested shoots, while lower down the stem the 
leaves have disappeared, and side-shoots, some of them similarly clubbed, 
have developed, though the stem was still green. The apices of other two 
shoots are similar, but each of the stems have developed several side- 
shoots; the tops of these side- shoots have been attacked and on one of 
them buds have appeared lower down and are giving rise to branches. 

Under normal conditions each of the leaders photographed would be a 
straight green stem, growing only at the apex; but in each case the apex 
has been converted into a cluster of short shoots, most of which have not 
been permitted to develop further, while on those which have temporarily 




FIG. 60. Mariaella dussumieri, Gray. 

escaped injury and grown for a short distance the same process is being 
repeated. This may be continued until the plant dies. In any case the 
damage is serious, as the development of the plant is arrested, and they 
may be so distorted as to be worthless. 

These slugs feed chiefly at night. Hence they are not generally observed 
in the act, and the injury may be attributed to insects. During the day- 
time they may be found under dead leaves, etc., etc., round the trees, or 
on the underside of living leaves on the tree itself. In Ceylon, they were 
found climbing the stems in the evening. Plants which had branched were 
not severely attacked, those which suffered most being the single-stemmed 
trees; the latter, after wintering, were not permitted to come into leaf 
again, every fresh green shoot being nibbled off and the green epidermis 
gnawed. 

The slugs probably drink the latex because of the sugar which it con- 
tains, 1 and they appear to attack the buds in order to obtain the latex. 

Mariaella dussumieri is a yellowish -brown slug, mottled with darker 

1 This sugar is Quebrachitol and its presence in latex has been reported by several 
observers. If further information regarding this particular sugar is required, the paper 
by Rhodes and Wiltshire (Jour. Rub. Res. of Mai., vol. iii. p. 160) should be con- 
sulted. 



CHAP. XIX 



ANIMAL AND OTHKR L'KSTS 



425 



dots and streaks. It is usually two to three inches long, but is said to grow 
to eight inches in India. The mantle, i.e. the fleshy fold which covers the 
middle of the body, bears two narrow ridges. Its minute shell is entirely 
hidden by the mantle. 

Parmarion reticulatus bears a small, thin, shield-like shell on the mantle. 




FIG. 70. Photograph illustrating type of slug damage seen in Malaya recently. 

(About T V natural size.) 

8, Slug on branch. 

Collection of the slugs has proved the most practicable method of deal- 
ing with this pest. Dead leaves, etc., should be raked away from the bases 
of the stems, and the field clean- weeded. The heaps of dead leaves may 
be utilised as traps for the slugs. The latter may be killed by dropping 
them into a weak solution of Izal or some similar soluble disinfectant. 

A report of slug damage was received in 1933. Fig. 69 shows 



426 DISEASES AND PESTS OF THE RUBBER TREE PT. m 

the natural size of this slug, and it conforms to the description 
given for Mariaella dussumieri. Fig 70 shows the type of damage 
done in this particular case. 



REFERENCES TO LITERATURE 

ANIMAL AND INSECT PESTS 

PRATT, H. C., 1909. "Notes on Termes gestroi and other Species of Termites 

found on Rubber Estates in the Federated Malay States", Bull. No. 1, 

Dept. of Ag. F.M.S. 
PKATT, H. C., 1909. "Observations on Termes gestroi as affecting the Para 

Rubber Tree, and Methods to be employed against its Ravages", Bull. 

No. 3, Dept. of Ag. F.M.S. 
GREEN, E. E., 1911. "The Rubber Slug (Mariaella dussumieri, Gray)", Circs. 

and Ag. Jour. Roy. Bot. Gards. Ceylon, vol. v. No. 22. 
GREEN, E. E., 1913. "Stem and Root Borer of Hevea", Bull. No. 3, Dept. of 

Ag. Ceylon. 
GREEN, E. E., 1916. "On some Animal Pests of the Hevea Rubber Tree", 

Trans. Third Int. Cong, of Trop. Ag. I. pp. 608-636. 
GREEN, E. E., 1916. "Termes gestroi as a Pest of the Para Rubber Tree", 

Trans. Third Int. Cong, of Trop. Ag. I. pp. 637-640. 
RICHARDS, P. B., 1917. "The History and Presen