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DISEASES OF TRUCK CROPS 

AND THEIR CONTROL 



OTHER WORKS 
BY THE SAME AUTHOR 

The Culture and Diseases oi 
the Sweet Pea - $2.00 net. 

Profusely Illustrated 



Diseases of Greenhouse Plants 

(In Preparation) 



Diseases of the Sweet Potato 

(In Preparation) 



E. P. DUTTON & COMPANY 

NEW YORK 



5ot. 
T. 



DISEASES OF TRUCK CROPS 



AND THEIR CONTROL 



BY 



J. J. TAUBENHAUS, Ph.D. 

Plant Pathologist and Physiologist to the Agricultural and Mechanical 

College of Texas 

Author of " Culture and Diseases of the Sweet Pea " 





NEW YORK 

E. P. DUTTON & COMPANY 

681 FIFTH AVENUE 



5^^ 



Copyright, 19 1 8 
P. DUTTON & COMPANY 



PRINTED IN THE UNITED STATES OF AMERICA 



TO MY FRIEND 

5. KACZER 



PREFACE 

The world never has faced a greater shortage of 
food than to-day. War's destructive agencies have 
added themselves to our old invisible foes, namely- 
parasitic and disease-producing bacteria and fungi. 

More than half of our diet is made up of vege- 
tables. They furnish the necessary food bulk which 
the body requires, supply important nutritive ele- 
ments, and act as stimulants to a better blood circu- 
lation. According to the Thirteenth Census of the 
United States the area devoted to truck crops in the 
United States in 1909 was estimated at 7,436,551 
acres. The total money value of the truck crops 
grown on this acreage was estimated at $301,104,144. 
The crops thus estimated included asparagus, beans 
(green), beans (dry), beets, cabbage, cauliflower, 
corn (pop and sweet), cantaloups, carrots, celery, 
chicory, cucumbers, egg plant, horse-radish, kale, 
lettuce, mint, okra, onions, parsley, parsnip, peas 
(green), peas (dry), peppers, pumpkin, radish, 
rhubarb, rutabagas, spinach, sprouts, squash, sun- 
flower, sweet potato and yam, tomatoes, turnips, and 
watermelon. 

We scarcely realize the large sums of money which 
the trucker loses annually from specific plant dis- 
eases, because there are few available data as to 



viii Preface 

the money losses. But as an example, the following 
figures, kindly given to the writer by Professor R. P. 
Haskell, Pathological Inspector of the United States 
Department of Agriculture, will be of compelling 
interest. 

''Potato Diseases. — It is estimated that the State 
of New York lost in 191 5, principally from late 
blight, about $20,000,000. This outbreak was wide- 
spread in the northern States and reduced the yields 
as shown below, in comparison with 1914. Other 
conditions than disease were relatively equal : 

Maine 10,000,000 bu. 
New Hampshire 1,200,000 " 
Vermont 1,600,000 " 

New York 30,000,000 " 

Pennsylvania 8,000,000 " 

Michigan 23,000,000 " 

Wisconsin 11,700,000 " 

"It is estimated that the market value of the 
potato crop in Aroostock County, Maine, in 19 15 
was reduced about 10%, or $1,078,000, on account of 
the occurrence of the powdery scab disease. In 
some sections the reduction amounted to as much 
as 50%. 

"It is estimated that 50% of the potato crop in 
Idaho was injured by diseases last year and from 10% 
to 20% rendered wholly unsalable. The total an- 
nual loss in this State is estimated at $196,000. 

''Sweet-Potato Diseases. — It is estimated that the 
annual loss due to sweet-potato diseases in the 



Preface ix 

United States is approximately $10,000,000. About 
$750,000 of this loss may be attributed to stem rot, 
the other important diseases being black rot, foot 
rot, and storage rots. 

"Asparagus Rust. — Asparagus rust has practically 
destroyed all of the original plantings of asparagus 
and driven the old varieties out of cultivation. These 
have now been replaced by partially resistant kinds 
and the new strain bred by this Department is almost 
wholly resistant, so that in the near future these 
losses will be eliminated. Tests of some of the new 
rust-resisting strains in 19 15 showed gains over the 
standard varieties amounting to more than $200 
per acre. 

" Cowpea Diseases. — It is estimated that the an- 
nual saving as a result of the introduction of wilt 
and root-knot resistant cow-peas is $3,000,000." 

A conservative estimate of the money loss from 
diseases would be about 20% of the total value of 
the truck crops grown in the United States. Accord- 
ing to the estimate given on page vii, the total value of 
the truck crop in the United States in 1909 amounted 
to the sum of $301,104,144. If 20% of this was lost 
through damage from diseases, it will be seen that 
in 1909 the American truckers lost $60,220,828. 
This does not include the large losses from insect 
pests, nor losses incurred in storing, or in shipping 
truck produce. 

It is no exaggeration to state that if our present 
knowledge of Plant Pathology were made use of by 
truck farmers, nearly 80% of this loss could be 



X Preface 

prevented. Can any one say that such a saving 
would be insignificant, untimely, or unpatriotic? 

The present work has been prepared with the aim 
of stimulating more research in truck-crop diseases, 
and also of assisting the trucker to make use of our 
present knowledge, in order to prevent avoidable 
losses, increase the trucker's profits, and assure a 
greater food supply. The writer seriously solicits 
suggestions or criticisms on his work. 

Acknowledgments are due to Dr. and Mrs. D. de 
Sola Pool, of New York City, for the inspiration, the 
encouragement, and the valuable assistance rendered 
in the preparation of the manuscript, and later in 
reading and criticizing it. To Dr. E. A. Bessey of 
the Michigan Agricultural College, and to Dr. Mel. 
T. Cook of Rutgers College, the author owes hearty 
thanks for the careful reading and the valuable 
suggestions and criticisms which they have given this 
work. Acknowledgments are also due to Dr. G. 
H. Coons of the Michigan Agricultural College, to 
Prof. F. B. Paddock and to Mr. W. T. Brink of the 
Texas Agricultural Experimental Station for reading 
the manuscript and proof. Grateful appreciation is 
likewise due to Dr. I. Adlerblum of the Metropolitan 
Life Insurance Co. of New York City for criticizing 
the manuscript and proofs. 

For the use of illustrations the author is indebted : 
to Dr. G. P. Clinton; to Dr. Mel T. Cook; to Drs. 
G. H. Coons and E. Levin; to Dr. H. A. Edson; to 
Dr. B. B. Higgins; to Prof. H. S. Jackson; to Dr. L. 
R. Jones; to Dr. T. F. Manns; to Prof. A. V. Osmun; 



Preface xi 

to Prof. F. B. Paddock; to Prof. W. G. Sackett; to 
Prof. A. D. Selby; to Prof. R. E. Smith; to Prof. H. 
E. Stevens; to Prof. J. A. Stevenson; to Prof. D. B. 
Swingle; to Prof. DeVault and to Dr. F. A. Wolf. 

Last, but not least, grateful acknowledgments are 
due my wife Esther Michla Taubenhaus, whose de- 
votion to art and science, and whose inspiration made 
this work possible. 



J. J. Taubenhaus 



College Station, TfixAS 
January 22, IQ18. 



PREFATORY NOTE 

With the greater specialization along all lines of 
industry the problems that confront such a specialist 
as the author of thns book are felt more keenly and 
the necessary remedies are more fully appreciated. 
So there has grown up in the last few decades in 
this country a body of agricultural experts, the 
truck growers, who have found, as they have con- 
centrated their attention more and more inten- 
sively upon a limited number of crops, that they 
are paying a great tax in the shape of losses due 
to diseases. Probably, in fact we know that very 
often it certainly is the case, similar losses are 
suffered by general farmers, but with their large 
plantings and less intensive culture these losses are 
not appreciated as they are by the truck grower. 
Other factors, too, enter in. In general the truck 
crops occupy land near cities or which from its 
adaptability to special crops or from its accessibility 
to markets is accordingly more valuable than ordinary 
farm lands. Furthermore, the crops themselves 
have a greater monetary worth than the staple 
crops. Both these factors make the losses by plant 
diseases much more keenly felt. With this recogni- 
tion of the losses incurred has arisen a demand for 



xiv Prefatory Note 

help in the prevention of the diseases responsible 
for the damage. So plant pathologists have had to 
direct their attention to diseases of truck crops. 
The present book is an attempt by such a pathologist 
who has specialized along this line to meet the de- 
mand for help in the way of giving information as 
to the diseases occurring on truck crops and, so far as 
it is possible, telling how these losses may be pre- 
vented or at least reduced. 

The last quarter century has seen a marvelous 
development of that division of the science of Botany 
that is devoted to the study of plant diseases, Plant 
Pathology. As each crop has been given greater 
attention the number of diseases found to occur 
upon it has been amazing. Plants nearly related 
to each other may have some of their diseases in 
common, but even with very closely related species 
some of the troubles affecting them will be different. 
When we now consider the large number of crop 
plants that are the subject of intensive culture as 
truck crops, and note, furthermore, that they re- 
present the most diverse families of plants, it is not 
to be wondered at that the number of organisms 
causing diseases of truck crops is a large one. The 
author by grouping the crop plants together by their 
botanical affinities has taken full advantage of the 
fact that nearly related plants may suffer from some 
of the same diseases and thus has made it possible in 
some cases to consider such diseases only once for 
several different, but closely related, crops. 

Considerable attention is directed to the symptoms 



Prefatory Note xv 

by which the various diseases may be distinguished. 
These descriptions are made in non-technical lan- 
guage so that the practical grower can understand 
them and recognize the diseases in question. Besides 
this the methods of control are also described in popu- 
lar terms. The author's long study of the subject has 
made it possible for him to approach this part of the 
work from the standpoint of the grower, so that as 
far as possible the remedies or preventive measures 
recommended are those with which he has practical 
experience. Occasionally it is impossible to recom- 
mend a remedy since sometimes a disease is of such a 
nature that by the time it becomes apparent the 
damage is done. But even in such cases directions 
are given which will reduce the loss or at least 
permit its avoidance another season. The discus- 
sions as to the cause of the disease are unavoidably 
given in somewhat more technical form from the 
very nature of the case, especially where it is the 
question of diseases caused by fungi or bacteria 
for which brief scientific characterizations are neces- 
sary. These technical discussions are essential for 
pathologists and other students of the subject so 
that the book will be appreciated by Experiment 
Station workers, Extension Specialists, college stu- 
dents, and others, as well as by the truck growers 
themselves for whom the book is primarily intended. 
Ernst A. Bessey, 
Professor of Botany, 
Michigan Agricultural College. 



CONTENTS 
PART I 

CHAPTER I 

PAGE 

The Normal Soil and its Requirements . 3 

CHAPTER II 
Sick Soils not Influenced by Parasites . 23 

CHAPTER III 

vSoiL Sickness Due to the Presence of Para- 
sites Harmful to Plants . . .41 

CHAPTER IV 

Methods of Treating Sick Soils ... 53 

PART II 
CHAPTER V 

The Healthy Host and its Requirements . 63 

CHAPTER VI 

Causes of Diseases in Crops . . .71 

A. Diseases of a Mechanical Nature 

B. Diseases Due to Physiological Causes 
c. Diseases of Unknown Origin 



XVlll 



Contents 



D. Diseases Due to Parasitic Bacteria or Fungi 

E. Diseases Induced by Parasitic Flowering 

Plants 



CHAPTER VII 



Poor Seed 



92 



PART III 

SPECIFIC DISEASES OF TRUCK CROPS 
CHAPTER VIII 

Family Agaricace^ .... 

Diseases of the Mushroom 



103 



CHAPTER IX 

Family Araliace^e 

Diseases of the Ginseng 

CHAPTER X 
Family Chenopodiace^e . 
Diseases of the Beet 
Diseases of the Spinach 

CHAPTER XI 
Family Composite .... 
Diseases of the Artichoke (Jerusalem) 
Diseases of the Artichoke (Globe) 
Diseases of the Lettuce 
Diseases of the Salsify 
Diseases of the Sunflower 



108 



116 



:37 



Contents xix 

CHAPTER XII 

PAGE 

Family Convol\tjlace^ 151 

Diseases of the Sweet Potato 

CHAPTER XIII 
Family Crucifer^ . . . . . .185 

Diseases of the Cabbage 
Diseases of the Cauliflower 
Diseases of the Horse Radish 
Diseases of the Kale 
Diseases of the Mustard 
Diseases of the Radish 
Diseases of the Turnip 

CHAPTER XIV 
Family Cucurbitac^ . . . . .218 
Diseases of the Cantaloupe 
Diseases of the Cucumber 
Diseases of the Citron 
Diseases of the Squash 
Diseases of the Watermelon 

CHAPTER XV 

Family Gramine/e ..... . 250 

Diseases of the Sweet Corn 

CHAPTER XVI 

Family Labiate ...... 255 

Diseases of the Balm 
Diseases of the Catnip 
Diseases of the Horehound 



XX Contents 



-Diseases of the Mint 
Diseases of the Peppermint 

CHAPTER XVII 

Family Leguminos.^ .... 259 

Diseases of the Bean 
Diseases of the Lima Bean 
Diseases of the Cow Pea 
Diseases of the Garden Pea 

CHAPTER XVIII 

Family Liliace^e 279 

Diseases of the Asparagus 
Diseases of the Chive 
Diseases of the Onion 

CHAPTER XIX 

Family Malvaceae . . . • , • • 295 
Diseases of the Okra 

CHAPTER XX 

Fajsiily Portulacace^ ..... 299 

Diseases of the Purslane 

CHAPTER XXI 

Family Solanace.e 300 

Diseases of the Egg Plant 
Diseases of the Pepper 
Diseases of the Potato 
Diseases of the Tomato 



Contents 


xxi 


CHAPTER XXII 






PAGE 


Family Umbellifer^ 


. 354 


Diseases of the Carrot 




Diseases of the Celery 




Diseases of the Parsley- 




Diseases of the Parsnip 




Weeds 





PART IV 
CHAPTER XXIII 

Methods of Control ..... 361 

CHAPTER XXIV 
Control of Insect Pests by Natural Factors 375 

CHAPTER XXV 

Treatment of Fence Posts . . . -378 
Glossary . . . . . . .381 

Index 387 



ILLUSTRATIONS 

PAOB 

Bacteria 4 

Structure of Fungi 

Nitre-Sick Beet Field, Showing Barren 
Spots 



Effect of Lime 
Pythium deBaryanum 
Rhizoctonia 
FusARiUM Wilt 
Nematode Root Knot 



25 
27 
43 
45 
47 
49 



Inverted Pan for Steam Sterilization 55 

Surface Watering, Showing Portable 
Spray Equipment Used in Gardens about 
Cold Frames and Hotbeds . . 55 

11. Watermelon Slice Showing Hail Injury 74 

12. Lightning Injury in Potato Field. 

Drought Injury of Sweet Corn . 78 

13. Malnutrition, Showing a Cabbage Leaf 

Affected by the Disease . . .81 

14. Blossom Drop 83 

xxiii 



xxiv Illustrations 




FIG. 




PAGE 


15- 


Mosaic ...... 


. 84 


i6. 


Bean Seeds Affected with Anthracnose 


J 




Colletotrichum lindemuthianum . 


. 84 


17- 


Dodder 


. 90 


i8. 


Mycogone Disease of' Mushrooms . 


. 105 


19. 


Ginseng Diseases .... 


. 109 


20. 


Beet Diseases .... 


. 119 


21. 


Spinach Diseases .... 


► 131 


22. 


Lettuce Drop . . 


. 143 


23- 


Lettuce Diseases .... 


. 144 


24. 


Southern Blight of the Salsify . 


148 


25- 


Sweet Potato Diseases . 


152 


26. 


Sweet Potato Diseases . 


159 


27. 


Sweet Potato Diseases . 


167 


28. 


Sweet Potato Diseases . 


170 


29. 


Sweet Potato Storage Houses 


183 


30. 


Cabbage Diseases .... 


187 


31- 


Cabbage Diseases 


196 


32. 


Cabbage Diseases 


198 


33- 


Diseases of the Cauliflower and Radish 


202 


34- 


Cercospora Leaf Spot of Horse-Radish . 


207 


35. 


Radish Diseases 


210 





Illustrations 


XXV 


FIG. 




PAGE 


36. 


Turnip Diseases 


. 215 


37- 


Turnip Diseases 


. 217 


38. 


Cantaloup Diseases 


. 221 


39- 


Resistant Cantaloup Strain . 


. 228 


40. 


Cucumber Diseases. 


. 230 


41. 


Squash Diseases 


. 235 


42. 


Watermelon Diseases . 


. 239 


43- 


Watermelon Anthracnose 


. 241 


44. 


Watermelon Diseases . 


. 244 


45- 


Sweet Corn Diseases 


. 251 


46. 


Bean Diseases 


. 260 


47- 


Bean Diseases 


. 262 


48. 


Diseases of Lima Bean . 


. 267 


49. 


Bean Diseases . . . . 


. 269 


50- 


Diseases of the Cow Pea 


. 272 


51- 


Diseases of the Garden Pea and I 


3ean. 274 


52. 


Asparagus Diseases 


. 280 


53. 


Onion Diseases . . . . 


. 285 


54. 


Onion Diseases . . . . 


. 286 


55- 


Diseases of the Okra . 


. 296 


56. 


Eggplant Diseases 


. 302 


57. 


Diseases of the Pepper 


. 305 



XXVI 



Illustrations 



58. Potato Diseases 

59. Diseases of the Potato 

60. Pox OR Pit of the White Potato, Showing 

Different Stages of Infection . 

61. Potato Diseases .... 

62. Potato Diseases .... 

63. Potato Diseases .... 

64. Tomato Diseases . . 

65. Tomato Diseases .... 

66. Tomato Diseases .... 

67. Tomato Diseases .... 

68. Sleeping Sickness of Tomato 

69. Celery Diseases .... 

70. Celery Diseases .... 

71. Spray Machinery . ._ . 

72. Parasitized Insects. Treatment of Fence 

Posts 



PAGE 



315 
322 

325 
331 
340 
346 

34/ 
351 
352 
356 
357 
372 

376 






INTRODUCTION 

The present world crisis has suddenly transposed 
the farmer from his former modest and humble posi- 
tion into the ranks of our foremost national figures. 
To-day the services of the tiller of the land are at 
a premium. The heroes of the day are not only 
those who can shoulder a gun at the front, but also 
those who can produce the food necessary to feed the 
great civil and military armies in the field and at 
home. It is to the credit of the American people 
that they have realized that intelligent farming re- 
quires as much skill, thought, and energy as is re- 
quired to build up industries or to formulate laws of 
government. 

Of the many phases of agriculture, trucking be- 
longs to the highest forms of intensified farming. 
Whether it is conducted on a large or on a small 
scale, it requires a thorough knowledge of plant life. 
An intelligent understanding of crop rotation is 
essential for success. Someone has well said that 
the farmer may be judged intellectually by the system 
of rotation which he practices. Great skill is also 
required to keep the land in a state of production 
during the greater part of the year. This is espe- 
cially true for our Southern States. As a whole, 



xxviii Introduction 

therefore, successful truckers must be a highly intel- 
ligent class of agriculturists. 

In trucking, as in all intensive farming, the aim is 
to produce superior crops, embodying both high 
yield and good quality. This can be made possible 
only through intensive breeding and culture. Un- 
fortunately, however, improvement in quality and 
yield is often accompanied by a loss of natural 
vigor and of power of resistance to disease. The 
great problem of the trucker is twofold — that of 
striving for quantity and quality, while protecting 
his crops from disease. This latter phase has gener- 
ally been overlooked- We all realize to-day that it 
is necessary not only to produce two blades of grass 
where one grew before, as Dean Swift declared, but 
also to conserve it during growth and prevent it from 
being carried off by various diseases. The great fam- 
ine in Ireland in 1844 resulted from an epidemic of 
late blight which destroyed the potato crop. Such a 
condition could hardly occur to-day, because we now 
have a better knowledge of plant life, the causes which 
induce disease, and the methods of coping with it. 

Considerable research has been carried out on the 
diseases of truck crops. The work of Professors Stew- 
art, Selby, Jones, Orton, Clinton, Lutman, Melhus, 
Manns, Harter, Sackett, Whetzel, and of others has 
already yielded valuable information on the diseases 
and their control in the case of some of our staple 
food crops. Still, in the case of many diseases, little 
is known as yet as to methods of treatment. But 
much is to be looked for from research in the future. 



Introduction xxix 

It was the writer's intention to avoid technical 
terms as far as possible. However, it was found ex- 
tremely difficult to omit every trace of a technical 
vocabulary, inasmuch as the popular terms are not 
always adequate in identifying a disease or in de- 
scribing its causal organism. As far as was consistent 
all popular names were accepted and retained in this 
work. However, there are many diseases which 
have as yet no popular names. As an illustration 
may be mentioned certain spot diseases of particular 
hosts. These spots may be caused by different fungi 
and yet resemble each other. In such a case how are 
we to name these diseases ? The surest way to avoid 
confusion is to call the diseases by the name of the 
causal organism, such as Phyllosticta leaf spot, Cer- 
cospora leaf spot, etc. Professor Stevens has sug- 
gested that we name all diseases by the name of their 
causal organism and add to it the term "ose, " such 
as Phyllostictose, Cercosporose, Sclerotinose, etc. 
The writer has not adopted Stevens terminology. 
In many cases the popular name of a disease de- 
scribes it far better than a technical term can do. To 
drop altogether such valuable popular terminology 
would only confuse the practical man. For instance, 
the popular term for lettuce "drop" is far more sug- 
gestive than "Sclerotinose." 

From a practical consideration, the healthy plant 
is of greater importance than the disease. If we were 
to bend all our energy and skill to safeguarding the 
health of our crops, we would not be pestered with 
diseases. This is the point of view of this work. 



XXX Introduction 

For this reason, too, much space has been given to a 
consideration of the healthy hosts and of the soil, the 
mother of all vegetation. 

For the sake of convenience, the crops here con- 
sidered have been taken up in the natural order of 
families to which they belong. The families have 
then been arranged in alphabetical order, and the 
crops in each family taken up alphabetically by their 
popular names. On the other hand, the diseases 
have been arranged according to their causes, classi- 
fied according to the system generally accepted by 
students in mycology. 

The present work is intended as a guide to the 
trucker and gardener, and to the student in Plant 
Pathology. It is the result of several years of re- 
search in truck crop diseases. Where information 
has been drawn from other sources full references 
have been given, so far as possible from the latest 
investigations. The writer has aimed at making 
this work as br-^ad and as generally useful as possible 
rather than confining it to local interest. 

Because of the great economic importance of the 
subject of truck crop diseases, it is felt that the pres- 
ent work fills a timely want and needs no apology. 
We cannot expect a general text-book on Plant Path- 
ology to go into lengthy treatment of all plant dis- 
eases, and even less so with those of the trucking 
crops. The subject in itself is too important and too 
broad to be dealt with adequately in a few pages. 
The time will undoubtedly come when the diseases 
of every important crop will be treated separately in 



Introduction xxxi 

book form. The Culture and Diseases of the Sweet 
Pea, by the writer, was an attempt in that direction. 
Meanwhile, until we have available the results of 
more extended researches on particular crops, the 
present work, it is hoped, will fill the gap. 



PART I 






i 



CHAPTER I 

THE NORMAL SOIL AND ITS REQUIREMENTS 

aE aim of this chapter is to study the conditions 
IT which a healthy plant lives and grows. Such 
vledge will prepare us to consider the causes or 
Drs which are responsible for abnormalities and 
ises. Plants are endowed with life, and to live 

must have food. Part of the food is derived 
I the air, but they cannot subsist on air alone. 

sustenance of plants is also derived from the 

is to be regretted that laymen often regard the 
as merely a conglomeration of inert particles of 
I rock. If this were true, plant life would be an 
Dssibility. It is because soils are teeming with 
Dus forms of organisms beneficial to them that 
t life is made possible therein. The science of 

Bacteriology, though still in its infancy, has 
idy taught us much to help make the trucking 
ness much more profitable and successful than 
IS been hitherto. 

ideed we may judge a soil by the kind of flora 
zh predominates there, and call it fertile and 
thy when this germ life helps to make it a favor- 
3 



4 Diseases of Truck Crops 

able medium for the plants. On the contrary, we 
call it sick or poor when it teems with bacteria and 
fungi which act as parasites on plants, or when the 
beneficial ones are absent or perform their duties 
imperfectly. 

Structure and Life History of Bacteria 

The term bacteria (singular bacterium) , or microbe, 
or germ, refers to the smallest microscopical form of 
plant life. As we shall see later, bacteria are but one 
of the many forms of life in the soil. The first man 
to recognize bacteria was Anton van Leeuwenhoek, 
a native of Holland, and a lens maker by trade. He 
made use of the microscope in testing materials for 
lens making. In 1675 he happened to mount in a 
drop of water some tartar which he scraped off from 
his teeth. To his great surprise he discovered mi- 
nute little "animals" which moved about in curious 
fashions. In 1882, Robert Koch succeeded in grow- 
ing bacteria artificially and outside their natural 
environment. Thus was laid the foundation of the 
modern science of Bacteriology. 

Bacteria are very simple in form. We recognize 
the rod-shaped known as Bacillus (fig. i a), the 
spherical form as Coccus (fig. i b), and the corkscrew 
or comma form as Spirillum (fig. i c). Bacteria are 
very minute. It would take about fifteen to twenty 
thousand individual bacteria placed end to end to 
make one inch in length. They occur, however, in 
tremendous numbers and this enables them to per- 




Fig. I. 



a. Rod shaped, h. coccus 
isolated from soil. 



Bacteria. 

d. plate culture, 



ihowing bacterial colonii 



Normal Soil and Its Requirements 5 

form wonderful tasks, as we shall soon see. Bacteria 
multiply in the simplest ways. A single individual 
upon reaching maturity becomes constricted in the 
center, then divides in two, each part now becoming 
a separate individual capable of nutrition, growth, 
and multiplication. It has been estimated by scien- 
tists that division of a single individual takes place 
about every twenty minutes. Granting that this 
rate of division is uninterrupted for twenty-four 
hours, the descendants of one germ would be in round 
numbers 1,800,999 trillions. These when placed 
end to end would make a string two trillion miles 
long, or a thread long enough to go around the earth 
at the equator seventy million times. It would take 
a ray of light four months, traveling as it does, to 
pass from one end of it to another. 

Individual bacteria can be detected only with a 
compound microscope. When grown on artificial 
media and under aseptic conditions, all the descend- 
ants of a single parent cell live together and constitute 
a colony, which becomes visible to the naked eye as 
a creamy jellylike drop (fig. i d). 

Relationship of Bacteria to the Function of 
A Soil 

The health of a soil as shown in its fertility is in- 
timately connected with the kind of bacteria present 
in it. We are as yet in the dark as to the possible 
function of numerous groups of the soil organisms. 
Bacteriologists are seeking to discover their proper 



6 Diseases of Truck Crops 

functions. A recent exhaustive study' of Actinomy- 
ces, or thread bacteria, in the soil seems to show that 
they serve to decompose grass roots, being more 
numerous in sod than in cultivated land. Other 
groups of bacteria undoubtedly must perform other 
important functions. 

The mere presence of friendly bacteria in the soil, 
however, would be insufficient to assure the welfare 
of our cultivated lands. What concerns us most is 
the work that they perform. Most of the plant's 
food as it is found in the soil is in a crude and una- 
vailable form. The bits of mineral matter, the 
manure or fertilizer, in the truck patches all con- 
tain plant foods but in a form which plants cannot 
readily use; they must be softened and predigested 
and this work is done by the friendly organisms. 
Plant food is therefore directly dependent on the 
work of these minute scavengers. An intimate re- 
lation exists between the higher and the lower forms 
of plant life, the one depending on the other. 

Distribution of Soil Bacteria 

For a practical purpose we ought to know in what 
soil and at what depth the beneficial bacteria are 
most likely to abound. Since the presence of bac- 
teria is necessary to maintain the fertility of a normal 
healthy soil, it is essential to study the main factors 
that determine their increase or decrease. We can- 
not expect to find them equally distributed in differ- 

' Conn, Joel H., New York (Geneva) Agr. Expt. Sta. Bui. 52 : 
3-1 1, 1916. 



Normal Soil and Its Requirements 7 



ent depths of the same soil. Brown' has shown that 
bacteria are generally more abundant in the upper 
eight inches. Table i, adapted from Brown throws 
much light on this phase of the problem. 

Table i 

Bacteria as Found in Various Depths of Soil and Under 
Different Cropping Systems 









Bacteria per Gram of Air-Dry Soil 


Plot 


Lab. 
No. 


Depth of 
Sampling 




No.' 


















I 


II 


III 


IV 


Average 


601 


A 


4 in. 


2033000 


1627000 


1793000 


1555000 


1752000 




B 


8 in. 


1437000 


121 1000 


I 241000 


I 104000 


1248250 




C 


12 in. 


541000 


567000 


559000 


525000 


546000 




D 


16 in. 


287000 


292000 


312000 


302000 


298250 




E 


20 iu. 


147000 


154000 


159000 


154000 


153500 




F 


24 in. 


92300 


96500 


95 1 00 


91500 


93850 




G 


30 in. 


49900 


46300 


50900 


46900 


48500 




H 


36 in. 


32900 


30000 


33100 


30400 


31600 


602 


A 


4in- 


3102000 


2870000 


2917000 


2947000 


2959000 




B 


8 in. 


2238000 


2177000 


2105000 


225S000 


2194500 




c 


12 in. 


498000 


531000 


531000 


528000 


522000 




D 


16 in. 


255000 


328000 


316000 


314000 


304250 




E 


20 in. 


182000 


192000 


188000 


177000 


184750 




F 


24 in. 


89200 


93300 


91600 


88300 


90600 




G 


30 in. 


53300 


54900 


53100 


51800 


54275 




H 


36 in. 


31700 


35700 


34200 


31300 


33225 


604 


A 


4 in. 


4606000 


3908000 


4210000 


3932000 


4164000 




B 


8 m. 


3132000 


2834000 


2976000 


2793000 


2943750 




c 


12 in. 


I 016000 


882000 


901000 


831000 


907500 




D 


16 in. 


320000 


309000 


31 1000 


320000 


315000 




E 


20 in. 


155000 


163000 


156000 


149000 


155750 




F 


24 in. 


89400 


96100 


92900 


88900 


91825 




G 


30 in. 


51900 


55800 


55000 


52400 


53775 




H 


36 in. 


35100 


36600 


34900 


32600 


34800 



'Brown, P. E., Iowa Agr. Expt.Sta. Research Bui. 8 : 283-321, 1912. 
'Plot No. 601. — Continuous com. 602. — 2-year rotation, com 
and oats. 604. — 3-year rotation, corn, oats, and clover. 



8 Diseases of Truck Crops 

In studying Table i we find that in every case 
there is a marked decrease in soil organisms with each 
increase in the depth of the soil tested. It was fur- 
ther found by Brown that the moisture content was 
higher for four inches than for a greater depth. It 
seems evident that the decrease of soil bacteria below 
twelve inches is dependent not so much on moisture 
but rather on a decrease of air in the lower substratum. 
It must not be expected that the data given in Table 
I are applicable to every locality. Differences in 
the mechanical and chemical composition of the soil 
and subsoil, differences in topography, climate, and 
weather conditions, will all no doubt tend to influence 
more or less the increase or decrease of bacteria. 

Influence of Depth of Cultivation on the 
Number of Soil Bacteria 

The work of King and Doryland' has shown that 
the depth of cultivation is a potent factor in influ- 
encing the number of bacteria in the soil. This is 
briefly summarized by them in Table 2. 

Table 2 
Influence oj Depth of Cultivation on Soil Bacteria 

Silt- 
plowed 4 inches deep increases the number of bacteria. . 15.46% 
plowed 6 inches deep increases the number of bacteria. . 10.94% 
plowed 8 inches deep increases the number of bacteria. .24.20% 
plowed 10 inches deep increases the number of bacteria . . 26.89% 



^ King, W. E., and Doryland, Ch., Kansas Agr, Expt. Sta. Bui. 
161 : 211-242, 1909. 



Normal Soil and Its Requirements 9 



Sand- 
plowed 4 inches deep increases the number of bacteria. .35.06% 
plowed 6 inches deep increases the number of bacteria. . 13.53% 
plowed 8 inches deep increases the number of bacteria . .22.90% 
plowed 10 inches deep increases the number of bacteria . . 5.1 1 % 

The Influence of Manure on the Number of 
Soil Bacteria 

Besides cultivation, there are other treatments 
which may lead to an increased bacterial flora in the 
soil. As shown by Temple' such a result is obtained 
through the application of manure. In working with 
a newly cleared sandy loam, and applying fresh cow 
manure (this included solid excreta and no bedding) , 
at the rate of ten tons per acre, Temple obtained the 
following results as shown in Table 3. 

Table 3 

Showing Number of Bacteria per Gram of Dry Soil 



Bate 
March 26, 1909 
April I, 1909 .. . 
April 9, 1909 . . 
April 15, 1909.. 
April 22, 1909. 
April 29, 1909 . . 
May 6, 1909. . . 



Soil No. 326 


Soil No. 326a 


No Manure 


With Manure 


1,220,000 


1,220,000 


1,633,000 


4,300,000 


6,120,000 


14,000,000 


3,780,000 


10,610,000 


2,730,000 


5,860,000 


2,770,000 


3,340,000 


5,510,000 


5,190,000 



As further evidence that manure increases the soil 
flora, Temple used a clay loam, dividing it in the 
following manner ; and treated as follows : 

' Temple, J. C, Georgia Agr. Expt. Sta. Bui. 95 : 6-35, 1911. 



10 



Diseases of Truck Crops 



Plat No. I — Stable manure. 

Plat No. 4 — Sodium nitrate. 

Plat No. 5 — A complete fertilizer, PKN. 

Plat No. 6 — Nothing, check. 

The effect of these treatments is briefly summarized 
in Table 4. 

Table 4 
Colonies per Gram of Dry Soil 



Date 



Dec. 9, 1910. . . 
March 30, 191 1 
May 26, 1911 .. 



Plal No. I 



28,230,000 
18,500,000 
20,200,000 



Plat No. 4 



11,430,000 
9,150,000 
4,850,000 



Plat No. 5 



19,850,000 
8,040,000 
6,720,000 



Plat No. 6 



8,250,000 
6,240,000 
5,010,000 



The above Table shows that although sodium ni- 
trate or a complete fertilizer increases the soil 
flora, neither one can be compared to manure in 
efficiency. 

Structure and Life History of Fungi 



Besides bacteria of all sorts, our cultivated soils 
are also teeming with fungi. The true function of 
the latter remains to be studied. There seems no 
doubt, however, that certain fungi like certain bac- 
teria in the soil work on the organic and the mineral 
matter to make it available as plant food. Parasitic 
fungi depend for their food on living plants alto- 
gether. Examples of these are the Uredinales, the 




Fig. 2. Structure of Fungi. 



a. Fruiting branch of PenicilHum, showing 
conidiophores and conidia, b. mycelium 
of Penicillium, c. an individual conidiophore 
and chain of conidia of Penicillium, d. two 
conidia of Penicillium, showing a.ttachment 
of spores in the chain, e. fertilization of 
female oogonium by male antheridium, /. 
mature oospore, g. fruiting stalks of Rhizo- 
pus, h. individual fruiting head of_ Rhizo- 
pus showing spores, ;'. sexual fertilization 
and k. zygospore of Rhizopus showing spores. 
I. perithecium, showing asci and ascospores, 
or winter spores, m. Pycnidium or sac in 
which the summer spores are borne. 



Normal Soil and Its Requirements 



II 



cause of the true rust diseases. Saprophytic fungi 
are those which depend for their food on the dead and 
decaying organic matter in the soil. Between these 
two extremes there are intermediaries. As an illus- 
tration of a soil fungus may be taken the ordinary 
blue mold, Penicillium expansum Lk. This organ- 
ism is made up of colorless feeding threads techni- 
cally known as hypha^ or mycelium (fig. 2 b). The 
spores, which correspond to the seed of higher plants, 
are borne on short stalks which bear broomlike tufts 
composed of chains of small bluish, round bodies, the 
spores (fig. 2 a-c). 

Fungi differ from the higher plants in their nu- 
trition and mode of reproduction. Fungi have no 
green coloring matter, chlorophyll, and are thus 
unable to manufacture their own carbon by the de- 
composition of carbon dioxide as do green plants. 
This is why fungi must depend for their supply of 
carbon on dead organic matter or on the higher plants. 
Unlike the green plants, fungi have no flowers and 
reproduce by means of spores (fig. 2 g-h). It has 
been estimated that over 61,000 species of fungi 
have been found and described on the higher plants. 
The Soil Bacteriologist however has scarcely touched 
on the soil fungi. 

Fungi are classified according to the mode of spore 
formation. In some the spores are formed by a 
regular sexual union of a female egg known as oogon- 
ium and of a male element, the antheridium (fig. 2 e, 
i, k). The resultant fertilized spore egg is known as 
oospore (fig. 2 f). The latter germinates by sending 



12 Diseases of Truck Crops 

out a germ tube, or as is more generally the case, by 
the outer wall dissolving and the inner mass breaking 
up into small bits of naked protoplasm known as 
zoospores. Most fungi have two spore stages, the 
summer form intended for rapid dissemination and 
spread, the winter form intended to carry it over 
through cold or any other unfavorable weather con- 
ditions. The term conidia is applied to all spore 
forms borne free on special fruiting stalks known 
as conidiophores (fig. 2 a). A pycnidium is a sac- 
like body (fig. 2 m) in which are borne the summer 
spores. A perithecium is a sac-like body (fig. 2 1) 
which bears the winter spores of certain fungi. 
Other terms here used in describing parts of fungi 
will be found in the glossary. 

Nature and Function of a Healthy Soil Flora 

The fimction of a normal soil is to provide avail- 
able plant food. About 95 per cent, of the com- 
bustible weight of a grov^^ing plant is made up of 
carbon, hydrogen, and oxygen and nitrogen. The 
remaining 5 per cent, constitutes the mineral or the 
ash of the plant. Carbon, hydrogen, and oxygen are 
taken in the form of carbonic acid and water ; nitrogen 
from nitrates produced by bacteria out of organic 
matter of the soil. The ash or the mineral elements 
of the plant are taken directly from the soil. Neither 
the organic nor the mineral elements are in a form 
which plants can make use of until they have been 
acted on by certain definite organisms in the soil. 



Normal Soil and Its Requirements 13 

A. The Transformation of Carbon 

Cellulose, which is but a form of carbon, consti- 
tutes a large per cent, of the woody tissue of plants. 
Soils contain large amounts of cellulose and this un- 
doubtedly helps to maintain their proper physical con- 
dition. Straw manure, or green vegetable matter all 
contain large amounts of cellulose. When it is in- 
corporated in the soil, living plants cannot make use 
of it, because of its complex form. It therefore must 
first undergo a certain decomposition. This is ac- 
complished by a group of soil bacteria known as 
Amylobacter. These feed on the dead vegetable 
cellulose, breaking it up and reducing it back to car- 
bon dioxide, hydrogen, and fatty acids. The carbon 
dioxide either returns to the air to replenish the at- 
mospheric supply, or unites with water to form car- 
bonic acid and soil carbonates. The carbon dioxide 
is taken in by the plants either directly from the air 
through the leaves, or from the soil in some carbon- 
ate form. Thus we see that it is not the cellulose nor 
the product of its decomposition that furnishes plant 
food, but certain inorganic elements which are set free 
in its decomposition. 

B. Elaboration of Available Nitrogen 

From the viewpoint of plant nutrition, nitrogen 
is unquestionably the most important of all elements. 
The nitrogen of the air, although totalling about 79 
per cent, of it, is not in an available form. In the 
transformation of proteids into available nitrogen 



14 Diseases of Truck Crops 

in the soil two definite processes take plax:e, all 
thanks to the work of certain soil bacteria. 

1. Ammonification. In this process, the soil 
bacteria attack the complex proteids and convert 
them into ammonia. The odor of ammonia from 
decomposed urea, manure, or any other organic 
matter is always an indication that ammonification 
takes place. According to Sackett' and others the 
ability to bring about this change is attributed to the 
following soil bacteria: Bacillus mycoides, Bacillus 
proteus vulgaris, Bacillus mesentericus vulgatus, Bacil- 
lus suhtilis, Bacillus janthinus, Bacillus coli-communis , 
Bacillus megatherium. Bacillus fluorescens liquefaciens, 
Bacillus fluorescens putridus, and Sarcina lutea. 

2. Nitrification. Both ammonia and ammonia 
compounds are forms of nitrogen that are not yet 
readily available to plants. They must be changed 
further into simpler compounds or, as the process is 
known, must undergo nitrification. The ammonia 
is first oxidized into nitrous acid and nitrates. This 
is accomplished by two species of soil bacteria, 
Nitrosomonas and Nitrosococcus. The nitrates are 
then oxidized into nitric acid and nitrates, through 
the work of the bacterium Nitrohacter. The nitrates 
are the only forms of nitrogen which plants can use. 

C. Action of Soil Flora on Mineral Substances 

We have already pointed out that the inert mineral 
substances in the soil are not in a form in which 

» Sackett, W, G., Colorado Agr. Expt. Sta. Bui. 196 : 3-39, 1916. 



Normal Soil and Its Requirements 15 

plants can readily assimilate them. These too must 
first be acted upon by certain soil bacteria. 

1. Changes of Phosphates. Phosphates as 
they commonly occur in nature are but little soluble 
in water. This is why they cannot be used in their 
first form, although they are required by most plants. 
Soils deficient in this element may be improved by 
such fertilizers as superphosphate of lime, ground 
bone, phosphate rock, or Thomas slag. In the pro- 
cess of decomposition that organic matter must un- 
dergo as it becomes available for plant food, large 
quantities of carbon dioxide are liberated which 
unite with the water in the soil to form carbonic acid. 
This acid attacks the insoluble phosphates, trans- 
forms them into superphosphates, — the only form 
soluble in water, — and renders them available to 
plant life. 

2. Changes in Potassium, Sulphur, and Iron. 
Like phosphorus, potassium, sulphur, and iron are 
made available for plants through the indirect action 
of soil bacteria. The carbon dioxide and other 
organic acids produced during the fermentation of 
organic matter, attack the potash feldspar which 
occurs in the soil. The product is potassium car- 
bonate which is soluble in water and hence readily 
taken up by plants. The nitric acid which is formed 
during nitrification may also combine with the raw 
potash in the soil forming potassium nitrate which is 
a form available for plants. 

As a result of the activity of soil bacteria, hydrogen 
sulphide is evolved from the decomposition of pro- 



i6 Diseases of Truck Crops 

teids. The sulphur may be further changed into 
sulphur dioxide, and, when combining with water and 
oxygen, into free sulphuric acid. The latter read- 
ily combines with calcium or magnesium, forming 
calcium or magnesium sulphate. The plant obtains 
sulphur for the construction of its proteids from some 
of the soluble sulphates. 

How TO Maintain the Fertility of Soils 

We have already seen that the fertility of a soil is 
directly dependent upon the activity of certain bene- 
ficial bacteria. The latter constitute the life of a soil. 
It is therefore evident that for a soil to produce its 
maximum, its germ flora must receive careful con- 
sideration at the hands of truckers and gardeners. 
We must at any cost encourage these organisms to 
do their full duty at all times. Should they cease 
activity the soil would become barren. 

There is no doubt that plants remove large quan- 
tities of plant food from the soil. Headen' has cal- 
culated that for 80,000 tons of sugar beet, there are 
consumed as fertilizers, 331 tons of potash, worth 
$31,100; 71 tons of phosphoric acid worth $5,680; 
160 tons of nitrogen worth $54,400, making a total 
of $91,180, or a trifle over one dollar per ton. What 
is true for the sugar beet is true for every other 
trucking crop. In other words, soil fertility is capa- 
ble of being exhausted. Most of it may be returned 
in the form of manure and chemical fertilizers, but 

• Headen, W. P., Colorado Agr. Expt. Sta. Bui. 99: 3-16, 1905. 



Normal Soil and Its Requirements 17 

these are very expensive and reduce the net profit 
from the crops. The object of every intelligent 
trucker should therefore be to reduce his manure and 
fertilizer bills by encouraging his soil bacteria to man- 
ufacture the greatest amount of the available food 
which his crops require. Like any other living form 
these bacteria require certain conditions of life if they 
are to thrive. 

Maintaining the Nitrogen Supply 

The nitrifying bacteria are air-loving organisms. 
Hence the more aeration we give them, the more pro- 
nounced their activity. Schlosing' determined that 
when a soil was entirely void of oxygen the nitrates 
were reduced, and brought about an actual evolution 
of free nitrogen which is useless to the plant. With 
1.5 per cent, of oxygen nitrification was marked. 
When 6 per cent, oxygen was added to the soil nitri- 
fication was more than doubled. It is therefore 
evident that cultivation which aims at soil aeration 
also accelerates nitrification. The effect of soil 
aeration cannot be too strongly emphasized. Ac- 
cording to Chester,'' every cultivation of the soil 
with its attendant aeration is equivalent to a dressing 
of nitrate of soda in its cheapest form. If we realized 
this, and that nitrate fertilizers are usually the most 
costly, the alert trucker would learn the economy of 
more cultivating. 

' Schlosing, Compt. Rend. Acad. Sci. Paris, Ixxvii, 203-253. 
» Chester, F. D., Pa. State Dept. of Agr. Bui. 98: 9-88, 1912. 
a 



i8 Diseases of Truck Crops 

Besides oxygen, the nitrifying organisms demand, 
as an indispensable condition for work, a sufficient 
moisture in the soil. In dry soils and during dry 
weather, nitrification is almost suspended within the 
upper layers of soil. A third important factor is the 
chemical reaction of the soil. The nitrifying organ- 
isms work best when the soil gives a slight alkaline 
reaction. Too much alkalinity, however, like too 
much acidity, is detrimental as we shall see further on. 
Nitrification is further dependent on soil temperature. 
At 99 degrees Fahrenheit it is at its highest. A de- 
gree less than 54 F. retards it considerably. At 122 
degrees F. very little nitrate is produced, and at 131 
degrees F. nitrification ceases entirely. The physical 
condition of the soil is another important element to 
be considered. The highest rate of nitrification is 
found in truck lands, that is, in the sandy loams. 

Nitrogen Fixation from the Air 

It has been the common knowledge of farmers and 
truckers that legume plants, such as peas and beans, 
cause the soil on which they are grown to become 
more productive. It is not necessar^^ here to enter 
into an abstract discussion of this phenomenon. 
Suffice it to say, that science has definitely shown 
that there is a bacterial soil organism, Pseudotnonas 
radicicola, which is capable of fixing the free nitro- 
gen from the air. This organism attacks the young 
rootlets of the legume crops as other parasitic forms 
also do. Its presence in the root results in a nodule 



Normal Soil and Its Requirements 19 

or swelling. Soon, however, it loses its parasitic 
character and becomes an agent for fixing the free 
nitrogen of the air, which is then stored up in the 
root nodule. In this form the nitrogen is consumed 
by the plant itself. As far as is known, P. radicicola 
can thrive on the roots of legume plants only. The 
Rhode Island Experiment Station' has found that 
an acre of soy beans for instance may fix about 
1000 pounds of nitrogen from the air during a period 
of five years, or 200 pounds per year. One hundred 
and forty pounds of the 200 were removed with the 
crop, and 60 pounds remained in the field. Since 
one pound of nitrogen was worth at least i6c., 200 
pounds would cost $32. We must not, of course, 
suppose that every acre of soy beans would produce 
200 pounds of nitrogen every year. This would 
depend somewhat on the nature of the soil, the degree 
of moisture, the amount of oxygen, and other condi- 
tions congenial or unfavorable. What is certain, 
however, is that every alert gardener and trucker 
should learn to use legumes more extensively in his 
system of cropping. 

Soils which have grown leguminous crops for a 
period of years are well supplied with P. radicicola. 
Other soils are deficient in it and must be artificially 
inoculated. The numerous types of pure cultures 
of the organism sold in liquid form have as a rule 
proven a failure. The organism dies out or loses its 
effectiveness in the artificial liquid media. The best 
forms of pure cultures now used are those grown on 

' Rhode Island Agr. Expt. Sta. Bui. 147. 



20 Diseases of Truck Crops 

sterilized soil. This method has been developed at 
Cornell University. The soil is after all the natural 
and best medium where soil bacteria can grow. On 
it P. radicicola lives longer, and hence when it is used 
for inoculation, better success may be expected. 
The Alphano Humus Co. of New York City have on 
the market cans with sterilized soils, in which the 
legume bacteria have been introduced. Each can is 
sufficient to inoculate one acre of soil. The ability of 
the organism of one legume crop to inoculate another 
crop has long been a subject of discussion and has not 
as yet been satisfactorily answered. Carman and 
Didlake' have shown that there exist six different 
species of legume organisms. For example they 
found that the organism of alfalfa is the same as or 
similar to the one which works on the sweet clover 
{Melilotus alba), trefoil or black medick {Melilotus 
lupulina), and bur clover {Melilotus denticulata) . 
This same organism, however, cannot produce nod- 
ules on the roots of any species of Trifolium, of Vicia, 
Pisum, Vigna, Glycine, or Phaseolus. The organisms 
of all the species of Trifolium (clover) are one and the 
same. The organisms of all the species of the vetch 
and garden pea are one and the same. They cannot 
work, however, on red or crimson clover, or on alfalfa. 
The cowpea organism seems to be adapted to the 
cowpea only. The same thing appears to be true for 
the soy bean organism and for that of the garden 
bean. Therefore when a land is to be inoculated 

' Garman, H. and Didlake, Mary, Kentucky Agr. Expt. Sta. Bui. 
184: 343-363. 1914- 



Normal Soil and Its Requirements 21 

with the garden bean organism, for instance, none 
must be used but those taken from the bean. Under 
ordinary conditions, where a soil is known to produce 
healthy crops of one (legume) variety, some of that 
soil may be used to inoculate other soils intended for 
the same crop. 

Economical Use of Commercial Fertilizer 

A knowledge of the functions of soil bacteria and 
a proper management of the soil means a saving of 
commercial fertilizer and the proper maintenance of 
soil fertility. In trucking more than in any other 
phase of farming, the soil is being made to produce 
the whole year around. This is especially true for 
our Southern States where the summer and fall 
seasons are longest, or where the winters are very 
mild. It, therefore, often becomes necessary to use 
chemical fertilizers to supplement the work of the 
soil bacteria. This is especially true for some par- 
ticular crops which draw heavily on certain mineral 
constituents. In order to obtain the greatest re- 
sults from the use of chemical fertilizers, the follow- 
ing items should be carefully considered. 

1. The Location of the Field. Uplands or 
hillsides will require heavier application of fertilizer 
since some of it is likely to be carried off by washing. 
Lowlands, especially those near uplands which wash 
badly, generally require less. 

2. The Character of the Soil. The chemical 
composition of the soil has a marked influence on the 



22 Diseases of Truck Crops 

effect of fertilizers. A chemical analysis of the soil 
will enable the trucker to make a more economical 
use of his fertilizer. If a land, for instance, contains 
too much iron and aluminium, applied phosphate 
fertilizers may be modified into ferric and aluminium 
phosphate, which become slowly available to plants. 
On the other hand when phosphate fertilizers are 
changed in the soil into tricalcium phosphate it 
becomes available more readily. Sandy soils are 
generally quick to respond to fertilization; they can 
therefore stand heavier application than the cold clay 
soils which respond more slowly. In the latter, the 
fertilizers are likely to be converted into forms un- 
available to plants. The trucker should therefore 
avoid depending altogether on the use of chemical 
fertilizers. The best results are always obtained and 
the fertility of the soil best preserved when the use of 
chemical fertilizer is supplemented v/ith animal or 
green manures. 



CHAPTER II 

SICK SOILS NOT INFLUENCED BY PARASITES 

We have seen that a normal and healthy soil is 
one in which the beneficial soil flora is at its maximum 
of normal activity, making the food of the plant 
assimilable. We have to discuss the abnormal or 
sick soils now. In this class we include those which 
are either physically or chemically so constituted as 
to have a detrimental effect on the activity of the 
soil flora; and those which are overrun with organ- 
isms directly parasitic on the plants grown in that 
soil. There are five classes to be considered in the 
first division. 

I. Denitrified Soils 

This detrimental condition in the soil is brought 
about by a group of undesirable organisms, some 
of which are Bacillus ramosus, B. pestifer, B. 
mycoides, B. subtilis, B. mesentericus vulgatus. 
In Chapter I we have seen that the nitrifying 
bacteria oxidize the nitrogen and make it avail- 
able for plants. In denitrification, the harmful 
bacteria tend to reconvert the available nitrogen 
into a non-available form, or else to liberate it into 
the air, where it may be considered as lost so 
23 



24 Diseases of Truck Crops 

far as the crops are concerned. Most trucking 
lands contain the nitrifying and denitrifying organ- 
isms in about equal proportions. To encourage 
the activity of the one over the other is the aim 
of intelligent trucking. The denitrifying bacteria 
thrive best in an abundance of carbohydrate foods. 
Fresh coarse manure with a high percentage of straw, 
when applied to the soil, will favor denitrification. 
It should therefore be avoided as far as is possible. 
There are, however, market gardeners who often use 
as much as fifty tons of such manure per acre in ad- 
dition to a nitrate fertilizer. Such action is very likely 
to encourage denitrification because of the large 
amount of carbohydrates incorporated in the soil. 

Indirectly denitrification will finally cause various 
physiological plant troubles, most of which are little 
understood. Poor growth and the shedding of 
blossoms will characterize plants deprived of avail- 
able nitrogen food. Denitrification may largely be 
prevented. A judicious use of manure, especially on 
the heavy soils, drainage, and proper tillage are all 
factors which induce nitrification, thereby also pre- 
venting denitrification. 

2. Nitre-Sick Soils 

This form of sickness, peculiar to certain Colorado 
soils, was carefully studied by Headen ' and Sackett. * 
Nitre-sick soils are those which contain such large 
quantities of nitrates that they inhibit plant growth. 

« Headen, W. P., Colorado Agr. Expt. Sta. Bui. 155. 

2 Sackett, W. G., Colorado Agr. Expt. Sta. Bui. 196:3-39, 1914, 



Sick Soils not Influenced by Parasites 25 

Truck crops (fig. 3), grains, and fruit trees rapidly 
deteriorate on such lands. This condition occurs in 
a variety of soils in Colorado. It is met with in the 
light sandy loams as well as in the heavy clay loams, 
on lowlands as well as on hilltops. It is to be dis- 
tinguished from true alkali troubles. 

The distinguishing characteristic of a nitre-sick 
soil is its brownish-black wet appearance. From 
afar the soil looks as if it had been wetted with crude 
oil ; however the soil is usually dry. Sometimes the 
soil may be moist and slippery, due no doubt to the 
presence of large quantities of deliquescent salts. 
Walking through such a field produces a sensation 
similar to that which one would get from walking 
on commeal or ashes. 

The accumulation of excessive amounts of nitrates 
in the soil is due to the activity of a bacterial soil 
organism, Azotohacter chroococcum. This organism 
has the power of fixing free nitrogen from the air and 
depositing it in the form of nitrates in the soil. The 
conditions which favor this activity still await study. 
Normally, soils contain from 140 to 150 pounds of 
nitrates per acre foot. In a nitre-sick soil, each acre 
foot contains 113,480 pounds, or 56.74 tons. With 
such a high concentration of nitrate, it is impossible 
for plants to grow. So far, we know of no methods 
to reclaim nitre-sick soils. 

3. Acid-Sick Soils 

Soils which contain an excess of acid in which 
crops refuse to grow, may be termed acid-sick. Acids 



26 Diseases of Truck Crops 

in soils have a directly poisonous effect on plants. 
Soil acidity may be brought about by the loss of lime 
and other bases; and by the decomposition of organic 
and inorganic matter. 

Crops are known to draw heavily on the lime of the 
soil, and thus increase the proportion of acidity. 
This then is one direct way of depleting the soil lime. 
A ton of alfalfa, for instance, is known to take up 50 
pounds of lime. With a yield of 6 tons per acre, the 
annual loss of lime per acre would be 2100 pounds. 

Lime and other bases are further lost from the 
soil by leaching. The soluble carbonates are but 
slowly soluble in pure water. However, carbon 
dioxide, nearly always present in soils, changes the 
calcium carbonate into calcium bicarbonate, which 
is rather soluble, and readily leaches out with the 
drainage water. 

Soils which are heavily manured are apt to become 
more acid. The decomposition of the organic matter 
yields large quantities of carbon dioxide which act on 
the carbonate in the manner above indicated. The 
annual leaching of lime from soils varies from 100 to 
1000 pounds per acre. 

In addition to these causes, poor drainage has a 
tendency to increase the soil acidity. The application 
of ammonium sulphate as a fertilizer leads to a devel- 
opment of acidity by the production of sulphuric acid. 
The same is true when muriate of potash is added. 
In the process of nitrification in which nitrogen is 
made more available for plants, acids are produced. 

Acidity in a soil is usually characterized by a Ian- 





Fig. 4. Effect of Lime. 

a. to d. R hubarb, e. to h. New Zealand Spinach, a. and 6., f . and /. both receiving 
sulphate of ammonia, a. and e. unlimed, b. and/, limed, c and d., g. and A. both 
received nitrate of soda, c. and g. unlimed, d. and h. limed (after Hartwell and 
Damon"*. 



Sick Soils not Influenced by Parasites 27 

guid condition of the growing crop. Sorrels, poverty 
grass, broomsedge, cinquefoil, and redtop thrive 
best, and are generally indicative of acid soils. Not 
all truck crops are equally sensitive to soil acidity, 
Hartwell and Damon ' have determined the degree in 
which truck crops are benefited by the application of 
lime to an acid soil. As a guide to the effect of Hme 
on crops, those which seem to benefit most are in- 
dicated by the number (3), lesser degrees of improve- 
ment are indicated by the numbers (2) and (i). 
Crops which tolerate a moderate amount of acidity 
are followed by the figure (o) , and those which thrive 
best without lime by ( — i) : Asparagus (3), beans (o), 
beets (3), cabbage (2), carrots (i), cauliflower (2), 
celery (3), chard (2), chicory (o), cowpea (0), cress 
(o), cucumber (i), eggplant (2), endive (3), okra (3), 
horseradish (2), kale (i), kohlrabi (i), leek (3), lettuce 
(3), mustard (2), muskmelon (0), onion (3), parsley (o), 
parsnip (3), pea, garden (i), pepper (3), potato (o), 
radish (i), rape (2), rhubarb (3), sorrel ( — i), spinach 
(3) (fig- 4a to h), turnip (0), watermelon ( — 1). 

Treatment of Acid Soils. The best remedy known 
is lime. Its effect is to neutralize the acidity, 
restoring the normal equilibrium for the activity of 
the soil flora, and thus enabling the plant to flourish. 
The amount of lime to be used depends largely on 
the kind of soil and the degree of its acidity. Ac- 
cording to Blair' a loamy to a clay loam will require 

• Hartwell, B. L., and Damon, S. C, Rhode Island Agr. Expt. 
Sta. Bill., 160: 408-446, 1914. 

* Blair, A. W., New Jersey Agr. Expt. Sta. Cir., 54: 3-1 1, 1916. 



28 Diseases of Truck Crops 

from 1500 to 2000 pounds of burned lime per acre. 
This is generally considered a moderate application. 
For sands and sandy loams it would be safe to apply 
1000 to 1500 pounds. If the soil is known to be very 
acid or to contain large amounts of organic matter, 
heavier application of lime may be given. Lime 
is sold as ground limestone or as burned lime. A ton 
of burned limestone will yield 11 20 pounds. If 
enough water is added, it will weigh 1480 pounds. 
If 1 1 20 pounds of burned lime or the 1480 
pounds of hydrated lime are allowed to air slack, 
the weight of both will be 2000 pounds. Air-slacked 
lime has the same composition as ground lime- 
stone. In buying hydrated lime we do not get 
any better quality, but merely pay an excess in 
freight for the amount of water it contains. The 
cost of delivery should determine the kind of lime 
to buy. 

Wood ashes may often be used instead of lime to 
correct soil acidity. Hardwood ashes contain about 
30 per cent, lime and 60 per cent, potash. Two and a 
half tons of good wood ashes are equivalent to one 
ton of burned lime to overcome soil acidity. Leached 
ashes have lost their potash and its lime is in the form 
of a hydrate or carbonate. 

Magnesium lime which contains high percentages 
of magnesia is not objectionable for use. In fact, 
a ton of limestone which contains magnesium car- 
bonate is more effective on acid soils than a ton of 
limestone without magnesium carbonate. Lime 
should be applied only when the acidity of the soil 



Sick Soils not Influenced by Parasites 29 

requires it. After that an additional application of 
1000 pounds of burned lime or 2000 pounds of lime- 
stone every five years will be desirable. Should lime 
be used at more frequent intervals, the organic matter 
of the soil will fast deplete. The saying that "lime 
makes the father rich and the son poor" is only true 
where the use of lime is overdone, and not otherwise. 

4. Muck or Peat Soils 

Muck or peat soil is sick because most plants 
refuse to grow there unless it is properly treated. 
However, muck may be transformed into the best 
trucking land. There are States in the Union 
which possess muck lands by the thousands of acres. 
Yet these are the last to be reclaimed. In 
Europe, scientists have long concerned them- 
selves with the reclaiming and utilization of muck 
lands. Norway, Sweden, and Denmark have dealt 
to a large extent and with fair success with the 
problem, though much of it still remains to be 
solved. As the term implies, peaty soils are those in 
which peat is the dominating constituent. Peat is 
always formed under water, in swamps or marshes, 
undrained fiat land, indeed, any place where water- 
loving plants grow in abundance. Most peat is 
made up mainly of sphagnum and moss. Grass peat 
is composed of swamp grasses, sedges, rushes, or 
flags. In swamps where rushes, sedges, or other 
grasses occur, peat formation is more rapid than 
where moss or sphagnum grows. Peat itself is 
nothing more than rotten vegetable matter. Com- 



30 



Diseases of Truck Crops 



plete decomposition is impossible, because of the 
absence of air and the accumulation of plant acids 
which contain antiseptic properties. 

The chemical composition of peaty soils, as given 
by Conner and Abbot,' may be seen in Table 5. 

Table 5 

Chemical Analyses of Different Types oj Unproductive 
Black Soils. 



Substance determined 



Kind of Sail 



Acid 
peal 



Neutral 
peat 



Acid 
peaty 
sand 



Neutral 
peaty 

sand 



Insoluble & soluble silica, etc. 

Potash (K2O) 

Lime (CaO) 

Magnesia (MgO) 

Iron oxide (FeaOs) 

Aluminum oxide (AI2O3) 

Phosphoric acid (PjOs) 

Sulphur trioxide (SO3) 

Carbon dioxide (CO2) 

Volatile matter 

Total nitrogen 

Total potash (K^O) 

Phosphoric acid soluble ir 
N/sHCl 

Total humus 

Acid humus 

Acidity in pounds calcium car- 
bonate (CaCOs) per acre foot 

Hygroscopic moisture 



10.40 

•23 

1.86 

.26 

2.87 

.36 

•49 

.20 

83.16 

3-82 
•34 

.032 
30.68 
27.74 



1940.00 
11.82 



9.00 
.12 

3.89 
•52 

4.27 

.40 

.28 

•63 

81.16 

3^5i 
.26 

.0506 

25^55 
3.22 

360.00 
18.57 



88.63 
.14 
.08 
.11 

3^25 
.08 
.04 
.10 

8.16 
.28 

1.62 

.0058 
4.86 
4.64 

3500.00 
1.65 



71-47 

.28 

5-91 

I-3I 

5-03 
.21 

4.42 

.22 

12.16 

•57 

i^25 

•037 
4.72 
none 

none 
3^30 



From the table it is evident that the chemical 
composition is not the same for all peaty soils. This 
is naturally to be expected, since no two soils are 

' Conner, S. D., and Abbot, J. B., Purdue Agr. Expt. Sta. Bui. 
157 : vol. 16, 1912, 



Sick Soils not Influenced by Parasites 31 

chemically identical. In treating peaty soils it 
should be remembered that what applies to one does 
not generally apply to another. 

Depth of Peat Soils. Hopkins, Readhimer, and 
Fisher' classify peaty soils according to the depth 
as follows : 

1 . Soils in which the very peaty material extends 
three or four feet at least, and often to much greater 
depths. 

2. Soils with one to three feet of peaty material 
resting on deep sand. 

3. Soils with one to three feet of peaty material 
resting on rock, usually with some inches of sandy 
material between the two. 

4. Soils with six inches to three feet of peaty 
material resting on a clayey subsoil. 

5. Soils with only a few inches resting on the sand. 
When the peat is about three feet in depth over a 

deep sand subsoil, the land may be lacking in potash. 
This must then be supplied in the form of potassium 
salts, or of manure. 

Of the many types of peaty soils, the best for truck- 
ing are those black deposits which have reached an 
advanced state of decomposition, are of a fine texture, 
and have a high ash content. Brown peat of a 
fibrous nature is not very desirable. Its physical 
condition is such that the water cannot be properly 
controlled. 

Treatment oj Peat Soil: Burning. The mistake is 

" » Hopkins, C. G., Readhimer, J. E., and Fisher, O. S., Illinois Agr, 
Expt. Sta. Bill. 157 : 95-131, 1912. 



32 Diseases of Truck Crops 

often made of burning over peaty soils with a view 
to improving them. This practice cannot be too 
strongly condemned. It is difficult to see where any 
permanent benefit can result from such treatment. 
Moreover, burning destroys the nitrogen and the 
organic matter, which are two valuable and expen- 
sive assets of such a soil. Should peat ever catch fire 
accidentally, pouring water or throwing soil on the 
flames will not smother them. In this case it is best 
to dig an open trench around the fire to a depth of 
moist earth and let it bum itself out within that limit. 

Drainage. The best method of reclaiming peat 
soils is drainage. This process is not so easily done 
as on ordinary land because peat holds water 
better than ordinary soils. Peat soils may be 
drained if sufficiently large tiles are used and a 
proper outlet is at hand. The best results are ob- 
tained when the tiles are laid in the underlying 
muck or clay, but not too deeply in the subsoil. 

Plowing. The second best method of improving 
peat soils is a proper working of them. Fall plowing 
is to be highly recommended. The peat in this case 
is exposed to the action of the frost, rain, and snow, 
all of which helps in the more rapid decay of the 
organic matter. In shallow peaty layers, deep 
plowing is of great value. This helps to mix the 
clay with the peat and makes it more readily avail- 
able by bringing up the potassium and the phos- 
phorus of the subsoil. In deep peaty layers, deep 
plowing exposes a larger part of the organic matter 
to the air and sunlight. Rolling should never be 



Sick Soils not Influenced by Parasites 33 

practiced in very shallow layers. It is recommended 
only where the layer is over sixteen inches deep. 
Frequent cultivation is also very beneficial and pro- 
vides aeration which favors a more rapid decay of 
the organic matter. It helps to keep down weeds. 

The Choice of a Crop. On newly reclaimed peat 
soils, the best crops to plant are timothy, sudan grass, 
or alsike clover, which may be pastured to advantage. 
Peat soils cannot be surpassed for trucking purposes. 
They seem especially adapted for onions, celery, 
tomatoes, and potatoes. 

Use of Fertilizers. The application of certain 
chemical fertilizers to peaty soils is decidedly bene- 
ficial. The kind of fertilizers will depend largely on 
the nature of the crop grown. Conner and Abbot 
present interesting data on the effect of fertilizer on 
onions. This is summarized in Table 6. 

Table 6 

Results of Field Fertilizer Tests with Onions on Various 
Peat Soils 



Experi- 
ment 


Pounds 

fertil- 
izer 
per acre 


Average 
unfer- 
tilized 
yield 


Increase in bushels per 


acre 


No. 


4-8-10' 


0-8-10 


4-0-10 


4-8-0 


4-31 
43-11 
92-21 

37-14 


1000 
1000 
1000 
1000 


606.9 

79.1 

307.0 

234.0 


1 13.0 

I33-I 
130.0 
3320 


124.2 

58.0 

240.0 

285.0 


76.3 
49.6 
145.0 
120.0 


75-5 
57.1 
20.0 
89.0 



' 4-8-10 formula indicates 4 per cent, nitrogen, 8 per cent, phos- 
phoric acid, and 10 per cent, potash made from dried blood, acid phos- 
phate, and sulphate of potash. Minus sign ( — ) indicates decrease. 



34 



Diseases of Truck Crops 



Table 6 — {Continued) 



Experi- 
ment 


Pounds 
fertil- 
izer 
per acre 


Average 
unfer- 
tilized 
yield 


Increase in bushels per 


acre 


No. 


4-8-10 


0-8-10 


4-0-10 


4-8-0 


37-15 
43-21 
57-11 
57-1 la 
Average 


1000 

1000 

1000 

500 


613.0 

628.0 
394-2 
372.8 
404.4 


73-7 
0.0 

89.0 
171-7 
130.3 


-27.1 

75-0 
49.1 
178.6 
122.8 


127.1 
-30.0 

55-2 
128.6 
84.0 


-64.6 

25.0 

47.6 

145-5 

49.0 


Cost of fprtilizRr 




$17.34 


$ 9.56 
51.84 


$12.84 
29.16 


$12.28 


Average 


profit pe 


r acre . . . 


.. 47.«i 


12.22 



We have as yet no definite data on the effect of Hme 
on peaty soils. Those in charge of the development 
of peaty soils caution against using it too freely. Of 
the forms to use, ground limestone or marl are per- 
haps the best kinds to apply. The amount to use 
will vary from one to four tons, depending largely on 
the acidity of the soil. Too much lime tends to de- 
stroy the nitrogenous compounds, and encourages 
serious plant diseases. 

5. Alkali-Sick Soils 

The alkali problem is even of more widespread 
concern, as it affects nearly all irrigated districts 
of the arid and semi-arid regions of the United 
States. An alkali-sick soil is one which contains 
an excess of accumulated soluble salts which are 
injurious to plant growth. For convenience, 
alkali soils are divided into black and white. The 
black alkali lands are known to contain sodium 
carbonate or washing soda as the essential salt. The 



Sick Soils not Influenced by Parasites 35 

latter does not act so much on the soil as on the or- 
ganic matter, turning it black. This black material 
is always found on the surface with the salts. The 
blackening of the soil, however, is not always an 
indication of black alkali. Many dark spots are 
found to contain the white alkali. Moreover, soils 
which contain little or no organic matter may con- 
tain large quantities of sodium carbonate and never 
turn black. The white alkali in reality is not a true 
alkali. The salts found in it are sodium chloride or 
table salt, calcium sulphate or gypsum, sodium sul- 
phate, magnesium sulphate or Epsom salt. In 
addition to these may be found salts of potassium. 
Table 7, taken from Harris, ' shows a comparative 
study of the total soluble salts which are found to be 
injurious to plants. 

Table 7 

Summary of Total Soluble Salts, Chlorides, Carbonates, 

and Sulphates in Alkali Soils. Average to a Depth 

of Four Feet, Parts per Million of Dry Soil. 



Parts of field producing best crop 



Counties 


Total 

Soluble 

Salts 


Chlorides 


Carbonates 


Sulphates 


Boxelder 
Salt Lake 
Millard 
Cache 


4,806 

2,440 

10,852 

5,792 


1,485 
545 
640 

1,573 


1,983 

858 

1,418 

1,515 


711 
2,334 
9-795 
2,539 



' Harris, F. S., Utah Agr. Expt. Sta. Bui., 145 : 3-21, 1916. 



36 



Diseases of Truck Crops 



Table 7 — (Continued) 



Parts of field producing medium crop 



Counties 


Total 

Soluble 

Salts 


Chlorides 


Carbonates 


Sulphates 


Boxelder 
Salt Lake 
MiUard 
Cache 


7,075 
4,228 

18,325 
17,318 


3,021 

875 

3,077 

2,541 


1,727 

792 

1,271 

888 


543 

1,812 

13,238 

13,126 



Parts of field where no crop would groz 



Boxelder 
SaltTflke 
Millard 
Cache 


10,079 
6,938 

21,488 
30,148 


6,767 
2,045 
6,289 
3,585 


1,874 
689 

1,875 
795 


1,154 

3,636 

13,304 

23,027 



Origm oj Alkali Soils. Soils are formed through 
the disintegration of rocks due to various agencies 
such as weather, water, chemicals and organic 
matter, and the action of the soil flora. In this pro- 
cess, substances are released, some of which are in- 
soluble while others are readily soluble in water. 

Although in moist and cold climates the more 
rapid decomposition of rocks leaves more salt de- 
posits in the soil, the abundant rainfall washes out 
these salts, which are carried off by the streams and 
rivers to the ocean. This is not the case in arid 
regions where the salts are gradually allowed to 
accumulate. Much of the rain in the arid regions 
does not find an outlet in streams, but accumulates 
in the lower regions, where the water finally evapo- 



Sick Soils not Influenced by Parasites 37 

rates, leaving a deposit of salts. This then is one way 
in which alkali spots are formed. Another source of 
alkali formation is through the decomposition of 
volcanic rocks. This condition is found in some parts 
of New Mexico. Another, and by far the most im- 
portant, source of alkali formation is through capil- 
larity and evaporation. This occurs when the water 
accumulated in the soil is insufficient to raise the 
water table high enough to permit evaporation. The 
condition which most favors such an accumulation 
of water is a bed or layer of a clayey character which 
prevents the percolation of water downwards, below 
a soil which does not have sufficient lateral drainage. 
The source of the water may be springs, or the perco- 
lation of surface rainwater, and in irrigated regions, 
leaky canals or over-irrigation. The depth of the 
water table, where capillarity becomes a source of 
trouble, is about three feet. As all soil water contains 
diluted salts, continual evaporation will leave alkali 
spots or beds. To realize further what the alkali 
accumulation means, Tinsley^ has worked out some 
interesting figures. 

"Suppose an acre of land, with the water table 
within less than two feet of surface, and that the 
amount of water evaporated from the surface in a 
year was enough to cover the acre to a depth of one 
foot, which the writer considers a low estimate for a 
bare soil. Suppose further that when it reached the 
surface, the water carried 100 parts of soluble matter 
in 100,000 parts of water, which is about the salt 

^ Tinsley, J. D., New Mexico Agr. Expt. Sta. Bui. 42 : 3-31, 1902. 



38 Diseases of Truck Crops 

content of the best irrigating waters in the Roswell 
district. This would give 43,560 cubic feet of water 
on the acre, which would weigh about 2,720,000 
pounds, and would leave on evaporation 2720 pounds 
of salt, about one and one half tons. 

"This would amount to an addition of .07 per cent, 
of salt to the surface foot of that acre per year. If 
this were continued about seven years, and none of 
the salts were removed, the amount added would be 
about .5 per cent, in the first foot of soil, which is 
more per foot than cultivated plants could usually 
withstand. Under actual conditions, it is probable 
that more than one and one half tons of salts per acre 
per year are carried to the surface in many cases, but 
the rain washes a portion of them back and they are 
distributed to a greater depth than one foot." 

Effect of Alkali on Plant Growth. Plants can 
stand the baneful effect of alkali only to a limited 
degree. The damage is always confined to the stem 
end. Here the epidermis turns brown for half an 
inch or more, gradually tearing away in a girdling 
fashion. This results in the collapse and death of the 
plant, which assumes a corroded appearance. The 
physiological effect of alkali is to plasmolize the cell 
contents of the bark. 

Crops Adapted to Alkali Lands. Unlike peaty 
lands, alkali soils are adapted to very few trucking 
crops. Sugar beets, carrots, and artichokes seem to 
thrive fairly well in such soils. Irish potatoes will 
thrive well in soils which do not contain more than 
18,400 pounds of alkali per acre, of which 4000 



Sick Soils not Influenced by Parasites 39 

pounds may be carbonate of soda, and 6880 pounds 
common salt. Broccoli, chard, fennel, and sweet corn 
will thrive fairly well in lands containing up to a total 
of 3720 pounds of alkali per acre. 

How to Reclaim Alkali Soils. We have seen that 
the accumulation of alkali in a soil is often brought 
about by the evaporation of water which is charged 
with mineral salts. To obviate this it is evident 
that the evaporation must be counteracted. Good 
surface cultivation will establish a dry surface 
mulch and prevent the rise of water to the upper 
level, thereby preventing evaporation. Tillage to 
be effective must be started early, because then, 
large quantities of salt would be carried into the 
subsoil by the spring rains. If the crop is started 
early, it may be forced to maturity before the effect 
of alkaH can make itself felt on the plants. Tillage, 
however, will afford only temporary relief, as it will 
not remove the salts from the soil. Drainage on the 
other hand affords permanent relief. The land is 
first flooded, preferably in the winter, and then the 
water which is now laden with soluble salts is removed 
by a system of drainage. Tile drainage, while more 
expensive in its initial cost, is cheapest in the long 
run. Such a system when laid down permanently 
will prevent the further accumulation of salts. 

The application of manure or straw to alkali land 
often brings marked relief. Many a barren spot has 
been reclaimed by this method. The beneficial 
action of manure or straw is easily accounted for. 
Both of these tend to loosen the surface soil, thereby 



40 Diseases of Truck Crops 

acting as a surface mulch, and indirectly preventing 
evaporation. They may also stimulate young plants 
to more rapid growth, enabling them to withstand 
the action of alkali. Young plants are much more 
sensitive to alkali than older ones. The older plants 
of cantaloupes, for instance, are far more resistant to 
alkali than the young seedlings. 



I 



CHAPTER III 

SOIL SICKNESS DUE TO THE PRESENCE OF PARASITES 
HARMFUL TO PLANTS 

When a soil is sick because its beneficial bacteria 
do not perform their functions properly, or because 
of abnormalities in its chemical properties, careful 
treatment and proper cultural methods will restore 
it to health. But when a soil becomes sick and un- 
productive because parasitic forms gain a foothold 
there, much greater skill and knowledge are required 
to cope with the problem. Its solution is of the 
greatest economic importance to the trucker and 
gardener. 

Parasitic fungi finding their way in a soil do not 
necessarily interfere with the work of the beneficial 
bacteria, such as the ammonifiers and nitrifiers, for 
instance. Neither do they always influence the 
chemical or physical nature of the soil. They attack 
directly the crop itself. Of the numerous parasites 
rendering soils unproductive, we will consider here 
only two types. 

I. Soil Sickness Due to Parasitic Fungi. 

Fungi which produce damping off in seedlings. 

41 



42 Diseases of Truck Crops 

Tungi which produce damping off as well as wilts, 
BLIGHTS, or ROTS in plants. 

Damping Off 

Caused by Pythium de Baryanum Hesse. 

This disease is very familiar to every grower of 
plants. The trouble is peculiar to seedlings or very 
tender plants. It is prevalent in the greenhouse, the 
hotbed, the cold frame, and frequently also in the 
field. The trouble is induced by the presence of 
definite parasitic fungi in the soil. They thrive best 
when the land is continually damp, and the at- 
mospheric temperature comparatively high. Damp- 
ing off is also favored by thick sowing and too much 
shade in the seed bed. 

Symptoms of Damping Off. Every experienced 
trucker knows the disease when he sees it. Seedlings 
freshly damped off are soft and water-soaked at the 
base of the stem. If they are pulled they often break 
off easily. A more careful examination shows that 
the root system is entirely decayed by this time, al- 
though the upper part of the stem and leaves may 
still be green, possibly also fresh. The degree of 
prostration in the seedlings is regulated by the 
amount of moisture in the soil. If the amount of 
moisture is slight, the seedlings will be flabby and 
wilted before they topple over. With a high mois- 
ture content, they are more firm, but become pros- 
trate as soon as infection starts in. Damping off 




Fig. 5. Pythium deBaryanum. 

a. Mycelium, b. conidiophore bearing con- 
idia, c. germinating conidiuni, d. fertil- 
ized oogonium and adjoining empty 
antheridium, e. oospore. 



Soil Sickness Due to Parasites 43 

usually begins in spots in the seed bed or in the field 
and then may spread in every direction. 

The Organism. Pythium de Baryanum was first 
named and described by Hesse in 1874. Ward^ 
found it to be a very prevalent parasite in the garden 
soils of Europe. In America the fungus was first 
recognized by Atkinson^ as of great economic im- 
portance. Pythium de Baryanum, when examined 
under a compound microscope, is seen to be made 
up of coarse, non-septate, highly granular, irregular 
branched hyaline vegetative threads or mycelium 
(fig. 5 a). The younger threads are more finely 
granular, the oldest ones are coarsely granular or 
more often empty. These threads penetrate the 
cells of the host, where they obtain food. 

Pythium de Baryanum does not often fruit freely 
on the dead host. The fruiting is better observed 
when it is grown in a pure culture. Under normal 
conditions the fungus produces two forms of spores, 
conidia (fig. 5 b) and oogonia (fig. 5 d, e). The 
summer spores, or conidia, are swellings formed at 
the tip of the hyphse. These swellings readily break 
ofl from the mother threads and germinate by send- 
ing out a slender tube (fig. 5 c) . This tube penetrates 
the seedling tissue, where it grows and develops and 
after due incubation reproduces the disease. The 
oospore or sexual spore is the stage which is most 
commonly found. The female oogonium first devel- 

» Ward, M., Quart. Jour. Micros. Soc, New Ser. 22 : 487, 1883. 
"^ Atkinson, G. F., New York (Cornell) Agr. Expt. Sta. Bui. 94 : 
233-272, 1895. 



44 Diseases of Truck Crops 

ops as a terminal enlargement which is cut off by a 
septum from the mother thread. Next or adjacent 
to it a slender tube is cut off from the mycelium by a 
septum. This tube now performs the function of the 
male sexual organ and is known as antheridium. 
The latter then comes into close contact and empties 
all its content into the oogonium (fig. 5 d) . Fertiliza- 
tion thus takes place, and a mature egg or oospore 
or winter resting spore is formed (fig. 5 e). 

The latest investigations have not yet disclosed 
whether or not Pythiuni de Baryanum is carried over 
from year to year by its oospores. It is apparently 
able to propagate itself indefinitely by. its vegetative 
mycelium. The seedlings of the following truck crops 
are subject to damping off by Pythium : Beans, beets, 
cabbage, cauliflower, endive, lettuce, pumpkin, tom- 
ato, and turnip. 

Of the othcx- fungi which are capable of producing a 
damping off in seedlings may be mentioned; Sclero- 
tinia liber tiana Fckl., Phoma solani Halst., Colle- 
totrichum sp., Fusarium sp., Sclerotiiim Roljsii Sacc, 
and Rhizoctonia solani Kuhn. The first five will be 
taken up separately in connection with the study of 
their respective hosts (see pages 45, 46, 143, 305, 324). 

Other Soil Diseases 

We have seen that Pythium de Baryanum is most 
active as a disease on young seedlings. Other fungi, 
however, may attack not only seedlings, but also 
older plants, in various stages of development. As 




Fig. 6. Rhizoctoma. 

a. Rhizoctonia cankers on stems of young bean plants, b. young growing hyphas 
of Rhizoctonia, c. young barrel shaped cells which compose the sclerotia of Rhizoc- 
tonia, d. older and empty barrel shaped cells of sclerotia (a. to d. after Peltier). 



Soil Sickness Due to Parasites 45 

a guide to the trucker and gardener, we shall consider 
two typical soil diseases, one which produces root 
rot, the other wilt only. 

Root Rot 

Caused by Rhizoctonia solani Kuhn. 

This fungus is of great economic importance be- 
cause of its widespread distribution. It is capable 
of producing a damping off on a variety of seedlings, 
as well as of attacking older and mature plants. 

Symptoms. The symptoms of Rhizoctonia wilt 
do not differ materially from those produced by 
Pythium de Baryanum. On older plants however 
Rhizoctonia produces cankers or deep lesions which 
are very characteristic (fig. 6 a). These are formed 
on the roots as well as on the base of the stem. 
The lesions are reddish brown and extend into the 
cortical or vital layer as well as into the woody tissue. 
There is perhaps no other parasitic fungus which is 
so widespread and capable of attacking such a vari- 
ety of hosts as Rhizoctonia. The work of Peltier^ 
shows that the following truck crops are susceptible 
to Rhizoctonia: Beet, bean, cabbage, cauliflower, 
celery, cowpea, cucumber, cress, eggplant, horse- 
radish, lettuce, muskmelon, okra, pepper, radish, 
squash, sweet potato, garden pea, parsnip, potato, 
and tomato. 

The Organism. In 1828 Duhamel described Rhi- 

» Peltier, G. L., Illinois Agr. Expt. Sta. Bui. 189: 283-391, 1916. 



46 Diseases of Truck Crops 

zoctonia for the first time. In the United States the 
first extended account of the fungus was given by 
Pammel. ' Many other excellent accounts by Amer- 
ican workers have appeared from time to time, to 
which we shall have occasion to refer later. 

The genus Rhizoctonia includes several forms of 
sterile fungi, all of which are distinguished by their 
manner of growth in pure culture, and by their 
mycelium form. Young hyphse of R. solani Kuhn 
are at first hyaline, then deepen in color from a yellow- 
ish to a deep brown. The young branches are some- 
what narrowed at their point of union with the parent 
hypha and grow in a direction almost parallel to each 
other (fig. 6 b). A septum is also laid down at a 
short distance from the point of union with the par- 
ent mycelium. There is another form of mycelium 
which is made up of barrel-shaped cells, each of which 
is capable of germinating like a spore (fi.g. 6 c, d). In 
pure cultures R. solani produces sclerotia, which are at 
first soft, whitish, and later become hard and dark. 
The fungus is carried over from year to year as scler- 
otia which are able to withstand the efiEect of heat, 
cold, drought, or moisture. 

Parasitic Soil Fusaria 

Next in importance to Rhizoctonia is a group of 
fungi which belong to the genus Fusarium. Lands 
infected with these species of fungi become unfit for 
cabbage, potatoes, tomatoes, etc., causing great finan- 

' Pammel, L. H., Iowa Agr. Expt. Sta. Bui. 15: 244-251, 1891. 




Fig. 7. FusARiuM Wilt. 

a. Early stage of Fusarium wilt of sweet potato, 6. sweet potato hill killed 
by Fusarium wilt, c. spores of Fusarium batatatis, d. spores of Fusarium hyper- 
o.xysporum, e. chlamydospores of Fusarium (c. and d. after Harter). 



Soil Sickness Due to Parasites 47 

cial losses to the trucker. We will take up the specific 
troubles in studying each of these crops respectively. 
As an illustration of a typical Fusarium-sick soil we 
will consider the wilt of sweet potatoes. 

Wilt or Yellows of the Sweet Potato 

Caused by Fusarium hatatatis Woll. and F. hyper- 
oxysporum Woll. 

Symptoms. The first indication of sweet potato 
wilt is a slight difference in the color of the foliage 
in the affected plants. The leaves become dull, then 
yellow between the veins and slightly puckered ; this 
is followed by the wilting of the affected vines (fig. 
7 a). If one of these vines be split open at the stem 
end, the interior of the woody portion will be found 
blackened. All parasitic soil Fusaria invade the 
interior of the water or fibro-vascular bundles which 
are situated in the woody tissue of the stem. Wilting 
and death of the plant follow (fig. 7 b). 

The morphology of Fusarium is identical in m.any 
species. They differ only from a pathological point 
of view, and in peculiarity of certain colors produced 
on media in pure cultures. Pathologically, many of 
the species are distinct. The Fusarium of the sweet 
potato wilt cannot, as far as we know, attack potatoes, 
tomatoes, or any other host. This is similarly true 
for the Fusarium which produces a wilt on tomatoes, 
etc. The mycelium of Fusarium is hyaline, septate, 
and branched. The spores are sickle-shaped and 



48 Diseases of Truck Crops 

very characteristic (fig. 7 c, d). Some Fusaria also 
produce chlamydospores or resting spores, by which 
the fungus is carried over winter (fig. ye). As far as 
we know the wilt-producing Fusaria do not form a 
winter or ascus stage. They are carried over as 
mycelium, or chlamydospores, in dead plants and in 
the soil. 

2. Soils Rendered Sick by Certain Forms 
OF Animal Life 

The present discussion deals with the root knot, a 
disease produced by a little worm generally known as 
nematode, or eel worm. 

Root KInot 

Caused by Heterodera radicicola (Greef) Mull. 

Root knot is most prevalent in light soils. This, 
however, does not exclude it from heavier lands where 
it may sometimes be found. The trouble is most 
widespread in the Southern States, where the winter 
is mild. In unprotected places in the North its 
numibers are probably greatly reduced each winter. 
The annual financial losses from this disease are 
staggering in extent. With proper culture and fer- 
tilization, however, a crop may be produced with 
practically very little loss where neglect would have 
caused a total failure. This is especially true under 
greenhouse conditions. 




Fig. 



Nematode Root Knot. 



a. Root knot of Irish potato, b. root knot of onion, c. root knot of parsnip, d. 
egg of nematode, Heterodera radicicola, e. young female worm, /. half-grown female 
worm, g. young male worm, h. matured male worm ready to emerge from old body 
covering, i. matured female worm (d. to i. greatly enlarged, after Stone and Smith). 



Soil Sickness Due to Parasites 49 

Symptoms. The disease is characterized by a 
swelling on the roots, showing itself in small knots 
formed either singly or in pairs, or in strings, giving 
the affected root a beaded appearance (fig. 8 a, b). 
Sometimes, however, the swellings are so large that 
they may be mistaken for the root nodules (fig. 8 c) 
of legume plants, which occur normally in great 
abundance. Infested plants usually linger for a long 
time, but they can be distinguished by a thin growth 
and yellow sickly looking leaves and stems. 

Distribution. The eelworm seems to be of world- 
wide distribution, being found in Europe, Asia, 
Australia, and both North and South America. 
And yet, there are many localities in which this pest 
has never been known. 

Life History. The eelworm is a very minute worm, 
seldom exceeding one twenty-fifth of an inch in 
length. It is semitransparent, so that it cannot be 
easily detected by the naked eye. In searching for the 
eelworm, break a fresh knot. Close examination will 
reveal two types of worms: a spindle-shaped worm, 
the male (fig. 8 g, h), and a pearly white pear-shaped 
organism, the female (fig. 8 e, f), firmly embedded in 
the gall tissue. The female is very prolific, depositing 
no less than 400 to 500 eggs during her lifetime. 
The eggs are whitish (fig. 8 d), semitransparent 
bean-shaped bodies, and too small to be noticed 
without the aid of a magnifying glass. The time 
which elapses until the eggs hatch depends largely 
upon weather conditions. In warm days the eggs 
hatch sooner than in cold days. Upon hatching, the 



50 Diseases of Truck Crops 

young larvae either remain in the tissue of the host 
plant in which they have emerged, or, as is more often 
the case, leave the host and enter the soil. This is 
the only period during which the worms move about 
to any great extent in the soil, where they either 
remain for some length of time or immediately pene- 
trate another root of the host. The nematodes in 
most cases become completely buried in the root 
tissue, establishing themselves in the soft cellular 
structure which is rich in food. The head of the 
worm is provided with a boring apparatus consisting 
of a sharply pointed spear, located in the mouth. 
This structure not only aids it in getting food but is 
also valuable in helping the young worms to batter 
through the cell walls before becoming definitely 
located. The two sexes during the development are 
undistinguishable up to fifteen or twenty days, both 
being spindle-shaped. In the molting or shedding 
of the skin, there is a marked change in the case of 
the female, especially in the posterior region of the 
body, which no longer possesses a tail-like appendage. 
Fertilization occurs soon after this molt, and many 
radical changes occur in the shape and structure of 
the organization of the worm. The fertilized female 
increases rapidly in breadth and becomes a pearly 
white flask- or pear-shaped individual (fig. 8 i). 
At this stage it is far from being wormlike and may, 
therefore, be overlooked by one unfamiliar with the 
life-history of the eel worm. The adult male is much 
like that of the young female larvae, being spindle- 
shaped in outline. The male does not cause as much 



Soil Sickness Due to Parasites 51 

damage to the root tissue as the female, and its pur- 
pose in life seems to be only that of fertilizing the 
female, for after this function has been performed, 
it is quite probable that the male worm takes no 
more food. 

Omnivorous Nature oj the Eelworm. There are 
almost five hundred species of plants known to 
suffer from the eelworm. This number includes 
all the important families of the flowering plants. 
According to Bessey^ the following are among the 
plants subject to root knot : 

a. Truck Crops. Asparagus, bean, beet, cabbage, 
carrot, cauliflower, celery, chicory, cucumber, dill, 
eggplant, endive, gourd, Jerusalem artichoke, leek, let- 
tuce, muskmelon, mustard, okra, onion, parsley, pars- 
nip, pea, pepper, potato, pumpkin, radish, rutabaga, 
salsify, shallot, Spanish oyster plant, spinach, squash, 
sweet potato, tomato, turnip, watermelon, yam. 

h. Garden Weeds. Birdsfoot trefoil, burdock, car- 
petweed, dandelion, dead nettle, Florida beggarweed, 
horse nettle, lamb's-quarters, mayweed, milkv^^eed, 
nightshade, pigweed, plantain, pokeweed, ribgrass, 
shepherd 's-purse, sheep sorrel, snow thistle, wild 
morning-glory. 

From the above large list of susceptible hosts, it 
is evident that the trucker cannot afford to permit 
infestation of his land. Once a soil becomes sick 
because of the presence of eelworm there is very 
little range left in the choice of a crop. 

' Bessey, E. A., U. S. Dept. Agr. Bureau PI. Ind. Bui. 217 : 
7-89, 191 1. 



52 Diseases of Truck Crops 

Soil-Infesting Insects 

Soils infested with insect pests are as sick as when 
infested with eel worm or parasitic fungi. The 
trucker, in sowing his seed, has often great difficulty 
in obtaining a good and even stand. The frequent 
reso wings invariably result in late crops, and this 
means heavy money losses. Frequently the stand 
is reduced by fifty per cent, in spite of the many 
resowings. The cause of this may be traced to the 
presence in the soil of certain insect pests. Among 
those dreaded most by the trucker and gardener are : 
Cutworms (A gratis sp.), {Lycophotia sp.) , {Peridroma 
sp.), wireworms {Melanotus sp.), and white grubs 
(Phyllophaga sp.). 



CHAPTER IV 

METHODS OF TREATING SICK SOILS 

^Damping off, whether induced by Pythium, Rhi- 
zoctonia, or any ®ther parasitic organism, is usually 
confined to seedlings in the seed bed, under cover or 
in the open. The loss of seedlings not only means a 
waste of seeds, but it also results in late crops. 
Growers are usually in the habit of using the same 
soil in the seed bed, year in and year out. This prac- 
tice cannot be encouraged, since contamination of 
the seed-bed soil is bound to take place. The dis- 
ease-producing organisms are usually brought in 
with the manure. A number of truckers make it a 
practice to empty their beds and fill them with fresh 
soil. This, unfortunately, is not always a safe 
method, for the reason that the new soil too may 
be contaminated, or that it may become infected 
as soon as it is placed in the bed previously con- 
taminated. Sick seed-bed soils may be freed from 
damping off in various ways. 

Formaldehyde. When steam sterilization is not 

feasible because of the absence of a steam boiler, the 

formaldehyde treatment is the next best. With this 

treatment we may control Fusarium, Rhizoctonia, 

53 



54 Diseases of Truck Crops 

and Pythium in infected beds. It is doubtful, 
however, if this treatment will entirely eradicate eel- 
worms from infested soils. The method is as fol- 
lows: the beds are thoroughly prepared in the usual 
way, and then drenched with a gallon per square 
foot of formaldehyde solution composed of one pint 
of commercial formaldehyde (40% pure) to thirty 
gallons of water. The solution should be put on with 
a watering can and distributed as evenl}:^ as possible 
over the bed, so as to wet the soil thoroughly to a 
depth of a foot. It will, in most cases, be necessary 
to apply the solution two or three times, as the soil 
may not absorb the full quantity of the liquid at one 
time. After the treatment the beds should be cov- 
ered with a heavy burlap to keep in the formaldehyde 
fumes for a day or two, and then aired for a week 
before planting. Stirring the soil at once would help 
the escape of the fumes. Formaldehyde m.ay be 
bought in any drug store 40% pure. 

Steaming. This method of treatment is far supe- 
rior to any other yet evolved. For seed beds on a 
large scale the inverted pan method is the best. This 
was first devised by A. D. Shamel of the U. S. De- 
partment of Agriculture. The boiler must be able to 
generate a pressure of not less than eighty pounds, 
which should be maintained for at least one and a 
half hours. In setting a pan the rim is sunk into the 
soil of the seed bed, to a depth of two to three inches, 
to make the inclosed chamber steam tight. In 
heavy soil, trenching may be necessary. It is also 
advisable to put a heavy weight on the pan when the 




Fig. 9. Inverted Pan for Steam Sterilization. (After Selbv.) 




10. Surface Watering. Showing Portable Spray Equipment 
Used in Gardens about Cold Frames and Hot Beds. 
(After Williams.) 



Methods of Treating Sick Soils 55 

steam operates. When one pan is used, a traction 
engine or a portable boiler of ten to twelve H. P. 
will suffice. While the standard size of the pan is 
six by eight feet, the dimensions may be modified 
to suit the size of the seed beds. 

Selby and Humbert' describe the method of con- 
structing an inverted (fig. 9) pan as follows : 

"Material used for construction of a pan is gal- 
vanized sheet iron; the most useful weight is No. 20 
gauge, which weighs 26.5 ounces per square foot. 
The heavier material requires little in the way of 
frame supports. The galvanized iron sheets come in 
sizes varying from two to three feet in width by eight 
to ten feet in length. Figure 9 shows a pan 6 x 10 
feet in size, 6 inches deep, constructed from five such 
strips 2^x8 feet in size. These sheets are joined by 
double-fold seam and riveted at intervals of 6 to 10 
inches to make the pan steam tight. This pan is 
further strengthened by a band of strap iron 2x1 inch 
riveted to the bottom edge, and stiffened by a brace 
oi 1)4 inch angle iron across the top and extending 
down the sides. This is bolted at the sides to the 
supporting strap iron stiffener. The corner illustra- 
tions show at 'A' the joint used for the galvanized 
iron sheets, and ' B ' a section of the angle iron sup- 
porting the top. 

"The entrance pipe for the steam may be placed 
at the side or end of the pan {see dotted construction 
lines oj fig. g) or may enter from the top as per illus- 

' Selby, A. D., and Humbert, J. G., Ohio Agr. Expt. Sta. Circ. 151 : 
65-74. 191 5. 



56 Diseases of Truck Crops 

tration. The latter form has the advantage in 
that it will not interfere with the box boards when 
used on frames. The pipe, after entrance, should 
be a T form, so that steam in being forced into 
the pan when in place does not blow holes in the 
soil." 

Surface Firing. This method of soil sterilization is 
used only in the absence of steam facilities or where 
formaldehyde cannot be obtained, which, however, 
is seldom the case. It consists simply in producing 
a hot fire for an hour or more over the bed to be ster- 
ilized. A combustible material such as brush, straw, 
or wood may be used for that purpose. The objec- 
tion to it is that the fire may destroy the organic 
matter in the soil. 

Roasting or Pan Firing. In this method the soil 
to be sterilized is removed from the bed and placed 
in a pan, underneath which fire is present. After 
roasting the soil is returned to the bed and more 
of it sterilized. This method is too slow and is 
open to the same objection as the surface burning. 
The advantage of steam sterilization and of the 
"fire" methods consists in the destruction of all 
weed seed, together with the fungi which cause 
damping off. 

Other Methods oj Control. Damping off may be 
largely controlled by careful cultural conditions. 
Unless the soil of the seed bed is to be sterilized, it 
is never wise to sow the seeds in beds where damping 
off was known to have occurred previously. Thick 
sowing especially should not be permitted. In 



Methods of Treating Sick Soils 57 

Table 8, Johnson' presents some interesting data on 
the effect of thick sowing on damping off. 

Table 8 
Effect of Thick Sowing on Percentage of Diseased Plants. 



Flat No. 


Weight of seed sown 


Plants Diseased 


per flat 


per 100 sq. ft. 




Crams 
0.1 
0.2 

0.3 
0.4 

0.5 
0.6 
0.7 
0.8 
0.9 

I.O 


Ounces 
0.16 
0.33 
0.49 
0.66 
0.83 
0.99 
1. 16 

1-33 
1.49 
1.60 


Per cent. 






■1 


8 


4.. 


15 
35 


i. 


7 


8 


80 




92 
96 







Certain soils are especially favorable to damping 
off. Soils which contain a high percentage of un- 
rotted vegetable matter and those which are hard to 
drain need especial attention. Great care should be 
taken that the seed bed is kept at the right tempera- 
ture. The latter cannot be guessed at by personal 
sensation. It should be accurately determined by 
thermometers placed in the bed at suitable distances. 
It should also be remembered that any covering cloth 
or sash will exclude light and air. Every precaution 

•Johnson, James, Wisconsin Agr. Expt, Sta. Research Bui. 31: 
31-61, 1914. 



58 Diseases of Truck Crops 

should be taken to prevent the seedHngs from be- 
coming "drawn," for at that stage they are most 
susceptible to damping off. The safest plan is to 
keep the temperature a trifle lower than is gener- 
ally required, and allow as much ventilation as 
possible. Very often damping off starts in one 
corner of the bed. To check the rapid spread of the 
disease, the infected area miay be removed. Spray- 
ing the seedlings with various fungicides in a bed 
where damping off has become well established will 
be of little help. 

Control of Fusarium- and Nematode-Sick Soils 

The formaldehyde or the steam sterilization meth- 
ods which are so effective in the treatment of sick 
seed beds cannot be used on a large scale for sick 
soils on account of the extensive cost involved. The 
trucker, therefore, must resort to other methods of 
control. Soils which are made sick by the presence 
of parasitic fungi or nematodes may be reclaimed by 
crop rotation as well as by the development of wilt- 
resistant varieties. Both of these methods will be 
discussed at length in pages 372, 373. 

Control of Insect-Infested Soil 

Spraying the soil will be of little value in the control 
of underground insect pests. Fortunately, however, 
we have more effective means for dealing with them. 
To destroy wireworms, sow corn which has been 



Methods of Treating Sick Soils 59 

soaked for ten days in water containing arsenic 
or strychnine sulphate before planting the regular 
crop. The larvse will feed on the poisonous corn 
kernels and die. Another way is to treat the seed 
with gas (coal) tar. 

White grubs may be controlled by the use of bisul- 
phide of carbon. Fall plowing is a valuable remedy, 
since many of the grubs are thus exposed to the cold 
winter weather and killed. 

Cutworms may be controlled by the use of a 
poisoned bran made as follows: to three ounces of 
molasses add one gallon of water and sufficient bran 
to make a fairly stiffened mixture. To this add Paris 
green or arsenic and stir well into a paste. A heap- 
ing teaspoonful of the mixture is scattered here and 
there over the infested land. 



PART II 



6i 



CHAPTER V 

THE HEALTHY HOST AND ITS REQUIREMENTS 

We have seen that soil is the medium in which 
plant life is made possible. We have also seen 
that to produce good yields in crops it is essen- 
tial to have a healthy soil — a condition directly 
dependent upon the work of friendly organisms. 
When these perform their work imperfectly, or 
when the soil is overrun by parasitic fungi or 
by pestiferous animal life, the soil is considered 
sick. 

Let us now consider the plant itself, since 
practically and economically it is the crop 
that concerns us most. We are interested in 
the soil only in so far as it is capable of main- 
taining economic crops. The general needs of 
plant life are the same to a striking extent for 
higher plants and for the lower microorganisms 
of the soil. 

Need of Air 

Plants must breathe, since air is indispensable 
63 



64 Diseases of Truck Crops 

for all life. Plants breathe through their leaves, 
and, according to Whitney, ^ through the roots also. 
Hence, cultivation is necessary not only to supply 
air to the microorganisms in the soil, but also to 
the roots of the crop. In the opinion of Whitney, 
cultivation accomplishes a step further; by 
stirring the soil we permit the escape of foul gases 
given off by the plant roots as well as by the soil 
organisms. 



Need of Water 

Plants to live must drink. This is one of 
the most important considerations from the 
trucker's point of view. It is generally sup- 
posed that roots are fixed things in the soil, 
receiving water and food material by capillary 
action. This occurs only in very moist and 
saturated soils. However, in dry seasons and 
in dry soils the roots have to move down- 
ward towards the water. This may be proved 
by a simple ingenious experiment described by 
Whitney. "If you take some soil from the 
field with what we call an optimum amount of 
moisture, or the best amount for plant growth, 
put it in a tumbler, filling the tumbler about 
half full, and put some dry soil on the surface, 

* Whitney, Milton, U. S. Depart, of Agr. Farmers Bui. 257 : 
5-35, 1909- 



Healthy Host and Its Requirements 65 

you can see the difference in moisture contents 
by the difference in color, the moist soil being 
darker than the dry. Then, if you cover the 
tumbler to prevent evaporation you can leave 
the dry soil in contact with the moist soil and 
there will be no appreciable interchange of mois- 
ture between the moist and the dry layers. This 
simple experiment demonstrates that if cultiva- 
tion is also to conserve the soil moisture, we 
must always strive to form a pulverized dry 
mulch on top. Capillary action practically ceases 
when a dry mulch or layer is found on top of the 
soil." 

From the trucker's point of view, the water re- 
quirement of crops deserves careful consideration. 
In intensive gardening the water supplied by natural 
precipitation of rainfall cannot always be depended 
upon for crop production, and must be supplemented 
by irrigation. In fact irrigation is often a funda- 
mental requirement, if we are to meet in a timely way 
the demands of the market. Irrigation when prop- 
erly carried out may mean success, and the opposite 
total failure. To be what farmers call a "water 
hog," using too much water, is detrimental to the 
crops, for they are very sensitive to an excess of it. 
Widtsoe and Merrill ' have shown that the yields of 
truck crops directly depend on the proper amount of 
water supplied. The result of their investigation is 
shown in Table 9. 

' Widtsoe, J. A., and Merrill, L. A., Utah Agr. Expt. Sta. Bui. 117: 
69-119, 1912. 

S i 



66 



Diseases of Truck Crops 



Table 9 

The Yields oj Trtick Crops as Harvested, with Different 
Quantities of Water 

Yield of crops is expressed in lbs. per acre; quantities of water used 
are expressed in acre-inches. ' 



1. Irrigation water supplied 

2. Rainfall and soil water . . 

3. Total water for use of 

crop 

4. Total yield of carrot; 

(lbs. per acre) 

5. Yield per inch of irriga 

tion water 

6. Yield per inch of total 

water 



3-75 
10.25 


7-50 
10.25 


15.00 
10,25 


25.00 
10.25 


35-00 
10.25 


14.00 


17-75 


25-25 


35-25 


45-25 


34577 


33223 


49507 


46755 


56930 


9221 


4430 


3306 


1871 


1627 


2469 


1872 


1963 


1326 


1258 



60.00 
10.25 

70.25 

68420 
1 129 
974 



1. Irrigation water supplied 

2. Rainfall and soil water 

3. Total water for use of crop. . . . 

4. Total yield of cabbage (lbs. per 

acre) 

5. Yield per inch of irrigation 

water 

6. Yield per inch of total water.. . 



12.50 

5-54 
18.04 


20.00 

5-54 
25.54 


25.00 

5-54 

30.54 


40.00 

5-54 
45-54 


18490 


18524 


16310 


20432 


1479 
1025 


926 

725 


652 

534 


511 
449 



70.00 

5-54 

75.54 

23098 

330 
306 



1. Irrigation water supplied 

2. Rainfall and soil water 

3. Total water for use of crop 

4. Total yield of onions (lbs. per acre) 

5. Yield per inch of irrigation water.. . 

6. Yield per inch of total water 



15.00 


20.00 


30.00 


5.54 


5-54 


5.54 


20.54 


25-54 


35-54 


2I47I 


22038 


32437 


1432 


1 102 


1098 


1045 


863 


913 



65.00 

5-54 
70.54 
34171 

526 

484 



» The term acre-inch means the quantity tltet will cover one acre to 
the depth of one inch. Likewise in speaking of an acre-foot of water, 
it means the water necessary' to cover one acre to a depth of one foot. 



Healthy Host and Its Requirements 67 

A careful study of Table 9 shows that excessive 
watering results in a decrease of yield. Widtsoe and 
Merrill in their work on sugar beets found that when 
30 acre-inches of water is spread over one acre 30 
inches deep, the yield was 20.82 tons. When this 
same amount of water was spread over two acres 
and for a depth of fifteen inches, the yield increased 
to 38.90 tons per acre. Finally when the 30 acre- 
inches of water were spread over six acres and five 
inches deep, the yield increased to 82.68 tons per 
acre. Every trucker should study the water require- 
ments of the crops under his conditions of soil and 
climate. To obtain the best results from irrigation 
we must be familiar with the root system of each 
particular crop and the depth to which it normally 
penetrates the ground. 

Methods of Irrigation. There are two methods of 
watering recommended. Each trucker can determine 
for himself which of the two will give him the best 
results under his particular conditions. 

{a) Suhirrigation. As this implies, the water is 
applied underground and through perforated pipes. 
The conditions necessary for suhirrigation are a clay 
subsoil or a hardpan capable of retaining the irriga- 
tion water. The topsoil must be of a sandy loam, 
neither too loose nor too compact. The land must 
be of a nature to admit of perfect drainage, having 
a fall of one inch to each one hundred feet. The land 
must also be level without raised places. Where 
these conditions cannot be fulfilled, suhirrigation 
will prove a failure. The crops that are best bene- 



68 Diseases of Truck Crops 

fited by subirrigation are celery, lettuce, and Irish 
potatoes. Tomatoes, watermelons, cantaloupes, or 
sweet potatoes are not benefited by it. 

The advantages claimed for subirrigation are many : 
(i) The moisture is better controlled in the soil and 
the roots will have easy access to it. (2) No crust 
is formed to shut out the air from the soil, or to fa- 
vor the development of fungous diseases. (3) The 
soluble salts and fertilizers are not washed down 
deeply and are not carried beyond the reach of the 
roots. 

(b) Surface or Spray Irrigation. As this implies, 
water is applied on the surface overhead, in the form 
of rain (fig. 10). The many advantages claimed for 
this system are as follows : (i) For the same volume of 
water a much larger area may be irrigated, or the 
same area may be watered with a smaller quantity of 
water. (2) Very little skilled labor is necessary in 
this system. (3) Large areas for irrigation can be 
rapidly covered. (4) The rain effect will control 
frosts. (5) There are no leaky wasteful channels, and 
no boggy roads. (6) An economy of land in channels 
and ditches. (7) Spray irrigation is independent 
of the topography of the field, and may be extended 
to lands too rolling or rough for subirrigation. 
Truckers in the arid sections seem in favor of a com- 
bination of spray and surface irrigation on the same 
field. The spray is used in preparing the seed bed, 
germinating the seeds, and for newly set out plants. 
Later, as the crop advances in age, especially during 
blossoming and fruiting, irrigation is carried out by 



Healthy Host and Its Requirements 69 

surface furrow or check methods. A portable 
spray equipment meets these conditions well. The 
disadvantage of this system like that of rain is the 
baking of the surface soil, thereby necessitating more 
frequent cultivations. Moreover, when spray ir- 
rigation is overdone it is likely to encourage the 
development of mildews and various leaf spots. 

Need of Sanitary Environments 

Science has shown us the reasons for sanitary liv- 
ing for men and animals and equally for plants. 
Since the soil is the home of the plant, we must keep 
that soil as clean as we do our houses, or the stalls in 
stables. The soil organisms give off numerous poison- 
ous excreta, which become harmful to them and to 
the crops. Through their own activities, the roots of 
plants, too, throw off certain poisonous excreta. If 
they are allowed to accumulate in the soil through 
growing the same crop too long in the same soil, a 
point is reached where that crop will refuse to grow 
there any longer, even if there is no evidence of soil 
exhaustion. The best purifier of soils is organic 
matter applied as manure or green vegetable matter 
which is converted into humus. 

Clean Culture. There are two other means by 
which we can keep soils in a sanitary condition. 
Rotation of crops is discussed on page 372. Clean 
culture, too, is an essential means of safeguarding 
the health of our economic plants. Not only do 
weeds help to carry fungous diseases which are also 



70 Diseases of Truck Crops 

common to crops, but they too excrete certain poisons 
into the soil which become harmful to the crop in 
the company of which they grow. Moreover, weeds 
rob the soil of vast quantities of water which other- 
wise would be utilized by crops. This is an important 
consideration where irrigation is not practiced ex- 
tensively and in the more arid regions. 



CHAPTER VI 

CAUSES OF DISEASES IN CROPS 

It is, indeed, very difficult to define the term dis- 
ease. Health and disease are only relative terms, and 
it is not easy to draw a line where health leaves off 
and disease begins. Disease, however, may be ap- 
plied to all deviation from the normal which threatens 
the life of the plant. Perhaps the nearest conception 
of health and disease is that of Marshal Ward, who 
says: "If we agree that a living plant in a state of 
health is not a fixed and unaltering thing, but is ever 
varying and undergoing changes as its life works out 
its labyrinthine course through the vicissitudes of the 
ever-varying environment, then we cannot escape the 
conviction that a diseased plant, so long as it lives, 
is also varying in response to the environment. The 
principal difference between the cases is, that whereas 
the normal healthy plant varies more or less regu- 
larly and rhythmically about a mean, the diseased 
one is tending to vary too suddenly or too far 
in some particular direction from the mean. The 
healthy plant may, for our present purposes, be 
roughly likened to a properly balanced top spinning 
regularly and well, whereas the diseased one is lurch- 
71 



^2 Diseases of Truck Crops 

ing here, or wobbling there, to the great danger of its 
stabiHty. For we must recognize at the outset that 
disease is but variation in directions dangerous to the 
life of the plants. That the passage from health to 
disease is gradual and ill-defined in many cases 
will be readily seen." Excluding the injury from 
insect pests, the diseases of truck crops may be con- 
sidered as follows: 

A. Diseases of a Mechanical Nature 

Diseases brought about by mechanical injuries are 
very numerous and varied. Truck crops such as 
spinach, lettuce, etc., are cultivated for their edible 
tender parts. It is not strange that such crops should 
be susceptible to injuries of a mechanical nature. 

WIND STORMS 

Wind storms are often the cause of great losses to 
the trucker. This is especially the case in soil dis- 
tricts of a sandy nature. Strong -wdnds cause the 
sand to be thrown about in the field with consider- 
able force and velocity. The small sand particles 
blown violently on plants cut the foliage and not 
infrequently the fruit too. Tomatoes, watermelons, 
eggplants, in fact, all the tender crops, suffer greatly 
from sand or dust storms. Besides this form of 
injury, dust or sand storms carry off large quantities 
of fertilizer. Moreover, sick particles of soils may 
be carried by the wind from farm to farm, and in this 



Causes of Diseases in Crops 73 

way soil diseases be spread. Wind storms cannot 
well be prevented. Perhaps the best safeguard is 
never to allow bare spaces in the field, and to have 
the soil thoroughly covered with vegetation. In 
windy localities, crops should be planted closer than 
is generally the custom. 

RAINSTORMS 

Heavy rains when pounding on tender plants may 
cause considerable damage in tearing tender foliage. 
Another indirect injury is the pounding and packing 
of the soil. This shuts out the free circulation of air 
and is bound to interfere with the normal metab- 
olism of the plant. Heavy rains by pounding on the 
soil, splash mud and sand on all parts of the plant. 
This encourages infection of numerous diseases, and 
reduces the shipping and market value of the crop. 

Besides rainstorms, frequent showers are detri- 
mental to truck crops cultivated for their fruit or 
seed. They prevent pollination by insects. There 
is, of course, no feasible method of preventing un- 
favorable weather conditions. Deep plowing may 
encourage the absorption of all the rain and prevent 
baking. Windbreaks too may protect crops from 
severe storms. 

HAILSTORMS 

The injury to truck crops from this source is con- 
siderable. It results in deep bruises or cuts in stem, 



74 Diseases of Truck Crops 

foliage, and fruit. The writer knows of cases where 
large areas of tomatoes, cantaloupes, and waterm jlons 
were totally ruined by hail. With the sweet potato 
hail does not always ruin the crop, but it retards it. 
The foliage and vines dry up as a result of the me- 
chanical cutting and bruising from hail, but new 
growth soon follows. Even when hail does not ruin 
a crop, there is danger of infection at the place of 
each cut or bruise (fig. ii). If the affected crop 
is valuable and shows promise of recovery, it should 
be sprayed with a good standard fungicide. 

LIGHTNING INJURY 

Injuries to trees from lightning are familiar to 
all. Jones and Gilbert' record an interesting case 
of lightning injury to potato plants. The injury is 
noticed in round spots in the field (fig. 12 a), the 
spots varying from ten to twenty feet in diameter. 
The potato tops appear broken and disheveled 
and upon drying off, within twenty-four hours 
they wilt and die. In examining the individual 
plant we find that the stem collapses and the top 
falls over, the stem browns and shrivels faster above, 
and less rapidly below this point. The pith at this 
region browns and collapses, leaving a hollow stem, 
but without any softening such as usually occurs 
with blackleg. No evidence of splitting or mechan- 
ical rupture of the stem has been observed. Light- 
ning injury may occur when thunderstorms are very 

' Jones, L. R., and Gilbert, W. W., Phytopath. 5 : 94-101, 1915. 




Fig. II. Watermelon Slice Showing Hail Injury. Arrows In- 
dicate Place of Injury Followed by a Rotting Due to the 
Secondary Invasion of Semi-Parasitic Fungi. 



Causes of Diseases in Crops 75 

prevalent, usually during July. It may be found in 
sandy as well as clay loam fields, and the contour of 
the land seems to have no influencing effect. The 
following is Jones and Gilbert's explanation of the 
phenomenon: "When an electric storm breaks sud- 
denly following a period of dry weather and the first 
rain wets the topsoil, there remains a layer of- dry 
earth between this wet surface and the moist soil 
underneath, which is a poor conductor of electricity. 
When the lightning strikes the wet surface spot, it 
disperses in all directions, horizontally and then 
downwards into the earth, following lines of least 
resistance. The plant stems and roots with their 
abundant water content are better conductors than 
the layer of dry soil just mentioned, and so the 
electric current passes through them. The tissues 
may thus be variously injured or killed, depending 
upon the amount of current passing through them." 

FROST INJURY 

The greatest profits in trucking are generally made 
when crops are available for the early market. 
This means that truckers must be prepared to meet 
losses directly due to spells of frost. Not all 
truck crops are equally sensitive to frost, but we 
have as yet no crops which are absolutely frost 
proof. When the temperature at v/hich condensa- 
tion of moisture in the air takes place is below freez- 
ing, ice may form in the intercellular spaces, and 
the plant is then destroyed, without any frost 



76 Diseases of Truck Crops 

deposited on the outside. Equal injury results 
when the exterior of the plant is at or below the 
freezing point, and frost is deposited on the plant. 
It is supposed that in this case the cold does not 
freeze the water in the cells, but draws it out. The 
more sap a plant has, the faster it is withdrawn. 
In this case, then, the plant dies not from cold 
but from drought. 

Frost conditions are determined by various fac- 
tors. Trucking lands situated near large bodies of 
water generally enjoy immunity from frost not found 
in inland localities. Tender crops growing on low 
hills or on greatly sloping hillsides, somewhat above 
the valley floor, are also well protected from frost. 
Lowlands, particularly those which have no outlet 
through which the cold air may drain off, are not 
suited for early trucking because of the danger from 
frost. Lands which are properly drained and cul- 
tivated will not only produce larger yields, but will 
also be protected from frost. 

How to Predict Frost. There are usually several 
signs which the trucker may use as a warning of the 
approach of frost. Frost should be looked for after 
unusual warm spells in the spring. The state of the 
sky is also an indication. Frost is not likely to occur 
when the sky is overcast because the heat given off 
by the earth at night does not easily penetrate the 
clouds and is therefore retained in the air below. 
On the other hand, during clear nights, the earth's 
heat readily escapes and this is likely to result in a 
disastrous drop of temperature. Frost is brought 



Causes of Diseases in Crops 77 

about also by a sudden change from wind to calmness 
of air. Winds prevent frost formation because they 
prevent the accumulation of the colder air at the 
surface. The trend of temperature is also an im- 
portant consideration. A temperature of forty 
degrees at about 6 P. m. with a clear sky may 
indicate the approach of frost. A fall of tempera- 
ture of two degrees an hour in the afternoon would 
also indicate the approach of frost. If the air pres- 
sure is increasing rapidly, as indicated by a rapid 
rise in the barometer, frost may be approaching. A 
change in pressure usually precedes, by a short in- 
terval, the change in direction of wind. 

How to Protect Crops from Frost. Crops may 
be protected from frost in two ways, (i) Arti- 
ficial covering is an old practice widely used by 
truckers, and consists in protecting the plants by 
covering them with newspapers, carpets, sacks, straw, 
tar paper, or a mulch of soil. This, however, is 
applicable only to small gardens or to seed beds. 
On a large scale it is not practical because of the 
labor involved. (2) Smudging and heating consists 
in the burning of any combustible material capable 
of producing heavy smoke, such as moist straw or 
coal tar. Through smudging we prevent the escape 
of the earth's heat. 

A better method consists in heating the air of the 
field by means of evenly distributed small fires gen- 
erally supplied by ovens of various designs. The 
material used is wood, coal, or oil, the choice being 
determined by the local price and supply. With 



78 Diseases of Truck Crops 

the warning from an alarm thermometer which rings 
a bell as the danger point in temperatiire is reached, 
the fires may be started. Smudging and heating are 
extensive^ used by orchardists. Truckers, however, 
have generally been slow to adopt this method. 

Drought Injury 

By drought is meant a scarcity of water in the soil, 
affecting and preventing the normal life process of 
plants. Drought injury is variously indicated by 
different crops. With beans, for instance, the leaves 
lose their chlorophyll, and the entire plant becomes 
whitish, brittle, dead, and dry. With cabbage, on the 
other hand, the tips of the lower leaves first bleach, 
then wilt, eventually drying and falling off. With 
sweet corn the plants shrivel and bend over (fig, 
12 b). The amount of injury from drought is pro- 
portional to the scarcity of the water in the soil. 
The only remedy for drought is, of course, irrigation. 
This is especially true for arid and semi-arid regions. 
Trucking is never safe unless provisions are made 
for proper irrigation. 

Smoke Injury 

As a rule, trucking centers are situated near large 
cities, which are usually centers for industrial pro- 
duction and manufacture. Truckers who are situ- 
ated nearest to manufacturing plants are apt to lose 
in crops from the effect of smoke and deleterious gases 
that escape from the furnaces into the air. 








Fig. 12. 

a. Lightning injury, showing killed spot in potato field, 1/ 
drought injury of sweet corn (.J. after Jones and Gilbert). 



Causes of Diseases in Crops 79 

The sources of smoke may be classified into 
three divisions: (i) Smoke from large buildings or 
from manufacturing plants. (2) Smoke from loco- 
motives. (3) Smoke from chimneys of dwelling- 
houses. Smoke is generally produced because of 
improper furnace construction, improper draft, 
overloaded boiler, insufficient air space, insufficient 
air supply to boiler room, and finally carelessness of 
operation. 

Smoke contains large quantities of carbon dioxide, 
steam, and sulphur dioxide, besides its characteristic 
soot. The latter consists of carbon, tar, and mineral 
matter mixed with small quantities of sulphur, 
arsenic, and nitrogen compounds which are of an 
acid nature. Soot adheres to plants, especially to 
foliage, giving these a burned, contorted appearance. 
Another effect of soot and smoke is to close up the 
stomata or respiratory openings of the leaf, which 
results in asphyxiation. The effect of smoke on 
plants is loss of leaflets in case of compound leaves, 
and abnormal vegetation because of curling and 
distortion. Lesions and spots may be formed on the 
foliage as a result of the sulphur dioxide which is 
present in smoke. The spots are at first small, but 
soon enlarge and finally involve the whole leaf, which 
dries and becomes gray. Smoke injury, although of 
a mechanical nature, may also be considered from 
a physiological point of view. The after effect of 
smoke on plants resolves itself into a question of in- 
sufficient food supply and assimilation. This is 
indirectly brought about by diminished illumination, 



8o Diseases of Truck Crops 

interference with the normal transpiration, and the 
reduction of leaf surface. 

It seems that not all truck crops are equally sub- 
ject to smoke injury. Potatoes seem to be very sen- 
sitive to its effect, while peas are the most resistant. 

Methods of Control. There is as yet no definite 
method of control known. All that the trucks can 
do is to avoid the smoke belts. The greatest in- 
jury occurs in the line of the general direction of the 
winds. These areas therefore should be avoided. 
As far as possible, irrigation should be postponed 
during windy days. The injury from the smoke is 
greatest when the soil is wet. Truckers have a 
right to expect reimbursement in case of loss from 
smoke injury, when the offending factory is set up 
subsequent to the trucker's settlement in that place. 

B. Diseases Due to Physiological Causes 

In this class are included disturbances which are 
due to unfavorable conditions of nutrition. There 
are numerous diseases of plants which are brought 
about by lack of, or by an excess of, certain food 
elements in the soil. The effect is an interference 
with the proper life functions of plants. 

MALNUTRITION 

Caused by improper food supply. 
Symptoms. The symptoms of malnutrition are 
not always the same. They differ somev/hat with 




Fig. 13. Malnutrition, Showing a 
Cabbage Leaf Affected by the 
Disease. (After Harter.) 



Causes of Diseases in "Crops 8i 

the crop, the nature of the soil, and the fertiHzer 
appHed. In malnutrition the symptoms to be 
looked for are retarded growth, change of color in the 
foliage, and root injury. Affected plants remain 
dwarfed at a time when maximum growth is expected. 
The color of the foliage turns lighter green, especially 
in the spaces between the veins (fig. 13) which be- 
come yellowish green to brown. Roots of such 
plants are poorly developed, and secondary roots or 
rootlets are often missing. 

Causes of Malnutrition. The work of Stone ^ and 
Harter^ and others seems to have established the 
fact that malnutrition cannot be attributed to the 
work of parasitic organisms. Stone cites instances 
where constant watering with liquid fertilizers or 
manure would cause malnutrition in cucumber plants. 
The same is also induced when pig and cow manure 
are mixed, or when manure is worked into a soil 
already well fertilized otherwise. Harter records 
cases of malnutrition brought about by an excess of 
acidity in the soil. In cabbage fields suffering from 
malnutrition, it often required from 3500 to 6000 
pounds of lime to neutralize the excess of the soil 
acidity. This condition is apparently the result of 
intensive trucking and the heavy applications of 
chemical fertilizers which leave the soil acid. Sul- 
phate of ammonia, muriate and sulphate of potash, 

' Stone, G. E., Massachusetts Agr. Expt. Sta., Ann. Rept., 5-13, 
1910. 

^ Harter, L. L., Virginia Truck Expt. Sta. Bui. i : 4-16, 1909 
(Norfolk, Va.). 
6 



82 Diseases of Truck Crops 

and acid phosphate when used continuously will 
leave the soil in a very acid condition. On the other 
hand, nitrate of soda, carbonate of potash, and 
Thomas phosphate tend to make the soil alkaline. 

Another important cause of malnutrition is the 
exhaustion of humus. This is a natural result where 
commercial fertilizers are used at the expense of 
any form of organic manure. 

Methods of Controlling Malnutrition. From what 
has already been said, the trucker is the loser if he 
uses his fertilizer injudiciously. Not only is malnu- 
trition favored by such a course, but the yields, too, 
are considerably reduced. For instance, with cab- 
bage, larger yields are obtained when looo pounds 
of commercial fertilizers are used than from any 
higher application. Liming to neutralize the soil 
acidity will help control malnutrition. To overcome 
the humus deficiency of a soil the application of 
stable or green manure is recommended. The 
amount of manure to use will vary with the crop. 
The important thing to guard against is the exces- 
sive use of organic matter. For green manure, 
the iron cowpea is recommended. This variety is 
resistant to wilt, and fairly so to root knot. The 
best time to plow under green manure is generally 
in October when the plants approach maturity. 

BLOSSOM DROP 

This is another trouble which may be termed 
physiological, and the cause of which cannot be 




Fig. 14. Blossom Drop, Showing to the Left a 
Normal Bunch of Tomato Blossoms and Fruit, to 
THE Right most of the Blossoms and Fruit Fallen 

OFF. 



Causes of Diseases in Crops 83 

attributed to the work of parasitic organisms. It 
is often noticed on tomatoes (fig. 14) and beans. 
Various causes may lead to it. A period of warm 
weather accompanied by cool nights, or by sudden 
drops of temperature, will induce many truck crops 
to shed their blossoms. In this case truckers are 
helpless, for weather conditions are not controllable. 
Blossom drop may also be brought about when too 
much nitrogen is applied to the soil in the form of 
manure, hen manure especially. To overcome this, 
the fertilizer in the soil must be balanced by the 
addition of 600 pounds of acid phosphate and 150 
pounds of muriate of potash per acre. 

C. Diseases of Unknown Origin 

MOSAIC 

This trouble extends practically to all parts of the 
host except the roots. To the tomato grower the dis- 
ease is very important, for it may reduce the yield 
of his crop by 50 per cent. 

Symptoms. Mosaic is readily distinguishable by 
a yellow dotting or mottling of the leaf, presenting 
in some instances a beautiful mosaic structure (fig. 
15), whence its name. Affected leaves linger for a 
time, but they eventually lose all of their chlorophyll. 
Another symptom is a curling of the leaves resembling 
the curling induced by green aphids, but in this 
case the insects have no association with it. The 
disease makes its appearance after the seedlings are 



84 Diseases of Truck Crops 

from two to three weeks old, but more often when the 
plants have attained full growth. Often the trouble 
is so serious and the curling so pronounced that the 
plants thus affected cannot make any headway and 
remain dwarfed. An attempt is made by the curled 
plants to produce blossoms, but the latter, too, are 
distorted and abnormal. Frequently, however, the 
affected plants outgrow the disease entirely, and thus 
a distinct line of demarcation is observed between the 
previously diseased part and the healthy part of the 
new growth. In rare cases, affected plants seem to 
thrive in spite of the disease. Such plants should be 
selected for the purpose of breeding resistant strains. 
Cause of Mosaic. The recent works of Allard^ 
and Freiberg^ have shown that the cause of mosaic 
is as yet a disputed question. Allard claims that 
mosaic is caused by an ultra-microscopic pathogen, 
that is, a parasitic organism which cannot be de- 
tected by our present technique in microscopy. 
Freiberg claims that the cause of mosaic is physio- 
logical. The following is a summary of the claims 
advanced by these two investigators. 

Allard Freiberg 

I. The virus is not inhibited i. The virus is not inhibitel 

by concentrations of one part of by formaldehyde, 
formaldehyde in loo, 200, 400, 
600, 800, 1000, 1200, and 1500 
parts of virus solution. 

'Allard, H. A., "Some properties of the virus of the mosaic 
disease of tobacco," Jour. Agr. Research, 6 : 649-674, 1916. 

=" Freiberg, G. W., "Studies in the mosaic diseases of plants," 
Ann. Missouri Bot. Gard., 4 : 175-232, 191 7. 




Fig. 15. Mosaic, vShowing Affected Pea Leaf. 




Fig. 16. Bean Seeds Affected 
WITH Anthracnose, CoUelotH- 
chuin lindemuthianum. 



Causes of Diseases in Crops 



85 



2. The virus is not inhibited 2. Treatment with either 

by either chloroform, carbon chloroform, carbon tetrachloride, 

tetrachloride, toluene, or ace- toluene, acetone or glycerine 

tone. do not destroy the infectious 

properties. 

2a. The infectious properties 
are destroyed by concentrations 
of alcohol which are destructive 
to enzymes. 

3. The temperatures which 
destroy the infectious portions 
are the same as those which affect 
enzymes or hydrolyze some or- 
ganic compounds. 

4. Cooling has no more effect 
on the infectious properties than 
is exerted on any chemical com- 
pound, enzyme included. 

5. Properties of the infective 
principle substantiate the view 
that the infectious substance is 
an enzyme and not a virus. 
This enzyme is not of the nature 
of the oxidases giving the guaia- 
cum reaction. 

6. The reproduction of the 
mosaic enzyme can be accounted 
for on purely physiological 
grounds, but the factors which 
originally induced its formation 
are still unknown. The con- 
tinued production of the mosaic 
enzyme in inoculated plants is 
in accord with the fundamental 
principles of pathology and 
physiology. 

Work of the future will no doubt establish the true 
cause of mosaic. 



3. The virus is quickly killed 
at temperatures near the boiling 
point. 



4. The virus is highly resis- 
tant to low temperatures at 
minus 180° C. with liquid air and 
its infectious properties were not 
weakened. 

5. The cause of mosaic is 
not an enzyme. 



6. The virus is a specific 
particulate substance which is 
not found in healthy plants. 
Since this virus is highly infec- 
tious and is capable of increasing 
indefinitely within susceptible 
plants, there is every reason to 
believe that it is an ultra micro- 
scopic parasite of some kind. 



86 Diseases of Truck Crops 

Mode oj Injection and Period of Incubation. Mosaic 
may be readily transmitted from plant to plant. 
The easiest way to prove this is to rub with the fin- 
gers a diseased plant, and then immediately rub a 
healthy plant. The disease will appear on the in- 
oculated host in about ten days. In the field, insects 
act as carriers of mosaic. The trucker may prevent 
much of this trouble by proper spraying against suck- 
ing and biting insects. 

D. Diseases Due to Parasitic Bacteria or 
Fungi 

We have already seen that certain classes of 
beneficial bacteria perform an important function 
in the soil. This, too, must be true for certain 
soil fungi. Not all microorganisms, however, are 
beneficial. But, fortunately for the trucker, only a 
small per cent, of bacteria and fungi are parasitic, 
and produce disease on plants. On page 4 a 
description was given of the nature and structure of 
bacteria. Before proceeding further it becomes 
necessary to familiarize ourselves with the nature 
of fungi. 

Fungi. As already stated, these are low forms of 
plant life, some of which are beneficial, while others 
live as parasites on the higher green plants, the results 
of which may be considered as follows : 

I. Actual death may result from the destruction 
of vital organs or tissues. 2. A crippling and dwarf- 
ing of plants due to the slow destruction of the root 






Causes of Diseases in Crops 87 

system. 3. Destruction of leaf, flower, and fruit 
without disturbing the root system. 

FACTORS WHICH FAVOR THE SPREAD OF FUNGOUS 

DISEASES 

The amount of soil moisture may either protect 
or predispose a certain crop to fungous disease. 
For instance, in dry seasons and with a limited rain- 
fall, truckers lose heavily from asparagus rust 
{Puccinia asparagi). In this case, the lack of soil 
moisture weakens the plants, making them therefore 
more susceptible to rust. An excess of water, such as 
is found in poorly drained soils, undoubtedly favors 
the spread of damping off, and the numerous 
root rots. Weather conditions exert a powerful 
influence on the prevalence or absence of plant 
diseases. Wet weather favors the spread of 
downy mildews (Peronosporaceas) . Late blight 
of potatoes (Phylophthora infestans), downy mil- 
dew of Uma beans (Phylophthora phaseoli), and 
many other similar diseases, are really wet weather 
troubles. 

HOW PARASITIC ORGANISMS ARE DISSEMINATED 

Fungi may be carried from place to place as bits of 
mycelium, as spores, or as sclerotia. Fungi produce 
enormous numbers of spores, not all of which find 
their way to receptive healthy plants. Large num- 
bers are destroyed by exposure to sunlight and air, 
others fall on crops upon which they are unable to 



88 Diseases of Truck Crops 

thrive, while a relatively small proportion find ideal 
conditions on the proper hosts. 

Wind. If we consider the microscopic minuteness 
of fungous spores we shall appreciate how easy it is for 
winds and air currents to become carriers of these 
spores. 

Water. Water is another important agent which 
helps in carrying and disseminating fungous spores. 
The latter may be actually carried in streams from one 
territory to another, or by rain washing and splashing 
from plant to plant. The spores of Phytophthora in- 
festans, for instance, the cause of late blight of Irish 
potatoes, are spread about from plant to plant by rain. 

Seed-Borne Diseases. A large number of our truck 
crop diseases are introduced with the seed. This 
is often brought about unconsciously or through 
carelessness. Seeds and tubers may carry fungous 
pests as bits of mycelium in the interior tissue. An 
example of this is the bean anthracnose {Colleto- 
trichum lindemuthianum) (fig. i6), which is carried 
as mycelium within the seed. The late blight of the 
Irish potato is carried in a similar way within the tub- 
ers. Seeds and tubers may also carry fungous pests 
as spores or sclerotia which adhere to the exterior of 
the seed coat. The smut of onions, for instance, is 
carried as spores on the onion seed. The Rhizoctonia 
disease of Irish potatoes is carried as sclerotia on the 
surface of the tuber. The same is true for numerous 
other diseases. The methods of prevention of seed- 
borne diseases is taken up on page 99. 

Insects. Little do we realize as yet the importance 



Causes of Diseases in Crops 89 

of insects as carriers and disseminators of plant dis- 
eases. We are becoming increasingly aware of the 
role which insects play in the carrying and dissem- 
inating of human and animal diseases. They are 
equally responsible in distributing plant diseases, 
acting as carriers of spores of parasitic fungi which 
may adhere to any part of their body. Insects both 
by feeding on plants or in searching for the nectar of 
the blossoms are likely to come in contact with dis- 
eased parts of plants. In this way their bodies may 
become coated with parasitic bacteria or spores of 
fungi, which are thus carried from plant to plant and 
from field to field. The striped cucumber beetle, 
for instance, is known to carry and to spread about 
the virus of cucumber mosaic, and the germ of 
cucumber wilt {Bacillus tracheiphilus) . Likewise, the 
Colorado potato beetle is a carrier of the germ of the 
Southern blight {Bacillus solanacearum) of tomato 
and potato. Noxious insects act not only as direct 
carriers of spores of parasitic fungi and bacteria, but 
also induce diseases through the bites and wounds 
which they inflict on plants when feeding. It is there- 
fore very essential that every effort which aims at con- 
trolling fungous pests should also take in consideration 
the control of noxious insects; see page 367. 

E. Diseases Induced by Parasitic Flowering 

Plants 

Fungi and bacteria, as we have seen, are low forms 
of plant life. These derive their food either from 



90 Diseases of Truck Crops 

living green plants and are termed parasites, or from 
dead organic matter and are referred to as sapro- 
phytes. Some higher flowering plants, too, have lost 
the power of manufacturing their own food, and have 
degenerated to the extent of assuming a parasitic 
life. Of those which concern the trucker may be 
mentioned the dodder. 

DODDER {CuSCUta Sp.) 

Dodders or love vines are a group of flowering 
plants which are closely related to the Convolvulus 
or Morning glory family. Dodders are peculiar in 
that they are destitute of the green coloring matter 
chlorophyll, and for this reason must lead a parasitic 
life. The plant obtains food by actually sending its 
own roots into the tissue of the attacked green plant. 

The Parasite. When the dodder seed germinates 
it is at first able to support itself and it then consists 
mainly of a yellow, threadlike stem. This independ- 
ent existence is maintained until the food in the seed 
is used up. By this time the young tendril-like plant 
attaches itself to its host (fig. 17 a, b) and sends in 
suckers or feeders which penetrate the interior tissue. 
The attacked plant naturally becomes weakened and 
may even die as a result of being robbed of its food, 
which is taken up by the dodder. After reaching 
maturity, the parasite blossoms and forms seed in the 
usual way as any other flowering plant. 

Methods of Control. Dodder is often introduced as 
seed mixed in with the seed which we buy. By care- 




Fig. 17. Dodder. 

Dodder on Tomato plant, 6. dodder on onion leaves (after Ilalsted). 



Causes of Diseases in Crops 91 

ful sifting, the dodder seed may be separated out from 
the others. Infested areas should be burned over so 
that the dodder would be prevented from spreading 
and producing seed. In case of large infested spots in 
the field it may be necessary to use drastic measures. 
Each trucker, of course, could best decide for himself 
the cheapest and speediest way of eradicating the pest. 



CHAPTER VII 



POOR SEED 



It has been briefly stated, page 88, that 
seeds can be carriers of various diseases. The 
trucker may also experience difficulty in the germi- 
nation of seeds which may be accounted for in man}'' 
ways. 

Age of Seed. In determining the causes of poor 
germination the age of the seed is to be considered, for 
after a certain age limit deterioration sets in. With 
many species of seeds there are apparently no ex- 
ternal symptoms to indicate loss of vitality due 
to age. Each seed has its own age limit, generally 
determined by the character of the seed itself, i. e., 
whether oily or starchy or lacking in both. Thus the 
vitality of the minute seed of tobacco is perhaps eight 
times as great as that of the large oily seed of the 
castor bean. 

Cultural Conditions. The viability of seed is also 
largely determined^ by the conditions under which 
the previous crop grew. The more vigorous the 
mother plant the more vitality will there be im- 
parted to its offspring. The vigor of the previous 
crop depends on favorable climatic conditions, 
92 



Poor Seed 



93 



care in cultivation and in fertilization. Old seed 
produced in a favorable season may be preferred to 
fresh seed but of an inferior quality, produced in a 
bad season. 

Weight and Color of Seed. As a rule, light weight 
seed is inferior to heavy seed of the same variety. 
The weight of the seed is influenced by culture and by 
imperfect fertilization which results in minute and 
weak embryos. The weight of seed may be readily 
determined by the water method. Place the seed in 
a tumbler filled with water. After shaking and let- 
ting it stand for a few minutes, the heavy ones sink 
and the light ones float. Using this method. Stone' 
has shown that the heavy sinking seed give a higher 
per cent, of germination than the lighter (see Tables lo 
and ii). 

Table io 
Showing the Results of Seed Separation by the Water Method 





No. of Seeds Germinated 




Name of Seed 




Per Cent, of Increase in 






Germination of Light 




Light 


Heavy 


over Heavy Seed 


Lettuce 


68 


90 


32. 


Onion 


lOO 


117 


17- 


Onion 


38 


85 


142. 


Lettuce 


44 


88 


100. 


Onion 


50 


58 


17- 


Average 


60 


87 


61. 



' Stone, G.E., Massachusetts Agr.Expt.Sta. Bui. 121 :3-i4, 1908. 



94 



Diseases of Truck Crops 



Table i: 



Showing Results of Seed Separation by the Water Method 

on Germination and Growth of Seeds of Oniofis. 

Total of 400 Seeds Used 



Per Cent, of Germination 


No. of 
Plants 


Wt. of Plants 
{grams) 


Per Cent, of Increase 
of Heavy over 




Total 


Average 


Light 


Heavy (sank) 45.5 
Light (floated) 19.5 


85 


18.1 
5-9 


.213 
•155 


37-42 



The color of the seed does not seem to have any 
influence on the germination. Darker colored seed 
is usually preferred to the lighter of the same variety. 
Color, however, depends largely on the degree of 
ripeness. 

Storage Conditions. The vitality of seed is greatly 
influenced by storage conditions. The longest 
lived seed may be ruined by improper storage. 
The ideal conditions of storage, however, are not 
always those which favor germination. Seed should 
be cured or dried before storing. The drier it is 
the less likely it is to spoil, and the higher will 
be the temperature it can stand. When large 
quantities of seed are to be handled by the trucker, 
it is advisable to build a seed house. The seeds 
are best kept in strong paper or cloth bags and 
placed in tin cans. 



Poor Seed 95 

Seed Testing. In buying seed we must never take 
it for granted that the germination will be perfect. 
To make sure, a sample of the seed should be tested 
for germination and for purity. The simplest method 
IS to sow a definite number of seeds in a shallow pan 
filled with moist sand. 

The fact that a seed sprouts does not always mean 
a full stand in the field. Some weak seeds may 
germinate and then fail completely to make proper 
growth. Allowance must be made for this possibility 
where germination tests are made in the laboratory or 
at home. In testing for germination, the purity of 
the seed is also to be considered. As a rule there is 
no danger of truck seed introducing weeds, due to the 
fact that vegetable gardens are kept in a clean state 
of cultivation. The honest seedman may be trusted, 
too, to screen his seed carefully. 

Effect of Fertilizer on Seed. With the hope of 
hastening germination, truckers apply various fer- 
tilizers to the seed bed. This practice cannot be too 
strongly discouraged, especially when muriate of pot- 
ash and nitrate of soda are used. These two fer- 
tilizers when used in strengths of one per cent, or more 
inhibit the germination of the seed, whether applied 
directly or mixed with the soil. Phosphoric acid or 
lime when not used in excess seem to have no injuri- 
ous action on germination. However, on no account 
should commercial fertilizers be brought into direct 
contact with the seed. The injury in this case is not 
apparent on the seed coat, but it will appear on the 
young tender sprouts. Although much remains to be 



96 



Diseases of Truck Crops 



investigated as to the effect of fertilizers on seed, the 
work of Hicks' will serve as a guide to the trucker. 
Tables 12 and 13, adapted from Hicks, clearly show the 
effect of chemical fertilizers on lettuce and radish seeds. 

Table 12 

Effect of Chemical Fertilizers on the Germination oj Curled 
Simpson Lettuce Seed 







First 
Sprouts 


Per Cetit. 


Per Cent. 


Fertilizer Used 


How Applied 


Germinated 


Germinated 






Fourth Day 


Twelfth Day 


Potash 


In the rows 
Mixed with the soil 




No sprouts 


No sprouts 


Phosphoric 


In the rows 


May 26 


i< « 


2.5 


acid 


Mixed with the soil 


" 21 


2.5 


45-25 


Nitrogen 


In the rows 
Mixed with the soil 




No sprouts 


No sprouts 


Lime 


In the rows 


May 23 


0.75 


36.0 




Mixed with the soil 


" 22 


4.00 


39-75 


Mixed 


In the rows 




No sprouts 


No sprouts 


fertilizer 


Mixed with the soil 




" " 


" " 


Check, 










no fertiUzer 




May 21 


40.5 


73.0 



Table 13 

Effect of Chemical Fertilizers on the Germination of Break- 
fast Radish Seed 



Fertilizer Used 



How Applied 



First Sprouts 



Per Cent, of 
Germination 



Potash 
Phosphoric acid 



In the rows 
Mixed with the soil 
In the rows 
Mixed with the soil 



No sprouts 

May 26 
" 24 



1-5 

1-5 

lo.o 

95-0 



' Hicks, G. H., U. S. Department of Agr., Div. of Botany., Bui. 
24 : 5-15, 1900. 



Poor Seed 

Table 13 — (Continued) 


97 


Fertilizer Used 


How Applied 


First Sprouts 


Per Cent, of 
Germination 


Nitrogen 

Lime 

Mixed fertilizer 

Check, no fertilizer 


In the rows 
Mixed with the soil 
In the rows 
Mixed with the soil 
In the rows 
Mixed with the soil 


May 25 

" 26 

May 24 

May 25 

" 24 

May 24 


2.0 

6.5 
37.5 
930 
34-5 
92.0 

96.5 



Treatment of Seed against Insect Injury. In 
storage, the greatest enemies of the seed are weevils. 
These feed on any part of the seed lobes or embryo, 
thus impairing the germinating power. Weevils and 
other seed-feeding insects may be destroyed by fumi- 
gating the seed house, the bin, or the seed can, with 
carbon bisulphide used at the rate of three pounds to 
each thousand cubic feet of space. The carbon bisul- 
phide is placed in a dish on top of the seed and allowed 
to evaporate. The fumes, which are heavier than air, 
fall to the bottom. The seed house or bin should be 
made air-tight for twenty-four hours during fumiga- 
tion, and all fires including lighted pipes should be 
kept away for fear of an explosion. 

A new and safer fumigant, para-dichlorobenzene, 
has recently been placed on the market. This is less 
poisonous when inhaled than carbon bisulphide. For 
each hundred cubic feet of space, twelve ounces of the 
former are dissolved in water. The liquid is soaked 
in rags which are placed in the air-tight seed house or 
bins to be fumigated. 
7 



98 Diseases of Truck Crops 

Seed beds are very often attacked by mole crickets. 
They may be kept out by a wire gauze floor. When 
the seed bed is made and the earth is dug out to a 
depth of one foot or more, a sheet of galvanized or 
copper mosquito netting is placed at the bottom, com- 
ing up at the sides, and projecting a couple of inches 
above ground. Ants, too, are often destructive to 
seed beds. They feed on the seed and carry it away 
to their nests. This is especially true with lettuce 
seed. Ants are best controlled by pouring half a 
pint of carbon bisulphide in each nest and immedi- 
ately plugging its entrance. 

Other Seed Treatment. Since seed may be a 
carrier of diseases, it is essential that we have a 
method of treatment capable of destroying the dis- 
ease-producing organism in its initial stage. Ex- 
posing the seed in hot water at various degrees of 
temperature is effective in controlling certain smuts of 
grains. Treating the seed with sulphuric acid accel- 
erates the germination of certain hard seed, destroy- 
ing at the same time spores of fungi which may adhere 
to the exterior of the epidermis. Unfortunately 
there have been no extensive trials made of the effect 
of hot water and sulphuric acid, in accelerating the 
germination, and preventing the diseases which are 
carried on or within the seed of truck crops. How- 
ever, the treatment of seed (especially tubers) with 
corrosive sublimate or formaldehyde is now exten- 
sively practiced. Where the soil in the bed is ster- 
ilized, seed treatment becomes necessary. With the 
exception of tubers or roots, seeds should preferably 



Poor Seed 99 

be treated in formaldehyde. Manns' recommends 
that before planting, all seed should be soaked for 
twenty minutes in a solution of one part of formalde- 
hyde in 320 parts of water, i. e., i oz. of 40 per cent, 
formaldehyde in 22 gallons of water. The cost of 
this treatment is very small, 

' Manns, T. F., Ohio Agr. Expt. Sta. Bui. 228 : 255-297, 191 1. 



PART III 



CHAPTER VIII 
SPECIFIC DISEASES OF TRUCK CROPS 

FAMILY AGARICACE^ 

In this important family of fungi we may consider 
the ordinary cultivated mushroom, Agaricus campes- 
tris. Few truckers as yet grow mushrooms on a large 
scale ; but as food is getting scarce and its prices soar- 
ing higher, more attention will no doubt be paid to 
this important crop. 

DISEASES OF THE MUSHROOM {Agaricus 
campestris L.) 

Mushrooms are subject to few diseases. There are 
but two which need concern the grower. 

Bacterial Spot 

Caused by Pseudomonas fluorescens (Fl.) Mig. 

This disease, although serious, seems to be re- 
stricted as yet to the mushroom caves in St. Paul, Min- 
nesota. The trouble was first described by Tolaas. ' 

Symptoms. It is characterized by an unsightly 

' Tolaas, A. S., Phytopath. 5 : 51-53, 1915. 
103 



I04 Diseases of Truck Crops 

spotting of the caps, the severity of which differs with 
the cultivated varieties, especially the large white 
kinds. The spots, which do not extend deep into the 
flesh, appear while the mushroom is in the but- 
ton stage, or when the cap is fully expanded. The 
spots are pale yellow, becoming a chocolate brown. 
Though the disease does not seem to reduce the 
yield, the market value of the spotted mushrooms 
is considerably reduced. 

The Organism. Pseudomonas fiuorescefts is a 
small rod rounded at both ends and motile by means 
of polar fiagella. It is a facultative anaerobe; pro- 
duces no endospores, no gas, but liquifies gelatine. 
On beef and potato agar it produces a shiny grayish 
white growth accompanied by a greenish pigmenta- 
tion, which diffuses in the substratum. 

Control. Spraying the mushroom caps with solu- 
tions of benetol, sodium carbonate, or copper sul- 
phate seems to have no beneficial effect. On the 
other hand, fumigating the beds with sulphur before 
planting the spawn insures the production later of a 
clean crop of mushrooms. The amount of sulphur 
to use is about one and a half pounds to each thou- 
sand cubic feet of cave space. 

The Mycogone Disease 

Caused by Mycogone perniciosa Mag. 

The Mycogone is a very destructive mushroom 
disease. The exact amount of its distribution in the 




Fig. 1 8. IvIycogone Disease of Mushrooms. (After Veihmeyer.) 



Family Agaricaceae 105 

United States is as yet unknown. However, if once 
introduced in a cave, it is likely to ruin the entire 
crop. 

Symptoms. The symptoms of the disease are often 
various. The presence of the malady may be indi- 
cated by small tubercules on the cap and by a form 
of fluffy white growth on the gills, which interferes 
with their normal development (fig. 18). The result 
is distorted caps and stipes and finally a general 
darkening and decay of the tissue. In severe cases 
monstrous soft masses with thick white fungus coat- 
ings are observed in houses in which the disease is 
very prevalent. In this case the affected plants have 
little resemblance to mushrooms. They decay rap- 
idly, and emit a very disagreeable odor. 

The Organism. The spores of Mycogone perniciosa 
are very characteristic. They consist of two cells, the 
upper spherical, rough, and covered with warts, the 
lower hyaline, smooth. Both cells possess a thick wall. 

Control. According to Veihmeyer, ' there are no 
evidences that tend to show that the IVIycogone 
disease is carried with the spawn manufactured by the 
"tissue culture" method. It is very probable, how- 
ever, that the disease was introduced into this coun- 
try from France with imported virgin spawn 
collected at random from fields. The disease may be 
introduced into a new place with the manure and 
then spread quickly in a number of ways. Immedi- 
ate temporary measures are essential for the control 
of this trouble. Diseased plants when first noticed 

• Veihmeyer, F. J., U. S. Dept. of Agr. Bui. 127 : 1-24, 1914. 



io6 Diseases of Truck Crops 

should be pulled out and disposed of by fire. Allow- 
ing these infected plants to decay in the beds is a sure 
means of spreading the fungus broadcast in the cave. 
The gain from keeping the beds free from diseased 
specimens will more than compensate for the trouble. 
At the end of the season the beds should be thor- 
oughly cleaned, the manure should be carried away 
to a distance where mushrooms will not be grown, 
although it may be used for garden purposes, since 
the Mycogone disease is only known to attack mush- 
rooms. After the cave has been thoroughly cleaned 
out, it should be disinfected with the formaldehyde 
gas method. This is carried out as follows: For 
every thousand cubic feet of cave space use three 
pints of formaldehyde and twenty-three ounces of 
potassium permanganate. The potassium perman- 
ganate is placed in two or three earthen or wooden 
vessels, each having a capacity of one quart for every 
ounce of permanganate. When ready for the opera- 
tion, the mushroom house is sprinkled with water, 
the potassium permanganate placed in the recep- 
tacles, the formaldehyde poured evenly over the 
permanganate, and the cave doors closed at once. 
They are kept closed for twenty-four hours and then 
opened to allow the formaldehyde fumes to escape. 
All lights must be kept away from the caves while 
they are being fumigated since formaldehyde gas 
explodes when coming in contact with fire. Mush- 
room houses thus treated may be thoroughly rid of 
the Mycogone disease, but care must be taken to 
prevent reinfection. 



Family Agaricaceae 107 

It is hardly necessary to add that all tools and 
wagons which were used in connection with the pre- 
viously infected caves should be disinfected before 
being used again. All such tools and vehicles should 
be washed in a solution of one pint of formaldehyde 
in twenty gallons of water. In all these operations 
extreme care is necessary for the man who operates 
not to inhale any of the poisonous formaldehyde 
fumes. 



CHAPTER IX 

FAMILY ARALIACE^ 

The ginseng is the only plant in this family which 
is ot economic importance. Although not exactly 
a truck crop, it is nevertheless grown by truckers. 
The distribution of the crop is limited. According 
to the Thirteenth Census of the United States, the 
area devoted to ginseng in 1909 was 23 acres, and the 
total crop valued at $151,888. The 23 acres are 
distributed in the following States : New York, Wis- 
consin, Missouri, Ohio, Pennsylvania, and Michigan. 

DISEASES OF THE GINSENG {Panax 
quinquefolium) 

Ginseng is subject to numerous diseases, most of 
which may be kept in check. 

Damping off (Fig. 19 a), see Pythium 

Downy Mildew 

Caused by Phytophthora cactorum (C. and L.) Sch. 

Downy mildew is a destructive disease and is 
found wherever ginseng is grown. It attacks all 
parts of the plant, rendering it useless. 
108 




>*^ 



Fig. 19. Ginseng Diseases. 

a. Damping off, b.-c. Phytophthora mildew on leaf and root, d. Phytophthora 
mycelium, e. germination of conidia by means of zoospores,/, germination of conidia 
by means of germ tubes, g. sexual fertilization of the female oogonium by the male 
antheridium, h. germinating oospore by means of a germ tube, i. cross section of a 
root mfected with Acrostalagmus showing diseased condition of fibro-vascular 
bundles, k. fruiting stalks of Acrostalagmus and sclerotia of same, /. cross section of 
root to show presence of mycelium of Acrostalagmus in vascular bundles, m. papery 
leaf spot, n. Alternaria blight on leaf, o. Alternaria spore, p. black rot showing fruit- 
mg cup of Schrotinia panacis (d. e. f. g., and h. after Rosenbaum, the other figures 
after Whetzel and Rosenbaum). 



Family Araliaceae 109 

Symptoms. The disease first attacks the petioles, 
resulting in the drooping of the leaflets. In severe 
cases, the leaf stalks are killed at the base where they 
join the stem. This causes the leaves to droop over 
the stem. The diseased areas usually become soft 
and slimy. On the leaves, the spots are dark green, 
watersoaked, and bent, soon becoming dry white in 
the center with a prominent dark green water-soaked 
margin (fig. 19 b). In wet weather, the disease at- 
tacks the stem, and from there works downward to 
the root causing it to decay (fig. 19c). 

The Organism. The mycelium (fig. 19 d) of Phy- 
iophthora cactorum somewhat resembles P. infestans, 
the cause of late blight of the Irish potato, but differs 
from it in producing an abundance of sexual or oos- 
pores (fig. 19 g) within the dead tissue. The oospores 
pass over the winter unaffected by cold weather. In 
the spring they germinate, each sending out a germ 
tube (fig. 19 h) which later may bear from one to 
two conidia. These as claimed by Rosenbaum' 
may germinate by means of a germ tube or by 
swarm spores. The conidia genninate in the same 
way (fig. 19 e and f). 

Control. Downy mildew may be controlled by 
spraying with 3-3-50 Bordeaux. Diseased plants 
should be pulled out and destroyed by fire. Plant- 
ing the roots deep in the soil will also protect them 
from rotting. This seems to prevent the working 
downward of the disease from the stem to the roots. 

'Rosenbaum, J., New York (Cornell) Agr. Expt. Sta. Bui. 363: 
65-106, 1915. 



no Diseases of Truck Crops 

White Rot 
Caused by Sclerotinia liber tiana FcM. 

White rot, although fairly destructive, attacks only 
isolated individual plants. It is prevalent in New 
York, Ohio, Michigan, and Wisconsin. The same 
disease also attacks cucumbers and numerous other 
crops later mentioned. 

Symptoms. The disease usually appears during 
continuous damp weather. It attacks the plant at 
its stem end near the soil line. The infected part 
becomes soft, watersoaked, bleached, and overrun by 
a white weft of mycelial growth on the surface of the 
epidermis. Later sclerotia or dark masses of fungal 
threads appear irregularly within the pith and on the 
surface of the diseased crown. Infected plants wilt, 
topple over, and collapse. For a description of the 
causal organisms, see lettuce, p. 143. 

Control. Spraying will not control this disease. 
Whetzel and Rosenbaum ' suggest that the soil be well 
drained, and that plenty of ventilation be given the 
shacks. The disease may also be eradicated in the 
same manner as prescribed for lettuce drop, p. 144. 

Black Rot 

Caused by Sclerotinia panacis Rank. 

Black rot is not as prevalent as white rot above 
mentioned. The disease was named and described 
by Rankin. ^ 

' Whetzel, H. H., and Rosenbaum, J., U. S. Dept. of Agr., Bur 
of PI. Ind., Bui. 250 : 7-44, 1912. 

= Rankin, W. H., Phytopath. 2 : 28-31, 1912. 



Family Araliaceae m 

Symptoms. Black rot is apparently a root disease 
only. Roots dug from affected areas are coal black, 
with no rootlets, but with intact bud, which, however, 
is also blackened like the root. On the surface of the 
latter are found numerous sclerotia the size of a small 
pea. On cutting open a diseased root only the outer 
rind is found to be blackened, while the center re- 
mains white, spongy, and watery. The affected root 
does not soft rot, but becomes very bitter in taste. 
If left over in the soil for two seasons the root will 
turn black all through, shriveling and decaying. 
Black rot works only in cold weather of early spring 
or late fall. In structure Sclerotinia panacis greatly 
resembles S. lihertiana (fig. 19 p). 

Control. Remove the diseased plants and the sur- 
roundi ng healthy ones on a strip a foot wide. Drench 
the soil with a heavy appHcation of one part com- 
mercial formaldehyde in 50 parts of water — about i 
gallon per sq. ft. 

Fiber Rot (Rust) 

Caused by Thielavia basicola (B. and Br.) Zopf. 

Symptoms. The manifestations of fiber rot depend 
largely on the age of the root and the part attacked. 
With seedlings and in dry weather the leaves lose 
their dark green color, become pale, tinting into 
shades of red, and finally the leaflets wither and the 
stems wilt. Often the leaves of infected seedlings 
take Oil a purple bronze color. In wet weather the 



112 Diseases of Truck Crops 

wilting is more sudden, and the stems bend into a 
curve. In this case affected seedHngs seem to preserve 
their natural green color. The disease is confined 
to the root fibers, which turn rusty brown or black. 
In severe cases, all that is left is a charred stub. 
The affected tissue is dry, although several soft rots 
may follow the primary injury. For a description 
of the causal organism see garden pea, p. 275. 

Control. For seed beds the soil should be treated 
with steam or formaldehyde as described in pages 
53-59. For large beds the application of acid phos- 
phate at the rate of one thousand pounds per acre 
will be found beneficial. The treatment, to be effec- 
tive, must be given to soils not too alkaline. Where 
the soil is strongly alkaline, heavier quantities of 
acid phosphate should be applied, so that the treated 
soil may become distinctly acid. 

Stem Anthracnose 

Caused by Vermicularia dematium (P.) Fr. 

Symptoms. Anthracnose is apparently a seedling 
disease of little importance. It appears as numerous 
black spots on the stems of the young plants. These 
enlarge and very frequently end by girdling and kill- 
ing the entire stem. 

Control. The disease may be controlled by spray- 
ing with Bordeaux mixture as soon as the plants are 
about three weeks old. Spraying should be repeated 
every two to three weeks until about August ist. 



Family Araliaceae 113 

Leaf Anthracnose 
Caused by Pestalozzia funerea Desm. 

Symptoms. This malady attacks the base of the 
leaves and flower stalks. It results in an early drop 
of the foliage which also indirectly affects the roots. 
Spraying with Bordeaux is said to control this 
trouble. 

ACROSTALAGMUS WiLT 

Caused by Acrostalagmus panax Ran. 

This wilt seems to be destructive only in the spring 
of the year. It is prevalent wherever ginseng is 
growing. 

Symptoms. The first evidence of the disease is a 
slow drying and wilting of isolated plants here and 
there in the field. At first the leaves droop, suggesting 
a lack of water in the soil. This, however, is not the 
case. Outwardly the roots of affected plants appear 
sound, but on cutting open one of these the fibro- 
vascular bundles will be found to be yellowed, indicat- 
ing the presence of the fungus within (fig. 19 i and I). 
The spores of the fungus are very minute and are 
formed on slender branched stalks (fig. 19 k) which 
appear on the surface of such decayed stems or roots. 
The fungus also produces sclerotia* like bodies (fig. 
19 k) which apparently serve in tiding it over un- 
favorable weather conditions. The fungus has been 
identified by Rankin' q.s Acrostalagmus panax. So 

' Rankin, W. H., Spec. Crops. U. S., 9 : 349, 1910. 



114 Diseases of Truck Crops 

far as is known, no definite method of control can be 
recommended. The use of healthy roots should be 
depended upon. Wherever possible soil sterilization 
with steam or formaldehyde is also recommended. 

Alternaria Blight 

Caused by Alternaria panax Whet. 

Blight is perhaps the most common of all ginseng 
diseases. It is found practically wherever this crop 
is grown. 

Symptoms. The disease at first manifests itself 
as dark brown spots on one side of the stem. Often 
the spots work in deep and cause the stem to rot and 
break at the point of the lesion. On the leaves, 
blight appears as watersoaked spots. These grad- 
ually dry out, becoming thin and papery with a 
distinct rusty brown border (fig. 19 n). The disease 
may also attack the leaflets at the point of attach- 
ment to the leaf stalk. This generally causes a 
dropping and dying of the leaflets. Later a velvety 
brown cover appears on the dead tissue which con- 
sists of the spores of the fungus. Frequently the 
seed heads are also infected. 

The Orgajiism. The mycelium of Alternaria panax 
is brown, septate. The conidiophores are erect, 
brown, septate, irregular at the tips, and tufted. 
The conidia are brown, borne in chains, and typical 
of Alternaria (fig. 19 s). 

Control. Blight may be effectively kept in check 
by spraying with a 3-3-50 Bordeaux mixture. 



Family Araliaceae 115 

Strong solutions will not injure the plants but are 
unnecessary. 

Root Knot, see Nematode 

Papery Leaf Spot 

Caused by drought. 

Symptoms. The trouble appears as thin, papery 
whitish to yellowish, transparent spots between the 
veins and along the margins of the leaves. This 
spotting is often mistaken for Bordeaux injury or 
for Alternaria blight. 

Cause. Papery leaf spot is brought about by a 
lack of sufficient moisture in the soil. Drought, large 
tree roots in the beds, or insufficient shading may 
deprive the plants of the amount of soil moisture 
which they require. Control measures should con- 
sist in eliminating as far as possible those factors 
which are conducive to drought. 

Bordeaux Injury 

. This form of injury is brought about when spray- 
ing with Bordeaux mixture which is followed by frost. 
Affected plants appear scalded, soft rot, and finally 
they dry and become papery (fig. 19 m). As a pre- 
caution plants should not be sprayed during periods 
when frost is predicted. 



CHAPTER X 

FAMILY CHENOPODIACE^ 

This family comprises the beet, chard, spinach, and 
the Strawberry Elite. The latter is not generally 
known to American truckers. In England it is culti- 
vated as a pot herb. The first three, however, are ex- 
tensively grown in home gardens on a small scale, or in 
trucking on a large scale for m.arket. According to the 
Thirteenth Census of the United States the 1909 area 
in beets was 3202 acres. New York leading with 
834 acres to her credit. The States which follow 
according to rank are: Massachusetts, California, 
Louisiana, Illinois, Pennsylvania, New Jersey, and 
Michigan. The remaining States each devote a 
very limited acreage to beets and are hence 
omitted. The area devoted to spinach in the 
United States in 1909 was 6668 acres. Of the leading 
States in the production of this crop may be es- 
pecially mentioned Virginia with 3058 acres. The 
other spinach States are classified according to rank 
as follows : Maryland, New York, New Jersey, Mas- 
sachusetts, Illinois, and Pennsylvania. The money 
value in the United States of the beet crop in 1909 
was $352,696 and of the spinach crop $817,069. 
116 



Family Chenopodiaceae 117 

We have no available statistics of the money losses 
to beets and spinach from the various diseases about 
to be mentioned. 

DISEASES OF THE BEET {Beta vulgaris) 

Beets are subject to numerous diseases, some of 
which are of great economic importance, while others 
are insignificant and need not be feared by the trucker 
or gardener. 

Water-Core Spots 

Cause unknown. 

Arthur' has described a disease of beets which he 
named water-core spots. 

Symptoms. The disease is characterized by well 
defined spots in the interior of the root. These 
spots greatly resemble the water-core spots of the 
apple. The spots generally occur between the 
fibrous rings. They are sharply defined and do 
not grade into the adjoining tissues. The spots 
range from a pin-head to half an inch in size, 
and resemble a pea in shape. Sometimes there 
are but one or two spots in the root, but more 
generally several are present. The disease does 
not seem to be of any great economic importance, 
and it is not likely that any financial losses will be 
attributed to it. 

'Arthur, J. C, Indiana Agr. Expt. Sta. Bui. 39, vol. 3 : 54-62, 1892. 



ii8 Diseases of Truck Crops 

Soft Rot 
Caused by Bacterium teutlium Met. 

This disease was originally described by Metcalf . ^ 
It is not known whether the garden beet is seriously 
affected by it. The trouble, however, is of economic 
importance where sugar beets are grown extensively. 

Symptoms. The disease in its initial stage is char- 
acterized by a soft rot at the lower portion of the 
root. At this stage the crown and leaves remain 
normal, but later the outer leaves die and fall off. 
The disease is primarily a root trouble; the decayed 
tissue is soft, yellowish gray, and contains a sour 
smelling liquid v/hich exudes at the least pressure. 
It is most prevalent in wet and poorly drained lands. 
The cause of soft rot is a bacterial organism, Bac- 
terium teutlium. 

Control. Since the disease works on the root 
underground it is clear that no exterior treatment 
will be effective. Thorough drainage, careful culti- 
vation, and crop rotation are the only methods of 
control known. 

Crown Gall 

Caused by Pseudomonas tumefaciens Sm. and Town. 

Crown gall is a very important disease because of 
its cosmopolitan nature. It prevails widely and 
attacks a large number of hosts. 

» Metcalf, Haven, Nebraska Agr. Expt. Sta. 17th Ann. Rept.: 69- 
112, 1904. 




Fig. 20. Beet Diseases. 

a. Crown gall, b. scab c. downy mildew, d. Conidiophore of Peroyiospora schachlii 
arising from a stomate of an infected beet leaf, e. germinating zoospore of P. schach- 

•/• °°?P.O'"e "f ^- schachlii, g. Cercospora leaf spot (after Halsted), h. conidiophore 
and conidia of Cercospora belicola (after Duggar), i. Phoma leaf spot (after Pool and 
McKay), k. pycnidium of Phoma belce (after T. Johnson) {d.-f. after PriUieux). 



Family Chenopodiaceac 119 

Symptoms. The disease does not usually manifest 
itself until the roots are nearly half grown. Abnormal 
outgrowths or galls (fig. 20 a) appear which vary in 
size from that of a garden pea to nearly two inches in 
diameter, depending on the severity of the attack. 
The galls are usually attached to the beet by a narrow 
string. In light cases of infection there may be but 
one gall on the root; in severe cases, however, the 
roots may be covered with numerous galls. 

The Organism. The cause of crown gall is a bac- 
terial organism, Pseudomonas tumejaciens Sm. and 
Town. It is a short rod, multiplying by fission, which 
moves about by means of polar flagella. On agar or 
gelatine it forms small round white colonies. Under 
unfavorable conditions it readily develops involution 
forms; in pure culture the organism is short lived. 
P. tumejaciens lives over in the soil from year to 
year. 

Control. Although crown gall is known to attack 
a large number of plants, it has never been found as a 
parasite on grain crops. Gardens or fields which 
refuse to grow beets because of the disease, should be 
given a rest for at least three years by planting sweet 
corn instead. According to Dr. Smith' the follow- 
ing truck crops are susceptible to crown gall : Tomato, 
potato, cabbage, beet, radish, and salsify. In infected 
fields, these crops should be left out when planning a 
rotation which is aimed at starving out the organism 
in the soil. 

'Smith, E. F., et. al., " Crown Gall of Plants," U. S. Dept. Agr., 
Bur. PI. Ind., Bui. 213 : 13-200, 191 1. 



120 Diseases of Truck Crops 

Tuberculosis 

Caused by Pseudomonas beticola Ew. Sm. 

Tuberculosis differs from the crown gall by the 
formation of small tubercules on the root. The part 
of the root nearest to the tubercule is brown and 
watersoaked and broken into hollow cavities. The 
diseased tissue is mucilaginous and stringy when 
touched. 

The Organism. Tuberculosis is induced by an 
organism, Pseudomonas beticola. In pure culture of 
agar the colonies are circular, smooth or wrinkled, 
and in color are yellow. The organism is rod shaped, 
single or in pairs, and moves about by means of polar 
flagella. 

Control. The disease, so far as is known, does not 
seem to be of any economic importance. Diseased 
material should be destroyed by fire and the infected 
soil soaked with formaldehyde made up of one pint 
of the chemical in twenty gallons of water and ap- 
plied at the rate of one gallon of the solution to 
each square foot of space. The organism seems 
able to gain entrance only through wounds. Care 
is therefore necessary to prevent cutting or bruising 
the roots during cultivation or at harvesting. 

Scab 

Caused by Actinomyces chromogenus Gasp. 

Scab on beets is the same as the scab of the Irish 
potato. The disease is of the greatest economic im- 



Family Chenopodiacese 121 

portance in localities where potatoes suffer heavily 
from the disease. 

Symptoms. The symptoms of the disease on beets 
(fig. 20 b) do not differ much from those of the Irish 
potato (see p. 317). Occasionally, the scabs which 
arise before the beet is full grown disappear entirely, 
leaving merely • a small scar. This is somewhat 
sunken and has a definite outline. In normal 
cases of infection, the scabby areas on the beet are 
greater in area, and thicker ; the corky layer of the 
spots decidedly bulging out. Immediately below the 
scabby areas the tissue is a discolored reddish brown. 

The Organism. The cause of beet scab is the same 
as that of the scab of the white potato (see p. 317). 
The parasite is a soil organism, and thrives best under 
alkali conditions. 

Control. Beets should not grow where Irish po- 
tatoes, carrots, or radish are known to suffer from the 
same disease. Lime and fertilizers which tend to 
make the soil alkaline should be avoided. 

Root Tumor 

Caused by Uroplilyctis leproides (P. Mag.) Trab. 

This trouble fortunately is as yet unimportant in 
the United States. The disease is characterized by 
the formation of nodules or outgrowths often the size 
of a walnut on the rootlets or leaves. The fleshy 
root itself is seldom attacked. The tissue of the 
tumors contains numerous cysts or spore-bearing 
cells. 



122 Diseases of Truck Crops 

Control. All infected plants must be removed or 
destroyed. To be successful this must be done early 
enough before the winter spores of the fungus are 
liberated in the soil. 

Damping off and Root Rot 

Caused by Pythium de Baryanum Hess. 

Symptoms. Damping off of the seedlings just as 
they emerge from the ground is often a common 
trouble under poor cultural conditions. The young 
seedlings topple over and die in the characteristic 
way so familiar to truckers. The greatest damage 
occurs after heavy rains when a hard crust is formed 
on the surface preventing the seedlings from emerg- 
ing normally. On old and mature roots, Pythium de 
Baryanum may cause a rot. According to Clinton, ' 
the disease is found to be severe on mangels. A 
peculiarity of the rot is that it seldom starts at the 
top of the crown. The latter appears to be perfectly 
healthy, although the leaves turn yellow, indicating 
a diseased condition further down. Rotted roots 
are found to be overrun by a varied flora, although 
Pythium de Baryanum is the original cause of the 
trouble. For a further description of the organism 
see p. 43. 

Control. The disease is more prevalent during wet 
weather, and in heavy soils which are poorly drained. 
Thorough drainage of the land and careful cultiva- 

' Clinton, G. P., Connecticut Agr. Expt. Sta. 39th. Ann. Rept.: 
433-436, 1915- 



Family Chenopodiacese 123 

tion will greatly help to control the rot on the ma- 
ture roots. To prevent seedlings from damping off 
care should be taken that no hard crust be allowed to 
form on the soil. After a rain the soil should be 
worked as soon as possible. 

White Rust 

Caused by Cystopns hliti (Biv.) Lev. 

This disease is of little economic importance as far 
as the trucker is concerned. Its occurrence on beets 
has been reported but once by Pammel. ' In appear- 
ance, infected leaves show white raised pustules or 
son on the under side. When the surface cover of 
the pustules bursts open a powdery mass of snow- 
white spores is liberated. The same disease also 
attacks * ' pigweeds. ' ' Clean culture is recommended. 

Downy Mildew 

Caused by Peronospora schachtii Fckl. 

This disease, like white rust, is of little economic 
importance in the United States. The trouble, 
however, is very prevalent in Europe. The mildew 
attacks the young seedlings in grayish patches on 
the under side of the foliage. On older plants the 
mycelium of the causative fungus works down- 
wards into the root where it is carried over \\dnter 
(fig. 20c- f). 

' Pammel, L. H., Iowa Agr. Expt. Sta. Bui. 15 : 234-254, 1891. 



124 Diseases of Truck Crops 

Drop 

Caused by Sclerotinia lihertiana Fckl. 

Drop on beets, which attacks young seedlings, but 
not older plants, is otherwise not very different from 
a similar trouble on lettuce. Clinton ^ reports a case 
of beet drop in an outdoor seed bed. The warm con- 
dition of the soil, soon after making the seed bed, 
was important in favoring the disease. Sterilizing 
the soil with formaldehyde, careful regulation of 
soil temperature and watering are methods to be 
observed in the control of the trouble. 

Rust 

Caused by Uromyces beta Kuhn. 

This disease has been reported only on beets in 
California. In Europe it is especially common on 
the wild beet {Beta maritima) . 

The Organism. The cause of this rust is a fungus, 
Uromyces betce, the latter having three spore stages, 
all of which occur on the same host, but at different 
times of the year. 

I. Spring or Cluster Cup Stage. This is seen as 
small, whitish, raised cups, grouped on a yellow spot. 
When opened, these cups emit a yellowish powder 
which is made up of large quantities of the yel- 
low colored aecediospores. The latter germinate 

•Clinton, G. P., Report of the Botanist for 191 5, Connecticut 
Agr. Expt. Sta. 39th Ann. Rept. : 433-436, 191 5, 



Family Chenopodiaceae 125 

by means of a germ tube which enters the beet leaf 
again. 2. U redo Stage. The result of infection from 
the aecediospores is manifested as raised small pus- 
tules which are thickly scattered over the leaf. 
When these burst open, uredo or summer spores are 
liberated. These are round, one celled, and spiny, 
and the cell wall is perforated at several places. 
3. Teleutospore Stage. As soon as infection of the 
beet leaves takes place as a result of the penetration 
of the germinated uredospore infection, other 
darker pustules are formed. These when rupturing 
hberate the winter or teleutospores, which are one 
celled, thick walled, smooth, and darker in color. 
Their function is to carry the fungus over winter. 
The infection from the teleutospores the following 
spring again results in the cluster cup stage. 

Control. It is doubtful if spraying will control the 
beet rust. The better way is to plow deeply under 
the affected leaves. This will prevent the germina- 
tion of the teleutospores in the spring. 

Leaf Spot and Heart Rot 

Caused by Pho^na betcB Frank. 

This disease is more prevalent as a storage rot, 
although it also produces a leaf spot in the field. 
The trouble is as yet of little economic importance. 
It is not certain whether this rot is the same as that 
described by Halsted' as root rot of beet which he 
attributed to a species of Phyllosticta. 

' Halsted, B. D., New Jersey Agr. Expt. Sta. Bui. 107 : 3-13, 1895. 



126 Diseases of Truck Crops 

Symptoms. It is characterized by minute brown- 
ish spots on the leaves (fig. 20 i and k). On the roots 
it is manifested as a dry black rot extending deep in 
the interior. The outside of the root has a shrunken 
appearance which closely follows the seat of the inte- 
rior rotting. 

Control. In the field, the disease first starts in the 
seed bed. Spraying with 4-4-50 Bordeaux is recom- 
mended. Two applications may suffice. In the 
field, spraying has not as yet given promising results. 
Clean culture and rotation will eventually free a field 
from the disease. 

The disease is introduced upon the seeds which 
frequently bear the fruiting bodies of the fungus. It 
has been shown that disinfection of the seed will 
prevent the carrying over of the disease. 

Leaf Spot 

Caused by Cercospora beticola Sacc. 

There is perhaps no beet disease that is of greater 
economic importance than leaf spot. The trouble is 
well known to truckers and it seems to be found where- 
ever beets can thrive. 

Symptoms. The disease first makes its appearance 
on the leaves as tiny circular whitish spots. These 
gradually increase in size and assume a brownish 
color. The spots soon increase in numbers and 
involve the entire area of the leaf (fig. 20 g), which 
becomes dry and brittle. Leaf spots attack the outer 



ji 



Family Chenopodiaceae 127 

and older leaves. As the inner foliage advances in 
age, it becomes infected in turn. As serious as the 
disease may appear, it never kills the plant. The 
result, however, is noticeable on the roots, which are 
undersized and elongated instead of round. Leaf 
spot generally appears during a moist spell followed 
by a period of dry weather. The disease increases 
in severity as the plants are weakened by heat and 
drought. 

The Organism. The fungus, Cercospora beticola, 
like most fungi, is composed of a vegetative part of 
mycelium and of spores. The latter are microscopic 
in size, somewhat needleshaped, and divided by 
means of a cross wall into two to seven cells (fig. 
20 h). Each of these cells may germinate by send- 
ing out a threadlike tube, which penetrates the leaves 
through the stomata. The spores are borne on a 
cluster of stalks or conidiophores, at the base of which 
is formed a small stroma. The temperature and re- 
lative humidity of the air influences the production 
and infection of conidia. According to Pool and 
McKay' a temperature of 80 or 90 degrees F. with a 
minimum of not less than 60 degrees at night is most 
favorable to the production of conidia. They are, 
however, checked By a temperature of 100 degrees or 
higher, or of 50 to 80 degrees F. Conidia are gener- 
ally formed on the lower surface of the leaves, no 
doubt because these are subject to a higher humidity. 

Control. For practical purposes leaf spot may 

' Pool Venus, and McKay, M. B., U. S. Dept. Agr. Journ. Agr. 
Research, 7 : 21-60, 1916. 



128 Diseases of Truck Crops 

be controlled by deep fall plowing and crop rotation. 
No hard and fast system of rotation can be laid down 
for the trucker. He himself must be the best judge. 
It seems that the conidia of the fungus are unable to 
live over winter. The parasite, however, winters 
over as mycelium within the affected leaves. Deep 
plowing, therefore, not only improves the land but 
will also help to bury the debris of infested leaves, 
thereby removing the fungus as a source of infection 
for the following year. Spraying will also help to 
control leaf spot. The formula recommended is 4 
pounds copper sulphate, 4 pounds fresh slaked lime, 
to 50 gallons of water. To succeed in keeping the 
disease in check, spraying must be carefully carried 
out. The leaves should be thoroughly coated with 
the mixture both from the upper and under sides. 
Clean culture and constant cultivation will also check 
leaf spot. This will tend to maintain the moisture 
in the soil, at the same time preserving the vigor of 
the plant. Any operation which tends to weaken the 
plant will also favor infection. 

Root Rot 

Caused by Corticium vagum B. and C. 

This disease is very prevalent in the United States, 
attacking a large number of truck crops in which the 
beet is included. It has been carefully studied by 
Duggar and Stewart^ and by others. It produces 

' Duggar, B. M., and Stewart, F. C, New York (Cornell) Agr. 
Expt. Sta. Bui. 186 : 50-76, 1901. 



Family Chenopodiaceae 129 

a damping off of the young seedlings, and "on older 
plants a rotting of the crown. In pulling out an 
infested plant, we find that the outer leaves are dead 
and dry, while the inner ones are somewhat curled. 
The roots of such plants invariably are rotted at the 
crown, the rot generally working inwards to a con- 
siderable extent. The peculiarity of this disease is 
that the lower half of the root is generally sound. 
Frequently the rotted crowns are also found to be 
cracked at various places. Beets thus affected are 
worthless for the market. This condition naturally 
indicates a sick condition of the soil, due to the pres- 
ence of Rhizoctonia solani. For a description of the 
fungus see p. 45. 

Control. There are no methods of control known. 
The factors which favor the trouble are poor drain- 
age, an excess of soil moisture, and lack of sufficient 
aeration. Every step taken to overcome these will 
in a degree help to control the rot. 

Root Knot 

Caused by Heterodera radicicola (Greef) Miiller. 

This disease is different from crown gall or tuber- 
culosis. Although the symptoms are sometimes 
manifested as knots or outgrowths on the m.ain 
roots, usually the knots are found at the tip end 
of the roots, thereby leaving unmolested the main 
root. The effect of this disease, however, is to re- 
duce the size of the marketable beet. Affected 



130 Diseases of Truck Crops 

plants in the field may be detected by their stunted 
growth, smallness and paleness of foliage. 

Cause and Control. The cause of this trouble is 
not a bacterium or a fungus but a minute micro- 
scopical worm, Heterodera radicicola. For further 
description of the parasite and for methods of control 
see p. 49-51- 

DISEASES OF SPINACH {Spinacia oleracea) 

Spinach is an important truck crop in the United 
States but one subject to numerous diseases. 

Malnutrition 

The result of an excess of acidity or of a lack of 
soil humus. 

This condition causes great losses in those districts 
where commercial fertilizers are used exclusively, at 
the expense of organic manures. 

The margins of the veins of the leaves become yellow 
and the central part takes on a mottled appearance. 
The outer leaves are usually the first to suffer; soon, 
however, the entire plant exhibits similar symptoms 
and ceases to grow. 

Control. Spinach, like lettuce and other crops 
which are eaten for their foliage, cannot be sprayed 
with poisonous fungicides. The trucker must look 
to other sources for relief. The methods for control- 
ling malnutrition have already been considered on 
pages 81-82. As regards the other diseases men- 




Fig. 



Spinach Diseases. 



a. Downy mildew, 6. cross section showing fruiting stalk of the downy mildew 
fungus on infected spinach leaf, c. cross section showing leaf affected with white 
smut, d. Anthracnose of spinach, e. cross section showing acervulus of Collclotri- 
chum spinaricc. f. leaf spot, g. spores of the leaf spot fungus Ilelerosporium variabile- 
{b. c. e. after Halsted, d. after Reed). 



kpamily Chenopodiaceae 131 

tioned above, clean culture is an important consid- 
eration. Diseased leaves should be collected and 
destroyed by fire; the diseased refuse should never 
find a place in the manure pile. Where spinach has 
been grown too long on the same land a rest must be 
given by rotating with other crops. 

Downy Mildew 

Caused by Peronospora effusa Rabenh. 

The downy mildew of spinach is of widespread 
occurrence. The disease causes great damage during 
seasons of heavy rainfall or during dry weather ac- 
companied by heavy dews at night. It is rare in dry 
weather and absence of dews. 

Symptoms. The trouble is characterized by yellow 
spots of conspicuous size on the upper part of the 
leaves (fig. 21 a). On the under side of the leaves 
and corresponding to the spots above, is seen a 
mat of dirty white to violet gray fruiting bodies of 
the fungus. 

The Organism. Downy mildew is caused by the fun- 
gus Peronospora effusa. The spores of the parasite 
are borne on branches which generally emerge through 
the breathing pores or stomata of the lower part 
of the leaf (fig. 21b) and germinate by sending out 
a slender germ tube. Infection takes place when the 
germ tube penetrates the upper side of the leaf, gen- 
erally through the stomata. The winter stage or 
oospores may be found in the affected leaves. The 



132 Diseases of Truck Crops 

fungus also seems able to pass from year to year as 
viable mycelium in the late infected leaves of the 
spinach. 

Anthracnose 

Caused by Colletotrichum spinacicE Ell. and Hals. 

This disease is apparently limited to New Jersey 
and Virginia, although it probably occurs also in 
other States where spinach is grown. 

Symptoms. It appears as minute round water- 
soaked spots on the leaves. These quickly enlarge 
and become gray and dry (fig. 21 d). In the spots 
will be found evenly scattered minute dark tufts; 
these are merely fruiting pustules which also contain 
minute black bristles or setse (fig. 21 e). The onset 
is not limited to any particular part of the plant. In- 
fection may take place anywhere on the foliage, 
stems, or petioles. The spore pustules may be formed 
on the upper as well as on the lower surface of the 
leaf. In wet moist weather the pustules take on a 
salmon tinge, indicating that there is an abundance of 
spores formed at that time. The spores may be 
carried from leaf to leaf and from plant to plant by 
insects, wind, or rainwater. In badly infected fields, 
picking should never be done during wet rainy 
weather, neither should spinach from infected fields 
be allowed to be shipped long distances, as in this 
case the product may rot before reaching its destina- 
tion. 



Family Chenopodiaceae i33 

White Smut 
Caused by Entyloma Ellisii Hals. 

Spinach smut is closely related to the smut of 
onions or even to the grain smuts. The disease is of 
rare occurrence. 

Symptoms. Instead of turning black, the leaves 
assume a white frosty appearance, which renders 
them, of course, worthless. The fungus has two forms 
of spores. Those within the leaf are spherical and 
grouped in small clusters just beneath the stomata, 
while the second form is needleshaped and is borne 
at the end of the minute threads on the surface of the 
affected leaf (fig. 21 c). 

Phyllosticta Leaf Blight 

Caused by Phyllosticta chenopodii Sacc. 

This is a common disease, especially with older 
plants. Like Anthracnose, leaf blight causes great 
damage when once introduced in a field. 

Symptoms. Numerous minute spots appear, more 
distinctly in the lower part of the leaf. Within them 
are found scattered minute black bodies known as 
pycnidia. These are microscopical, saclike bodies, 
within which the spores of the fungus are borne. 
During moist weather, the spores are seen to ooze 
out as long white tendrils. The latter are made up 
of millions of spores held together by a mucilaginous 



134 Diseases of Truck Crops 

substance which Is dissolved by the least contact 
with rainwater or dew. The spores are then carried 
about by the same agencies as mentioned for the or- 
ganism of spinach anthracnose. 

Black Mold 

Caused by Cladosporium macrocarpum Preuss. 

This disease attacks the oldest leaves of the plant 
in dark patches which are covered with numerous ir- 
regular dark spore-bearing branches or conidiophores. 
It is of little economic importance. 

Leaf Spot 

Caused by Heterosporium variahile Cke. 

This disease is very prevalent on winter spinach 
in Eastern Virginia. It generally attacks plants 
which have been weakened by downy mildew, or by 
other diseases. Reed and Cooley, ^ who have studied 
it carefully, find that indirectly it causes considerable 
losses to the growers. It necessitates, for instance, 
the trimming off of dead or diseased leaves, this 
requiring extra labor and reducing the quantity of 
marketable spinach. The disease is at its height 
when the plants attain their maximum, beginning in 
January and continuing until about March, the close 

' Reed, H. L., and Cooley, J. S., Virginia Agr. Expt. Sta. Ann. 
Rept. 1909 and 19 10. 



Family Chenopodiaceae 135 

of the season. Leaf spot does not develop to any- 
appreciable extent under dry conditions. In dry 
winters it is of no economic importance. It is best 
favored by poor soil conditions, that is by an excess 
of acidity or a lack of humus. 

The Organism. It is caused by Heterosporium 
variabile, a semi-parasitic fungus which causes circu- 
lar, or subcircular, sooty brown spots, having a 
definite outline (fig. 21 f) on both sides of the leaf, 
surrounded by a brown area of dead leaf tissue. 
The spots at first have a light color, becoming darker 
with age, finally turning velvety to olive black. This 
color is largely due to the appearance of the spores 
on the surface of the spots. These occur singly, 
although they may involve the entire leaf when a 
great number coalesce. The mycelium grows in the 
host cells and consists of septate branches, the cells of 
which are olive green in color, irregular in shape, 
granular and oily in content. Conidiophores pro- 
ceed vertically from cracks in the epidermis of the 
spot, and at the tip end of each a spore is borne on a 
small short pedicel. As the conidiophore continues in 
growth, new spores are formed at the tip end, thus 
giving the fruiting stalk a twisted appearance. The 
mature spore is three celled (fig. 21 g), cylindrical, 
with round or slightly pointed ends, spiny, and sooty 
or olive green in color. On pure culture the fungus 
may produce only one-celled spores. The latter 
seem to retain their vitality for at least six months. 

The very serious spinach blight of the Norfolk, 
Va., trucking region should be mentioned. It was 



136 Diseases of Truck Crops 

erroneously confused by Harter with the true mal- 
nutrition which is also found there (but rather rarely). 
The blight has been shown by McClintock and Smith 
to be a true mosaic, communicated by aphids. " 

WEEDS 

Disease is not confined to cultivated crops only, 
but it also attacks weeds. In attempting to control 
the diseases of cultivated crops, we cannot lose sight 
of the various weed pests of the truck garden, inas- 
much as they are liable to several important diseases 
in common with the cultivated crops. Clean culture 
tends to destroy those weeds which act as carriers of 
some of these diseases. The more important weeds 
in this family are lamb's-quarters {Chenopodium 
album), the wormseed (Chenopodium anthelminticum) , 
orache (Ar triplex patula), and Russian thistle (Salsola 
tragus, Salsola kali, and Salsola pestifer). As far as 
we know, none of the diseases which attack beets are 
known to prey on these weeds. However, the downy 
mildew of spinach, Peronospora effusa, attacks also 
the lamb's-quarters, the worm seed, and the orache. 
From this fact may be seen the importance of clean 
culture in the control of downy mildew. In trucking, 
as in every system of intensive culture, weeds are sel- 
dom tolerated. But they are often overlooked on the 
roadside and around old fences, where they cause 
clean culture to be of no avail. Weeds should 
never be tolerated anywhere within the reach of the 
trucker or gardener. 



CHAPTER XI 

FAMILY COMPOSITE 

This important family includes the artichoke 
(globe and Jerusalem), chicory, endive, lettuce, salsi- 
fy, and sunflower. As far as we know, there are no 
available statistics of the acreage and money value in 
the United States of artichoke, chicory, salsify, and 
sunflower. They are, nevertheless, of considerable 
economic importance. According to the Thirteenth 
Census of the United States (1909) the area in lettuce 
was 5489 acres, and the crop is estimated at $1,595- 
085. Florida leads with 1450 acres and New York 
follows with 1012 acres. The other States in order 
of importance are California, Louisiana, Massachu- 
setts, Illinois, New Jersey, Missouri, Pennsylvania, 
Ohio, Virginia, and Maryland. States with less than 
100 acres of lettuce are omitted. 

DISEASES OF ARTICHOKE, JERUSALEM 
{Helianthus tuberosus) 

Jerusalem artichoke is subject to the attack of but 
few diseases. With the exception of downy mildew, 
none needs to be feared by the trucker or gardener. 
137 



138 Diseases of Truck Crops 

Downy Mildew 

Caused by Plasmopara Halstedii (Farl.) B. and D. 

This mildew attacks the Jerusalem artichoke as 
well as the sunflower. The disease is of little eco- 
nomic importance. The trouble is apparent as 
downy whitish patches on the under side of the leaves 
which soon spread, involving the entire area of the 
affected foliage. This soon turns yellowish, becomes 
dry and brittle, and dies. 

Rust 

Caused by Puccinia helianthi Schw. 

This rust is supposed to be the same as the rust of 
the sunflower. However, the work of Arthur ^ shows 
that no infection takes place when the teliospores 
from the sunflower are sown on the Jerusalem arti- 
choke. It is probable that we deal with physiological 
races. The rust on the artichoke is characterized 
by numerous spore pimples, yellow at first but later 
turning to dark brown. 

Leaf Blotch 

Caused by Ramularia cynarcB Sacc. 

This disease has as yet proved to be of little 
economic importance in the United States. In 
Europe, however, leaf blotch seems to cause con- 

' Arthur, J. C, Mycologia, 11 : 53, 1905. 



Family Composite 139 

siderable damage. Grayish irregular spots appear 
on the leaves and often become so numerous as to 
involve the entire surface, in which case the affected 
leaf becomes brown and eventually dies. 

DISEASE OF ARTICHOKE, GLOBE {Cynara 
scolymus) 

The globe artichoke is little cultivated and very 
little known to the people of the United States. In 
Europe and especially in Asia this delicious truck 
crop is more extensively grown. Globe artichoke is, 
as far as known, attacked by few diseases. 

Leaf Spot^ 

Caused by Cercospora ohseura H. and W. 

Heald and Wolf found this disease on the globe 
artichoke in Beeville, Texas. The disease is char- 
acterized by minute gray spots on the upper surface 
of the leaf. The gray color is brought about by the 
appearance of the tufts of conidiophores and conidia 
on the surface of the spots. 

The conidiophores of the fungus are non -septate, 
borne in groups of four to seven, and hyaline at the 
tips. The conidia are cylindrical in shape, straight 
or curved. 

Control. None of the diseases of the Jerusalem or 
the globe artichoke are ever serious enough to attract 
attention. However, where these crops are grown 

' Heald, F. D., and Wolf, F. A., Mycologia, 3 : 5-22, 191 1. 



140 Diseases of Truck Crops 

extensively, spraying with Bordeaux 4-4-50 is re- 
commended for downy mildew (Plasmopara Halstedii) 
of the Jerusalem artichoke, and for leaf blotch {Ramu- 
laria cynarcB) . In damp weather it may be necessary 
to spray from three to four times during the season. 

DISEASES OF LETTUCE {Lactuca sativa) 

Lettuce is subject to numerous diseases in the field 
on account of the extreme tenderness of the foliage. 
None of the diseases to be mentioned should be 
allowed to gain a foothold in the fields. 

Bacterial Blight 

Caused by Pseudomonas viridilividum Br. 

This is a serious disease, common especially in 
Louisiana and in other States where lettuce is grown 
extensively. The disease was first described by 
Brown ' who found that large acreages of lettuce were 
ruined by the blight. The growers at first believed 
that the trouble was brought about by the use of 
cottonseed meal. However, this vv^as proven to be 
not true, since the trouble was also found to a very 
serious extent where no cottonseed meal was used as 
a fertilizer. The writer has found the same trouble 
in the lettuce fields in Texas. 

Symptoms. The disease seems to attack only the 

I Brown, Nellie A., U. S. Dept. of Agr. Jour. Agr. Research, 4 : 
417-478, 191 5. 



Family Compositae 141 

outer leaves of a head. The affected foliage is first 
covered with numerous watersoaked spots which 
enlarge, fuse together, and involve the entire area of 
the affected leaves. The latter either soften or dry- 
up, opening up the way for the entrance of other 
decay organisms, which may now attack the other- 
wise sound head. 

The organism is rod-shaped, occurring singly or 
in pairs, or in chains, and it moves about by means 
of polar flagella. On agar, the young colonies are 
round with entire smooth margins; they are trans- 
lucent cream white in reflected light but bluish in 
transmitted light. The older colonies are not always 
uniform in color, but may take on yellowish bands 
or become mottled. The organism does not form gas 
and it liquefies gelatine slowly. It is not especially 
sensitive to sunlight. 

Control. It is not as yet known whether Bordeaux 
mixture will control the disease. The disease should 
not be allowed to gain any headway in the field. 
Diseased plants should not be fed to cattle nor al- 
lowed to find a place in the manure pile, but should 
be destroyed by fire. In severely affected fields other 
crops should be grown and the land be given a rest 
from lettuce for at least three years. 

Downy Mildew 

Caused by Bremia lactuccE Reg. 

Downy mildew is a disease which is more trouble- 
some in Europe than in the United States, and it is 



142 Diseases of Truck Crops 

more serious on greenhouse lettuce than on that 
grown in the open. In the field it usually attacks fall 
lettuce. 

Symptoms. Affected leaves lose their natural 
green color and turn yellow. A careful examination 
will disclose a delicate downy web on the under side 
of the foliage which will have a wilted appearance. 
The downy web consists of the conidiophores of the 
fungus. These appear singly and are much branched. 
The conidia germinate by means of a germ tube. 
Downy mildew attacks not only lettuce, but also chic- 
ory and numerous other Compositae. 

Control. Spraying lettuce is not recommended. 
Clean culture and careful regulation of the soil mois- 
ture will help to control this trouble. Downy 
mildew is seldom found on well drained lands. In 
greenhouses, the disease may be checked by the 
sudden lowering of temperature for a day or two. 
Soil sterilization with formaldehyde (see p. 53) will 
also be effective. 

Gray Mold 

Caused by Sclerotinia Fuckeliana De Bary 

Gray mold attacks grapes in Europe but in the 
United States it is commonly met with in the lettuce 
fields, especially on plants which are fully developed 
and somewhat overgrown. 

Symptoms. The disease is manifested by soft, 
watersoaked spots on the foliage causing a wilting. 
The spots soon become coated with the fruit of a 



-'^gCS^ 




Fig. 22. Lettuce Drop. 

To the right, artificially inoculated plant; to the left, healthy. 






Family Compositae 143 

gray mold. The fungus has two stages. Botrytis 
cinerea Pers. of wilted lettuce leaves appears as a 
gray mold, the other is the winter or apothecial stage. 
American botanists have not as yet been able to con- 
nect these two forms. It seems, however, that 
Istvanffi' was able to confirm the work of De Bary, 
who first indicated the relationshp of Botrytis cinerea 
with Sderotinia Fuckeliana. 

Lettuce Drop 

Caused by Sderotinia libertiana Fckl. 

Drop is a disease which is found wherever lettuce 
is grown. The greatest damage is reported from the 
South Atlantic States, North and South Carolina, 
Alabama, Georgia, Florida, Louisiana, although the 
trouble extends also to such States as Massachusetts, 
New York, Ohio, Pennsylvania, Connecticut, Rhode 
Island, Wisconsin, Iowa, Washington, Vermont, 
Maine, Maryland, Delaware, and Virginia. 

Symptoms. The term drop best describes the 
symptoms of the disease. The first sign is a wilting 
of the lower leaves (fig. 22), which is immediately 
followed by a drooping of upper ones until the entire 
plant is involved. The affected plant has a sunken 
appearance as if scalded with boiling water. In 
examining a dead plant, a white cottony fungus 
growth is found on the under side of the lower leaves, 
and near the moist regions at the stem end. 

' IstvanflB, G. De, Ann. de I'institut central ampd. roy. Hongrois: 
183-360, 1915. 



144 Diseases of Truck Crops 

When the plants are fairly rotted, there appear on 
the cottony mycelial growth mentioned above, black 
bodies, or sclerotia, which vary in size from a pin- 
head to a grain of corn. The three definite symptoms 
of the disease may be summarized: (i) drooping, (2) 
cottony-like mycelial growth on the under surface of 
the affected leaves, (3) the appearance of sclerotia 
(fig. 23 c). The latter help to carry over the fungus 
during the winter. After the sclerotia have been in 
the soil over winter, they germinate in the following 
spring by sending out small mushroom-like fruiting 
bodies known as apothecia (fig. 23 a). The latter 
contain small sacs or asci which bear the spores (fig. 
23 b and d). 

Control. The work of Stevens ' seems to show that 
lettuce drop may be controlled by the following 
method: The field is inspected as often as possible 
during the season. Every plant which shows indica- 
tions of disease is pulled out and burned and the 
place where it grew is drenched with a solution of one 
pound of bluestone dissolved in seven gallons of water. 
If these directions are carried out for three years the 
disease will be controlled. The simplicity of the 
method should make it appeal to truckers and gar- 
deners. 

Leaf Spot 

Caused by Septoria lactucce Pass, and Septoria 
consimilis E. and M. 

' Stevens, F. L., North Carolina Agr. Expt. Sta. Bui. 217 : 7-21, 





Fig. 23. LETTL'cii Diseases. 

a Germinating sclerotium of Silerolinia liherliana 
the cause of lettuce drop, b. section of fruiting cup 
(apothecium) showing asci, ascospores and paraphyses 
of .S'. Uberliana, c. section through sclerotium of 6. 
librrHanii. d. germinating ascospore of .S'. liherliana (a. 
to d. after F. S. Stevens), e. Cercospora leaf spot. 



( 



Family Compositae 145 

This disease is induced by two species of Septoria 
fungi. The symptoms produced by both are so 
nearly aHke that it is difficult to distinguish one from 
the other, except by microscopic examination. Pale 
brown discolored spots appear on the older leaves 
with numerous black pycnidia in the center. The 
disease is of little economic importance, as it usually 
occurs late in the season, on plants which have nearly 
passed their usefulness. The Boston variety is con- 
sidered resistant, while the Salamander and the 
Wonderful are more susceptible to leaf spot. 

Shot Hole 

Caused by Marsonia perforans E. and E. 

The disease is of little economic importance. Af- 
fected leaves are covered with dry spots which drop 
out, leaving irregular perforations. Along the border 
of these holes, the causative fungus may be found 
abundantly fruiting. The disease attacks the mid- 
ribs of the leaves as well as the stem of the plants. 
It seems to be more prevalent under conditions of 
surface irrigation. With sub-irrigation, on the other 
hand, it is not found to cause any damage. 

Cercospora Leaf Spot 

Caused by Cercospora lactuccE Stev. 

This disease is as yet of no importance in the 
United States. The trouble occurs in Porto Rico, 



146 Diseases of Truck Crops 

where it has been recently described by Stevenson. ^ 
The causative fungus attacks the older and lower 
leaves, forming numerous irregular, ragged spots 
(fig. 23 e). 

Rosette, see Rhizoctonia, p. 45 

Root Knot 

Caused by Heterodera radicicola (Greef) Muller. 

This disease is prevalent in the light sandy loams 
which are infected with eelworm. Small, stringy, 
bead-shaped knots form on the roots and rootlets. 
Lettuce thus affected seldom succeeds in heading out, 
but remains dwarfed and sickly looking. For a 
further description of the trouble and its control 
see p. 49. 

DISEASES OF SALSIFY {Tragopogon 
porrifolius) 

Salsify, or oyster plant as it is commonly known, is 
subject to but few diseases, all of which are generally 
of little economic importance. This is perhaps due 
to the fact that it is little grown and that its edible 
qualities are little appreciated by the American 
consumer. 

Soft Rot 
Caused by Bacillus carotovorus Jones 

'Stevenson, J. A., Journal Department of Porto Rico, i :93- 
117, 1917. 



Family Compositae 147 

Soft rot of salsify is more a storage trouble than a 
field trouble. The disease, as it has been studied by 
Clinton, ^ was found to be the same as the soft rot of 
the carrot and of various other vegetables. It was 
found in salsify roots stored in poor cellars, lacking 
the necessary ventilation. 

Symptoms. Soft rot usually begins at the crown 
and works downwards into the heart of the root. 
The outside and harder tissue remains sound and 
seems to form a firm coating to the centrally decayed 
tissue. The bacteria work first in the fibro-vascular 
bundles, the soft rotted portion being found in the 
center of the root. The germ Bacillus carotovorus, 
the cause of the soft rot of carrots, is responsible also 
for this disease of the salsify. 

Control. It is suggested that roots which show soft 
rot should not be used for seed crops. Diseased 
roots should not be fed to cattle nor should they be 
dumped on the manure pile. The storage cellar 
should be allowed plenty of ventilation, especially 
during the first three weeks of storage. 

White Rust 

Caused by Albugo tragopogonis (D. C.) Gray. 

White rust is a field disease that seldom gives any 
trouble in dry seasons, nor is it found to any appre- 
ciable extent on new lands. The disease is charac- 

' Clinton, G. P., Connecticut Agr. Expt. Sta., 38th, Ann. Rept.: 
25-27, 1914. 



148 Diseases of Truck Crops 

terized by whitish blisters or sori on the leaves. 
When these blisters are mature, they burst open, liber- 
ating a white dust composed of the spores of the para- 
site. In badly infected plants diseased leaves turn 
black and split and tear lengthwise. The rust at- 
tacks leaves only, resulting indirectly in small and 
dwarfed roots. To keep this trouble in check salsify 
should be planted on new land. 

Rust 

Caused by Puccinia tragopogoni (Pers.) Cda. 

This rust resembles the white rust in appearance, 
except that the blisters here are brown instead of 
white. It is found wherever salsify is grown, but it 
does not seem to have caused considerable damage. 
The life history of the fungus is little known. 

Southern Blight (fig. 24), see Pepper, p. 305 

DISEASES OF THE SUNFLOWER 
{Helianthus annuus) 

The sunflower can hardly be considered a truck 
crop. Nevertheless, this plant finds a place in truck- 
ing, as it is often grown for its seed as a poultry 
feed. Sunflower seedlings are subject to damping 
off, Pythium de Baryanum Hesse. For a detailed 
description of this trouble, see pages 42-44. 

Downy Mildew {Plasmopora Halstedii Farl.) 
of the sunflower is not different from the same dis- 
ease on Jerusalem artichoke, p. 138. 




c**^i^^ 



Fk.. 24. Southern Blight of the Salsify. 

To the right healthy plant, to the left diseased plant, with root rotted off. 



Family Compositae 149 

Rust 

Caused by Puccinia helianthi Schw. 

Rust attacks the wild as well as the cultivated sun- 
flower, producing blisters or sori on the leaves. The 
former are at first yellow or brown, but later in the 
season become black. Badly infected leaves turn 
yellow, then curl and dry up. This results in a re- 
duction in the yield of seed, which for the most part 
fails to fill out properly. This rust seems to attack 
the sunflower only and is apparently unable to infect 
the Jerusalem artichoke. Clean culture and des- 
troying the refuse by fire is advised. 

WEEDS 

The family Compositae contains a large number of 
weeds. The following are often troublesome: rag- 
weed {Ambrosia artemisijolia) , great ragweed {Am- 
hrosia trifida), Mayweed {Anthemis cotula), burdock 
{Arctium minus), ox-eye daisy {Chrysanthemum 
leucanthemum pinnatifidum) , blue sailors {Cicorum 
intyhus), bull thistle {Cirsium lanceolatum) , fireweed 
{Erechtites hieracifolia) , wild or tall lettuce {lactuca 
canadensis), prickly lettuce {Lactuca scariola), fall 
dandelion {Leontodon autumnalis) ', Canada golden- 
rod {Solidago canadensis), dandelion {Taraxacum 
officinale), cocklebur {Xanthium commune). 

Of the weeds which are attacked by downy mildew, 
Plasmopara Halstedii Farl., may be mentioned the 
ragweed, the great ragweed, and Canada goldenrod. 



150 Diseases of Truck Crops 

None of the weeds here mentioned is attacked by 
rust, Ptcccinia helianthi Schw. If downy mildew is to 
be kept in check the truck patches must be kept free 
from weeds. 



CHAPTER XII 

FAMILY CONVOLVULACE.E 

This important family includes but one truck 
crop, the sweet potato. The latter is of great eco- 
nomic importance to truckers who are situated in 
sandy or sandy loam regions. Sweet potatoes cannot 
thrive in heavy clay soils. 

According to the Thirteenth Census of the United 
States, the total acreage of sweet potatoes in 1909 
was 641,255 acres, with a total production of 52,232,- 
070 bushels, worth $35,429,176. North Carolina 
has the distinction of having the largest acreage in 
sweet potatoes, 84,740. The other States which 
follow, according to rank, are, Georgia, Alabama, 
Louisiana, Mississippi, South Carolina, Texas, Vir- 
ginia, Tennessee, New Jersey, Arkansas, Florida, 
Kentucky, Illinois, Maryland, Missouri, Delaware, 
Oklahoma, Kansas, Iowa, and West Virginia. States 
with less than 2000 acres are here omitted. 

DISEASES OF THE SWEET POTATO 
{Convolvidus batatas) 

Sweet potatoes are subject to numerous field and 
storage diseases, many of which may be controlled. 
151 



152 Diseases of Truck Crops 

Slime Mold 

Caused by Fuligo violacea Pers. and Physarum 
plumbeum Fries. 

Very often the plants in the seed beds are covered 
with white, yellov^^ish, or purple jellylike growths. 
These patches may vary from three to six inches or 
more in diameter and cover the foliage, peduncles, 
and stems. In 12 to 24 hours this slime thickens and 
becomes covered with a white or yellowish crust 
which readily cracks and liberates the spores in the 
form of a dark brown pov/der. The growth, which 
is a slime mold, has been determined as Fuligo 
violacea Pers. (fig. 25 a). The organism is not a 
parasite on the sweet potato plant; nevertheless its 
presence in a seed bed is not desirable. The slime 
mold covers the plant, shutting off light which is es- 
sential for its proper nutrition. There is another 
slime mold, Physarum plumbeum Fries., which often 
grows on the foliage (fig. 25 b). These molds are 
seen only in seed beds in the open or on sweet potato 
beds in the greenhouse. 

"Soil Rot," "Pox," or "Pit" 

Caused by Cystospora batatas E. 

The term soil rot is somewhat misleading, as the 
disease does not produce a rot. The name "pox" 
or "pit" is a better description of the disease. 




Fig. 25. Sweet Potato Diseases. 

a. Slime mold {Fuligo violacea), b. slime mold (Physarum plumbeum), c. pox or 
pit, d. formation of a cyst and liberation of spores of Cyslospnra halala (after Elliot), 
e. white rust, /. oospore of the white rust fungus, g. soft rot, h. ring rot, i. fruiting 
stalks of Rhizopus nigricans. 



Family Convolvulaceas i53 

Symptoms. This disease is early marked by 
small, dark, dry spots on the surface of the potato 
(fig. 25 c). Later the infected portion in most cases 
cracks, dries, and falls out, leaving a pit with a newly 
formed, roughened skin. It is an underground trou- 
ble and is not detected in the field until late in the 
season, at a time when healthy hills have formed well 
developed vines. At this time the lack of an abun- 
dant vine growth is a characteristic symptom, and the 
rather meager stem development gives the impression 
that the soil is very poor and exhausted in plant food. 
The symptom appears when the sweet potato is begin- 
ning to form. At this stage the spotted portion 
ceases to grow, while the healthy portion on each side 
continues to develop. Frequently roots that are 
very badly spotted cease to grow altogether, and if 
they are stored, the spots usually dry and fall out. 
Unlike black rot, roots affected with soil rot do not 
lose their food value, as the disease is only skin deep 
and imparts no bad taste to the potato. The disease 
also attacks the young rootlets of the plant, and when 
this is the case there is practically no crop formed. 
This, however, happens only in badly diseased fields, 
and especially where lime is used. The latter should 
never be applied to lands infected with the pox organ- 
ism. The trouble, unlike many others, seems to be 
worse in dry weather. 

Besides affecting the sweet potato, pox also causes 
circular shallow pits on the white potato, and on 
turnips, the pits on the latter being even more shal- 
low than on the former. It is also suspected of at- 



154 Diseases of Truck Crops 

tacking beet and tomato plants, although complete 
proof is still wanting. 

The Organism. The cause of pox was first thought 
to be the fungus Acrocystis batatas E. and H. In- 
vestigations of the writer showed that this was not 
the case. Finally Elliot ' found that pox was caused 
by a slime mold organism which he named Cysto- 
spora batatas E. 

The swarm spores of the slime mold are very 
small, round, but slightly pointed at both ends. 
They often fuse in pairs, forming spherical bodies 
with a single nucleus. The amoebae soon become 
circular, and four central nuclei together with a dis- 
tinct wall membrane become apparent. Nuclear 
division takes place and many nuclei are now formed 
within the cyst body. As the cyst advances in age, 
a cell wall is laid down, and each nucleus with its 
surrounding protoplasm now begins to round up into 
individual spores. The latter when mature break 
through the wall of the cyst, which dissolves ap- 
parently through the secretion of an enzyme within 
(fig- 25 d). 

It is very doubtful if the organism is carried with 
infected sweet potatoes, since the spots nearly always 
dry and fall out. The organism is carried over in 
the land from year to year. The exact means by 
which it is carried from place to place is not definitely 
known. The organism does not seem to spread very 
rapidly to adjoining neighboring fields, nor to places 
on the same farm. 

' Elliot, J. A., Delaware Agr. Expt. Sta. Bui. 114 : 3-25, 1916. 



Family Convolvulaceae 155 

White Rust 
Caused by Cystopus ipom(BCB-pandurancB Farl. 

White rust is a disease of the foliage only. It is 
present in nearly every field where sweet potatoes are 
grown. Although prevalent, the disease is almost 
unrecognized as such by the growers. The losses 
from it are indirect. While it is true that the sweet 
potato is grown only for its roots, nevertheless, a good 
crop depends upon a healthy and abundant stand of 
leaves. The sugar and the starch in the potato are 
not manufactured from the soil, but are made by the 
leaves from the air and sunlight, and are then stored 
in the roots. The effect of white rust is to kill much 
of the foliage, thereby curtailing the amount of sugar 
and starch manufactured, and this in turn results in a 
shorter crop and poorer keeping roots. It is gener- 
ally agreed that the more starch a root has, the better 
it keeps. The White Southern Queen variety is one 
of the best keepers, being richest in starch content. 

Symptoms. White rust appears late when the 
plants have usually made most of the vine growth and 
when the hills are beginning to set, i.e., to form new 
sweet potatoes in the soil. A typical symptom of 
white rust then is the yellowing of leaves in the center 
of the hill, which later turn brown, shrivel, and die. 

In carefully examining the center leaves as they 
begin to yellow, we see that on the under side of such 
leaves there are many minute white raised pimples, 
(fig. 25 e-f) each of which when touched mth the 



156 Diseases of Truck Crops 

finger sheds a white dust made up of millions of 
spores of the fungus. Each white pimple on the 
under side of the leaf is denoted by a small yellow 
area on the upper surface. In case of mild infection 
there are usually few pimples on the upper leaf, but 
when the disease is bad, the leaves are literally pep- 
pered with them. White rust is severest when the 
weather is dry and the nights are cool. It is also 
more abundant in the shaded portions of the field. 
With the exception of the Southern Queen, all 
varieties of the sweet potato^grown are subject to it. 

Soft Rot 

Caused by Rhizopus nigricans Ehr. 

Soft rot is mostly a storage trouble, although it is 
commonly met with in the field at digging time and 
in the seed bed. It is constantly associated with 
poorly ventilated houses, causing more damage to 
stored sweet potatoes than all other diseases com- 
bined. On an average, fully twenty per cent, of the 
total crop in storage is lost from diseases and nine 
tenths of this loss may be attributed to soft rot. 

Sympto?ns. The term "soft rot" best describes 
the symptoms of the disease. Affected roots are 
very soft and watersoaked, and when pressed, a clear 
liquid oozes out. Its presence in the bins may be 
detected in the wetting of adjacent healthy roots. 
Under storage conditions, infected roots do not pro- 
duce the sporangia of Rhizopus unless broken or 



Family Convolvulaceae 157 

bruised. Where this is the case, a black mass of 
short-stemmed sporangia or fruiting bodies of the 
fungus are formed at the crack (fig. 25 g), through 
which opening the Hquid from the root drips. When 
no such cracks are formed, the fungus fails to fruit 
and the roots dry by gradual evaporation through 
the epidermis. 

Resistance to Soft Rot. While soft rot causes the 
greatest damage to sweet potatoes in storage, not all 
the roots alike are susceptible to its attack. There 
is a certain per cent, of the crop which when housed 
poorly will soft rot shortly after the potatoes are 
taken into storage, while another per cent, seems to 
possess a degree of resistance. These latter will 
usually keep for a month or two and then rot, par- 
ticularly if the winter is mild and the roots undergo 
what is known as the second sweat. There is a 
third class of root which seems to be resistant for a 
long time. 

Odor of Soft Rot. Often storage men claim that 
soft rot emits strong, disagreeable odors. Observa- 
tions show that soft rot in bins is odorless for a week 
or ten days, after which time fermentation sets in, 
and an odor is quite noticeable. After a short time, 
the affected potatoes will become fairly dried out 
and other fungi such as Diaporthe batatis, Fusarium 
batatatis, Sderotium bataticola, and a number of sap- 
rophytic fungi gain entrance. Sometimes putrefac- 
tion follows the acetic fermentation. 

Soft rot is not carried from year to year in the 
dried-out roots which were previously destroyed by 



158 Diseases of Truck Crops 

Rhizopus ; however, the spores of the fungus preserve 
their vitaHty for a considerable time. When we 
consider how abundant these spores are in nature, 
it is not difficult to conceive how easy it is for soft 
rot to get a start every year. The storage house is 
undoubtedly the place where the greatest amount of 
Rhizopus spores are carried over from year to year. 
The main problem, therefore, is to prevent the Rhizo- 
pus spores from germinating or to use some fumigant 
which will kill them all together. 

Ring Rot 

Caused by Rhizopus nigricans Ehr. 

Ring rot is a form of soft rot. The disease is 
prevalent as soft rot and is found in poorly venti- 
lated houses. The amount of loss varies from i 
to 20 per cent. 

Symptoms. There are two forms of ring rot. 
The first stage is the soft ring which is characterized 
by a rotted area which girdles the root at any point 
(fig. 25 h-i). As the roots are usually put in bins in 
bulk and as soft ring, like soft rot, is confined to the 
roots more or less buried in the bulk of the bin, the 
onset of the disease is usually overlooked. It is at 
first odorless, but in a week or ten days it is followed 
by a characteristic fermentation. The soft ring 
gradually begins to dry, resulting in a shrinkage and 
contraction of this area, and thus a slight groove is 
formed (fig. 25 h). In two to six weeks, it becomes 




Fig. 26. Sweet Potato Diseases. 

a. Black rot at place of a bruise, 6. black shank, c. showing a pycnidium of the 
black rot fungus, d. dry rot, e. cross section throug'i /, to show the effect of the 
disease on the root. /. Java black rot surface view, showing strings of spores oozing 
out from the center of spot, g. cross section through diseased sweet potato root to 
show pycnidia of the fungus Diplodia tubericola. 



Family Convolvulaceae 159 

very dry and more or less hardened, varying with 
the nature of the fungi which act as secondary 
invaders. The second form, or dry-ring rot, is 
nothing more than the last or dried-out stage of 
the soft ring in which the primary parasite has died. 

Dry Rot 

Caused by Diaporthe hatatis (E. and H.) H. and F. 

Dry rot is a disease of stored sweet potatoes. 
Although it has a wide distribution, the trouble is 
not considered of great economic importance. The 
disease usually follows a complication of others. 
It begins at the end of the potato, producing a firm 
dry rot which progresses slowly. The rotted potato 
is brown, finally becoming hard and shriveled. The 
surface later becomes black, rough, and uneven (fig. 
26 d) and when examined under the microscope will 
be found to be studded with numerous pycnidia. 
From the mouths of the latter are seen to ooze out 
whitish strings which are made up of millions of the 
pycnidia or summer spores. The Diaporthe or as- 
cospores are formed only when the infected roots are 
allowed to hibernate. 

Foot Rot 

Caused by Plenodomus destruens Hart. 

Foot rot is a disease which, so far as is known, is 
found only in Virginia, Ohio, Iowa, and Missouri. 



i6o Diseases of Truck Crops 

Wherever present it causes serious losses to sweet 
potatoes in the field. 

Symptoms. The disease first manifests itself as 
sunken brown to black spots at the stem end of the 
plant near the soil line. The spots gradually enlarge, 
girdling the stem and working upwards. In a dis- 
eased field, all the ends of the vines nearest the soil 
line are rotted, so that the entire hill may be easily 
pulled out. Although the feet of the vines in a dis- 
eased hill rot off, the vines manage to remain partly 
alive, owing to the nourishment obtained from the 
secondary rootlets produced at the leaf nodes on the 
vines which lie flat on the ground. Diseased hills 
fail to produce any sweet potatoes, since the under- 
ground roots are cut off from the main vines. In- 
fection takes place in the field or in the seed bed. 
Moisture appears to favor the disease. With the 
death of the vines appears a pimply growth consist- 
ing of numerous pycnidia. It is believed that foot rot, 
like many other sweet potato diseases, is carried with 
the seed. The fungus Plenodomus destruens so far as we 
know possesses only the pycnidial or summer fruiting 
stage. No ascospore stage has as yet been found. 

Black Rot' 

Caused by Sphceronemafimbriatum (E. and H.) Sacc. 

Of all the diseases of the sweet potato, black rot is 
the most dreaded by growers. It is found in all 

' Material drawn from the author's work. Taubenhaus, J. J., 
Delaware Agr. Expt. Sta. Bui. 109 : 3-56, 191 5. 



Family Convolvulacese i6i 

sections where sweet potatoes are grown. Not in- 
frequently the disease is mistaken for other troubles, 
and too often its nature is unknown to the truckers. 

Symptoms, Black rot is a seed-bed disease, a field 
disease, and a storage trouble. Irregular dark areas 
or circular spots, varying in size from that of a dime to 
a silver dollar, appear on the seed (seconds) or on the 
prime potatoes. These spots extend only through 
the skin and are hard to the touch. When the roots 
are injured through cultivation, by rodents, or 
through rough handling in the field or in storage, the 
spots lose their circular outline and follow the line 
of injury (fig. 26 a). In this case the bruise is in- 
vaded by secondary parasites which may induce 
rotting of the entire root. 

The symptoms shown by the sprouts are a dwarfing 
in growth and yellowing of the foliage. In this latter 
case the end of the shank is blackened and charred 
from ^ to I inch in distance (fig. 26 b) . Where this 
stage (known as the "black shank") is present, the 
leaves of the infected sprouts wither, and turn black 
and crisp. Frequently the disease affects the stem 
and even the petioles and is indicated by black areas 
on them. In early stages of infection, and in the 
absence of the black shank stage, the rootlets are 
usually affected. For this reason it is essential to 
examine carefully the appearance of the rootlets 
when sprouts are pulled from the field. The early 
symptoms in the field are the same as those described 
for the sprouts in the seed bed. Black girdling spots 
on the vines, which are confined to areas usually 



1 62 Diseases of Truck Crops 

between two leaves, are the first symptoms on the 
plant. The disease seldom blackens the full length 
of the stem. The part below the black spot remains 
healthy, while the part above wilts and dies, since 
the infected area prevents the upward flow of water 
and plant food to the part beyond the killed area. 
Stem infection does not always indicate underground 
infection. Often where the vines are affected, the 
roots, when pulled out, seem to be free from black 
rot. In case of underground infection, sometimes 
every root in the hill is black rotted and there may 
not be the least indication of the disease on the stem 
of the plant. At digging time, roots which show the 
disease are somewhat paler in color than the healthy 
ones of the same variety, a symptom which seems to 
be general in some soils and not in others. When 
roots are infected with black rot, the edible qualities 
are poor because of the bitter taste. This becomes 
more marked the longer the roots are kept in storage. 
Although the black rot spot is only superficial, the 
bitter taste in cooking is imparted to the entire root, 
showing that it is soluble and easily diffused into 
adjacent tissue. 

Introduction and Spread of Black Rot. In the seed 
bed, the trouble begins with diseased seed. Even 
though the greatest care is exercised in discarding 
the seed, some infected roots will find their way into 
the bed. Not all gi'owers are careful in their selec- 
tion of seed, and often through lack of knowledge of 
the malady, diseased roots are used in bedding, or are 
discarded and thrown out near the bed. These seeds 



Family Convolvulaceae 163 

are then trampled upon and crushed and make a good 
starting point for the spread of black rot. As the 
seed begins to germinate, the sprouts on or near a 
mother diseased root will contract the disease. On 
pulling out this root, nearly every sprout will show 
the black shank which, upon careful examination 
with a hand lens, will be found to be strewn with the 
long-necked pycnidia of the fungus. At the tip of 
these roots are seen minute waxy droplets which con- 
sist of the pycnospores. Small mites, white minute 
spider-like animals, crawl about everywhere, especi- 
ally on and around the pycnidia. These mites, 
as well as watering, help to spread the pycnospores 
in the seed bed and result in the further infection of 
new sprouts. 

In storage, black rot is first introduced with dis- 
eased roots and is spread from one to another, fruit- 
ing best in the presence of moisture. In poorly 
ventilated houses, it is invariably noticed as soon 
as the roots begin to sprout. These sprouts turn 
black and die at the tender tip or throughout. In 
the first stage, while growing in the interior tissue, 
the fungus does not produce pycnidia. Therefore, as 
long as the epidermis on the spot is unbroken and the 
roots are kept dry, the disease cannot spread. How- 
ever, if the skin is broken or accidentally bruised, or if 
the roots are kept in a house which is overheated and 
damp, the black rot fungus will produce fruit by the 
formation of pycnidia which appear as minute raised 
dots in the center of the spot. 

The Organism, The parasite consists of a vegeta- 



i64 Diseases of Truck Crops 

tive portion known as "mycelium" which, when 
young, is hyaline, but which becomes gray with age. 
Whether young or old, they are capable of breaking 
up into as many cells as there are septa, and each cell 
may assume the function of a spore, since it will 
readily germinate. In another stage, chains of 
hyaline spores are born and pushed out from within 
long terminal cells of the mycelium. The chlamy do- 
spores apparently serve as resting spores to carry the 
fungus over winter, and the cells of the infected tissue 
are usually filled with these brown thick-walled spores. 
A last stage is that of pycnospores which are born 
within long-necked spore sacks called pycnidia (fig. 
26 c). These are minute globular spores oozing out 
in a gelatinous mass which stick to the open end of 
the long neck of the pycnidium. In pure cultures 
the spores ooze out in strings just as in the case 
of certain species of Phoma or Phyllosticta. The 
spores can germinate in water or in any nutritive 
fluid. 

Phyllosticta Leaf Blight 

Caused by Phyllosticta batatas E. and M. 

Leaf blight appears as roundish to angular spots 
on the upper side of the leaf and is separated from 
the healthy tissue by a dark line. Inside this line is 
a strip of brownish tissue which has lost most of the 
green color. Within this ring is a circular area much 
lighter in color in which the pycnidia 9.re found 



Family Convolvulacese 165 

protruding. The fungus, so far as is known, lives 
only on sweet potato foliage. 

Septoria Leaf Spot 

Caused by Septoria hataticola Taub. 

Leaf spot is a disease which is of little economic 
importance. The trouble appears as soon as the 
plants attain full growth and are beginning to 
lose in vigor. The disease has been found in New 
Jersey, Delaware, Maryland, Virginia, Iowa, and 
other States. 

Symptoms. Leaf spot is characterized by small 
whitish spots scattered indiscriminately over the 
leaf. The spots are nearly always surrounded by 
a brown border (fig. 2^ b). On the surface of the 
dead tissue are found the pycnidia which are usually 
few in numbers, often not more than one or two to a 
spot. The pycnospores are carried about from leaf 
to leaf by winds or insects. 

Septoria hataticola attacks only sweet potato foliage. 
It is very likely that the fungus hibernates on the 
dead leaves in the field. Leaf spot is never serious 
enough to warrant special methods of control. 

Java Black Rot 

Caused by Diplodia tuhericola (E. and E.) Taub. 

The disease was first found on some sweet potatoes 
that were brought to the Louisiana station from 
Java in the spring of 1894. The potatoes appeared 



i66 Diseases of Truck Crops 

sound, but failed to grow when planted. Upon 
examination the roots were found to be rotted. The 
fungus which caused the rot was sent to Ellis, who 
identified it as a new genus and gave it the name of 
Lasiodiplodia tuhericola. Sweet potatoes brought 
from Java in the spring of 1895 were found to be 
affected with the same fungus when they were re- 
ceived at Baton Rouge. This seems to indicate that 
the fungus was introduced in the United States from 
Java. 

Symptoms. Sweet potatoes affected by the fungus 
show dark shriveled patches over which are scattered 
numerous pycnidia. These emit either mature one- 
septate dark spores of Diplodia type, heaped to- 
gether, or white strings (fig. 26 f), which are made up 
of hyaline Macrophoma spores, or both (fig. 26 f). 
In making longitudinal sections through different 
stages of affected roots, it will be found that the fun- 
gus attacks the interior tissue, beginning at the point 
and gradually invading the whole of the interior of 
the root. The infected tissue is jet-black (fig. 26 e), 
somewhat resembling the charcoal disease. In- 
fected roots dry and shrivel and become brittle. 
Complete rotting of the root is effected in four to 
eight weeks. The active enzyme from the fungus 
precedes the mycelium some distance, for in a longi- 
tudinal section of a newly infected root two zones 
may be observed, one, a dark area which is occupied 
by the fungus, and the other, a brown zone which 
precedes the dark patch in which the mycelium is 
absent. The pycnidia are bom singly or in groups 




Fig. 



Sweet Potato Diseases. 



a. Trichoderma rot, b. Septoria leaf spot, c. soil stain d Charcoal rot ^ T 

Tre'Jfn^o"'?'. V^';.'""'"'' "^.^'^^ ^"' '^ d^^'^' ^^ile the si'de'shoots are lu^e as ttev 
are supported by the secondary roots formed at the nodes of the vines /,wlJ 
potato artificially inoculated with Sclerotium Rolfsii. g. net necrosfs. ^' 



Family Convolvulaceae 167 

under the epidermis, and the latter is ruptured at an 
early stage (fig. 26 f). They are also formed through 
the interior tissue of the infected root, and it seems 
that in this case the spores can escape only when the 
roots break up and disintegrate. ^ 

Trichoderma Rot 

Caused by Trichoderma Koningi Oud., and Tricho- 
derma lignorum (Tode.) Harz. 

The symptoms of several of the different rots on the 
sweet potato are often so similar that it is difficult to 
find appropriate, popular names with which to char- 
acterize each disease. Trichoderma rot by itself 
does not exist under the average storage conditions. 
But it follows other rots, particularly ring rot, and 
soft rot, causing further destruction of the partially 
affected roots. Trichoderma rot is a storage trouble 
only, and the causative organism is no doubt brought 
in from the field adhering to particles of soil. 

Symptom. In the earliest stages, the spots are 
circular, and of a light brown color, with a tendency 
to wrinkle. The flesh is hard and watersoaked, 
brown in color with a black zone in the region be- 
tween the healthy and diseased tissue (fig. 27 a). 
The spot enlarges in all directions and eventually 
destroys the entire root. When the decay is well 
advanced, a very luxuriant, white, mycelial growth 
is formed on the surface. Spores are produced very 

» For further details of this fungus see Taubenhaus, J. J., Ameri- 
can Jour, of Bot., 2 : 324-3-31, 1915. 



i68 Diseases of Truck Crops 

sparingly from this growth when in contact with the 
decayed tissue, but very abundantly on that part of 
the mycelium which has spread over the healthy sur- 
face or into the glass or filter paper of the moist cham- 
ber. Trichoderma lignorum is common and widely 
distributed on decaying wood and various other sub- 
stances. Trichoderma Koningi was originally iso- 
lated from the soil by Oudemans and is still looked 
upon as a soil organism. The spores are elliptical and 
are borne on characteristic conidiophores (fig. 28 p). 

Soil Stain or Scurf 

Caused by Monilochaetes injuscans E. and E. 

Soil stain is not a disease to be feared in the sense 
that it may produce a direct rot in the mature roots. 
Nevertheless, it is economically important. Growers 
whose lands are badly infected assert that stained 
roots keep better in storage. Others find consolation 
in saying, "There is no such thing as stain, the dark 
color of the skin being merely a varietal character- 
istic." The fact remains, however, that many 
Eastern markets discriminate against stained roots. 
In years of over-production the New York market 
refuses stained roots altogether. The Western buy- 
ers, on the contrary, are lax on this point; other- 
wise, many growers in the United States would be 
forced to cease producing sweet potatoes for want 
of a market, since soil stain is prevalent on practi- 
cally all sweet -potato land. 

Symptoms. Soil stain is characterized at first by 
small, circular, deep clay-colored spots on the surface 



'' Family Convolvulaceae 169 

of the sweet potato root. These spots occur singly; 
but usually several occur in a given area. When 
very numerous, the spots coalesce, forming a large 
blotch, which sometimes takes the form of a band, 
or which may cover the entire root. Soil stain is 
particularly conspicuous on the white-skinned varie- 
ties, such as the Southern Queen. Here the color of 
the spots is that of a deep-black clay loam. On the 
darker-skinned varieties the color of the spots does 
not appear so conspicuous. Soil stain is a disease of 
the underground parts of the plant. The vines and 
foliage are never attacked so long as they remain free 
from the soil. But when they are covered, the peti- 
oles as well as the stems become infected. 

After several months of storage, badly affected 
roots become a deep brown, contrasting strongly with 
non-infected potatoes. Occasionally, badly stained 
roots seem to be subject to more rapid drying and 
shrinking. This, however, is not often the rule. 
Usually soil stain is prevalent in over-heated storage 
houses. It may be, therefore, that the rapid shrink- 
age is due to the overheating and not to the effect of 
the disease itself. More data are necessary to deter- 
mine this point. Soil stain is a disease not only of the 
epidermis that considerably reduces the market value 
of the mature roots, but it also attacks the very 
young rootlets, preventing their further development 
and indirectly reducing the yield. In badly affected 
fields the writer has estimated a loss of 10 per cent, of 
the crop from the rootlet infection. 

The type of soil seems to be a determining factor 



I/O Diseases of Truck Crops 

in the development of soil stain. Sweet potatoes, 
grown on very light sandy soils, especially those 
which are hilly, are usually free from the disease. 
Heavier lands, or those rich in humus, rarely produce 
a clean crop. The application of manure favors the 
spread of the fungus and increases the stain. In 
fact, the manure itself is often a carrier of the disease, 
since diseased roots of all sorts find their way 
ultimately to the manure pile. The trouble is also 
carried directly with the seed stock. This, when 
planted in the seed bed in diseased condition, will 
produce lOO per cent, of diseased sprouts. Wet 
weather is favorable to the spread and increase of 
stain. During wet seasons the disease is more 
plentiful than in dry seasons. 

The Organism. The spores are born in distinct 
chains which break up very readily when moistened 
(fig. 28 a-1). The conidiophores are bom on the 
surface of the epidermis (fig. 28 n). Careful ob- 
servation of these chains have shown them to be 
made up of from 10 to 28 conidia. The spores (con- 
idia) are one celled, hyaline, with a greenish tinge, 
but never dark or brown. The spores readily germi- 
nate in water or in any nutrient medium (fig. 28 o). 

Vine Wilt or Yellows (Stem Rot) 

Caused by Fusarium hatatatis WoU. Fusarium 
hyperoxysporum Woll. 

The terms "stem wilt, " "vine wilt, " or "yellows" 
are commonly used to describe this disease, and 




Fig. 28. Sweet Potato Diseases. 

a. and /. Chains of conidia of the soil stain fungus MonilochcEtes infuscans, 
b. to /. manner in which the chains of conidia of M. infuscans are breaking up 
into individual spores, o. germinating conidia of M. infuscans, n. part of a 
cross section of a sweet potato root showing the relationship of M. infuscans 
to the epidermis of the host, p. conidiophores of Trichoderma Koningi, a, 
young strands of mycelium of Phymatolrichum omnivorum, r. mycelial strands 
of the Texas root rot fungus, Ozonium omnivorum from dead cotton plant (g. 
and r. after Duggar), m. sclerotia of Sclerolium balaticola. 



Family Convolvulaceae 171 

they are more appropriate than the name "stem 
rot." 

Symptoms. There is no doubt that "stem wilt" 
has its origin in the seed bed. In badly infected 
soils, it is often difficult for the plants to get a stand, 
as they die a week or two after being put out. They 
first lose their green color, and turn pale, and when 
they are pulled out, they will be found to be cracked 
lengthwise because of the swelling. The presence of 
stem wilt may easily be determined by inserting the 
nail into the stem and peeling off a piece of epidermis 
and cambium ; the vessels will be found to be a brown 
color. Frequently the stem is covered with a pink- 
ish layer of sickle-shaped spores of the Fusarium 
parasite. Often, and particularly in moist seasons, 
infected sprouts continue to grow, sometimes until 
digging time, and even produce fair sized roots, pro- 
vided no secondary invaders set in to destroy the 
hill. Sometimes black rot, as a secondary parasite, 
sets in at the base of the stem near the ground, kill- 
ing the bark or covering of the stem, thus shutting 
off all food supply, and resulting in the dying of the 
entire hill in a short time. Frequently a wet bacte- 
rial rot starts in the base of the plant where black rot 
has followed stem wilt. This stage helps to convey 
the erroneous impression that stem wilt induces an 
actual rotting in the field. Yellowing of the affected 
stems and vines, while a frequent symptom, is not 
always pronounced. Often the disease in plants 
can hardly be detected, as the fungus is hidden inter- 
nally in the fibro-vascular bundles and the roots main- 



172 Diseases of Truck Crops 

tain a thriving green appearance. In clipping the 
tip end of such a root, the bundles appear brown in 
color, and usually the disease may be traced^through 
the entire length of the root. Sometimes only a few 
bundles in the root are affected, while in others 
each shows the brown ring near the cambium. It 
is better that the affected sprouts should die 
early, for if they grow and produce roots of the 
No. 2 type, they carry the disease to the seed bed. 
This is more of a field than a storage trouble. In 
large and badly infected roots in storage, the 
fungus may produce a punky, dry rot which has 
a peculiar cinnamon odor and a deep chocolate 
color which may make the roots light and shriveled 
(see fig. 2'] a-e). 

A diseased hill one year will mean several diseased 
hills the following year. In plowing up the land for 
sweet potatoes the original hill is broken, and the 
stem wilt fungus is carried some distance in both 
directions by the plow and the harrow. The culti- 
vator, too, may, during the season, help to carry the 
disease and induce new infections by injuring the 
sprouts. Dead sprouts and dead hills, if left over 
in the field, furnish material on which the fungus will 
fruit abundantly. 

The two organisms greatly resemble each other in 
spore form (fig. 7 c-d). Yellows is prevalent in New 
Jersey, Maryland, Virginia, Illinois, Iowa, Alabama, 
Arkansas, Missouri, North Carolina, Ohio, Georgia, 
Texas, Oklahoma, and Mississippi. A conservative 
estimate of the losses from yellows would be at least 



Family Convolvulace^ i73 

three quarters of a million for the entire sweet potato 
crop of the United States, 

Charcoal Rot 

Caused by Sclerotium hataticola Taub. 

"Charcoal rot" is a new name for an old trouble. 
It is mainly a storage trouble and is found most com- 
monly in overcrowded houses and in bins nearest the 
stoves,. It is especially plentiful in houses which 
lose heavily from soft rot. After the work of Hal- 
sted, from 1890 to 19 13, the fungus which caused 
charcoal rot was believed to be a stage of the black 
rot fungus. But it has been shown by the writer that 
charcoal rot is a distinct disease and that the fungus 
which causes it is in no way connected with or re- 
lated to the black rot organism, SphcBronema fim- 
briatum (E, and H.) Sacc. 

Charcoal rot is commonly mistaken for black rot. 
While black rot produces only superficial spots on the 
roots, and does not produce a rot of the entire root, 
charcoal rot is a disease which penetrates the entire 
root. The parasite does not produce surface spots, 
but turns the interior tissue into a black charcoal 
mass (fig. 27 d) caused by the formation of minute 
colored sclerotia (fig. 28 m). With the exception of 
drying and slight shrinkage, there are no external 
symptoms to distinguish the disease unless the skin 
is bruised, showing the blackened contents. It can 
be recognized when the roots have been completely 
invaded. Recent studies on this disease seem to 



174 Diseases of Truck Crops 

indicate that infection takes place from a bruise on 
the epidermis and from there the fungus works slowly 
inward. It is not uncommon, therefore, in slight 
cases of infection, to find, upon making a cross section 
of the root, a jet black ring ranging from one third 
to one half an inch in diameter immediately under the 
epidermis, the color grading off from dark to a light ash 
as it nears the center of the root. At this stage the 
infected sweet potato is watersoaked but quite solid. 
A liquid, brownish in color, may be squeezed from 
such roots. Charcoal rot is almost unknown in well 
ventilated houses. There seems little doubt that 
the fungus S. bataticola is a common field saprophyte, 
which may be brought into the storage house with 
the sand or soil which clings to the roots. Diseased 
roots kept dry for one year will readily yield a pure 
culture of the fungus, thus showing that these roots 
carry the fungus from year to year. 

The Organism. The sclerotia are jet black, very 
minute, smooth, and made up exteriorly of anasto- 
mosed black hyphae. The interior of the sclerotia is 
light to dark brown, composed of thick walled cortical 
hyphal cells (fig. 28 m). The sclerotia appear singly, 
and oftentimes in long chains, and abound through- 
out the entire affected root. 

Cottony Rot 

Caused by Sclerotium Roljsii Sacc. 

Cottony rot is mostly a disease of the seed bed. 
Infected sprouts suddenly wilt and topple over, giv- 



Family Convolvulaceae i75 

ing the effect of damping off. In examining an 
infected sprout it will be found that in the earlier 
stages of attack the foot of the plant is soft, water- 
soaked, and covered at the exterior by fungus 
threads. Later this growth becomes thick, giving 
the appearance of fluffy cotton placed at the foot of 
the sprout. Soon after, the cottony mycelial growth 
anastomoses, then disappears, giving birth to small 
roundish brown bodies like mustard seed known as 
sclerotia. 

Sderotium Roljsii seldom attacks mature sweet 
potato roots. However, when the fungus is arti- 
ficially inoculated in sound roots, a punky dry but 
slow rot is the result (fig. 27 f). For further dis- 
cussion of this fungus as it attacks other hosts see 
P- 305. 

Texas Root Rot 

Caused by Ozonium omnivorum Shear. 

So far as is known, this disease occurs only in Texas, 
New Mexico, Oklahoma, and Arizona, The disease 
is of great economic importance in these States, since 
numerous other crops are subject to its attacks. 
The symptoms of Texas root rot are a girdling of the 
vines at the stem end, and a similar effect on the roots 
(fig. 27 e and fig. 28 g and r). In these cases, the 
epidermis and cambium may be readily slipped off 
from the main body of the infected stem and root. 
For a more detailed account of the Texas root rot, 
see okra, p. 297. 



176 Diseases of Truck Crops 

Root Knot 
Caused by Heterodera radicicola (Greef) Miill. 

Root knot of sweet potatoes is commonly found in 
the Southern States in light sandy soils. It is char- 
acterized by small swellings on the lateral feeding 
roots. For further description, see p. 49. 

Methods of Controlling Sweet Potato Diseases 

The grower in dealing with sweet potato diseases 
has a fourfold problem. No amount of care will 
suffice to keep down his losses from disease, unless 
he handles the problem thoroughly, beginning with 
the seed and continuing through the seed bed, the 
field, and the storage house. No one method of 
control will suffice alone; each phase must be dealt 
with separately. 

Methods of Obtaining Seed Free from Disease. The 
selection of clean seed from bins, while working suc- 
cessfully with other crops, is not to be practiced in 
the case of sweet potatoes, since much disease is 
carried inside of the roots or in the dust which coats 
them. Seed treatment should be preceded by seed 
selection. The use of seconds for seed is not satis- 
factory, since they may be the small roots produced 
from diseased hills, and hence carriers of disease. 

The use of slips is very desirable, since in this case 
a beginning is made with healthy cuttings from which 
hills of slip seed are produced. These in turn are 
healthy, since they are not hampered by disease 



Family Convolvulaceas i77 

from the mother cuttings. However the growing of 
slip seed every year is a tedious process. To im- 
prove the strain and avoid disease sHp seed may be 
grown every second or third year, from hill selected 
primes. Following the use of such slip seed, primes 
may be used for one or two seasons, to be followed 
again by a high strain of slip seed. Roots which are 
round, chunky, and smooth should be chosen. Seeds 
which have sprouted in storage should be discarded, 
as these roots often carry diseases. The seed of some 
varieties, however, are known always to sprout, no 
matter under what storage conditions they are kept. 
In these cases, the sprouts should be broken or rubbed 
off and the seed be treated with corrosive sublimate 
before being bedded. No injury results from this 
process and new sprouts soon follow. As the seeds 
are being carefully selected one by one, the stem end 
of each root should be clipped off with a sharp knife to 
a distance of one third of an inch. Every cut surface 
should present a clean white appearance. Brown 
spots in the interior of the root mean the presence of 
disease in the vessels. Such seeds should be discarded, 
even though the exterior is healthy looking. In us- 
ing primes for seeds, selection should be made in the 
fall at digging time. The roots from the highest yield- 
ing and healthiest hills should be chosen, marked, and 
stored separately under the best possible conditions. 
Before bedding, these should be sorted over again and 
the stem ends of the most choice should be clipped to 
make sure of their freedom from internal disease. 
Seed Treatment. Having selected good sound seeds, 



178 Diseases of Truck Crops 

it is not wise to bed them untreated. In using prime 
seed they might easily soft rot in the bed. This 
rotting may be increased where the ends are cHpped. 
To obviate this possibiHty and to destroy the spores 
of disease, the seed should be disinfected with a solu- 
tion of corrosive sublimate made up of one ounce of 
the chemical dissolved in eight gallons of water, and 
the seed soaked for ten minutes. Usually it is 
advisable to treat one bushel at a time. For large 
quantities of seed, 100 to 200 gallons of the solution 
may be prepared in several fifty gallon barrels. 

Besides treating the seed, the soil in the seed bed 
must be disinfected. This may be done with the 
steam method, see pages 54-56, or with the for- 
maldehyde method, page 53. 

Where flue, hot water, or manure heated beds are 
used permanently, the wooden framework should be 
disinfected every year by thoroughly sprinkling or 
soaking with corrosive sublimate solution or the 
formaldehyde solution of the same strength as used 
for the seed. As soon as the framework begins to 
rot, it should be discarded. 

FIELD METHODS OF CONTROL 

The grower's efforts to stamp out the diseases of 
the sweet potato cannot stop with care that the seed 
shall be healthy and the seed bed clean. It has al- 
ready been shown that several diseases like black 
rot, stem wilt, ground rot or pit, and soilstain may be 
and are carried over in the soil. These diseases con- 



Family Convolvulaceac 179 

stantly spread and increase in the land, as the sweet 
potato is grown continuously on the same ground. 
This being the case, we cannot expect healthy plants 
to thrive or be free from disease on land that is badly 
infected with disease. Cleanliness is, therefore, the 
only means of keeping out disease from fields de- 
voted to sweet potatoes. 

Sprout Treatment. Before being planted, sprouts 
should be treated, in order to insure the best stand. 
Not only are untreated sprouts subject to chance con- 
tamination, but they are also the prey to flea beetles 
as soon as they are planted. When the sprouts are 
pulled from the seed bed they should be taken at 
once to a shaded place and dipped into a Bordeaux 
mixture, 3-3-50. 

Other Field Control Measures. Growers will do 
well to make it a point to inspect their fields every 
week or two and pull out and burn stunted plants 
which are yellow, sickly looking, and which fail to 
grow. These should never be left near the seed bed, 
but should be destroyed so that the disease cannot 
spread to the healthy plants. Clean cultivation is 
essential in preventing field diseases with the sweet 
potato. In cultivation, great care should be taken 
to prevent injury to the roots, as an injury means 
a possible opening for disease. 

STORAGE METHODS OF CONTROL 

Before satisfactory conditions can be found for the 
proper storing of sweet potatoes, there must be a 



i8o Diseases of Truck Crops 

clear understanding of the storage problem. Investi- 
gations have shown definitely that the greatest loss 
from disease in storage is due to soft rot. It has been 
estimated that 90% of the loss is due to this one 
disease, 9% to black rot, and 1% to all other rots. 

Table 14 gives part of the data collected in Novem- 
ber, 1909, at the storage house of Huston Darbee, 
Seaford, Del. The thermometer readings are re- 
corded in Fahrenheit degrees and the compara- 
tive moisture readings are taken with Mitthof's 
hygrometers. Whenever the readings of the hy- 
grometer run over 70 and remain there for some 
time, soft rot sooner or later sets in. 

Table 14 also shows that not only is the tempera- 
ture different in the different parts of the same floor, 
but that it differs on different floors. Any ventila- 
tion which will bring down the moisture content ten or 
twelve per cent, will help keep sweet potatoes. How- 
ever, natural ventilation will not always accomplish 
this, since the moisture content of the outside air is 
the great governing factor. For instance, it is seen 
in Table 14 that from the ist to the 5th of November, 
1 913, the weather was fair and the air dry; hence by 
opening up doors and windows in the morning, the 
moisture readings were greatly reduced. However, 
on the 7th, the moisture increased when the ventila- 
tors were opened on the first floor. A fair day, there- 
fore, does not always indicate dry air, just as a cloudy 
day does not always mean moist air, as is indicated 
by the hygrometer readings on both floors during the 
14th of November. Rainy days and damp weather 



Family Convolvulaceae 



i8i 



offer no opportunity for the lowering of the moisture, 
as will be seen on November i6th, when opening the 

Table 14 

torage Temperature and Moisture Reading for November, iQog, for 
1st and 3d Floors. 





Ther 


mometer Reading 
























First Floor 




Ther. 


Moist. 


Moist. 


















Read. 
Third 


Read. 
First 


Read. 
Third 


Outdoor 
Temp. 
















'>aie 


East Sidf 


M'est 


Floor 


Floor 


Floor 






Kind of Day 




of House 


Side 






















A.M. 


P.M. 


A.M. 


P.M. 


A.M. 


P.M. 


A.M. 


P.M. 


A.M. 


P.M. 


A.M. 


P.M. 




I 


54 


50 


50 


54 


57 


57 


62 


49 


66 


46 


32 


48 


Fair 


2 


46 


S3 


SO 


58 


57 


62 


65 


55 


67 


57 


38 


54 


Fair 


3 


42 


S3 


45 


60 


55 


60 


67 


46 


70 


42 


33 


52 


S^l*" 


4 


S2 


56 


56 


63 


57 


62 


68 


54 


65 


50 


54 


60 


Fair 


S 


46 


52 


48 


57 


56 


60 


63 


52 


65 


48 


37 


54 


Fair 


6 


41 


53 


44 


60 


52 


62 


67 


60 


68 


47 


30 


60 


Fair 


7 


43 


54 


49 


60 


54 


64 


68 


72 


67 


60 


35 


64 


Fair 


8 


53 


58 


58 


64 


59 


66 


80 


77 


70 


67 


54 


60 


Fair and cloudy 


9 


58 


54 


65 


57 


62 


54 


70 


71 


72 


60 


63 


50 


Rain 





50 


50 


54 


54 


45 


52 


70 


55 


60 


52 


38 


45 


Cloudy and fair 


[I 


45 


47 


SO 


51 


51 


50 


65 


54 


62 


48 


33 


38 


Fair and windy 


2 


45 


SO 


49 


SS 


50 


54 


65 


56 


63 


55 


36 


42 


Fair 


3 


48 


SS 


54 


60 


52 


62 


71 


SS 


64 


42 


4S 


62 


Fair 


4 


54 


58 


SO 


64 


57 


63 


70 


62 


65 


56 


52 


63 


Cloudy 


s 


46 


SO 


42 


52 


54 


56 


6r 


62 


65 


62 


38 


43 


Cloudy and rainy 


6 


52 


54 


56 


58 


S6 


58 


75 


79 


68 


70 


50 


52 


Rainy 


17 


50 


50 


56 


55 


54 


56 


72 


62 


68 


60 


42 


48 


Fair 


S 


47 


55 


50 


6r 


54 


60 


72 


50 


63 


45 


37 


62 


Fair 


9 


55 


60 


58 


68 


58 


68 


71 


59 


66 


49 


42 


67 


Fair 


20 


S8 


63 


62 


70 


58 


72 


68 


65 


63 


55 


55 


70 


Fair 


JI 


58 


6S 


62 


69 


62 


72 


67 


71 


65 


58 


49 


68 


Fair 


22 


55 


65 


61 


70 


64 


68 


68 


65 


67 


53 


48 


70 


Fair 


23 


57 


65 


62 


71 


64 


72 


74 


62 


66 


57 


50 


73 


Pair 


24 


SO 


58 


56 


62 


64 


72 


59 


46 


63 


44 


50 


73 


Fair and windy 




47 


55 


52 


59 


62 


60 


SS 


47 


54 


55 


38 


50 


Fair and cloudy 


26 


SO 


55 


55 


58 


60 


60 


64 


64 


56 


62 


34 


46 


Cloudy and rainy 


27 


52 


54 


60 


60 


58 


63 


62 


65 


65 


6S 


45 


SO 


Cloudy 


28 


57 


58 


62 


62 


60 


55 


72 


75 


70 


70 


46 


45 


Rainy and cloudy 


29 


60 


68 


62 


62 


58 


60 


7S 


74 


70 


74 


50 


53 


Cloudy 



house increased the moisture reading from 75 to 79 
degrees. During certain rainy and damp days, the 
outside air is more moist than the air of the storage 
house. To ventilate on such days means to bring in 



1 82 Diseases of Truck Crops 

an excess of moisture and not to ventilate has the same 
result, since by shutting off all ventilation the inside 
moisture will accumulate. Thus on days when the 
inside air is moist, natural ventilation is insufficient. 
Hence the many critical periods during the storage 
season. 

How to Meet the Ventilation Problem in Storage. 
The best means of natural ventilation is from the 
sides, either through doors and windows or through 
special ventilators (fig. 29 a-c). The bins should be 
constructed with false slat -bottoms, raised from three 
to four inches from the floor; the sides should be 
slatted, and at least eight inches from the wall, this 
space being connected directly with the opening to 
the floor below. 

The ventilation between the floors must be pro- 
vided by means of trap-doors. In small houses with 
one row of bins on each floor, these ventilators may be 
12 to 16 inch trap-doors running parallel and adjacent 
to the side walls. In medium sized houses with two 
rows of bins and the main aisle through the center 
running lengthwise through the house, the bins 
should be 12 to 16 inches from the wall and the trap- 
door alongside the wall should occupy the distance 
between the wall and the bin. In the center aisle, 
which is usually three feet wide, this entire walk 
could well be converted into two parallel trap-doors, 
each i}4 feet wide. Large houses should have their 
main aisle along the side walls. These should be at 
least 2)^2 feet wide. A center aisle between the two 
rows of bins should be three feet wide. All these 




J' 






Fig. 29. Sweet Potato Storage Houses. 

a. An ideal large commercial dry kiln potato house, showing windows and top 
ventilators, b. a small poor potato house lacking means of ventilation, c. a close 
side view of the top of the ventilator shown at a. 



Family Convolvulaceae 183 

aisles should be converted into trap-doors of two pairs, 
at least lyi feet wide, opening by means of weights 
either way from the center, and occupying the entire 
length. 

A series of roof ventilators should be provided, 
sufficient to carry off at least most of the moisture. 
In small houses there should be at least two such 
ventilators, each about three feet square and about 
five feet high. In medium sized houses there should 
be three of similar dimensions. In large houses 
from four to six ventilators should be provided 
(fig. 29 a and c). 

Where sweet potatoes are stored in bins, they 
should first be put into every other one, beginning 
with the lowest and finishing with the top floor. 
Thus the filled bins will have a chance to dry out. 
Bins deeper than seven feet should be divided by two 
partitions, leaving a two or three inch air space 
between them. The inner bins throughout should be 
filled first. It is a mistake to close doors and venti- 
lators when the potatoes are sweating, for during this 
stage all the ventilation possible should be given, even 
at night, provided of course that the temperature 
does not go so low as to cause chilling. 

Artificial Aids in Storage. Each floor should be 
provided with an accurate recording thermometer and 
hygrometer. With the help of these two instru- 
ments, the critical point of excess heat and moisture 
may be easily determined. It is possible that in order 
to bridge over these critical periods in storage some 
system of artificial drying may be required. This 



1 84 Diseases of Truck Crops 

may be accomplished by the use of fans or blowers 
run by electricity or by a small gasoline motor. 

WEEDS 

There are but few weeds in this family which 
are subject to the same diseases as the sweet potato. 
The wild morning-glory {Ipomosa purpurea), the 
wild sweet potato {Ipomxa pandurata), and the 
small and great bindweed {Convolvulus arvensis and 
C. sepium) are all subject to black rot, SphcEronema 
fimhriatum. All these weeds are also attacked by 
white rust, Cystopus ipomcecB-pandurance. Whether 
this rust is the same as the white rust of the sweet 
potato, or whether it is another physiological species 
or race, still remains to be determined. But in any 
case, these weeds must be kept out of sweet potato 
fields if we desire to keep the black rot of sweet 
potato in check. 



CHAPTER XIII 

FAMILY CRUCIFEFLE 

This family ranks high in the number of impor- 
tant cultivated plants that it contains. Of the 
truck crops of economic importance may be men- 
tioned the Brussels sprouts, cabbage, cauliflower, col- 
lard, horseradish, kale, kohlrabi, mustard, radish, 
rutabaga, sweede, turnip, and watercress. 

According to the Thirteenth Census of the United 
States, the area devoted to cabbage in 1909 in all the 
States was 125,998 acres, and the total crop was val- 
ued at $9,719,641. The important cabbage States, 
ranked according to area, were as follows : New York, 
Wisconsin, Virginia, Ohio, Pennsylvania, Illinois, 
New Jersey, Texas, Michigan, California, Maryland, 
Florida, Colorado, Iowa, Massachusetts, Minne- 
sota, Louisiana, South Carolina, Mississippi, Ala- 
bama, Tennessee, and Kansas. States with less than 
1000 acres are omitted. 

The total area of cauliflower in 1909 in the United 
States was estimated at 3466 acres and the total 
crop was valued at $602,885. The States which 
produced most of the crops are: New York, Cali- 
fornia, Illinois, Massachusetts, and Florida. 
185 



i86 Diseases of Truck Crops 

The total 1909 area in horseradish was estimated at 
1475 acres, and the total crop valued at $233,885. 
The crop is grown mostly in North Dakota, Pennsyl- 
vania, New York, New Jersey, and Illinois. 

The total 1909 area in kale was estimated at 1495 
acres, and the total crop valued at $146,010. The 
crop is principally grown in Virginia, Kentucky, 
Maryland, and New York. 

The total 1909 area devoted to radish was esti- 
mated at 2269 acres, and the total crop valued at 
$293,062. The crop is grown in the following States, 
ranking in order according to acreage: New York, 
Alabama, Virginia, Illinois, Mississippi, Louisiana, 
Missouri, and Texas. 

DISEASES OF CABBAGE {Brassica oleracea) 

The cabbage, although a hardy plant, is neverthe- 
less subject to numerous diseases. Disease may re- 
duce the profits of the crop by fifty per cent., or even 
mean total failure. 

Club Root 

Caused by PlasmodiopJiora hrassiccB Wor. 

Club root is a field disease only. Few plant dis- 
eases are as cosmopolitan as this trouble. It is 
found in many of the European countries, and in 
Australia, New Zealand, and in the United States. 
The loss from club root ranges from forty to seventy 




Fig. 30. Cabbage Diseases. 

a. Club root (after Cunningham), b. cell filled with spores of the club root or- 
ganism, c. spores and swarm spores of Plasmodiophora brassica (b. and c. after 
Chuff), d. black rot of cabbage (after F. C. Stewart), c. individual black rot germs of 
Pseudomonas campeslris, f. black-leg on young cabbage seedling, g. black-leg lesion 
on foot of older cabbage plant, h. black-leg lesion on cabbage leaf, i. pycnidium of 
Phoma oleracecE.j. pycnos pores of P. olcracece (i. a.ndj. after Manns), 



Family Cruciferas 187 

per cent, of the crop, although most of it may be 
prevented. 

Symptoms. Affected plants show a wilting of the 
foHage in the day, although recovering in the even- 
ing or during cloudy weather. Diseased plants are 
dwarfed, pale, and sickly looking. The seat of the 
trouble is at the roots. The latter swell considerably 
in size, often taking on the form of a hernia (fig. 30 a). 
The disease is more severe on seedHngs in the seed 
bed, from whence it is carried to the field. 

The Organism. Club root is caused by a slime mold. 
The spores of the parasite (fig. 30 b) are nearly round 
and possess a transparent and refractive cell wall. 
According to Chupp, ' the first signs of germination 
are a swelling of the spores, followed later by 
a bulging at one side. The inner pressure exerted 
spHts the spore wall, thus permitting the protoplasm 
(swarm spores) to ooze out. The latter is with- 
out a cell wall (fig. 30 c), and is capable of motion by 
means of a thick flagellum at the small end. The 
germination of the spores is improved by exposing 
them for a short time to cold and drying. The best 
medium is water which has been filtered through 
muck soil. 

Infection of the host takes place through the wall 
of the root hair while the organism is in a uninucleate 
stage. Entrance of the parasite is evidenced by the 
browning and shriveling of the root hair. The dis- 
ease does not seem to be spread from place to place 

'Chupp, Charles, New York (Cornell) Agr. Expt. Sta. Bui., 
387:421-452,1917- 



i88 Diseases of Truck Crops 

by the wind. But infected manure in the seed bed 
will result in infected seedlings carrying the disease 
into a new field. Club root is known to attack a 
large number of cruciferous hosts, the more suscepti- 
ble of which include all of the cultivated species. 

Control. The best method of controlling club root 
is to grow cabbage on new land, or on land that 
was rotated with other crops, and given a rest from 
cruciferous crops for some time. Where it is not 
possible to do this, infected fields should be limed. 
Table 15, adapted from Cunningham,' clearly shows 
the effect of lime in controlling club root. 

From Table 15, it is seen that the use of fresh or 
air-slaked lime lowers the percentage of club root as 
compared with the calcium chloride on check plats. 
Moreover, when clubbing appeared in the limed 
areas, the disease seemed to be confined to the lowest 
roots and outside of the reach of lime. This then 
enabled the affected plants to make a crop in spite of 
the disease. The best effect of liming may be ex- 
pected when the lime is thoroughly incorporated in 
the soil to a depth of six to nine inches. As far as 
possible the trucker should avoid susceptible varieties 
of cabbage, among which may be mentioned : Mam- 
moth Rock Red, Dark Red Erfurt, American Savoy, 
Perfection Savoy, All Seasons, and Volga. Of the 
more resistant varieties of cabbage may be mentioned 
Hollander, Stone Mason, Large Late Flat Dutch, 
and Henderson's Early Summer. Finally, care 

' Cunningham, L. C, Vermont Agr. Expt. Sta. Bui., 185 : 67-96, 
1914. 



Family Cruciferse 



189 



9J0Y J,34 psqqnjj 


1-1 >-■ vd d >-I 06 r< t^ d 


9X3y 294 p^qqnjj 

K.jpvq 9'SvfU90A.9J 




3X3y 

j,34 psqqnij 92vjU9U9j 


d vd 6 d 10 d rA vd d 


a^yy j,94 
paqqnjj fou 9?vju9yi9j 


CN f<b d d 10 c> ts po d 


p9qqntj 


?^?:^°^::^ ^^ 


vmMD ^ip^a m^^M 




paqqniJ 29qmni^ 


00 rOfO'O 1- w c< r- M 


psqqnij jou U9qtunj^ 




uo sjuvjj fo j.9qiuni\i 


N vo fC rn CTvoo •T^ 


Quantity per Acre and Form Used 
on Soil before Setting 


150 bushels of air-slaked lime 

150 bushels of fresh unslaked lime 
650 pounds of calcium chloride . . . 

Control 

150 bushels of air-slaked lime 

1 50 bushels of fresh unslaked lime 

Control 

100 bushels of air-slaked and 100 

bushels of fresh unslaked lime 

650 pounds of calcium chloride . . . 



190 Diseases of Truck Crops 

should be taken to exclude club roots from the seed 
bed, since many an outbreak of this trouble may be 
traced back to the use of previously infected seedlings. 

Black Rot 

Caused by Pseudomonas campestris (Pammel) 
Ew. Sm. 

The disease is known to growers as stem rot and 
black rot. The latter perhaps is the more common 
name. The trouble may now be found wherever 
cabbage is grown on a large scale. 

Symptoms. Black rot has distinct symptoms 
which cannot easily be confused with other cabbage 
diseases. On the leaves, the symptoms are mani- 
fested as a burning appearance on the edges (fig. 
30 d) and a yellowing of all the affected parts except 
the veins, which remain blackened. From the mar- 
gin of the leaves the disease works downwards to the 
stalk. From there the disease travels up again to 
the leaves and from there to the stems. The parasite 
works in the fibro-vascular bundles of the leaves and 
main stalk, causing a premature defoliation. Occa- 
sionally, the disease enters one side of the stalk, the 
latter becoming dwarfed and the cabbage head be- 
coming one sided. In severe cases of attack, there is 
a total lack of head formation. In splitting open a 
stump of an affected plant, we will find a black ring 
which would correspond to the places of the fibro- 
vascular bundles invaded by the organism. Smith' 

' Smith, E. F., U. S. Dept. of Agr. Farmers BuL, 68: 5-21, 1898. 



Family Cruciferae 191 

found that the infection takes place through small 
openings naturally found on the leaves and known as 
water pores which are found scattered over the teeth 
of the leaves. Infection by means of insect bites is 
also a very common occurrence. Outbreaks of black 
rot in new fields may undoubtedly be traced back 
to the use of infected manure. Black rot also at- 
tacks broccoH, Brussels sprouts, cauliflower, char- 
lock, coUard, kale, kohlrabi, black mustard, rape, 
rutabaga, radish, sweede, and turnip. 

The Orga?iism. Pseudomonas campestris is a rod- 
shaped organism, slightly longer than it is broad. 
When young it is actively motile by means of long 
polar flagella (fig. 30 e). It is found single or in pairs 
and produces no spores. It liquefies gelatine com- 
pletely in about fifteen days. On agar plates the col- 
onies are round, yellow in color, and the margin entire. 
On potatoes a copious growth is produced with 
no odor and no browning of substances. The in- 
vestigations of Harding' and others have proved 
that the black rot germ may be introduced into the 
seed bed and into new fields from infected cabbage 
patches. The virulence of black rot is largely de- 
pendent on the weather. It is unfortunate that 
favorable weather conditions for the cabbage plants 
are also favorable for the disease. 

Control. Before planting, cabbage seed should be 
disinfected for fifteen minutes in a solution of % pint 
of pure (40%) formaldehyde diluted in seven gallons 

' Harding, H. A., New York (Geneva) Agr. Expt. Sta. Bui., 
251: 178-194, 1904. 



192 Diseases of Truck Crops 

of water. In making the seed bed, manure known to 
be free from cabbage refuse should be used . All insect 
pests should be kept in check by spraying, and no 
animals should be allowed to roam in sick patches. 
Insects and farm animals act as carriers of black 
rot. The disease cannot be controlled by merely 
cutting off diseased foliage. If anything, this 
operation aggravates the trouble. Diseased plants 
should be pulled out and destroyed. Crop rotation 
should be practiced wherever the disease is well 
established. 

Soft Rot 

Caused by Bacillus carotovorus Jones. 

Soft rot, although a field trouble, causes great 
damage to stored cabbage. The greatest losses 
are reported from New York and Wisconsin where 
cabbage is stored on a large scale. 

Symptoms. The disease is characterized by a soft, 
mushy to slimy decay of the entire plant. The dis- 
ease works very rapidly under favorable conditions 
of moisture and temperature. The causal organism 
can gain entrance only through a wound or bruise. 
Rough handling of the crop during hauling and stor- 
ing therefore opens the way to heavy infection and 
consequently loss from soft rot. 

The Organism. The Bacillus is rod-shaped, long 
or short, and usually formed in chains. It moves 
about by peritrichous fiagella. It completely lique- 



Family Cruciferae 193 

fies gelatine in about six days. Gas is produced with 
a majority of strains. 

Control. The greatest loss in storage occurs where 
the temperature is maintained much above the freez- 
ing point and where the facilities for ventilation are 
poor. To remedy this, the temperature, as far as possi- 
ble, should be maintained one or two degrees above 
freezing. The crop should be thoroughly dried and ex- 
posed to the sunlight before being entered into storage. 
Diseased fields should be rotated to other crops. 

Damping off 

Caused by Olpidium brassicce (Worr.) Dang. 

The symptoms of damping off are similar to those 
produced by Pythium de Baryanum, p. 43. The 
sporangia of the parasite may be found singly or 
in groups in each infected host cell. The zoospores 
are globose, uniciliate. The resting spores are 
globose, wrinkled, and star-like in appearance. 

The disease is found mostly in seed beds, where it 
does considerable damage. For methods of control 
see p. 43. 

White Rust 

Caused by Cystopus candidus (Pers.) Lev. 

White rust of cabbage is seldom troublesome 
enough to attract attention. The symptoms of the 
disease are the same as on other cruciferous hosts 
such as mustard or radish, p. 211. 



194 Diseases of Truck Crops 

Downy Mildew 
Caused by Peronospora parasitica (Pers.) De By. 

Downy mildew, while a common field disease, 
causes considerable damage to young seedlings. 
It is characterized by whitish downy patches on the 
under side of the leaf. Seen from above, the af- 
fected areas are angular, pale yellow, and somewhat 
shmnken. The spots seem to be limited by the 
veins of the leaf. The disease is common in damp 
weather. Besides the cabbage, cauliflower, radish, 
turnips, and numerous other cruciferous hosts are 
known to be susceptible to downy mildew. 

The sporophores of the fungus are stout and 
numerously branched, each branch repeatedly forked. 
The tips of the smaller branches are slender and 
curved. The conidia are broadly elliptical, and the 
resting spores are globose and smooth, becoming 
wrinkled with age. 

In the seed bed or in the field, spraying with 
4-4-50 Bordeaux will control the disease. The first 
appHcation should be given as soon as the disease 
makes its appearance. Later the appHcation will 
be governed by weather conditions. 

Drop 

Caused by Sclerotinia libertiana Pckl. 

Drop is a disease fairly common on cabbage. The 
trouble may be recognized by a drooping and wilting 



Family Cruciferas 195 

of the leaves. The bases of the affected foliage are 
covered with a white weft of mycelial growth, later 
by sclerotia. For a more extended discussion of the 
disease see lettuce drop, p. 143. 

Black Leg or Foot Rot 

Caused by Phoma oleracea Sacc. 

Black leg, first noticed in the United States by 
Manns ^ in Oliio, was undoubtedly introduced here 
from Europe. 

Symptoms. The disease is usually manifested in 
the seed bed about two to three weeks before trans- 
planting in the field. The trouble at first appears 
as white elongated sunken lesions on the stem and 
below the leaf attachment (fig. 30 f) . Scattered over 
the lesions are minute black specks which constitute 
the pycnidia or fruiting sacs of the fungus (fig. 30 i 
and j). Infected seedHngs usually collapse and take 
on a bluish color. In the field, the foliage of the 
older but affected plants (fig. 30 h) usually take on a 
mottled, metallic, bluish-red color at the margins, 
and the lower outer leaves wilt. On examining such 
plants there will always be found sunken lesions 
(fig. 30 g) which often girdle the foot of the plant. 
In wet weather affected plants attempt to produce 
new roots above the infected area, which, however, 
are never able sufficiently to support the plant. 
Foot rot is often confused with forms of injury 
brought about by maggots. 

> Manns, T. F., Ohio Agr. Expt. Sta. Bui., 228: 255-297, 1911. 



196 Diseases of Truck Crops 

Treatment. Manns recommends treatment of the 
seed bed with 4-4-50 Bordeaux to be appHed im- 
mediately after planting, at the rate of one gallon to 
each ten square feet of bed space. The bed is again 
sprayed with Bordeaux about two weeks before and 
once again at transplanting. 

Black Mold 

Caused by AUernaria hrassiccB (Berk.) Sacc. 

Black mold is a serious disease of the cabbage in 
the Southern States. It also attacks collards. 

Symptoms. Affected leaves are covered with 
spots which are nearly black on the under side of the 
leaf. The spots are composed of a series of rings, 
the smaller ones enclosed within the larger (fig. 31a). 
There is no distinct border separating the diseased 
from the healthy, the spots gradually shading off 
into the healthy tissue. Little is known of the causa- 
tive fungus or of the control of this disease. It is 
probable that spraying with 4-4-50 Bordeaux will 
be of value. 

Leaf Spot 

Caused by Cercospora bloxami B. and Br. 

Leaf spot is of little economic importance. It only 
attacks the leaves of weak or languid plants. The 
spots are pale, somewhat circular, surrounded by a 
slightly raised, faintly purple border. The conidial 



I 



M^ ^^ 




Fig. 31. Cabbage Diseases. 

a. Alternaria black mold, 6. cabbage seedlings growing in a cabbage sick soil 
which has been steam sterilized, c. sick cabbage seedlings in a cabbage sick soil, 
(after Jones and Oilman), d. an old wilt infected cabbage plant: notice bare stalk, 
c. conidia of Fusarium conglutinans, f. clamydospores (resting spores), of F. con- 
glutinans. g. wilt infected cabbage seedlings: notice how the leaflets drop off as a 
result of the disease. 



Family Cruciferae 197 

tufts are prevalent in the center of the spots, and are 
pale brown and sparingly septate. The conidia are 
long clavate, tapering, straight to curved, many sep- 
tate, and hyaline to faint smoky color. 

Wilt or Yellows 

Caused by Fusarium conglutinans Woll. 

There is no other cabbage disease that is economi- 
cally so important as wilt. This trouble is threaten- 
ing the cabbage industry in many parts of the United 
States. In the cabbage centers of Ohio and Wiscon- 
sin, truckers lose so heavily from wilt, that in many 
sections, the growing of the crop has been made very 
unprofitable. 

Symptofns. The term ' ' yellows " well describes the 
disease. Affected seedlings are yellowish and stunted 
in growth with a tendency to drop their lower leaves 
at the least touch (fig. 31 g). Such plants when 
transplanted in the field either die outright or make 
very slow growth. The symptoms in the older 
affected plants are the same as on the seedlings. 
The outer leaves turn yellow and drop off one by one, 
until a bare stump and top head are left (fig. 31 d). 
Usually the plant is uniformly attacked ; but the in- 
fection may be confined to one side. This one-sided 
check results in the lateral warping and curving of 
the stems and leaves. Under field conditions, high 
temperatures are very favorable for the spread and 
development of yellows. 

The Organism. The best description of Fusarium 



198 Diseases of Truck Crops 

congluHnans Woll. is given by Oilman. ' Sporo- 
dochia, lacking or greatly reduced, pionnotes never 
present, conidia borne on short conidiophores strewn 
throughout the mycelium. The majority of spores 
are non-septate, a few are one to three septate 
(fig. 31 e); conidia with higher septation are rare. 
In old cultures, chlamydospores are produced in 
great abundance (fig. 31 f). 

Control. Cabbage yellows cannot be readily 
controlled. Naturally a clean seed bed should be 
chosen (fig. 31 b-c). However, the healthy seedlings 
when transplanted into infected fields will soon con- 
tract the disease. The same also holds true even 
when the seeds are disinfected. Neither is crop 
rotation a sure method of control. It is doubtful if 
fifteen years' rest from cabbage will free a soil from 
the causative parasite. The best method of control 
is the development of resistant varieties. This has 
already been accomplished by Jones and Oilman^ 
who selected a strain from the Hollander which 
they named Wisconsin Hollander No. 8. This strain 
is said to be nearly 100 per cent, resistant to wilt. The 
same is also true for the Volga (fig. 32 a-b). The 
question arises as to whether a cabbage selected for 
resistance under Wisconsin soil will show it in a like 
degree in other climatic conditions and soil. For 
the cabbage the answer may be given in the affirma- 
tive. For instance, the Houser and the Volga, which 

' Oilman, J. C, Annals Missouri Bot. Garden, 3 : 2-84, 1916. 
^ Jones, L. R., and Oilman, J. C, Wisconsin Agr. Expt. Sta. Bui., 
38 : 1-69, 1915. 




Fig. 



Cabbage Diseases. 



a. Two rows of Volga, a highly resistant commercial cabbage growing in a 
cabbage sick soil (yellows), b. resistant cabbage strains in a cabbage sick soil 
(a. and b. after Jones and Oilman). 



Family Cruciferae I99 

have proved wilt proof in Maryland, have proven 
equally resistant under Wisconsin conditions. It is, 
however, advisable to grow seed in the same locality 
where the resistant cabbage has been developed. 
The method of developing resistant varieties is 
given more fully on p. 374. 

Root Knot 

Caused by Heterodera radicicola (Greef) Mull. 

Root knot is very widespread in the Southern 
States, but is confined mostly to the light sandy soils. 
It is often mistaken for club root. Careful observa- 
tion will show the differences. Root knot is char- 
acterized by small swellings on the lateral feeding 
roots. For a description of the parasite and meth- 
ods of control see p. 49- 

Decay of Cabbage in Storage 

Not all field-grown cabbage is consumed when 
harvested. A large part of the crop is stored away 
for winter use. It is estimated by Harter' that of 
the thousands of tons stored every fall, from 10 to 
50 per cent, is annually lost from decay. With 
the exception of yellows, practically all the other 
field rots of cabbage may be active also under storage 
conditions. Therefore, to store a clean crop we 
must produce a clean crop in the field and on no 
account should infected cabbage be allowed in the 

' Harter, L. L., U. S. Dept. Agr.Bur. PI. Ind. Circ, 39: 3-8, 1909. 



200 Diseases of Truck Crops 

storage house. Cabbage from badly diseased plants 
should be disposed of early. 

Poor Storage Conditions. Cabbage houses are 
usually built as permanent structures. When this 
is the case, they must be thoroughly cleaned out and 
disinfected every year before storing a fresh crop. 
All indoor framework should be sprayed with a solu- 
tion of one pint of formaldehyde in forty gallons of 
water. This is done a week or two before storing in 
order to allow the house to dry thoroughly. 

In harvesting and handling the crop, every care 
should be taken to prevent unnecessary bruising of 
the heads. Storers of cabbage are confronted with 
the same difficulties as storers of sweet potatoes. 
With both, the great problem is the ventilation and 
the elimination of excess of moisture given off by the 
crop in storage. In warm houses quantities of mois- 
ture soon accumulate in the house, which, if not 
carried off, soon deposit on the cabbage. 

Storage houses may be so constructed as to take 
care of the ventilation and moisture under normal 
conditions. The walls of the buildings should pro- 
vide a dead air space to prevent the penetration of 
the outdoor moisture. With brick walls, two four- 
inch walls could be laid and tied up by a header 
course, thus providing an air space of two to three 
inches between them. Wherever possible thick 
walls should be preferred, as these make it possible 
to keep the interior cool during hot weather. The 
roof should be provided with a good outer covering 
of shingles, and with an inner lining so built as to 



Family Cruciferae 201 

provide a dead air space. If the inner lining is made 
up of lumber, the boards should run parallel with the 
rafters, rather than at right angles to them, so that 
any condensed water may run off to the eaves rather 
than fall from each joint. Ventilation should be 
encouraged by means of top ventilators on the roof. 
These should be provided with dampers, manipulated 
and controlled by ropes extending to the passage- 
way. Small windows installed above the foundation 
line in the walls will admit air from below and induce 
a better circulation. The windows may be screened 
with an iron netting in order to keep out mice. 

There are two ways of storing cabbage — in bins or 
on shelves. The latter is preferred because there is 
less bulk to undergo a sweat, and each individual 
cabbage being exposed to more air prevents rotting. 
In storing, the cabbage should be placed with the 
stem end upward so that all possible moisture may 
readily run off and not be caught and held by the 
head leaves. 

So far as possible, the temperature of the storage 
house should be maintained at about thirty-four 
degrees F. throughout the storage period. As soon 
as the house is filled, it should be kept closed during 
the day and be opened at night in order to benefit 
from the cool outdoor air. During extremes of cold 
weather, ventilation should be reduced to a minimum 
and the house kept warm by an oil heater to prevent 
freezing of the cabbage. The Danish Ball Head, 
from imported seed, seems to be an ideal cabbage for 
storage. 



202 Diseases of Truck Crops 

DISEASES OF THE CAULIFLOWER (Brassica 
oleracea var. hotrytis) 

The cauliflower with few exceptions is subject to 
the same diseases as the cabbage. For a discussion 
of black rot, see p. 190; soft rot, p. 192, club root, 
p. 186, and drop, p. 143. 

Bacterial Leaf Spot 
Caused by Pseudomonas macuLicola McC. 

Bacterial leaf spot was first studied and described 
by McCulloch ^ who found it to be prevalent in south- 
eastern Virginia and in Florida. The disease un- 
doubtedly must have a wider and more geographical 
distribution than is generally known. The author 
has met with this disease in New Jersey, Delaware, 
Maryland, and Texas. 

Symptoms. The disease is characterized by numer- 
ous small brownish to purple-gray spots (fig. 33 a). 
When the small spots coalesce, the entire leaf surface 
may be involved. Practically all parts of the leaves 
are affected. When the midribs and veins are at- 
tacked, the tissue becomes shrunken, and the leaves 
have a puckered appearance. In early stages of 
infection, the spots on the leaves are watersoaked, 
later becoming dry and dark to purplish gray. In 
transmitted light the centers of the spots are thin, 
almost colorless, and surrounded by a dark border. 

• McCulloch, Lucia, U. S. Dept. of Agr. Bur. PI. Ind. Bui. 225 : 7- 
15. 1911- 




Fig. 33. Diseases of the Cauliflower and Radish. 

a. Spot disease of cauliflower (after McCuUoch), b. white rust of radish, c. conidio- 
phore of the white rust fungus, Cystopus candidus, d. fertilization in Albugo Candida, 
e. germination of the oospore of Albugo Candida, f. ring spot on cauliflower head. g. 
perithecium of Mycosphcerella brassicicola, h. ascus of MycosphcrrcUa brassicicola, i. 
ascospores of Mycosphmrella brassicicola (g. to i. after Osmun and Anderson). 



Family Cruciferae 203 

The diseased leaves become yellow and drop off 
prematurely. The trouble apparently does not at- 
tack the cauliflower head. The same disease may 
also attack cabbage, but not radish, rutabaga turnip, 
or mustard. 

The Organism. Pseudomonas maculicola is a 
rod-shaped organism, with rounded ends, usually 
forming long chains in certain media, but producing 
no spores. The organism is actively motile by means 
of polar flagella. Involution forms are produced in 
alkaline beef bouillon; and pseudo-zoogloeae occur 
in acid beef bouillon. No gas is produced and the 
organism is aerobic, and is killed by drying and 
exposure to light. 

Control. Badly diseased plants should be pulled 
up and destroyed. Spraying with 4-4-50 Bordeaux 
is recommended. In spraying cauliflower with 
copper compounds, and especially if the latter are 
in a concentration somewhat stronger than the plant 
can stand, numerous warts will appear on the leaves 
in about three days after spraying. These warts 
should not be mistaken for a disease induced by a 
parasitic organism. The wart formation is appar- 
ently due to a stimulation by the salts absorbed by the 
host cells. Von Schrenk' found that warts on cauli- 
flower leaves may be readily produced by spraying 
them with a solution made up of 5 oz. copper car- 
bonate dissolved in a mixture of three pints of am- 
monia to fifty gallons of water. He further found 

' Von Schrenk, H., Missouri Bot. Gard., i6th Ann. Rept. : 125, 
1905- 



204 Diseases of Truck Crops 

that leaf warts may be produced by spraying with 
weak solutions of copper chloride, copper acetate, 
copper nitrate, and copper sulphate. 

Ring Spot 

Caused by Mycosphcerella brassicola (Duby) Lind. 

The exact distribution of this disease is as yet un- 
known. The trouble was studied by Osmun and 
Anderson' on cauliflowers shipped from California 
to Boston. 

Symptoms. On the leaves, the disease appears as 
numerous small spots and the affected foliage turns 
yellow. Most of the spots are formed on the laminae, 
but others are also formed on the large midribs. 
The spots are definite in outline, round and visible 
on both surfaces of the leaf (fig. 33 f). The color is 
light brown to gray, with dry centers surrounded by 
olive green or blue green borders which shade off in 
the natural color of the leaf. The outer edge of the 
spot is covered with the fruit of the fungus (fig. 33 
g-i). Ring spot also attacks the cabbage. Spray- 
ing with 4-4-50 Bordeaux is recommended. 

DISEASES OF THE HORSERADISH {Cochlearia 
armoracia) 

The horseradish is generally considered a hardy 
plant. However, it is subject to numerous diseases. 

' Osmun, A. V., and Anderson, P. G., Phytopath. 5: 260-265,1915. 



Family Cruciferae 205 

The black rot, Pseudomonas campestris, is the same 
as that of the cabbage, p. 190, and the white rust, 
Cystopus candidus, is the same as that of the mus- 
tard, p. 211. 

Root Rot 

Caused by Thielavia basicola (B. and Br.) Zopf, 

Root rot of horseradish is of little economic im- 
portance. The disease is confined to the roots of the 
plant. In advanced stages the normal root system 
may be entirely lacking, leaving a charred, blackened 
stub. New roots are constantly formed above the 
diseased area, but these in turn become affected 
and die. It is these new roots which the plant 
attempts to produce that manage to keep the 
infected host alive in a stunted and useless form. 
For a description of the organism and methods of 
control, see p. 275. 

AscocHYTA Leaf Spot 

Caused by Ascochyta armoracicB Fckl. 

This form of leaf spot is rather scarce in the United 
States and may be easily overlooked. The disease 
is manifested as brownish leaf spots of various sizes. 
Within the spots numerous pycnidia are formed 
which bear numerous elliptic-oblong, hyaline one- 
septate spores. 



2o6 Diseases of Truck Crops 

Shot Hole 

Caused by Septoria armoracicE Sacc. 

Shot hole is a very serious disease which attacks 
the foHage of horseradish. Diseased leaves turn 
yellow and become peppered with round spots, 
whitish in the center, surrounded by a pale yellow 
border. The spots drop out and give the leaves 
a ragged shaggy appearance. The pycnidia of the 
fungus are formed in the center of the spots previous 
to their dropping out or on the remaining margin 
of the spot. 

Macrosporium Black Mold 

Caused by Macrosporium herculeum E. and M. 

This mold is confined to the leaves only. Late 
in the summer the leaves are attacked by round 
spots which at first are whitish, and later become 
coated with a black mold made up of the spore bodies 
of the fungus. Horseradish may also be attacked 
by another form of black mold, Alternaria brassiccB 
(Berk.) Sacc, see p. 196. 

White Mold 

Caused by Ramularia armor acicE Fckl. 

White mold is frequently met with on foliage of 
the horseradish. The spots are indefinite, irregular, 




Fig. 34. Cercospora Leaf Srcrr 
OF Horse Radish. 



Family Cruciferae 207 

and usually occupy large areas of the leaf. At first 
they are yellowish red in color ; but they become gray 
with age. 

Leaf Spot 

Caused by Cercospora armoracicR Sacc. 

Leaf spot is characterized by pale spots on the 
leaves (fig. 34). The spots are usually confined to 
weakened leaves. The disease is of no importance. 

Control. Usually the diseases of the horseradish 
are not serious enough to warrant treatment. How- 
ever, when the crop is grown on a large scale, it 
should not be planted anywhere near cabbage or 
other cruciferous plants in order to protect it from 
black rot. If any of the leaf spots become serious 
the affected parts may be removed and destroyed 
and the plants sprayed with 4-4-50 Bordeaux. 
The plants should be carefully cultivated and 
fertiHzed in order to maintain their vigor, thereby 
also preventing the leaf diseases from getting 
troublesome. 

DISEASES OF THE KALE {Brassica oleracea 
var. acephala) 

Kale is considered a very hardy plant ; it is, however, 
subject to black rot, Pseudomonas campestris (Pam.) 
Ew. Sm. On the leaves, black rot is characterized 
by dark discoloration of the veins, and on the root, 



2o8 Diseases of Truck Crops 

by a blackening and decaying of the stem; see 
also p. 190. Kale is also attacked by club root Plas- 
modiophora brassiccz Wor., see p. 186. 

DISEASES OF THE MUSTARD {Brassica 
Japonica) 

Garden mustard Brassica Japonica is cultivated 
for its foliage. It is used as a green, relished for its 
edible quaHties, and as a spring tonic. Mustard is 
subject to the following diseases: 

Black Rot, see Cabbage, p. 190. 

Club Root, see Cabbage, p. 186. 

White Rust (fig. 35 b-e), see Radish, p. 193. 

DISEASES OF THE RADISH {Raphanus sativus) 

Radish is subject to many diseases in common with 
the cabbage and numerous other crucifers. 

Club Root, see Cabbage, p. 186. 

Black Rot 

Cansedhy Pseudomonas campestris (Pam.) Ew. Sm. 

Black rot on radish is confined mostly to the tender 
white-rooted varieties, especially the Icicle. The 
black-rot germ penetrates the lateral feeding rootlets, 
from which it works its way in the main root. In 
cutting across a diseased radish, its interior fibro- 
vascular bundles are found to be blackened. Such 



Family Cruciferae 209 

radishes are useless for the market. The disease 
seldom attacks the red or the black-skinned varieties. 
For further consideration of black rot see p. 190. 

Scab 

Caused by Actinomyces chromogenus Gasp. 

Scab is not a common field disease of radishes. It 
is, however, found to be troublesome on the crop 
grown in greenhouses. The French Breakfast is 
commonly susceptible to the disease. The trouble 
may be expected if the crop is planted in a soil which 
previously produced a potato crop that was badly 
scabbed or where infected manure was used, or too 
much lime applied. For further description of scab, 
see p. 317. 

Damping Off 

Caused by Rheosporangium aphanidermatum Ed. 

This disease, which was studied and described by 
Edson,^ is very troublesome, attacking radish and 
beet seedlings alike. 

Symptoms. The disease is confined to the root 
system, seldom appearing above ground. Diseased 
plants have a flabby appearance, and the normal green 
of the foliage is displaced by a slightly yellowish tinge. 

' Edson, H. A., U. S. Dept. of Agr., Jour. Agr. Research, 4: 279- 
292, 1915. 
14 



2IO Diseases of Truck Crops 

In severe cases the entire stand may be wiped out. 
On carefully pulling out a diseased plant, we shall 
find the side rootlets blackened, shriveled, and dead 
(fig- 35 a-)- Frequently the plant attempts to pro- 
duce new roots above the diseased area. In this 
case, however, there is only partial recovery. The 
disease is most prevalent in the heavy soils. 

The Organism. In general characters, the organ- 
ism may be mistaken for Pythium de Baryanum, but 
it differs from the latter in its asexual fruiting bodies. 
The mycelium of Rheosporangium aphanidermatum 
is hyaline, non-septate (fig. 35 c), and grows profusely 
on solid media. Mycelium of cultures one or two 
days old exhibits considerable streaming of proto- 
plasm which seems always directed toward the tip 
end of the hyphse. This protoplasmic streaming 
results in the final accumulation in protoplasmic 
material, and in consequence of a considerable en- 
largement of the tip of the thread. Finally a cell 
wall is laid down which cuts off the swollen portion 
from the rest of the mycelium. This swollen body 
which Edson named presoporangium (fig. 35 b) has 
the appearance of a zoosporangium but in reality 
it differs from it since it gives rise not to zoospores, 
as might be expected, but to an independent body 
which later gives rise to zoospores. The pre- 
soporangium now absorbs water and its outer wall 
ruptures, from which is seen to flow out a mass of 
protoplasm enclosed in a thin cell wall. This es- 
caped mass is really the young zoosporangium, the 
cytoplasm of which finally cleaves into zoospores. 




Fig. 35. Radish Diseases. 

a. Young radishes attacked by Rheosporangium damping off, 6. presporangium. 
C. mycelium of Rheosporangium aphanidermatum, d. fertilization of the female 
oogonium by the male antheridium, e. mature oospore, /. root knot ih. to e. after 
Edson). 



Family Cruciferae 211 

With the matiirity of the sporangium its cell wall 
dissolves, liberating the swarm spores which swim 
about for a time, then come to rest, round up, and 
increase in size and germinate by sending out a germ 
tube. Oospores are produced in a fashion somewhat 
similar to Pythium. The oogonia are formed as 
terminal spherical bodies. The antheridium de- 
velops terminally, lying close to the oogonium. 
The content of the antheridium is emptied into the 
body of the oogonium (fig. 35 d) and fertilization is 
effected. The mature oospore (fig. 35 e) is spherical 
with a thick smooth or undulated wall and germin- 
ates by means of a germ tube. 

Control. When the disease is present on a large 
scale, it is useless to attempt to control it. The 
fungus, as we have seen, is a soil parasite, hence soil 
treatments discussed on p. 53 could not be consid- 
ered on a large scale. As far as we know, this disease 
attacks only radish and beet seedlings. Badly in- 
fected fields should be devoted to other crops for 
several years until the parasite is starved out. On 
a small scale, infected soils may be treated with 
formaldehyde (see p. 53), or fire (see p. 56). 
Downy Mildew, see Cabbage, p. 194. 

White Rust 

Caused by Cystopus candidus (Pers.) Lev. 

The damage caused by white rust depends largely 
on seasonal conditions. The disease is most preva- 



212 Diseases of Truck Crops 

lent on early spring or fall radish. The greatest 
damage done by this trouble is to the seed crop. 

Symptoms. On the leaves, white rust is manifested 
as white raised pimples or sori (fig. 33 b) character- 
istic of all white rusts. When the surface of the 
sori breaks open a white powder, which consists of the 
spores of the fungus, is liberated. On the flower 
organs of the radish, the symptoms of the disease are 
especially striking. The ovary sacs, the stamens, 
corolla, and calyx become hypertrophied and dis- 
tended, resembling abnormal leaves. 

It has been questioned whether the white rust of 
the radish is the same as that which attacks other 
crucifers such as cabbage, mustard, etc. While 
much remains to be learned, the investigations of 
Melhus throw much light on the subject. Melhus^ 
had no trouble in infecting the rat-tail radish {Raph- 
anus caudatus) with conidia taken from ordinary radish 
{Raphanus sativus). Melhus also secured infection 
by sowing conidia from the radish on white mustard 
{Brassica alba) and cabbage {Brassica oleracea). At 
no time, however, was it possible to infect more 
than fifty per cent, of the cotyledons or leaves of the 
white mustard which were inoculated. With the 
cabbage it was still more difficult to secure infection. 
Of the fifteen varieties inoculated less than one per 
cent, of the plants became infected. 

No infection could be obtained when sowing spores 
of Cystopus candidus from radish on ten varieties of 

• Mdhus, T. E., Wisconsin Agr. Expt. Sta. Research Bui., 15: 25- 
83,1911- 



.Family Cruciferae 213 

turnips {Brassica rapa), black mustard {Brassica 
nigra), rutabaga {Brassica campestris), shepherd's 
purse {Capsella bursa-pastoris) , garden cress (Le- 
pidium sativum) , wild pepper grass {Lepidium virgini- 
cum), hedge mustard {Sisymbrium officinale and S. 
altissimum), candy- tuft {Iberis umbellata), water cress 
{Nasturtium officinale), and wall flower {Cheiranthus 
cheiri). From the above experiments, it would seem 
that in dealing with the white rust fungus, Cystopus 
candidus, it is possible that there exist distinct races 
or strains, all of which are specialized to certain 
special hosts of the various crucifers. The best 
infection is secured when the seedlings of the host 
plant are chilled. This is why white rust is more 
prevalent in cool seasons. 

The Organism. Cystopus candidus has two fruit- 
ing stages. The summer or conidial stage is made up 
of simple chains of spores (fig. 33 c). The latter are 
separated one from the other by a minute beak-like 
projection. Each spore or zoosporangium germi- 
nates by six or more swarm spores, or zoospores. 
These, when set free, swim around, then come to rest 
and germinate by means of a germ tube. The 
oospore or sexual spore of the Cystopus is formed 
later in the season. The oogonia and antheridia (fig. 
33 d) are developed within the infected host tissue. 
FertiHzation proceeds in the same way as in Pythium. 
The mature oospore has a thick, sculptured wall, and 
is brown in color. The oospores germinate in the 
same way as the zoosporangium, i. e., by the forma- 
tion of zoospores (fig. 33 e). 



214 Diseases of Truck Crops 

Control. Burning of all infected trash and crop 
rotation are the best effective remedies. 
Root Rot, see Beet p. 122, 128. 
Root Knot (fig. 35 f), see Beet p. 129. 

DISEASES OF THE TURNIP {Brassica Rapa) 

Club Root, see Cabbage, p. 186. 

Black Rot 

Caused by Psetidomonas campestris (Pam.) Ew. Sm. 

Black rot in turnips is apparently confined to the 
roots. Infected plants may live a long time, and 
show no symptoms on the leaves. The roots of 
such plants, however, are stunted, abnormal in shape, 
and very narrow. The interior tissue is dry rotted 
and blackened, emitting a characteristic strong odor. 
For further description of the black rot, see p. 317. 

Scab, see Beet, p. 120, and Potato p. 317. 

White Rust, see Radish, p. 211. 

Downy Mildew, see Cabbage p. 194. 

Drop (fig. 36 g), see Cabbage, p. 194. 

Anthracnose 

Caused by Colletotrichum Higginsianum Sacc. 

Anthracnose is a new disease which has recently 
been studied and described by Higgins' in Georgia. 

' Higgins, B. B., U. S. Dept. of Agr., Jour, of Agr. Research, lo: 
157-161, 1917. 




Fig. 36. Turnip Diseases. 

a. and h. Anthracnose, c. cross section through acervulus, d. anthracnose spores, 
e. Cylindrosporium leaf spot, /. Phoma rot, g. Sclerotinia rot (r. and d. after 
Higgins). 



Family Cruciferae 215 

The disease attacks the leaves (fig. 36 a-b), causing 
small circular gray or straw-colored spots. The 
acervuli and the salmon-pink spore clusters appear 
only under moist conditions. The causative fungus 
differs from Colletotrichum brassiccB Sch. and Sacc. 
The acervuli are small, scattered on both surfaces 
of the spots. The conidiophores are short (fig. 36 c), 
conidia hyaline cylindrical one celled (fig. 36 d), setae 
dark brown to black, slender, i to 3 septate (fig. 36 c). 
On the stems the spots are more elongated. On 
the leaves the spots are said to be much smaller 
than those produced by Cylindrosporium brassicce 
F. and R. (fig. 36 e). Anthracnose is not carried 
with the seed. No method of control is as yet 
known. 

Phoma Rot 

Caused by Phoma napobrassiccs Rost. 

Phoma rot is a disease which is common in the 
north of England. It is also found in New Zealand 
and in Canada. In the United States it has been 
reported but once, by Clinton' of Connecticut. 

Phoma rot seems to be a storage trouble, although 
the disease is first introduced from the field. 

Symptoms. In the field, the disease is first noticed 
at digging as a rot around the crown, the top of the 
plant readily pulling off. In storage the disease is 

'Clinton, G. P., Connecticut Agr. Expt. Sta.., ^Gth. Ann. Rept. : 
355-358, 1912. 



2i6 Diseases of Truck Crops 

manifested on the roots as a dry rot which appears 
first as scattered sunken spots bordered by dark areas 
(fig. 36 f). The pycnidia of the fungus are generally 
absent from the spots, but they appear in great 
abundance when the roots are placed under favor- 
able conditions of moisture. 

Control. It is doubtful if Phoma rot can be con- 
trolled by spraying the foliage in the field. Since 
the disease is carried over in the roots, it would be 
dangerous to feed them to stock or dump them on the 
manure pile. Rotation should be practiced where 
the disease has appeared more than once in the same 
field. Care should be taken that no diseased roots 
be permitted to enter the storage house or cellar. 
The roots should be thoroughly dried before storing, 
and the house or cellar should be kept moder- 
ately cool and ventilation resorted to wherever 
possible. 

Powdery Mildew 

Caused by Erysiphe polygoni D. C. 

Powdery mildew has not been known to cause 
any considerable damage to turnips in the United 
States. It is characterized by the presence of 
powdery white patches on both surfaces of the leaf. 
Besides affecting the turnip, Erysiphe polygoni has 
been recorded on about three hundred different hosts, 
especially the garden pea. For methods of control, 
see p. 367. 





Fig. 37. Turnip Disease. 

a. Macrosporium leaf spot, h. Macrosporium hercuUum, showing 
conidiophores and conidia, c. individual conidium of M. herculeum 
{a. to c. after F. C. Stewart). 



Family Cruciferae 217 

Macrosporium Leaf Spot 

Caused by Macrosporiimi herculeiim E. and M. 

Leaf spot often attacks the flat turnip and horse- 
radish. On turnips it is manifested as brittle circular 
spots on the leaf (fig. 37 a). When numerous, the 
spots usually fall out, giving a shot-hole appearance. 
The long club-shaped spores (fig, 37 c) of the fungus 
are borne on long conidiophores (fig. 37 b) on the 
exterior of the dead tissue. Should treatment seem 
advisable, spraying with Bordeaux mixture is re- 
commended. 

Weeds 

Of the many cruciferous weeds which truckers have 
to contend with, the following few may be mentioned : 
Winter cress {Barbarea vulgaris), shepherd's purse 
(Capsella bursa-pastoris) , cow cress {Lepidiiim cam- 
pestre), pepper grass {Lepidium virginicum). The 
above mentioned weeds and many other crucifers 
are subject to club root, black rot, white rust, and 
downy mildew. 

It is evident therefore that clean culture is impor- 
tant. These weeds must not be tolerated if we are 
completely to eradicate the diseases of the cultivated 
crucifers. 



CHAPTER XIV 

FAMILY CUCURBITACE^. 

The Cucurbit family contains numerous valuable 
truck crops. Those grown for their economic value 
may be mentioned: cantaloupe, cucumber, pumpkin, 
squash, and watermelon. According to the Thir- 
teenth Census of the United States, the total area 
devoted to cantaloupes and muskmelons in America 
was 52,419 acres, and the total crop valued at 
$3,604,636. The States, ranked according to the 
acreage devoted to these crops, were California, 
New Mexico, New Jersey, Indiana, Maryland, 
Florida, Georgia, Illinois, North Carolina, Michigan, 
Colorado, Missouri, Texas, Ohio, Tennessee, and 
Delaware. States with less than one thousand acres 
are omitted. 

The total area in the United States in 1909 given 
up to cucumbers was estimated at 32,310 acres, 
and the total crop valued at $2,719,340. The States 
ranked according to the area devoted to cucumbers 
were Michigan, New York, Illinois, Indiana, Florida, 
Virginia, New Jersey, Wisconsin, Texas, and Min- 
nesota. States with less than one thousand acres 

are omitted. 

318 



Family Cucurbitaceae 219 

The total area devoted to watermelons in the 
United States in 1909 was estimated at 137,005 acres, 
and the total crop valued at $4,453,101. The States 
which lead in rank according to acreage devoted to 
watermelon were : Texas, Florida, Georgia, Missouri, 
Indiana, Illinois, California, Oklahoma, North Caro- 
lina, South Carolina, Alabama, Iowa, Arkansas, 
Kansas, Virginia, Tennessee, Maryland, New Jersey, 
Mississippi, Kentucky, and Louisiana. 

DISEASES OF THE CANTALOUPE 

{Cucumis melo) 

The cantaloupe is subject to numerous diseases 
which often reduce the yield of the crop and en- 
tail heavy money losses. Fortunately most of the 
diseases may be controlled. 

Bacterial Wilt 

Caused by Bacillus tracheiphilus Ew. Sm. 

Bacterial wilt may be regarded as one of the most 
serious diseases of the cantaloupe. It has a very wide 
distribution, but it is said to be restricted in its 
Southern distribution. The same disease also at- 
tacks the cucumber, pumpkin, and squashes. The 
trouble is not known to occur on hosts outside of the 
Cucurbitaceae. Even in this family there are plants 
which are not subject to its attack. Dr. Erwin 
Smith succeeded in artificially inoculating the fol- 
lowing cucurbits : Cucumis odoratissimus, C. anguria, 



220 Diseases of Truck Crops 

Benincasa cerijera, Cucurhita foBtidissima, C. cali- 
Jornica, Echinocystis lobata. 

Symptoms. The symptoms of bacterial wilt are 
very striking. At first a few leaves of the plant are 
wilted. Soon after the entire plant wilts and dies. 
In cutting through an infected stem, a whitish viscid 
exudate oozes out from the vascular bundles of the 
cut surface. In placing one finger on the viscid 
substance and then gently removing it, the bac- 
teria will be strung out into numerous delicate 
threads resembling cobwebs. The disease works 
quickly and the change of leaf color from bright 
to dull green is also sudden. Cantaloupes, unlike 
squash, show no tendency to recover temporarily 
from wilt. 

Bacterial wilt is spread about through the bites of 
leaf-eating beetles, such as striped cucumber beetle, 
{Diabrotica vittata). 

The Organism. B. tracheiphilus is a short straight 
rod with rounded ends. The organism occurs singly 
in pairs and rarely in chains of four; it is motile by 
means of flagella. It grows slowly on gelatine which 
is not liquefied. On potato cylinders growth is vigor- 
ous, resulting in a gray-white film with no changes 
manifested in the substratum. There is no gas pro- 
duction and the organism is aeorobic. 

Control. Infection begins at a place of injury 
produced by the bite or puncture of insects. Hence 
any attempt at controlling wilt should first aim 
at controlling insect pests. For further control, 
see p. 232. 




Fig. 38. Cantaloup Diseases. 

a. Soft rot, b. individual germs of soft rot (a. and b. after Giddings), c. young 
cantaloup plant artificially inoculated with Mycospharella wilt, d. section through 
a perithecium of Mycospharella citrullina, showing immature asci, e. ascospores of 
M. citrullina (r. to e. after Grossenbacher),/. Alternaria leaf blight, g. Conidiophores 
and spore of Macrosporium cucumerinum (after Chester), h. Southern blight. 



Family Cucurbitaceae 221 

Soft Rot 
Caused by Bacillus melonis Gid. 

Soft rot is a disease which attacks the melon fruit 
only. The losses from this trouble often run as high 
as twenty-five per cent, of the crop. It is prevalent 
in seasons with prolonged dry weather followed by a 
wet spell. This results in the uneven growth and 
development of the fruit and hence in various crack- 
ings in its surface. Infection follows the place of 
injury, especially Vv^hen the crack (fig. 38 a) occurs 
at a place where the cantaloupe touches the ground. 
The rot produced is soft with an offensive odor. 

The Organism. Bacillus melonis is a short rod 
(fig. 38 a) with rounded ends, occurring singly or in 
short chains of two to three, and motile by means of 
fiagella. It forms no endospores, no capsule, and no 
involution forms. It completely liquefies gelatine 
in fourteen days. No gas is formed, and no very dis- 
tinct odor is noticed. It dies by drying and exposure 
to light. 

Control. Wherever possible, irrigation should be 
resorted to in dry weather. This will encourage 
even growth and prevent cracking of the fruit. In 
wet weather spraying with Bordeaux mixture is re- 
commended. Occasional turning of the melons to 
expose them to light on all sides will also help. Dis- 
eased refuse should be destroyed and not be fed to 
stock. 

Downy Mildew, see Cucumber, p. 230. 



222 Diseases of Truck Crops 

Powdery Mildew 

Caused by Erysiphe polygoni D. C, 

This disease is the same as the mildew which at- 
tacks garden peas, cucumbers, and numerous other 
hosts. Mildew is more prevalent on greenhouse 
melons and cucumbers than on those grown outdoors. 
It is characterized by powdery white patches on the 
leaves. The trouble is seldom serious enough in the 
field to warrant treatment. 

Mycospilerella Wilt 

Caused by MycospkcereUa citrulina (Sm.) Gr. 

Although this form of wilt is often a greenhouse 
trouble, it is nevertheless a serious disease on out- 
door cantaloupes and watermelons. Grossenbacher^ 
found that infection is localized at the nodes and not 
at the intemodes (fig. 38 c). The injury from Red 
Spider or other sucking insects is perhaps responsible 
for opening the way to this disease. A character- 
istic of the trouble is that the edges of the infected 
areas are oily green to raisin-colored gum. The 
older parts of the spots are either dark and gummy 
or gray and dry, bearing numerous brown pycnidia. 

The Organism. The perithecia (fig. 38 d) are 
globular to inverted top-shaped, rough, dark brown 

' Grossenbacher, J. G., New York (Geneva) Agr. Expt, Sta. 
Tech. Bui. 9 : 197-229, 1909. 



Family Cucurbitaceae 223 

to black, erumpent, and finally almost superficial. 
The necks of the perithecia are papillate. The 
ascospores are cylindrical, two-celled, hyaline, and 
slightly constricted at the septum (fig. 38 e). 

Control. Spraying with Bordeaux mixtures when 
the plants are about half grown and before the disease 
appears is recommended. Spraying should be con- 
tinued so that the growing parts are kept covered 
with the fungicide. 

Anthracnose, see Watermelon, p. 240. 

Leaf Blight 
Caused by AUernaria brassicce var. nigrescens Pegl. 

Leaf blight is a very destructive disease, often 
ruining entire patches which otherwise looked very 
promising. In some seasons, it is the greatest draw- 
back to successful melon culture. 

Symptoms. The disease begins as small round 
spots which gradually enlarge. These spots are dry, 
brown in color and made up of concentric rings or 
zones (fig. 38 f and g). Usually the spots are very 
numerous and their presence causes the leaves to curl 
and dry up prematurely, leaving bare vines and un- 
protected fruit. As a result, the melons ripen early 
and have an insipid taste, and are very poor shippers. 
Leaf blight is most serious in fields where canta- 
loupes are grown too long on the same field. 

Blight Resistant Cantaloupes. In selecting for 
blight resistant cantaloupe (fig. 39 a- b), we must con- 



224 Diseases of Truck Crops 

sider (i), the yielding quality of the strain; (2), the 
earHness in maturing; (3), resistant qualities; (4), 
form, size, and netting; (5), texture and edible quali- 
ties; (6), shipping qualities. Blinn ' found that resis- 
tance in cantaloupes seems to go hand in hand with 
the netting of the rind. Good netting seems also to 
favor good shipping melons with fine flavor. It 
seems that the closer the netting the better will the 
fruit be protected from loss of weight from evapora- 
tion. The Rocky Ford Pollock strain is claimed to be 
resistant to blight. Control by spraying, see cu- 
cumber, p. 232. 

Phyllosticta Leaf Spot 

Caused by Phyllosticta cucurbitacearum Sacc. 

This disease has not proved as serious as leaf 
blight. It is characterized by spots which are light 
in color. The pycnidia are pointed, the spores 
oblong and curved, hyaline and one-celled. The dis- 
ease may be controlled by spraying, see p. 232. 

Cercospora Leaf Spot 

Caused by Cercospora cucurbitcB E. and E. 

This disease behaves very much like leaf blight. 
In the former, however, the spots are usually of a 

• Blinn, P. K., Colorado Agr. Expt. Sta. Bui. 104: 3-15, 1905. 



Family Cucurbitaceae 225 

lighter color, and are more angular in form, being 
limited by the veins of the leaf. The methods of 
control are the same as for leaf blight, see p. 223. 

Southern Blight 

Caused by Sclerotium Rolf sit Sacc. 

Southern blight, a disease that attacks a large 
variety of hosts, is a serious cantaloupe disease in the 
Southern States. The injury in most cases is con- 
fined to the foot of the stem, resulting in its girdling 
and rotting and the final dying of the affected plant. 
With the cantaloupe, the disease attacks the fruit, 
infection usually taking place at a point where it 
touches the ground (fig. 38 h). The disease appears 
first as a slight soft spot which enlarges quickly, 
changing the entire mass of the fruit to a mushy pulp. 
The exterior of the affected melon is seen to be cov- 
ered with a white cottony growth consisting of the 
mycelium of the fungus. Later there appear numer- 
ous whitish bodies known as sclerotia which turn 
yellowish and then brown. They help to carry the 
fungus over the winter. For methods of control, see 
tomato, p. 353. 

Root knot, see nematode, p. 49. 

Care in the Shipping of Cantaloupes 

As a rule, the greatest per cent, of the cantaloupe 
crop is shipped to distant markets. Growers often 



226 Diseases of Truck Crops 

lose heavily from rotting of the fruit before it reaches 
its destination. Most of the loss may be reduced to 
a minimum or entirely prevented, provided growers 
are willing to devote more attention to certain 
fundamental considerations suggested by More and 
Branch. ^ 

a. Need of Quality. No one can deny the fact 
that products which are poorly grown, poorly har- 
vested, and poorly packed and shipped, are a direct 
loss to the grower and a serious drawback to the 
market. The consumer to-day insists on quality, 
and the grower who is to succeed cannot ignore this 
demand. Cantaloupes to-day are grown more ex- 
tensively than formerly. Competition therefore is 
more keen, and growers in the West are more handi- 
capped, because their products must travel longer 
distances, and therefore require more care in handling. 
By selecting fruit which matures early and at the 
same time possesses better edible and shipping 
qualities the difficulty will be at least partly solved. 

b. Care in Picking and Handling. Success in 
shipping depends largely on proper picking and hand- 
ling. With the "Netted Gem" or "Green Nets," 
the melons should not be harvested until completely 
netted. The netting should be well raised and 
rounded out on the surface. With immature melons 
the netting is flat and creased on top. For shipping 
short distances the melons may be picked "full slip, " 
i. e. just as soon as the stem separates cleanly from 

• More, C. T., and Branch, G. V., U. S. Dept. of Agr. Farm. Bui. 
707 : 1-23, 1916. 



Family Cucurbitacese 22^ 

the melon, leaving a cuplike cavity and tearing with 
it none of the rind. When shipping long distances 
the melons are picked on "half slip," in which case 
only part of the stem pulls away from the fruit, the 
rest breaking. It is essential that the fruit be 
handled carefully in the field, avoiding bruises and 
cuts. At the packing shed, the same care should be 
observed. 

c. Care in Packing. Good shipping also depends 
on careful packing. Only standard containers for 
shipping should be used. The crate has become the 
standard container for shipping melons. Crates 
should be made of clean, smooth, strong lumber, with 
all knotty and cross-grained slats discarded. Dirty 
and second-hand crates should not be used. Crates 
used in the field in harvesting should not be used 
for shipping. 

d. Need of Grading. Up-to-date growers take pains 
to grade their product carefully before packing. 
A careful grading excludes melons which are poorly 
netted, also known as "slickers." It is also essen- 
tial to exclude melons which are cracked, bruised, 
diseased, ill-shaped, over ripe, as well as those that 
are immature and those with soft stems. In pack- 
ing, melons of the same size and grade only should 
be put in the same container. 

e. Care in Handling. In hauling melons from the 
packing sheds to the car, only wagons with good 
springs should be used. Hauling wagons should also 
be provided with tarpaulin covers to protect the fruit 
from the sun, rain, or dust. The crates should be 



228 Diseases of Truck Crops 

carefully unloaded into cars which are iced, if the 
melons are to be shipped long distances. When the 
cars have been properly filled, they should be dis- 
patched as early as possible. Freight agents should 
see that cars are not delayed on the road. 

DISEASES OF THE CUCUMBER (Cucumis 

sativus) 

Cucumbers, like cantaloupes, are subject to vari- 
ous diseases which render them unfit for the market 
or for pickling. 

Mosaic or "White" or "Little Pickle" 

Cause unknown. 

Mosaic has been found in Wisconsin, Michigan, 
Indiana, Ohio, Iowa, Illinois, Vermont, New York, 
Louisiana, New Jersey, Minnesota, Massachusetts, 
and Virginia. 

Symptoms. The first sign appears as a yellow 
mottling near the stem end of the fruit. Later the 
light areas are found all over the cucumber, and the 
darker portions frequently form protuberances. 
Some fruits retain their green color and show the dis- 
ease only by being distorted. The leaves too be- 
come mottled, light to dark green (fig. 40 a), and 
sometimes wrinkled; the stems and petioles too are 
dwarfed and distorted. Affected leaves die prema- 
turely and are replaced by others, which in turn con- 



■■v>;'--' *4 



,,\.- 



"-"' 4v 



'r ft 



i&^ 







* if, ^ ■ " m - «*;. 







t'^--#^ 













1m(.. 39. Resistant Cantaloup Strain. 

a. Cantaloup hill, destroyed by Alternaria leaf blight, b. cantaloup hill resistant 
to Alternaria lalight. a. and 6. same variety (Rockyford) growing in same field 
under equal condi'.ions. 



Family Cucurbitaceae 229 

tract the disease. The trouble is spread by insects, 
the principal of which is the melon louse, Aphis 
gossypii Glov., as well as the striped cucumber beetle, 
Diahrotica vittala. Satisfactory control methods are 
still wanting. Diseased plants should be destroyed 
and the field sprayed for insect pests. 

Bacterial Wilt 
Caused by Bacillus tracheiphillus Ew. Sm. 

The symptoms and damage caused by this wilt 
have already been discussed under the cantaloupe, 
p. 219. Recent investigations by Rand and Enlows"" 
have shown that seeds from diseased plants fail to 
reproduce wilt. This is true not only for the cucum- 
ber, but also for all the other cucurbit hosts which are 
subject to this trouble. Of the numerous varieties 
of cucumber and cantaloupe tested, none shows 
promise of resistance. While the Marblehead, Gol- 
den Bronze, and Boston Marrow are very susceptible 
varieties of the squash, the Mammoth White Bush 
and the Early White Bush seem to be immune to wilt. 

Angular Leaf Spot 
Caused by Pseudomonas lachrymans Sm. and Bry. 

This disease seems to be common on cucumbers in 
Florida, Michigan, and in Wisconsin. It has been 

' Rand, F. V., and Enlows, E. M. A., U. S. Dept. of Agr., Jour. 
Agr. Research, 6 : 417-434, 1916. 



230 Diseases of Truck Crops 

recently studied by Smith and Bryan, ' who described 
it as a new disease occurring in the Eastern and 
Middle- Western States. 

Symptoms. The trouble is characterized by angu- 
lar brown spots which tear or drop out when dry 
(fig. 40 b) , giving a ragged appearance to the infected 
leaves. In the early stages, a bacterial exudate 
collects in drops on the lower surface of the spots. 
These exudates usually dry and become whitish. 
It seems that angular leaf spots attack only the foli- 
age but rarely the fruit. 

The Organism. The parasite is a short rod with 
rounded ends (fig. 40 c), occurring singly, or in pairs 
with a decided constriction; and occasionally in 
chains of twelve individuals or more. It is motile by 
means of polar flagella, produces capsules on agar 
and milk ; no spores, and no gas is formed. The or- 
ganism completely liquefies gelatine in about three 
or four weeks. 

Damping off, see Pythium, p. 43. 

Downy Mildew 

Caused by Pseudoperonospora cubensis (B. and C.) 
Rost. 

Downy mildew is prevalent in New Jersey, New 
York, Florida, Texas, and possibly other States. It 



' Smith, E. W., and Bryan, M. K., U. S. Dept. of Agr., Jour. Agr. 
Research, 6 : 465-476, 1915. 




Fig. 40. Cucumber Diseases. 

a. Mosaic, b. angular leaf spot (after Smith and Bryan), r. individual germs of 
Pseudotnonas lachrymans, d. downy mildew (Manns), e. conidiophore and conidia of 
Plasmopara cubensis, f. germinated conidia and swarm spore, g. germinated swarm 
spores {e. to g. after Clinton), h. anthracnose. 



Family Cucurbitaceae 231 

attacks cantaloupes, gourds, squashes, pumpkins, 
and watermelons. 

Symptoms. The disease appears as yellowish spots 
on the leaves, which have no definite outline (fig. 
40 d). With warm moist weather, numerous spots 
coalesce, and soon the affected leaves turn yellow 
and die. With cool weather the spots seem to spread 
less rapidly. The disease appears to work on the 
older leaves, beginning on those on the center of the 
hill and working outward. With infected plants 
the center of the hill is clearly marked by a cluster 
of yellow leaves. Diseased plants may flower pro- 
fusely, but no fruit is produced. The few cucumbers 
which set are small, deformed, and unfit for the 
market. 

Downy mildew is most prevalent in August with 
moderate rainfall and hot weather. The disease 
spreads very rapidly and a large cucumber field 
may be a total loss in less than from eight to ten 
days. 

The Organism. The fungus derives its food from 
the host cells by means of suckers or haustoria. The 
myceliimi is hyaHne, non-septate ; the conidiophores 
(fig. 40 e) arise in small clusters through the leaf 
stomata and are branched and flexuous. The 
zoosporangia are hyaline but slightly violet, tinted in 
mass. Germination of zoosporangia is by means of 
motile zoospores (fig. 40 f-g) . The oospore, or sexual 
fruiting stage, was first found on the host by Ros- 
tovtsev. Downy mildew may be kept in check by 
spraying with Bordeaux mixture. 



232 Diseases of Truck Crops 

Powdery Mildew 
Caused by Erysiphe cichoracearum D, C. 

Powdery mildew of cucumbers is not a serious 
trouble, since it usually attacks plants which have 
somewhat passed their usefulness. Like all powdery 
mildews, the causative fungus grows on the surface 
of the leaf, giving it a white mealy appearance. 
From the mycelium are produced erect threads which 
bear the summer spores of the fungus. According 
to Humphrey, ^ the ascus or winter stage appears as 
minute dark-brown rounded capsules enclosing a 
group of spore sacs within which are formed the 
ascospores. 

Anthracnose (fig. 40 h), see Watermelon, p. 240. 

Root Knot, see Squash, p. 237. 

Spraying Cantaloupes and Cucumbers 

Cantaloupes and cucumbers cannot always be 
grown profitably unless the crops are sprayed. It is 
fortunate that most of the foliage and fruit diseases 
may be kept in check by spraying with Bordeaux 
mixture. The work of Orton^ and others has shown 
that not only does spraying control the various dis- 
eases, but viewed from the point of view of dollars 
and cents it undoubtably pays. 

' Humphrey, J. E., Massachusetts Agr. Expt. Sta. loth Ann. 
Rept.: 225-226, 1892. 

^ Orton, W. A., U. S. Dept. of Agr. Farm. Bui, 231: 5-24, 1905. 



Family Cucurbitaceae 233 

Cucumbers grown for pickles, however, should not 
be sprayed, as spraying reduces the number of fruit, 
although it is so beneficial for fruit which are to be 
left to grow to market size. 

For an area less than one acre, a small hand pump 
sprayer, or preferably a good small compressed-air 
sprayer will answer the purpose. For fields of one 
to five acres a barrel sprayer is recommended. For 
fields above five acres or more, a good power sprayer 
must be able to apply at least one hundred gallons 
per acre. To do thorough spraying, a slow walking 
team should be chosen, but the pump should be geared 
correspondingly high so as to maintain full pressure 
at a low speed. 

The strength of Bordeaux recommended by Orton 
as safe from burning is a 3-6-50 formula. From the 
writer's experience, he would not advise using formu- 
las stronger than this, especially under Southern 
climatic conditions. The time to spray first is when 
the vines begin to run. The number of succeeding 
applications should be governed by climatic condi- 
tions. In damp warm weather, spraying should be re- 
peated every second or third week. The object is to 
keep all growing parts of the plant thoroughly covered 
with the fungicide. For further directions on spraying 
and the preparations of the ingredients, see p. 361. 

In some seasons, the melon louse, Aphis gossypii, 
causes great damage to cantaloupes and cucumbers. 
The pest sucks the life of the plant by feeding on its 
juices. Durst' recommends spraying with "Black 

■ Durst, C. E., Illinois Agr. Expt. Sta. Bui. 174 : 321-334, 1914. 



234 Diseases of Truck Crops 

Leaf 40," used at the rate of one part to one thousand 
of water. This will control the aphids. "Black 
Leaf 40" readily mixes with Bordeaux mixture. To 
control both fungus and plant lice, add to every one 
hundred gallons of Bordeaux one pint of "Black 
Leaf 40." To control chewing insects, such as the 
cucumber striped beetle or caterpillars feeding on 
the plants, add to each one hundred gallons of Bor- 
deaux three pounds of powdered arsenate of lead. 

DISEASES OP THE CITRON {CitruUus vulgaris) 

Citrons are not grown commercially. They are 
found as weeds in melon patches or anywhere in the 
farm where permitted. The citron is a very hardy 
plant, and it is subject to but fev/ diseases. 

Anthracnose, see Watermelon, p. 240. 

Leaf Spot, see Watermelon, p. 243. 

Gourd Disease, see Squash, p. 234. 

MusKMELON Diseases, see Cantaloupes, p. 219. 

Pumpkin Diseases, see Squash, p. 234. 

DISEASES OF THE SQUASH {Cucurbita 
maxima, C. pepo, and C. Moschata) 

Squashes, with but few exceptions, are subject to 
the same diseases as affect the cantaloupe and the cu- 
cumber. Squashes are usually grown for local mar- 
kets, and because of their diseases in many places 
their culture has been abandoned. 

Bacterial Wilt, see Cucumber, p. 229. 




Fig. 41. Squash Diseases. 

a. Showing squash blossoms invaded by the fungus Choanophora ciicurbitarum, 
b. squash entirely rotted by the Choanophora fungus, c. young conidiophore of 
Choanophora with ramuli developing on the primary vesicle, d. mature capitulum 
covered with a layer of conidia, e. conidia, /. sporangia and columella, g. sporangio 
spores with tufts of hair-like appendages, h. mature zygospore («, c. to /;. after 
Wolf), i. Fusarium wilt of young squash plants, .;'. Rhizopus rot. 



Family Cucurbitaceae 235 

Fruit Rot 

Caused by Choanophora cucurbitarum (B. and Rav.) 
Thax. 

Fruit rot is a common disease of the summer 
squashes. It has been found in North and South 
Carolina, Alassachusetts, New York, Ohio, Michigan, 
Connecticut, Florida, and Texas. The disease is of 
little importance in dry seasons. It is, however, 
favored by conditions of high humidity and excessive 
rainfall, or by heavy dews at night. 

Symptoms. It usually attacks the flowers, or 
especially the remnants, of the old calyx (fig. 41 a). 
The latter when affected become shriveled and cov- 
ered with a thick crop of brown conidiophores of the 
causative fungus. From the floral parts, the my- 
celium works downward and into the young squash, 
which wilts very rapidly, turning into a soft rot and 
later covered by a gray growi;h of conidiophores 
(fig. 41 b). As far as is known, the fungus does not 
attack any other part of the squash plant except the 
floral parts and the fruit. 

The varieties of squash most affected by fruit rot 
are the "patty pan" types, commonly known as 
cymblings. Wolf^ has found Choanophora cucurbi- 
tarum on fading flowers of cucumber, Althea, scarlet 
hibiscus, okra, and cotton. 

The Fungus. The conidiophores when young are 
whitish, but at maturity take on a metallic luster. 

• Wolf, P. A., U. S. Dept. of Agr., Jour. Agr. Research, 8 : 319-328, 
1917. 



236 Diseases of Truck Crops 

The top end is broadest, becoming dilated into a 
caputate vesicle. From this head are produced from 
a few to a dozen small branches, the tips of each in 
turn becoming vesicular (fig. 41 c). Each vesicle 
now becomes covered with a dense layer of conidia 
(fig. 41 d). The latter are light to reddish brown 
in color (fig. 41 e). The conidia germinate by means 
of a germ tube. Sporangia are formed in pure 
culture but not on the host. Sporangia are first 
evident as white pendant enlargements, becoming 
separated from the sporangiophore by a globular 
columella (fig. 41 f). Mature sporangiospores are 
larger than the conidia, are smooth, and possess 
terminal hyaline appendages (fig. 41 g). The spores 
germinate by means of the germ tube, as is the case 
w4th the conidia. Chlamydospores are not uncom- 
mon and they have often been observed during the 
winter. The formation of zygospores is a common 
occurrence on culture media, but not on the host. 
The method of zygospore formation and germina- 
tion has not as yet been definitely worked out. 

Control. The spores of Choanophora cucurhitarum 
are undoubtedly carried from flower to flower by 
insects. Spraying, as outlined for cucumbers, is also 
recommended for the squash, p. 232. 

Soft Rot 

Caused by Rhizopus nigricans Ehr. 

Soft rot very often cannot be distinguished from 
the fruit rot above mentioned (fig. 41 j). The symp- 



Family Cucurbitaceae 237 

toms in both diseases are very much ahke. The only- 
disparity consists in the difference of the two causa- 
tive organisms. For a further study of Rhizopus 
nigricans, see soft and ring rot of the sweet potato, 

pp. 156-159- 
Powdery Mildew, see Cucumber, p. 232. 
Anthracnose, see Watermelon, p. 240. 
Leaf Spot, see Cantaloupe, p. 224. 

Wilt or Yellows 

Caused by Fusarium cucurbitcE Taub. ^ 

One of the greatest drawbacks to squash culture 
in many of the Southern States, especially in Texas, 
is a disease known as wilt (fig. 41 i) or yellows. The 
symptoms of the squash wilt are identical with those of 
the watermelon wilt, see p. 244. However, the organ- 
ism F. cucurbitcB is different and distinct from the three 
species of Fusarium which are capable of producing a 
wilt on watermelon. The name Fusarium cucurbi- 
ts n. sp. is therefore given to the squash wilt 
organism to distinguish it from other species of Fusa- 
rium. From investigations by the writer there has 
been found no variety which is resistant to wilt. On 
the other hand, the pumpkin Cucurbita pepo, and the 
"sugar through" gourd Lagenaria vulgaris will 
thrive in soils where squashes are known to fail from 
wilt. Watermelons, cowpeas, cotton, and okra will 
also thrive well in Fusarium-sick soil of squashes. 
Occasionally it is found that cowpeas and okra will 

' From unpublished data of the author. 



238 Diseases of Truck Crops 

die from a wilt in the same field where squashes are 
not thriving. However, the writer has been able to 
prove that the wilt of cowpea and okra are diseases 
caused by two distinct species of Fusarium, and that 
both of these parasites may be found in the same field 
also infected with Fusarium cucurbitcz of the squash. 

Root Rot, see Rhizoctonia, p. 45. 

Root Knot, see Nematode, p. 49. 

DISEASES OF THE WATERMELON {Ciirullus 
vulgaris) 

Malnutrition 

Cause, physiological. 

Malnutrition seems to occur in fields deficient in 
potash. The trouble is apparently new, brought 
about by the scarcity of potash, due to war conditions. 
The disease is characterized by light brown spots 
located around the veins and margins of the leaf. 
The disease must be further investigated before re- 
medial measures may be suggested. 

Bacterial Wilt, see Cantaloupe, p. 219. 

Downy Mildew, see Cucumber, p. 230. 

Powdery Mildew, see Cucumber, p. 222. 

Honey Dew or Sooty Mold 

Caused by Capnodium sp. 

Watermelon stems, petioles, and leaves often be- 
come coated with a black sooty growth. This is 




Fig. 42. Watermelon Diseases. 

a. Stem end rot (after Meier), b. anthracnose of foliage, c. anthracnose on fruit, 
d. Fusarium wilt of young seedlings, e. blossoni end rot. 



Family Cucurbitacese 239 

more abundant on the older leaves, or even on the 
nearly mature melon fruit. Although the mold seems 
to grow superficially on the outside of the affected 
parts, the result is a general suffocation, since sun- 
light and free circulation of air are interfered with. 
Sooty mold undoubtedly grows on the sweetish ex- 
creta of plant lice, and is severest during seasons of 
Aphis epidemics. Spraying with "Black Leaf 40" 
to control Aphis gossypii will also control sooty mold. 
The fungus Capnodium apparently does not derive 
any nourishment from the watermelon, but from the 
honey excreted by plant lice. 
Mycosphaerella Wilt, see Cantaloupe, p. 222. 

Stem End Rot 

Caused by Diplodia tubericola (E. and E.) Taub. 

This disease was first studied by Meier' who found 
the trouble confined mostly to watermelons in transit. 
Many carloads when reaching their destination 
showed a loss from it of 75% to 95%. 

Symptoms. The first indication of the rot is a 
browning and shriveling of the stem end of the fruit 
(fig. 42 ^). Rotting begins at the point of attach- 
ment of the melon to the stem of the plant. The 
flesh of the affected melon blackens, softens, and 
becomes watersoaked and then slimy. Such melons 
when left to themselves become black, wrinkled, and 
mummified. Infection undoubtedly must take place 

' Meier, F.C., U.S.Dept. of Agr., Journal ojAgr. Research, 6 : 149- 
152, 1916. 



240 Diseases of Truck Crops 

in the field before loading. The disease incubates 
while in transit and makes its appearance when 
the assigned shipment reaches its final destina- 
tion. 

The Organism. The organism which causes stem 
end rot of watennelon is the same which is re- 
sponsible for the Java black rot of the sweet 
potato. This has been proved by Meier and by 
the writer. For further discussion of the fungus, 
see p. 165. 

Control. Diplodia tuhericola may easily live over 
from year to year on the cull melons left in the field, 
on the sweet potato refuse or on any other trash. 
Therefore infected culls and refuse should be de- 
stroyed. In hauling melons to the car, only wagons 
with springs should be used. The cars should be 
carefully swept and cleaned before loading. Rough 
handling or bruising should be avoided as much as 
possible and only sound melons should be loaded in 
the car. The fruit should be carefully packed so as 
to avoid bruising from shaking when the cars are 
moved. 

Anthracnose 

Caused by Colletotrichum lagenarium (Pass.) E. 
andH. 

Anthracnose is a disease the seriousness of which 
depends on weather conditions, it thriving best dur- 
ing hot, moist weather. It is very prevalent in many 







''^]i''f:ff:\-- .i.m^'''_^'~ ■"' 



A^^'t?^ '' 'St^'^ 






Fig. 43. Watermelon ^nthracnose. 

a. Healthy watermelon hill, b. field destroyed by anthracnose. 



Family Cucurbitaceae 241 

States, although it has not as yet been found to be 
serious in Texas. 

Symptoms. It attacks all parts of the plant except 
the root. On the stems it causes watersoaked 
spots, which in time turn brownish and become 
depressed and cracked. On the leaves, somewhat 
circular dark spots become so numerous as to involve 
the entire area (fig. 42 b), resulting in the death of the 
leaf. Diseased leaves soon crinkle, turn black, and 
have the appearance of being burned by fire. On the 
fruit, anthracnose is manifested on the rind as cir- 
cular deep depressions (fig. 42 c) which soon become 
covered with a salmon-colored coat made up of the 
spores of the fungus. Ordinarily the spots do not 
go deeper than the rind. Under improper methods 
of shipping, the fungus eats into and penetrates the 
flesh of the melon which decays rapidly. Anthrac- 
nose reduces the market value of the melons, and 
makes shipping a very risky affair, since the disease 
readily spreads in the car. This is especially true 
when the cars are sidetracked and held too long in 
transit. In the field, anthracnose may ruin the 
entire stand (fig. 43 a-b). 

Besides attacking watermelons, anthracnose also 
attacks cucumbers, cantaloupes, citrons, and gourds. 
The disease is not usually serious on new land; but 
on land where watermelons have been grown in suc- 
cession for a period of years, or where melons fol- 
lowed cantaloupes or cucumbers, the disease may 
become serious. 

The Organism. In structure, Colletotrichum lage- 



242 Diseases of Truck Crops 

narium resembles the organism of bean anthracnose, 
see p. 263. The watermelon fungus has a peculiar 
ability to remain dormant during dry weather; but 
it is easily revived by rains or dew. This is why 
anthracnose often appears overnight in carloads 
shipped to market. The fruits of the fungus are 
borne in masses on the pustules which take on a 
salmon color. The spores are typical of all Colleto- 
trichums — that is, oval, one-celled, and hyaline. The 
setae in C. lagenarium are not very plentiful. In 
pure culture it resembles C. lindemuthianum; how- 
ever, pathologically it is distinct from the latter, since 
numerous attempts by the writer and by others 
have failed to infect growing bean plants with the 
watermelon anthracnose or the watermelon with 
that of the bean. 

Control. With this disease, prevention is, of course, 
the cheapest method of control. From what has 
been said, it is evident that it is never wise to grow 
watermelons too long on the same land. In prevent- 
ing the disease from gaining a foothold on the land, 
a three-year rotation will probably answer the pur- 
pose. On lands in which the crop has suffered severely 
from anthracnose, a longer rotation, say six years, 
may be necessary. The disease is carried over in the 
soil from year to year on the dead leaves, vines, and 
diseased fruits which remain in the field. These, 
therefore, should never be plowed, but destroyed 
by fire. Spraying, too, will help to keep the disease 
in check. Bordeaux in this case is the standard 
fimgicide to use. However, it should be borne in 



Family Cucurbitaceae 243 

mind that watermelon leaves are very tender and 
hence susceptible to injury. Recent experiments by 
the writer have shown that a very weak Bordeaux 
with a large excess of lime should be used in order to 
prevent the burning of the foliage. Where this pre- 
caution is overlooked, a greater injury will result 
from the use of the fungicide than from the disease 
itself (fig. 44 b). A Bordeaux made up of three 
pounds of copper sulphate, eight pounds of lime, and 
fifty gallons of water, to which is added one pound 
of powdered arsenate of lead, will answer the 
purpose well. The lead arsenate in this case is 
used against various caterpillars which often feed 
on the leaves of the plants. Paris green should 
not be used because of its tendency to bum the 
foliage. 
Cercxdspora Leaf Spot, see Cantaloupe, p. 224. 

Cercospora Leaf Spot 

Caused by Cercospora citrullina Cke. 

This form of leaf spot is induced by a species of 
Cercospora different from that which attacks canta- 
loupes. The trouble usually appears on the oldest 
leaves as circular spots bordered by a dark brown 
or purplish zone beyond which is an area of yellow. 
The mature spots have gray centers. This form of 
leaf spot is prevalent on watermelons in Texas. It 
may be controlled by spraying in the same way as 
recommended for anthracnose. 



244 Diseases of Truck Crops 

Vine Wilt or Yellows 

Caused by Fusarium niveum Ew. Sm.; Fusarium 
citrulli Taub.^; Fusarium Poolensis Taub.^ 

Failure of the watermelon crop in many of the 
Southern States may be safely attributed to wilt. 
There is no other watermelon disease that is so diffi- 
cult to control. The reason is obvious. The causa- 
tive fungi live in the soil as semi-saprophytes. The 
longer watermelons are grown on that soil, the worse 
the disease becomes. In severe cases the crop may 
be a total failure, or the loss run as high as fifty per 
cent, of the crop. 

Symptoms. There is no outside spotting nor are 
there any lesions to indicate the presence of wilt. 
The source of the trouble is confined entirely to the 
interior of the roots and stems. The leaves of an 
affected plant suddenly droop; this is followed by a 
rapid wilting of all the vines in that hill (fig. 44 a) 
from which they never revive. The wilting is more 
intensified during a warm dry spell. Occasionally 
only one or two vines in the hill wilt and die while 
others in the same hill remain alive for some time 
before succumbing to the disease. In pulling out a 
plant that has recently died, its roots are found to be 
sound with the exception of a dull yellowish color 
which the exterior exhibits. In splitting open a vine 

• From unpublished data by the writer, the organism was carried 
as Fusarium No. 106. 

* The organism was carried as Fusarium No. 1 16. 



SAi^i < ^^H 



^■, -.i^^iiSr -stv V- -T -u^. ■■ --41 




Fig. 44. Watermelon Diseases. 

a. Wilt (Fusarium niveum), b. Bordeaux injury, c. Tom Watson, 
an ideal shipping melon, d. macroconidia of Fusarium niveum. 



Family Cucurbitacese 245 

or root of the diseased plant, its interior fibrovascular 
bundles will be browned. The browning indicates 
the presence of the parasite. 

Wilt is not always confined to the older plants. 
In badly infected fields young seedlings begin to die 
at an early age (fig. 42 d), resulting in a very poor 
stand. From the investigations of the writer, it has 
been found that Fusarium citruUi is more active on 
seedlings than are the other two species of Fusarium. 
This, however, is not intended to convey the idea that 
F. niveum and F. Poolensis are not capable of pro- 
ducing wilt on the younger seedlings. 

The Organisms. The three species of Fusarium 
which produce wilt of watermelon may be readily 
distinguished when grown in flasks on cornmeal. 
Fusarium citrulli is entirely different from the two 
others in that it forms a glistening, flat, compact, 
flesh-colored dry growth confined to the surface of 
the cornmeal. Growth is slow, and no color is pro- 
duced in the substratum for a considerable time, 
about two months or more. Fusarium Poolensis at 
first greatly resembles F. niveum in growth and in 
color. Later, however, F. Poolensis takes on a deep 
blue to almost indigo which is retained indefinitely. 
The three species of Fusarium have been definitely 
proved by the writer to be the cause of the water- 
melon wilt. Infection can take place only on water- 
melons and not on any other cucurbit hosts, nor on 
cotton, okra, or cowpea, the wilts on all of which are 
caused by different species of Fusarium. It is possible, 
however, that a sick watermelon field may also be 



246 Diseases of Truck Crops 

infected with Fusarium cucurbitcB, thus making it 
also sick to squashes. 

Control. Since the disease works in the interior of 
the plant, it is obvious that spraying would be of 
little help. Rotation of crops is the only practical 
method of control. It usually takes from two to 
three years for wilt to establish itself very seriously 
in the field. Because of this, growers often fail to 
appreciate its importance until too late. Any 
possible profits made during the time the crop has 
been grown in succession on the same land are more 
than offset by the fact that the infected soil is ren- 
dered sick and unfit for watermelons for ten years 
or longer. Watermelon plants suffering from wilt 
should never be plowed under, but should be pulled 
out, dried, and burned. Wilt may be spread by 
cattle and horses which are allowed to pasture in the 
sick melon patches, and then brought to healthy 
fields. Finally a method which promises great re- 
lief is the development of resistant varieties which 
are able to grow in sick soils. The United States 
Department of Agriculture has developed a wilt re- 
sistant variety named Conqueror. This is a cross 
between the citron and the Eden. The Conqueror, 
however, is not as yet popular with the market be- 
cause of the uncertain qualities of the citron which it 
still has. Resistant varieties may no doubt be ob- 
tained by selection with the best commercial vari- 
eties. For methods of selection for resistance see 

P- 374- 
Root Knot, see Nematode, p. 49. 



Family Cucurbitacese 347 

Fruit Rot 

Caused by Sclerotium Rolfsii Sacc. 

This form of rot is seldom serious enough to war- 
rant any treatment. The fungus does not seem to 
find the watermelon fruit as suitable a host as the 
cantaloupe. On watermelons, rotting starts at a 
bruise and at points where the melon touches the 
ground. Decay is slow and is always indicated by a 
cottony growth at the rotted area. 

Blossom End Rot 

Cause : probably due to fungi. 

This is a disease which attacks the blossom end of 
the fruit (fig. 42 e) and causes a dry rot, but which 
does not usually penetrate very deep. Nevertheless, 
affected melons are unfit for the market, although 
they ripen earlier and have a much sweeter taste. 
The cause of this trouble is as yet unknown. How- 
ever, numerous observations seem to indicate that 
with at least one form of blossom end rot it seems to 
be brought about by a dry spell and a lack of mois- 
ture in the soil. This is especially the case in fields 
where coarse manure is used instead of good compost. 
In dry seasons, the coarse manure fails to decompose 
properly and, at the same time, dries, and hence re- 
sults in injury to the fruit. To prevent this, so 
far as possible, only well rotted manure should be 



248 Diseases of Truck Crops 

used. If the coarser manure has to be used, care 
should be taken to apply it from four to eight weeks 
before planting, thus giving it ample time to decom- 
pose. To have the greatest effect, manure should 
be applied as deep in the furrows as possible, since the 
tap-root grows very deep in the soil. It should be 
remembered that the watermelon plant has numer- 
ous long secondary roots which are heavy feeders 
and which do not benefit from manure if it is applied 
in the center of the hill. Such superficial application, 
therefore, often results in starved plants, which be- 
come further weakened by spells of dry weather, or 
by other unfavorable conditions. To obviate this 
condition, some chemical fertilizer should be applied 
broadcast. The amount of manure necessary for 
one acre is about seven tons, applied at the rate of 
one good forkful to each hill. In connection with 
this, about four hundred pounds of well balanced 
fertilizer should also be worked in. In very dry 
seasons, small amounts of nitrate of soda, applied 
broadcast, will decidedly benefit the plants. The 
aim in fertilizing should be to supply sufficient humus 
to the soil, thus also taking care of the soil moisture 
at a time when the plant needs it most. Moreover, 
the use of proper food supply will result in more 
vigorous plants, with an abundance of foliage protect- 
ing the plants from burning and, at the same time, 
reducing blossom end rot. 

There are other forms of blossom end rots. Some 
may possibly be attributed to imperfect fertilization 
or weak pollen, while others are undoubtedly caused 



Family Cucurbitaccae 249 

by parasitic bacteria and fungi. However, without 
further knowledge it is impossible to suggest other 
methods of control. The best shipping melon is 
the Tom Watson (fig. 44 c). This melon, however, 
is no less susceptible to diseases than any other 
variety grown under similar field conditions. 

WEEDS 

The wild cucumber Micrampelis (or Echinveyster) 
lobate is subject to cucumber mosaic and to bacte- 
rial wilt. With this exception no cuciirbit weeds are 
subject to the diseases which attack the cultivated 
species. 



CHAPTER XV 

FAMILY GRAMINEiE 

Of this great family the only crop that concerns 
the trucker and gardener is sweet com. This is 
grown to a great extent in the more northern States. 
In the South, the ordinary field com is grown instead 
of sweet com and is sold for "roasting ears" or on the 
cob in the milky stage. The present discussion will 
limit itself to sweet com only. It is estimated in the 
Thirteenth United States Census that the total area 
of sweet com in the United States in 1909 was 
178,224 acres and the crop was valued at $2,719,340. 
The States ranked according to area in sweet corn 
were: New York, Illinois, Maryland, Ohio, Iowa, 
Pennsylvania, New Jersey, Maine, Indiana, Michi- 
gan, Massachusetts, Wisconsin, Kansas, Nebraska, 
Missouri, California, Minnesota, Virginia, Connecti- 
cut, Delaware, Louisiana, Vermont, and Kentucky. 
States with less than one thousand acres are omitted. 

DISEASES OF THE SWEET CORN {Zea Mays) 

Although corn is considered a hardy plant, it is 
nevertheless subject to numerous diseases. Of the 
250 



/ 







f,J /. 



%'\ 






a 



/f.\v 




Fig. 45. Sweet Corn Diseases. 

a. Bacterial blight, 6. individual blight organisms (a. to 6. after F. C. Stewart), 
c. smut, d. smut spores, e. and/, germinating spores of Uslilago zeir (</. to/, after J. b' 
S. Norton). 



Family Gramineae 251 

sweet com but three diseases need concern the 
trucker. 

Bacterial Wilt 

Caused by Pseudomonas Stewarti Erw. Sm. 

Bacterial wilt is perhaps one of the most serious 
diseases of sweet corn. The trouble is very prevalent 
in Long Island, New York, where it was first studied 
by Stewart.' It is also prevalent in New Jersey, 
Maryland, West Virginia, Ohio, Iowa, Illinois, and 
probably many other States. 

Symptoms. Bacterial wilt has been carefully 
studied by Dr. Erwin F. Smith, ^ who finds that the 
symptoms of this disease are very distinctive. The 
first mark on good sized plants is a drying out and 
whitening of the tassel, giving the top of the plant 
a peculiar whitish appearance. Another sign is 
a dwarfing of the plant, followed by a drying of the 
basal leaves which gradually works upwards (fig. 
45 a). The aflected leaf dies from the tip downwards 
or from the margin inwards. The disease often 
attacks young plants and even seedlings, in which 
case they dry and die out at an early stage. If an 
infected plant is cut across the stem, we find a yellow 
slime oozing out from the bundles; this slime is 
teeming with the bacteria. In cutting through a 

' Stewart, P. G., New York (Geneva) Agr. Expt. Sta. Bui. 130 : 
424-439, 1897. 

^ Smith, E. P., Bacteria m Relation to Plant Disease, 3 : 89-174, 
Washington, D. C. 



252 Diseases of Truck Crops 

stem longitudinally, it will be found that the bundles 
from which the yellow slime oozes out are browned 
or bright yellow. This shows that the germ is con- 
fined to the fibrovascular bimdles of the stem and 
leaves. 

The Organism. Pseudomonas Stewarti is a short 
rod with rounded ends (fig. 45 b). It occurs singly, 
in pairs, or fours, and moves about by means of polar 
flagella. It grows slowly on gelatine without lique- 
faction. On agar plates it grows slowly, forming 
small round colonies. It produces no gas and is 
strictly aerobic ; the organism is very sensitive to light. 

Control. It is likely that the disease is carried with 
the seed. Hence the latter should be secured from 
localities free from wilt. Before planting, seed 
should be disinfected in formaldehyde, see p. 99. 
Not all varieties of sweet corn are equally subject to 
wilt; hence truckers are advised to try to develop 
a resistant strain or strains of commercial varieties. 
On the methods of selection for resistance, see p. 374. 
Finally, fields badly infected should be rotated and 
devoted to other crops for about three to four years. 
As far as is known the disease only attacks corn, 
so other cereals may be used in the system of ro- 
tation. 

Smut 

Caused by Ustilago zecz (Beck.) Ung. 

Corn smut is different from any smut which at- 
tacks other cereals. The greatest damage is experi- 



Family Gramineae 253 

enced when the disease attacks the ear, destroying or 
rendering it useless for market purposes. 

Symptoms. Corn smut does not usually make its 
appearance before the plants are about three or 
four feet high. It is manifested as boils which 
may attack any part of the leaves (fig. 45 c), stalks, 
tassels, or ears. The boils are whitish to glossy, 
then purple, finally rupturing and liberating a black 
powdery mass of the spores (chlamydospores) of the 
fungus. 

The Organism. Within the tissue of the affected 
host the smut mycelium consists of short slender 
branched filaments closely interwoven. These 
slender filaments swell, gelatinize, and portions of 
them round off as spores. The latter retain their 
vitality for more than one year. The chlamydo- 
spores (fig. 45 d) germinate by sending out a tube 
which in turn bears true conidia (fig. 45 e, f). The 
latter germinate by sending out a tube which pene- 
trates the host. 

Control. Corn smut is not carried with the seed 
as is the case with oat or wheat smut. Seed treat- 
ment in this case will therefore be useless. The dis- 
ease is carried with the manure or in the soil. The 
best remedy, therefore, is to cut out and destroy by 
fire all smut boils as they appear. This must be 
done before the boils are ruptured. If this is care- 
fully practiced by everyone in each community corn 
smut will soon disappear. Smutted ears or stover 
should never be fed to animals, as this is a common 
way of infecting the manure pile. 



254 Diseases of Truck Crops 

Rust 

Caused by Puccinia sorghi Schw. 

Corn rust is a disease which is of restricted dis- 
tribution and which is never serious enough to war- 
rant treatment. It is characterized by chocolate 
colored pustules on the leaves and leaf sheaths. The 
ascidium of this rust occurs on oxalis and is known as 
yEcidium oxalidis Thum. The uredo and puccinia 
stages both occur on the com. 

WEEDS 

So far as is known, none of the Graminaceous 
weeds are subject to the three diseases of the sweet 
com here mentioned. Nevertheless, weeds should 
never be tolerated. 



CHAPTER XVI 

FAMILY LABIATE 

This family contains numerous plants which are 
of very slight economic importance. If grown at all, 
they are cultivated on a very small scale, and sold 
for condiments. Many of them are tropical or 
semi-tropical, but most of them could be grown in 
frames or indoors. The following is a list of plants 
which belong to the Labiate: Balm, catnip, clary, 
horehound, hyssop, lavender, mint, peppermint, 
pennyroyal, rosemary, sage, spearmint, summer 
savory, sweet basil, and sweet marjoram. Of all 
these hosts, peppermint and spearmint alone are 
extensively grown in the United States. The vola- 
tile oil distilled from these plants is the principal 
marketable product, although there is also a limited 
demand for the dried herb, especially the spearmint, 
which is used as a culinary herb for flavoring sauces 
and cooling drinks. Of recent years, these herbs 
have come into extensive use for flavoring chewing 
gum and confectionery. The United States, Japan, 
Russia, Germany, and England produce all of the 
peppermint and spearmint oils. Fleet ' has estimated 

' Fleet, W. v., U. S. Dept. of Agr. Farm. Bui. 694 : 1-12, 1915. 

255 



256 Diseases of Truck Crops 

the total annual production of these oils to be 600,000 
pounds, 250,000 of which are produced in the United 
States. Peppermint and spearmint are grown in 
Wayne County, New York, and in a few northern 
counties of Ohio, Maryland, and Indiana. Accord- 
ing to the Thirteenth Census of the United States 
the 1909 area devoted to mint in America was es- 
timated at 8,195 acres. The total crop was valued 
at $253,000. Of the States growing most on a com- 
mercial scale may be mentioned Indiana, Michigan, 
New York, and Tennessee. 

DISEASES OF THE BALM {Melissa officinalis) 

Rust 

Caused by Puccinia menthcE Pers. 

The disease attacks about thirty-five members of 
the mint family. All the three stages i. e., aecidio- 
spores, uredospores, and teleutospores, occur on the 
same host. The disease is characterized by brown 
son which are at first cinnamon colored and later 
chestnut brown. Diseased leaves curl and dry up. 
The disease is not sufficiently important to warrant 
treatment. 

Leaf Spot 

Caused by Septoria melisscd Desm. 

The disease is characterized by numerous brownish 
spots which are angular and apparently limited by the 



Family Labiatae ^257 

veins of the leaves. Leaf spot has not been found in 
the United States, but it is said to be common in 
Europe. 

DISEASES OF THE CATNIP {Nepeta cataria) 

Stem Rot 

Caused by Didymella catarice (C. and E.) Sacc. 

This trouble causes spots on the stems. The 
disease was first found in New Jersey, but it is of 
little importance. 

Leaf Spot 

Caused by Septoria nepet(Z E. and E. 

Leaf spot is characterized by purplish brown cir- 
cular spots which are surrounded by a band of deeper 
brown. The disease was first found in Racine, Wis- 
consin, and is apparently prevalent on the Canadian- 
American border. 

Stem Rot 

Caused by Diplodinia herbicola (B. and C.) Sacc. 

Stem rot was first reported from Pennsylvania, but 
it is of no economic importance. 
17 



258 



Diseases of Truck Crops 



DISEASES OF THE HOREHOUND {MarruUum 
vulgare) 

Powdery Mildew 



Caused by Erysiphe galeopsidis D. C. 

Powdery mildew is characterized by powdery 
white patches on the leaves and stems. The trouble 
is not known to occur in the United States. 

Leaf Spot 

Caused by Diplodia herbarum (Corda) Lev. 

The spots are roundish to irregular, numerous, 
brownish to dark in color. The disease attacks the 
older leaves, causing them to drop off prematurely. 

DISEASE OF THE MINT 

Rust, see Balm, p. 256. 

DISEASE OF THE PEPPERMINT {Mentha 
pepenta) 

Peppermint is a very hardy plant. With the ex- 
ception of Rust (see Balm, p. 256), it is practically 
free from attacks of fungus diseases. The same is 
also true for the spearmint, Mentha viridis, which is 
known to be attacked by the same rust diseases as 
the balm and all the other Labiatae. As far as we 
know the weeds in this family are not carriers of 
diseases which concern the trucker. 



CHAPTER XVII 

FAMILY LEGUMINOS^ 

This important family includes crops which are 
greatly valued by the consumer. Of the numerous 
legume plants, we will consider only those which 
concern the trucker, — viz., bean, lima bean, cowpea, 
and the garden pea. 

According to the Thirteenth Census of the United 
States, the total area devoted to dry edible beans 
in the United States in 1909 was estimated at 802,991 
acres, and the total crop valued at $21,771,482. 
That of green beans was 53,610 acres, the total crop 
valued at $2,844,951. The important leading bean 
States are Michigan, California, New York, New 
Mexico, Kentucky, and Maine. The estimated area 
in dry peas in 1909 was 1,305,099 acres, and the total 
crop valued at $10,963,739; while the area for green 
peas was 70,487 acres, yielding a crop valued at 
$2,785,502. The States ranked according to largest 
area devoted to peas ' were as follows : South Carolina, 
Georgia, North Carolina, Michigan, Alabama, Wis- 
consin, Mississippi, Arkansas, Texas, Illinois, Tennes- 

' In the Thirteenth Census, no distinction is made between the 
garden pea and the cowpea. 

259 



26o Diseases of Truck Crops 

see, Louisiana, Colorado, Missouri, Indiana, Virginia, 
Kentucky, Florida, and Oklahoma. 

DISEASES OF THE BEAN {Phaseolus vulgaris) 

Bean growers annually lose heavily from various 
bean diseases. There is no other truck crop, potatoes 
excepted, which has received as much attention from 
plant pathologists as the bean. With our present 
knowledge, many of the diseases may be controlled. 

Blight 

Caused by Pseudomonas phaseoli Ew. Sm. 

Symptoms. If the weather is wet during planting 
time, the seed may rot in the ground and never germi- 
nate. At other times the root of the young seed- 
lings may decay and the result will be a very poor 
and uneven stand. In dry weather a better germi- 
nation is obtained, but the disease works on the older 
plants in irregular spots in the field. Due to the 
lack of a normal root system, the affected plants 
are yellowed and wilted at daytime, but they slowly 
revive at night. Should the weather become muggy 
in midsummer, infected fields appear as though they 
were drenched with hot grease, the leaves having a 
burned appearance (fig. 46 a) . As a result, the injured 
plants seem to make a desperate attempt to produce 
new foliage which in turn becomes affected, hence 
the pods cease filling and ripening is very uneven. 

In carefully examining diseased seed, it is found to 
be yellowed and shriveled ; or, in light cases of attack, 




Fii.. 40. Bean Diseases. 

a. Bacteriosis on leaf, b. bacteriosis on pods, c. individual germs of bacteriosis 
(after Smith), d. bean plant killed by streak {b. to d. after Sackett), e. streak on 
pods. 



Family Leguminos^ 261 

there are found indefinite yellow spots or blotches. 
On the leaves the trouble appears as watersoaked 
spots which later are amber colored (fig. 46 a). On 
the stems and pods (fig. 46 b) a canker is formed 
which somewhat resembles the canker produced by 
Colletotrichum lindemuthianum. From the stem the 
disease works down to the main root, causing it to rot. 

The Organism. Pseudomonas phaseoli is a short 
rod rounded at both ends, motile by means of polar 
flagella. It liquefies gelatin slowly, coagulates milk, 
and the whey separates slowly with acidity. 

Control. The same as for anthracnose, p. 265. 

Streak 

Cause, Bacterial. 

Streak is a disease which is little known. It has 
been recently studied by Sackett, ^ although the cause 
has not been definitely determined. The trouble 
may perhaps be the same as the streak of the sweet 
pea, caused by Bacillus lathyri Manns and Taub. 

Streak attacks stems, leaves, and pods (fig. 46 d,e) 
of the bean plant. On the pod and on the leaves the 
disease appears as peculiar rusty to orange brown 
spattered spots which run down in streaks. Dis- 
eased foliage drops off prematurely, giving the plant 
a denuded appearance. For methods of control, see 
bean anthracnose, p. 265. 

Damping Off, see Pythium, p. 43. 

Downy Mildew, see Lima Bean, p. 267. 

I Sackett, W. A., Colorado Agr. Expt. Sta. Bui. 226 : 27, 1917. 



262 Diseases of Truck Crops 

Rust 
Caused by Uromyces appendiculatus (P.) L. 

Rust is seldom serious enough to warrant treat- 
ment. The disease attacks all parts of the bean 
plant except the roots. On the foliage, it appears as 
little brown pimples or sori (fig. 47 a) the size of a 
pin's head. These pimples soon appear on the pods 
(fig. 47 b) , petioles, and stems, being more numerous 
however on the leaves and pods. The pimples as 
they get older turn from brown to black in color. 
The powder discharged from the sori is made up of 
countless numbers of the fungus spores. Rust does 
not live over on the seed, but rather on the dead re- 
fuse of the bean plants. Bean rust has the aecidio- 
spores, uredospores (fig. 47 d), and teleutospores (fig. 
47 c) on the same host. 

Clean culture, burning of trash and dead plants, 
and selection of resistant strains or varieties is re- 
commended. 

Powdery Mildew 

Caused by Erysiphe polygomi D. C. M 

Powdery mildew is serious on fall beans in many of 
the Southern States, and on beans grown for the early 
market. It is characterized by white, mealy patches 
on the surface of the leaves and stems. The foliage 
soon turns yellow and dry. Powdery mildew may be 
controlled by dusting the plants with flowers of sul- 




Fig. 47. Bean Diseases. 

a. and b. Rust on leaf and pods, c. section through bean leaf showing bean rust, 
summer spores, d. section through bean leaf, showing bean rust, winter spores, e. 
anthracnose, /. section through bean seed, showing relation of anthracnose to the 
host (f. d. and /. after Whetzel), g. Cercospora leaf spot, h. Isariopsis griseola leaf 
spot, i. conidiophores and conidia of Isariopsis. 



Family Leguminosas 263 

phur, or by spraying with potassium sulphide at the 
rate of three ounces of the chemical dissolved in ten 
gallons of water. 

SCLEROTINIA ROT 

Caused by Sclerotinia lihertiana Fckl. 

Sclerotinia rot is a disease which attacks fall snap 
beans. The trouble is prevalent in Norfolk, Virginia, 
where it has been studied by McClintock. ^ During 
a period of hot humid weather in September the 
disease may suddenly break out in great severity. 
Usually withering and decaying of stems and pods 
where the plants are thickest is the first symptom that 
attracts attention (fig. 51 c). On closely examining 
infected stems and pods, we find that they are water- 
soaked, and overrun by the white mycelial growth 
on which appear numerous hard, black sclerotia. In 
the field, the Black Valentine snap bean seems to be 
more resistant to rot. For a description of the 
causative fungus and methods of control, see lettuce 
drop, p. 143. 

Anthracnose 

Caused by Colletotrichum lindemuihianum (Sacc. 
& Magn.) B. and C. 

Anthracnose may be considered one of the most 
destructive bean diseases. However the trouble 

' McClintock, J. A., Phytopath. 6 : 436-441, 1916. 



264 Diseases of Truck Crops 

depends on weather conditions. It is most prevalent 
during periods of heavy night dews, or during pro- 
longed rains, and in hot muggy weather. 

Symptoms. Anthracnose is so characteristic, that 
it cannot be mistaken for any other disease, except 
perhaps the blight. In light attacks, the seeds are 
covered with sunken brown to black specks. These 
are especially evidenced on the black seeded varieties. 
In severe attacks, the seeds are covered with deep 
sunken black spots which are rifted in the center. 
On the leaves the disease attacks the veins, which 
become blackened and somewhat shrunken. Fre- 
quently it attacks the petioles, especially at the point 
of leaf attachment. In this case the foliage drops off, 
leaving the bare petioles or stems. Anthracnose on 
the leaves begins as small, circular, pin-point, dark red 
spots which enlarge, and later elongate into maroon 
colored pits, cracks, or cankers (fig. 47 e) . On young ft 
seedlings the stem rots off a short distance above 
ground. 

The Organism. Spores are formed on the spots or 
cankers on all parts affected (fig. 47 f). These are 
imbedded in a gelatinous substance and can become 
loosened only by rain splashing or dew. It is at this 
stage that the disease becomes serious, since it is then 
spread about from plant to plant. When the spores 
are lodged on a new bean plant or on a new part of 
the same plant, infection takes place through the 
penetration of the germ tube of the germinated 
spores. It is estimated by Edgerton' that from one 

' Edgerton, C. A., Louisiana Agr. Expt. Sta. Bui. 119 : 3-55, 1910. 



Family Leguminosae 265 

half to a million spores are formed on one infected 
pod alone. The period of incubation usually varies 
from four to six days. 

In culture media, the growth is at first white, but 
it soon becomes jet black in color. The mycelium 
of the fungus is hyaline, small at first, but later be- 
coming larger and darker. 

Control. Spraying has not given satisfactory 
results. The best control is to plant clean seed se- 
lected from clean pods. The latter before shelling 
may be dipped for ten minutes in a solution of one 
part of corrosive sublimate to a thousand of water. 
The treated pods are then dried in the sun, shelled, 
and the seed put away in dry mason jars until the 
following spring. Should weevils threaten these 
seeds, they may be fumigated with carbon bisulphide. 
By reserving a plot destined for bean seed, by care- 
fully destroying infected plants, and by selecting 
clean pods and seed, anthracnose and blight may be 
kept in check. 

Under no circumstances should an infected field be 
cultivated in damp weather, or when the dew is still 
on the plants. When this is done the spores of the 
fungus are scattered broadcast in the field. As 
for resistant varieties, there is very little to select 
from. However, Barrus' found that the Wells 
red kidney bean is most resistant to anthracnose. It 
is therefore recommended for trial in localities where 
anthracnose prevails. In selecting for seed resistant 
varieties, these must of course be artificially inoculated 

' Barras, M. F., Phytopath. 5 : 303-311, 1915. 



266 Diseases of Truck Crops 

with spores of the fungus. This will make sure that 
the parasite has been placed on the host. If there 
is any difference in resistance, it will be evidenced by 
the amount of infection developing on each variety 
tested. In this connection it should be remembered 
that there are numerous strains of C. lindemuthianum, 
some of which are very virulent while others are less 
so. In inoculating for resistant varieties, an attempt 
should be made to secure pure culture strains from 
various localities. 

Stem Anthracnose 
Caused by Colletotrichum caulicolum H. and W. 

A serious stem rot attacks the Kentucky Wonder 
bean. The disease differs from anthracnose described 
above in that the former destroys the stems of the 
plant. Observations made by Heald and Wolf 
show that the disease girdles the stem, and also 
causes deep fissured cankers on one side of it. The 
trouble has been found in only one locality in Texas, 
and it is doubtful if it is prevalent elsewhere. Little 
is known of the control of this disease. 

Angular Leaf Spot (fig. 47 g), see Cowpea, p. 271. 

Southern Blight, see Pepper, p. 305. 

Root Rot (fig. 49 a), see Rhizoctonia, p. 45. 

Texas Root, see Sweet Potato, p. 175. 

Root Knot, see Nematode, p. 49. 

' Heald, F. D., and Wolf, F. A., U. S. Dept. of Agr. Bur. PI. Ind. 
Bui. 226 : 35-36, 1912- 




Fig. 48. Diseases of Lima Bean. 

a. h. c. different stages of downy mildew on pods, d. tuft of conidiophores and 
conidia of Phylhophthora phaseoli, e. same as d. but greatly enlarged, /. g. conidia 
germinating by means of a germ tube, h. i. j. k. germination of conidia by means of 
zoospores, /. germinating zoospores {d. to /. after Thaxter), m. n. fertilization of the 
oogonium by the antheridium, o. Phoma blight on foliage, p. Phoma blight on pods 
(o. and p. after Halsted), r. mature oospores of P. phaseoli (a. to c, m. n. and r. 
after Clinton). 



Family Leguminosae 267 

DISEASES OF THE LIMA BEAN {Phaseolus 

lunatus var. macrocarpus) 

Lima beans, whether climbing or dwarf, are usually 
considered hardy. This is generally true under 
favorable weather conditions. But in hot moist 
weather, truckers may lose heavily from various 
diseases. 

Blight, see Bean, p. 260. 

Downy Mildew 

Caused by Phytophtora phaseoli Thax. 

Perhaps the greatest damage in wet seasons to 
lima bean culture of both the pole and the dwarf 
varieties is downy mildew. The damage from this 
disease equals that from the anthracnose on snap and 
other varieties of Phaseolus vulgaris. 

Symptoms. It is most conspicuous on the pods, 
where it forms a dense, dirty white mycelial growth 
(fig. 48 a-c). The trouble appears first on one side 
of the pod, and then works its way through to the 
other side. Infected pods wilt, shrink, and eventually 
6.Ty up and die. In early cases of infection, the dis- 
, eased area is separated from the healthy by a purplish 
'border. Occasionally the blossoms are affected, in 
which case they wither and drop off. On the leaves 
the disease is manifested as irregular purplish dis- 
coloration, especially on the veins, but there seems 
to be no evidence of the fungus growth on it . 



268 Diseases of Truck Crops 

The Organism. The mycelium is hyaline, non-sep- 
tate, and in other respects not different from other 
downy mildews. The conidiophores are long and 
little branched (fig. 48 d, e), the conidia are hyaline, 
elliptical to ovoid in shape, germinating by means of 
motile zoospores (fig. 48 f-1). The oospores or sexual 
resting spores are formed in the same way as in 
P3rthium (fig. 48 m, n, r), see p. 43. 

Control. Downy mildew is carried over in the seed 
as dormant mycelium. Hence all shriveled seed 
should be discarded. In badly infected fields, crop 
rotation should be resorted to. The burning of trash 
and old bean plants is also advised. Finally three 
sprayings with 4-4-50 Bordeaux mixture during the 
growing season will keep the disease well in check. 

Rust, see Bean, p. 262. 

Powdery Mildew, see Bean, p. 262. 

Pod Blight 

Caused by Phoma suhcircinata E. and E. 

As the name indicates, the disease chiefly attacks 
the pods. Blight is indicated on them by the appear- 
ance of large brown patches (fig. 48 o, p). The 
pycnidia of the fungus are arranged in concentric 
zones. In severe cases, the disease works from the 
pods to the seed, considerably reducing the yield. 
On the leaves the symptoms are the same as on the 
pods. Spraying with Bordeaux will control the 
trouble. 





Fig. 49. Bean Diseases. 

a. Rhizoctonia root rot, b. root knot on lima beans. 



I 



Family Leguminosae 269 

Leaf Blotch 

Caused by Cercospora canescens E. and M. 

This disease, so far as is known, is not generally 
distributed. It is found in certain trucking centers 
in Texas. On the leaves the spots are circular, but 
somewhat angular. The center of the spots is gray 
with a reddish brown border, the outside of which 
divides the diseased from the healthy tissue. The 
conidiophores are equally abundant on both surfaces, 
the spores are hyaline, straight or curved, slender and 
one to many septate. While no experiments have 
been made on the disease, spraying with Bordeaux 
is recommended. 

Leaf Spot 

Caused by Isariopsis griseola Sacc. 

The disease is confined to the foliage only. The 
spots produced are small and angular with no 
colored borders (fig. 47 h, i). On the under side 
of the leaf, the fungus forms a gray moldy growth 
on the spot, where large numbers of the spores 
are produced. The disease is not widely dis- 
tributed, and may be controlled by spraying with 
Bordeaux. 

Root Rot, see Rhizoctonia, p. 45, 

Texas Root Rot, see Sweet Potato, p. 175. 

Root Knot (fig. 49 b), see Nematode, p. 49. 



2^o Diseases of Truck Crops 

DISEASES OP THE COWPEA iyigna sinensis) 

In the South, the cowpea is extensively grown as a 
truck crop. It is cultivated for its edible green pods, 
and dried peas, and often takes the place of the bean. 

Streak 

Caused by Bacillus laihyri Manns and Taub. 

Streak is a serious disease which until now has 
usually been mistaken for other troubles . The disease 
is the same as streak on the sweet pea and clovers. 

Symptoms. Like the bacteriosis of the bean, streak 
makes its appearance in a season of heavy dew. On 
the cowpea it usually appears just as the plant begins 
to bloom. It is manifested along the stems by light 
reddish brown to dark brown spots and streaks, the 
older of which are almost purple, having their origin 
usually near the ground. This indicates distribution 
by spattering rain and infection through the stomata 
or through insect injury. The disease becomes 
distributed quickly over the mature stems until the 
cambium and deeper tissues are destroyed in con- 
tinuous areas, and the plant dies prematurely. From 
the stem the disease spreads to the petioles, peduncles, 
and pods, the symptoms in these cases being similar 
to those on the stems. On the leaves, however, the 
disease appears as small circular spots, which grad- 
ually coalesce and eventually involve the entire leaf. 
When killed, the leaf presents a dark brownish ap- 
pearance. 



Family Leguminosae 271 

The Organism. Bacillus lathyri as worked out by 
Manns, ' is rod-shaped, occurring singly, never found 
in chains, and seldom united by twos or fours, 
motile by means of flagella. It produces no spores, 
no capsules, no zooglea, liquefies gelatin completely 
in about three weeks, and produces no gas. 

Control. Rotation of crops is helpful; but since 
streak attacks numerous leguminous crops, such as 
bean and clovers, these should be excluded. Other 
methods of control are as yet unknown. 

Rust, see Bean, p. 262. 

Powdery Mildew, see Bean, p. 262. 

Angular Leaf Spot 

Caused by Cercospora cruenta Sacc; Cercospora 
dolichi E. and E. 

Angular leaf spot is a common disease on cowpeas. 
When it attacks the leaves, they are covered with 
angular :rusty red spots, the leaves turn yellow and 
drop prematurely. On the stems the spots are ir- 
regular, elongated, dark colored, slightly sunken, 
and later forming cankers. The latter often crack 
and expose the stems to the attacks of various other 
parasitic and even saprophytic fungi. Under favor- 
able conditions of moisture, the spots on the leaves 
or stems are covered with a brownish downy growth 
made up of the conidiophores and conidia. No 
methods of control are known. 

« Manns, T. F., Delaware Agr. Expt. Sta. Bui. io8 : 3-44, 191 5. 



272 Diseases of Truck Crops 

Wilt, Yellows 
Caused by Fusarium tracheiphila Ew. Sm. 

In the light sandy to loamy soils, wilt is the greatest 
drawback to pea culture. The disease is most pre- 
valent in the Southern States. 

Symptoms. It does not seem to attack young 
seedlings, but appears only when the plant is about 
six weeks old and upwards. In the field, scattered 
plants turn yellow and begin to drop their leaves, the 
stems become bare (fig. 50 a), and the plants finally 
die. On pulling out a diseased plant, the main root 
will apparently be sound, but the lateral rootlets 
will be dead, marking the seat of infection. A 
more definite symptom of wilt is a browning of 
the interior fibrovascular bundles of roots, stems, 
and petioles. This may be readily ascertained by 
splitting open lengthwise a root or stem of a sus- 
pected plant. 

The Organism. From unpublished work by the 
author, it is definitely proven that F. tracheiphila is 
distinct from Fusarium wilts of the cotton, okra, 
and watermelon. The Fusarium wilt of the cowpea 
is caused by F. tracheiphila, which produces only the 
conidial stage and has no relationship whatsoever 
with Necosmospora, or any other ascospore stage. 
The cowpea Fusarium may be found in fields which 
are also infected with okra Fusarium. In this case, 
the field is infected with two distinct organisms, thus 
making it sick to both cowpeas and okra. The cow- 




Fig. 50. Diseases of the Cow Pea. 

a. Pusarium wilt, b. field of cow peas killed by Texas root rot, c. root knot, d. 
row of iron cow pea resistant to Pusarium wilt in sick field where other varieties of 
peas have died (a. and d. after W. A. Orton). 



Family Leguminosae 273 

pea Fusarium is parasitic only on the cowpea, and 
so far as is known does not attack any of the other 
cultivated legumes. 

Control. Diseased fields may be sown with beans 
or any other legume except cowpeas. Crops other 
than legumes may also be grown there. The develop- 
ment of resistant varieties is also a promising method 
of control. Or ton' has already developed the Iron 
cowpea (fig. 50 d), a variety which is resistant to wilt 
and partly also to Nematode. 

Root Rot, see Rhizoctonia, p. 45. 

Texas Root Rot (fig. 50 b), see Okra, p. 175. 

Root Knot (fig. 50 c), see Nematode, p. 49. 

DISEASES OF THE GARDEN PEA {Pisum 
sativum) 

Like the bean and cowpea, the garden pea is sub- 
ject to numerous diseases, some of which are of great 
economic importance. However many of these dis- 
eases may be controlled. 

Stem Blight 

Caused by Psetidomonas pisi Sack. 

Bhght is a new disease recently found by Sackett^ 
in the pea fields of Colorado. So far as is known, the 

' Orton, W. A., U. S. Dept. of Agr. Bur. PI. Ind. Bui. 17 : 9-36, 
1902. 
^ Sackett, W. G., Colorado Agr. Expt. Sta. Bui. 218 : 3-43, 1916. 
18 



274 Diseases of Truck Crops 

trouble does not seem to occur in the other States 
where peas are extensively grown. In Colorado, 
blight has suddenly made its appearance on a pea 
area of 500,000 acres, seriously threatening the pro- 
fitable growing of the crop. 

Symptoms. On the stems and leaves (fig. 51 b) 
the disease may be recognized by watery olive green 
to drab brown spots and by yellowish watery bruises 
on the leaflets and stipules. The roots seem to be 
free from the attacks of blight. Infection seems to 
start on the stem, near the ground level, and from 
there to work upwards. Lower leaves are usually 
the first to die. Occasionally the infected plants 
send out new shoots below the infected area. The 
new growth is sometimes unmolested but ordinarily 
it too becomes blighted. 

The Organism. Pseudomonas pisi is a short 
rod, rounded at both ends, and motile by means 
of polar flagella. It produces no spores, no cap- 
sules, and no zooglea and no involution forms. 
It produces no gas, and can stand drying of thirteen 
days. 

Control. Certain varieties seem to be more re- 
sistant than others. The development of resistant 
varieties is recommended. All trash and diseased 
materials should be destroyed by fire and not fed to 
animals. It is not known if spraying will control 
this disease. In badly affected fields, spraying with 
Bordeaux may be tried. 

Damping Off, see Pythium, p. 43. 

Rust, see Bean, p. 262. 




Fig. 51. Diseases of the Garden Pea and Bean. 

a. Thielavia root rot, to the right diseased plant with no root system, to the left 
healthy, b. stomatal leaf infection by Pseudotnonas pisi, c. Sclerolinia libertiana 
rnt on bean pods, d. endospore of Thielavia basicola, e. chlamydospores of T. basicola. 



i 



'Family Leguminosae 275 

Thielavia Root Rot 
Caused by Thielavia hasicola Zopf . 

Root rot is a common disease in fields devoted to 
peas for a period of years. The trouble on the garden 
and field pea is identical with that on the sweet pea. 

Symptoms. Plants severely infected with Thie- 
lavia have practically no root system, since this is 
destroyed by the fungus as rapidly as formed (fig. 
51 a). All that is left of the root system is a charred 
blackened stub. The diseased host constantly at- 
tempts to produce new roots above the injured part 
but these in turn also become infected. Such plants 
linger for a long time, but fail to set pods which are 
of any value. 

The Organism. The mycelium of Thielavia basicola 
is hyaline, septate, and branched. The mycelium 
becomes somewhat grayish with age. Three kinds of 
spore forms are produced — endospores (fig. 51 d), 
chlamydospores (fig. 51 e), and ascospores. Endo- 
spores are so called because they are formed inside 
a special thread of the mycelium. This is the spore 
form that commonly occurs in pure cultures of arti- 
ficial media and on the host. The endospore case is 
formed on terminal branches with a somewhat 
swollen base and a long tapering cell. The endo- 
spores are formed in the apex of this terminal cell and 
are pushed out of the ruptured end by the growth of 
the unfragmented protoplasm of the base. They are 
hyaline, thin walled, and oblong to linear in shape. 



276 Diseases of Truck Crops 

The chlamydospores are thick walled, dark brown 
bodies borne on the same mycelium as the endospores. 
This type of spore is formed in great abundance on 
the host and particularly within the affected tissue. 
The ascospores are lenticular in shape and are borne 
in asci or sacs within black perithecia. This stage 
however has not been found on the pea or in pure cul- 
ture. 

Control. Thielavia basicola is a soil-inhabiting 
fungus. With infected pea fields, soil sterilization is 
of coiirse out of the question. The method of control 
suggested is crop rotation. Investigations by John- 
son^ have shown that the following vegetable crops 
are not subject to Thielavia root rot: potato, sweet 
corn, sweet potato, cabbage, onion, parsnip, carrot, 
beet, eggplant, and peppers. These crops may there- 
fore be safely used in a crop rotation, the system of 
which is best worked out by the trucker himself. 

Powdery Mildew, see Bean, p. 262. 

Pod Spot 

CcLUsed by Sphcerella pinodes (Berk, and Bl.) Niessl. 

Pod spot is a disease which is of even greater eco- 
nomic importance than Thielavia root rot. The 
disease does not confine itself to the pods alone, but 
also involves the leaves and stems. The trouble 
however is known by truckers as pod spot. 

' Johnson, J., U. S. Dept. of Agr. Jour. Agr. Research, 7 : 261-300, 
1916. 



Family Leguminosae 277 

Symptoms. On the stem the trouble appears as 
numerous elongated lesions. These spread to such 
an extent as actually to girdle the affected stem. On 
the leaves are formed oval spots, grayish in the center, 
and limited by a dark band. The pods too become 
badly attacked and the symptoms there resemble 
those on the stems. The disease works its way from 
ihe pods to the seed within. 

2^he Organism. The causative fungus has two 
spore stages. The pycnidia bear the hyaline, two 
celled spores and are formed within the dead tissue of 
the affected stems, leaves, or pods. The pycnidial 
stage is known as Ascochyta pisi Lib. The winter or 
ascospore stage has only recently been discovered 
by Stone, ^ who found it on pods and stems previously 
affected, and on culture media. The fungus may be 
carried from year to year as dormant mycelium within 
the seed, or in the ascospore stage. 

Control. Seed treatment will not be of any value 
since the fungus is hidden within the seed. No out- 
side treatment is capable of reaching the parasite 
within. Seed should be secured from locaHties 
known to be free from the disease. Rotation of 
crops is also recommended. Giving the field a 
rest from peas or hairy vetch for at least three 
years is recommended. In badly affected local- 
ities, susceptible varieties, such as French June, 
Market Garden, American Wonder, should be dis- 
carded. The Alaska variety is claimed to be more 
resistant. 

' Stone, R. E., Annales Myccl., lo : 564-592, 1912. 



278 Diseases of Truck Crops 

Septoria Leaf Spot 
Caused by Septoria pisi Westd. 

The disease greatly resembles pod spot. But a 
microscopical examination of the fruit of the two will 
reveal the difference. Septoria leaf spot is of little 
economic importance. 

Root Rot, see Rhizoctonia, p. 45. 

Root Knot, see Nematode, p. 49. 

WEEDS 

Of the numerous legume weeds, few if any are 
troublesome in trucking. None are likely to be 
carriers of the diseases which attack beans and peas. 



CHAPTER XVIII 

FAMILY LILIACE^E 

This family is an important one, since it furnishes 
such crops as asparagus, chive, garlic, leek, onion, 
and shallot. According to the Thirteenth Census 
of the United States, the total 1909 American area 
devoted to asparagus was estimated at 25,639 acres 
and the crop valued at $2,246,631. The States 
ranked according to largest area devoted to aspara- 
gus are as follows: California, New Jersey, Illinois, 
South Carolina, Pennsylvania, and New York. 
States with less than 1,000 acres are here omitted. 
The total area in the United States devoted to 
onions in 1909, including chive, garlic, leek, and 
shallot, of which there are no records, was estimated 
at 47,625 acres, and the total crop valued at $6,709,- 
047. The States ranked according to acreage in 
onions were as follows : Ohio, New York, Texas, Cali- 
fornia, Illinois, Indiana, Louisiana, Massachusetts, 
Kentucky, New Jersey, Michigan, and Minnesota. 
States with less than one thousand acres are omitted. 

DISEASES OF THE ASPARAGUS (Asparagus 
officinalis) 

Asparagus may be considered a hardy host when 
grown under proper cultural and climatic conditions. 
279 



28o Diseases of Truck Crops 

Where this is not the case it soon becomes subject to 
a few, but serious, diseases. 

Leopard Spot 

Cause, Unknown. 

The disease, as the name indicates, consists of large 
irregular ashen colored spots, each surrounded by a 
dark border. No treatment which keeps the disease 
in check is known. 

Rust 

Caused by Puccinia asparagi D. C. 

Asparagus rust does not seem to be limited in its 
geographic distribution, as it has been found in all 
States where the crop is grown. It is especially se- 
rious in California, New Jersey, and all the other im- 
portant asparagus regions. 

Symptoms. Rust does not attack the asparagus 
tips which are cut for the market. It attacks the 
green tops which develop after cutting has ceased. 
Affected tops redden, and these when carefully ex- 
amined will reveal reddish rusty pimples or son on 
the stems (fig. 52 a) and needles. In severe infection, 
the reddened tops become bright yellow, the needles 
fall off prematurely, exposing a bare dead stalk cov- 
ered with numerous rust sori. The symptom is 
generally found in September and the pimples are 



'^^^^1^^ 







^rn<^-?igLJfes!r .-o*-'-!- 





^:^:f<^^b'>^iH<f^ 




Fig. 52. Asparagus Diseases. 

a. Asparagus rust on stems, showing sori with winter spores, b. cluster cup stage 
of Puccinia asparagi, c. Uredo or summer spores of P. asparagi, d. Teleuto or winter 
spores of P. asparagi (6. to d. after R. E. Smith). 



Family Liliaceae 281 

made up of the teleuto or winter spores of the fungus. 
In old asparagus fields, rust may appear early in the 
season. In this case instead of rusty brown son 
there appear on the main stems and branches, but 
not on the needles, numerous bright cup-shaped 
bodies, containing the aecidial or spring spores. 
This form occurs about May but disappears in June 
or July. This stage is immediately followed by red 
pustules which contain the uredo or summer spores. 
Later in August and September, and as already 
stated the teleutospores appear. The latter help 
to carry the fungus over winter and unfavorable 
conditions. The efTect of asparagus rust is an in- 
direct weakening of the crowns of the plant. Affected 
tips fail to store up the necessary starches and sugars 
for the underground crowns. The latter being un- 
der-fed become weak, soft, and subject to the attacks 
of various, soil-inhabiting parasites. 

The Organism. The life history of Puccinia as- 
paragi has been carefully worked out by Smith ' and 
others. The mycelium of the fungus is long and 
narrow, extensively branched, deriving its food by 
means of suckers or haustoria which penetrate the 
cells of the host. The ascidiospores are formed in 
chains, coming up from the mass of mycelium at the 
base of the cup (fig. 52 b). The uredospores (fig. 
52 c) are dark in color and are borne singly in the 
uredo pustules. Both the aecidio- and uredospores 
are one celled, and both germinate by means of a germ 
tube which penetrates the host. The black rust or 
' Smith, R. E., California Agr. Expt. Sta. Bui. 165 : 5-99, 1905. 



282 Diseases of Truck Crops 

teleutospores (fig. 52 d) are two celled, thick walled, 
dark colored, and borne singly on long stalks. The 
teleutospores must first winter over before they can 
germinate. In germination each cell sends out a 
thick short germ tube which divides at the tip into 
four parts, each of which produces a side bianch 
which bears secondary spores known as sporidia. 
The latter break away, and when falling on a fresh 
green asparagus top germinate by sending out a germ 
tube which penetrates the host. After proper incu- 
bation, the cluster cup stage appears, and the same 
Hfe cycle is repeated over again. 

Control. Asparagus rust may be kept in check by 
taking advantage of certain cultural conditions. 
Rust is more abundant in seasons with insufficient 
rainfall or on lands which dry out rapidly, while 
soils which have an abundance of moisture harbor 
little or no rust. In moist soils, asparagus plants are 
more vigorous than those grown under dry conditions 
and vigorous plants are less subject to rust than weak 
ones. Irrigation, therefore, wherever possible will 
help to keep the rust in check. Rust infection can 
never take place unless there is plenty of dew to 
enable the spores of the fungus to germinate. In 
low lying places, dew formation is heavier and hangs 
on longer than in more elevated regions. As far as 
possible, asparagus should be grown on high, well 
exposed moist lands. In regions subject to rains and 
heavy dews, spraying is recommended. Sirrine' has 

» Sirrine. F, A.. N. Y. (Geneva) Agr. Expt. Sta. Bui. l88 : 122- 
166, 1900. 



Family Liliaceae 283 

obtained good results by spraying with 5-5-40 Bor- 
deaux to which was added 2 gallons of a resin 
mixture (made up of 5 lbs. resin, i lb. potash, or lye, 
I pint fish oil, and 5 gals, water) to each 10 gallons of 
Bordeaux. Another good treatment is dusting the 
asparagus tops with flowers of sulphur. To be 
effective, this must be applied in the form of a fine 
smoke-Hke dust. If the tops are too dry they may be 
wetted with whale oil soap water, or the grower must 
wait for a heavy dew or rain. There are many * ' dust 
sprayers" on the market, many of which have their 
good qualities. There are two main types of dust 
sprayers, the "seed sower" and the "fan blower." 
The former throws a tremendous dust cloud. The 
fan blower sends out small clouds and covers less 
area. The number of applications will depend on the 
amount of dew in the season. In general, three 
applications using one half a sack of flowers of sul- 
phur per acre during the season will suffice. The 
practice of applying ordinary salt (NaCl) to the soil 
will not injure the asparagus crop but it will fail to 
control rust. 

Resistant Varieties. It is a well-known fact that 
some varieties of asparagus are more resistant to rust 
than others. The Canovers Colossal which is the 
canning type is a variety which is badly subject to 
rust. The same is also true for the Columbian 
White and the Moore's Cross-Bred variety. On 
the other hand the Palmetto Type and the French 
or Argenteuil Barrs mammoth are fairly resistant. 

Natural Enemies. Puccinia asparagi, although 



284 Diseases of Truck Crops 

itself a parasite, is in turn parasitized by three other 
fungi. 

1. Darluca filum Cast. This fungus develops on 
the rust pustules, living directly on the mycelium 
and spores of its host. 

2. Tuhercidaria persicina Dilt, This fungus is 
not as common as the first one. 

3. Cladosporium sp. This is a common fungus 
which is often abundantly found on rust pustules. 
All or any of these three natural enemies may be 
readily grown in pure culture and spread about 
broadcast wherever the rust is abundant and of 
economic importance. 

Damping Off, see Rhizoctonia, p. 45. 

DISEASES OF THE CHIVE {Allium sdwenopo- 
rasum) 

Rust 

Caused by Puccinia porri (Sow.) Wint. 

This rust, though prevalent in Europe, has been 
reported but once in the United States by Clinton' 
as attacking also onions. It is characterized by a yel- 
lowing of the leaves which die prematurely. On care- 
fully examining the infected leaves we find the uredo 
pustules, which are minute, reddish, and covered with 
a reddish powder. The teleuto pustules are black and 

' Clinton, G. P., Connecticut Agr. Expt. Sta. Rpts. 1909-1910 : 
726. 




Fig. 53. Onion Diseases. 

a. Bacterial rot (after Stewart), b. Botrytis rot, c. healthy, d. Sclerotium rot e 
onion storage house, /. type of commercial storage houses, ;?. interior of storage 
house, showmg method of stackmg crates (/. and g. after W. R. Beattie). 



Family Liliaceae 285 

covered by the host epidermis. Chive rust is dis- 
tinct from the onion rust. 

DISEASES OF THE ONION (Allium cepa) 

The onion is commonly attacked by numerous dis- 
eases. Fortunately most of them may be controlled, 
by proper care, and timely preventive methods. 

Soft Rot 

Caused by Bacillus caratovorus Jones. 

The disease was first studied by Stewart, * who how- 
ever did not determine the causative organism, but 
merely referred it to a species of Bacillus. The writer, 
however, was able to prove that soft rot of onions is 
caused by the same organism which causes a similar 
rot on carrots and other vegetables. 

The rot on the onion often starts at the neck of the 
bulb which is spoken of as " weak in the neck." Sound 
bulbs are hard at the neck, but when rot sets in, the 
outer layer remains sound while the interior tissue 
soft rots (fig. 53 a) . Sometimes a single scale is found 
rotted within the bulb, and the others apparently 
remain healthy. At other times a sound scale may 
be found between two rotted ones. Occasionally 
the rot is confined to the outer fleshy scale, in which 
case it is spoken of as "slippery onion. " In storage, 

' Stewart, F. C, New York (Geneva) Agr. Expt. Sta. Bui. 164: 
209-212, 1899. 



286 Diseases of Truck Crops 

under proper conditions of ventilation and tempera- 
ture, the rot progresses very slowly. However, in 
poorly constructed houses the bulbs rot very fast and 
the disease then spreads by contact. 
Damping Off, see Pythium, p. 43. 

Blight, Downy Mildew 

Caused by Peronospora schleideni, Ung. 

Of all the onion diseases, blight (also known as 
downy mildew) is perhaps the most important from 
an economic standpoint. It may often wipe out 
from seventy per cent, of the vStand to the entire crop. 
The disease usually accompanies muggy, damp, or 
rainy weather. 

Symptoms. The disease is best diagnosed early 
in the morning when the dew is still present on the 
foliage. Diseased parts have a peculiar violet tint. 
This is due to the downy cover of the fruit by the 
fungus. Soon the affected leaves lose their green 
color, becoming yellow in spots, and by the second 
or third day they have all collapsed, and are entirely 
covered by the downy fruiting stalks of the causative 
fungus (fig. 54 a) . If the weather is unfavorable the 
disease will be seen to work in restricted spots in the 
field with the tops of the affected plants collapsed. 
However, after several days the diseased onions begin 
to recover by sending out new top growths. The 
previously diseased leaves now dry and break away. 




Fig. 54. Onion Diseases. 

a. Downy mildew, 6. mature conidiophore and conidia of Peronospora schleideni, 

c. fertilization of the female oogonium by the male antheridium, d. oospore (a. to 

d. after Wh2tzel), e. onion smut, /. spore ball of the smut fungus, g. spore germina- 
tion, formation of sporidia at x, h. Vermicularia anthracnose, i. section through 
acervulis of Vermicularia circinans, j. setas and spore formation in 1-'. circinans {e. 
to g., i. and i. after Thaxter), k. pink root of onion, healthy and diseased bulbs, /. 
pink root of onion showing nipple formation, m. a formaldehyde drip attachment 
to a planet junior seed sower, n. a copper tank drip with flexible black tin tube and 
valve (m. and n. after Stone). 



Family Liliacese 287 

The blight in this case does not entirely disappear. 
With the coming of wet muggy weather the epidemic 
may begin a new course. 

The seriousness of bHght is usually overlooked by 
growers, because it usually works best when the 
onions have attained considerable bottoms. The 
latter are not disfigured or attacked in any way. But 
there is an indirect loss from the disease, because the 
food which is stored in the leaves is eventually des- 
tined for the bulbs. When the foliage is destroyed 
there is bound to be a reduction in yield of market- 
able onions. 

The Organism. The conidiophores or fruiting 
stalks come out on the surface through the leaf 
stomata (fig. 54 a). The conidia are borne at the 
tip end of branches of the main fruiting stalk. They 
germinate by means of a germ tube. The oospores 
or sexual spores (fig. 54 c, d) are formed in the same 
way as in Pythium. The contents of the antheridium 
is emptied into the oogonium, and fertilization takes 
place. The oospore is thick walled, granular and oily 
within. The mycelium of the fungus is non-septate, 
hyaline, and derives its food by means of suckers or 
haustoria which it sends to the host cells. 

Control. Good results have been obtained by 
Whetzel' from spraying with Bordeaux. The form- 
ula recommended is 5-5-50. The number of appli- 
cations will vary with the climatic conditions and 
with the severity of the disease. It is doubtful if 

' Whetzel, H. H., New York (Cornell) Agr. Expt. Sta. Bui. 218 : 
139-161, 1904. 



288 Diseases of Truck Crops 

one application will suffice; two to four applica- 
tions may sometimes be necessary, especially in low, 
wet, and poorly drained lands where the disease 
is severest. 

Smut 

Caused by Urocystis cepulce Frost. 

Next to blight, smut is the most important disease 
of the onion. The trouble is found wherever onions 
are grown, and it does not seem to be limited by 
climatic or soil conditions. 

Symptoms. Smut is at first characterized by dark 
spots on the seedling leaves (fig. 54 e). When held 
up to the light these spots are opaque. Later longi- 
tudinal cracks appear on one side of the spot, which 
widen, exposing within a fibrous mass covered with a 
black powder made up of the ripe spores of the fungus. 
Young infected seedlings usually die early. Those 
which survive later show smut pustules on the leaves 
and the outer scales of the bulbs. The disease may 
be carried from infected fields with the seed, with 
infected manure, and by man himself on infected soil 
particles adhering to his shoes or implements. 

The Organism. The spores of the fungus are able 
to retain their vitality for a long time, possibly 
twelve years. The spore ball (fig. 54 f) is made up of 
sterile cells and spores. The latter (fig. 54 g) germ- 
inate in the same way as spores of other smuts, see 
com smut, p. 252. 



Family Liliacese 289 

Control. A very effective treatment is to sow the 
seed in a seed bed and later transplant the sets. 
This method not only insures a crop free from smut, 
but the quality and the yield are benefited. An- 
other method which generally gives good results is 
to apply to the soil at sowing time from 500 to 700 
gallons per acre of a solution made up of one pint of 
formaldehyde in thirty gallons of water. This is 
applied with a drip attachment of the seed drill. 
For this method to be effective the soil must be in 
good condition of tilth. 

Rust 

Caused by Puccinia allii D. C. 

Rust is a rare disease with onions in the United 
States, and very little is known about it. It is 
doubtful if it will ever cause damage serious enough 
to warrant treatment. 

Anthracnose 

Caused by Vermicularia circina^is Berk. 

This disease seems to be confined to the bulbs 
only. It is characterized by black spots (fig. 54 h) 
which are made up of various rings one within the 
other. Each ring consists of minute black dots, 
which are the acervuli of the fungus and which pos- 
sess numerous black hairs or bristles (fig. 54 i, j). 



290 Diseases of Truck Crops 

It causes the greatest damage under poor storage 
conditions. For methods of control, see p. 292. 

BoTRYTis Rot (fig. 52 b) is a storage trouble 
usually of little importance. 

Black Mold 

Caused by Macrosporium parasiticum Thuem. ; 
Macrosporium porri Ell. 

Black mold frequently follows injury from downy 
mildews or any other causes which weaken the plant. 
Spraying to control downy mildew will also prevent 
this disease. 

Bulb Rot 

Caused by Fusarium sp. 

This disease is usually a storage trouble; but the 
injury starts in the field and is favored by a wet sum- 
mer season. The rot is prevalent in Ohio and Con- 
necticut and possibly also elsewhere where onions are 
stored in bulk. It works inward, attacking the heart 
of the bulb so that the interior easily slips out. For 
methods of control, see p. 292. 

ScLEROTiuM Rot or Black Neck 

Caused by Sclerotium cepivorum Berk. 

Sclerotium rot is a serious storage trouble of white 
onions in Ohio. The disease seems to be favored by 



Family Liliaceae 291 

improper storage conditions, and by early topping 
in the field where a green neck offers a favorable 
entrance of the rot. The latter is of a dry nature, 
and the affected bulbs become blackened and 
wrinkled at the neck (fig. 52 d). Selby' recommends 
treating the bulbs with formaldehyde gas as recom- 
mended for the white potato, p. 336. 

Pink Root 

Cause Unknown fungus.'^ 

Pink root is a serious disease which is threatening 
the onion industry in the Laredo districts of Texas. 
The disease apparently is not new, but it has not 
been investigated before. The work of the writer is 
as yet incomplete, hence no complete statement can 
be made at this time relative to the disease. 

The roots of affected sets first turn slightly yellow- 
ish, when they are known as "Yellow root, " and then 
pink. Affected roots dry up, and the bulbs con- 
stantly make an attempt to produce new rootlets, 
which even under favorable conditions become pink 
and die. At the end of the season and because of the 
attempt of the bulb to produce new roots, a nipple is 
usually formed at the bottom of the center plate of 
the bulb (fig. 54 1 and k). The disease is carried with 
the young sets from the seed beds to the field. It 

' Selby, A. D., Ohio Agr. Expt. Sta. Bui. 214 : 414, 1910. 
' Investigations by the author seem to show that pink root is 
caused by a pathogenic fungus. 



292 Diseases of Truck Crops 

may also be introduced with infected soils clinging to 
the rootlets of the sets. 

Control. It is severest in fields where onions have 
been grown too long in the same field. Crop rotation 
will not control nor reduce the losses from pink root 
in the field. The use of new land, especially for the 
seed bed, is strongly urged. 

Pink root attacks the onion, chive, shallot, garlic, 
and leek. 

Onion Storage 

Since the greatest profits are derived when onions 
are sold at a time of greatest demand, it is necessary 
to store the crop. In the field, onions intended for 
winter storage should be allowed to ripen well. The 
degree of ripeness is indicated by a shriveling of the 
tops, and when the outer skin of the bulbs becomes 
dry before being pulled. The ripening process in the 
field may often be hastened by rolling a light roller 
on the tops to break them. After being pulled, the 
onions are allowed to lay in the rows for several days. 
They are occasionally stirred with wooden rakes to 
encourage an even drying of the bulbs. After the 
necks are clipped, the bulbs are put in crates and are 
either allowed to dry further in the field or they are 
carried to curing sheds where the crates remain for 
about two weeks until finally placed in storage. 
This method is preferred by most growers, as it is 
not desirable to expose the red and yellow varieties 
to the full sunlight in the field. The immature, 



Family Liliaceae 293 

soft, or "thick necks" should be disposed of early, 
as they keep very poorly in storage. Good storage 
onions will rattle like wood blocks when poured out 
from the crate. 

After curing in the sheds, the bulbs are sorted over 
on the sorting racks where only the soundest are 
stored away. In some localities, onions are stored 
in pits. This may serve the purpose where only 
small quantities are grown. On a large scale storage 
plants (fig. 52 e-g) are in operation. 

Storage Conditions. The essentials necessary in 
storing onions are summarized by Beattie' as follows: 
"Plenty of ventilation, storing in small quantities, 
a comparatively low temperature, dryness, and safety 
from actual freezing. ' ' The construction of a storage 
house is not different from that of a sweet potato 
house, see p. 182. The house should be double 
walled throughout, with plenty of felt or paper 
lining. In this way a dead air space in all the 
walls will permit of more even indoor tempera- 
tures. Top ventilation is provided by means of 
roof ventilators. Bottom ventilation is secured 
by means of bottom windows or drain pipes built 
into the foundation at the surface of the ground. 
A false floor is also constructed inside, leaving an 
air space of about two to three inches from the 
main floor. 

The temperature of the storage house should be as 
low as possible, but kept above the freezing point, 
i. e. above 32 to 36 degrees F. During severe cold 

' Beattie, W. R., U. S. Dept. of Agr. Farm. Bui. 354 : 5-36, 1909, 



294 Diseases of Truck Crops 

weather all openings should be closed. Occasionally 
heat may be necessary and this can be applied by 
stoves. Onions are often stored in bags or in slat 
bins holding lOO to 300 bushels each. However, 
neither bags nor bins are satisfactory. The best 
method is storing in crates. 

Of the Liliaceae weeds, the only one of importc^nce 
is the wild garlic, Allium vineale. It, however, is not 
known to harbor any of the diseases which attack 
onions and its other closely related species. 



CHAPTER XIX 

FAMILY MALVACE^ 

This important family has but one plant which is 
of interest to the trucker, i. e. the okra. This crop 
is grown more in the Southern States. It is to be 
regretted that more of the people of the United States 
have not as yet learned its great food value. Accord- 
ing to the Thirteenth Census of the United States the 
area devoted to okra in 1909 was estimated at 347 acres 
and the value of the crops at $24,969. Of the few 
States which grow this crop may be mentioned Georgia, 
Texas, Louisiana, Florida, and North Carolina. 

DISEASES OF THE OKRA (Hibiscus esculentus) 

Generally speaking, the okra may be considered a 
hardy plant. But it is subject to a few diseases which 
in severe cases may threaten the profitable raising of 
the crop. 

Leaf Spot 

Caused by Cercospora hibisci T. and Earle. 

The disease seems to be as yet restricted to Porto 
Rico. It is of no economic importance in the United 
29.5 



296 Diseases of Truck Crops 

States. According to Stevenson- the trouble ap- 
pears as indefinite sooty patches (fig. 54 c) on the 
lower surface of the leaves. This saps the vitality 
of the foliage, causing it to turn yellow and to drop 
off prematurely. Great care should be exercised not 
to allow the above disease to gain a foothold in the 
United States. 

Wilt 

Caused by Fusarium malvacearum Taub.* 

Wilt is perhaps the main drawback to okra culture. 
The disease is found in light sandy soils, and some- 
times seems to work hand in hand with root knot. 

Symptoms. The disease does not seem to attack 
young seedlings. It is common on older plants, which 
however remain stunted as the disease works slowly. 
In severe attacks, however, the lower leaves wilt, 
droop, dry, and fall off. This is followed by a droop- 
ing, wilting, and falling off of the upper foliage, leav- 
ing thus a bare stalk, which eventually dries up. On 
pulling up a diseased plant, we find that the root 
system is apparently sound. But on splitting a 
diseased root and stem lengthwise the interior fibro- 
vascular bundles are found to be brown, indicating 
that the seat of the trouble is there localized. 

The Organism. Unpublished work by the author 
has definitely established that okra wilt is caused by 

' Stevenson, J. A., Jour. Dept. Agr. of Porto Rico, i: 93-117, 1917. 
" From unpublished work by the writer. 







4tf^\ 



mi 



m\ ^[?^ 



-' % "% 








Fig. 55. Diseases of the Okra. 

a. Okra field badly affected with the Texas Root 
rot, to the front two resistant hills, b. root knot, 
c. Cercospora leaf spot. 



Family Malvaceae 297 

a new species of Fusarium, technically named F. 
malvacearum. The okra wilt is distinct and different 
from the wilt of cowpea, cotton, or watermelon, all 
of which are caused by distinct species of Fusaria. 
A full description of the organism will soon appear 
elsewhere. 

Control. The only remedy known for this disease 
is crop rotation. Since okra wilt attacks only the 
okra, any other truck crop may be used in the rota- 
tion system. It is also probable that wilt may be 
controlled by the development of resistant varieties. 

Root Rot, see Rhizoctonia, p. 45. 

Texas Root Rot 

Caused by Ozonium omnivorum Shear. 

Texas root rot is a disease which is perhaps of 
equal importance with wilt. The disease is not found 
on sandy soils, but on okra grown on the typical 
waxy heavy lands such as are found in Texas. It 
appears after a rain or after irrigation. 

Symptoms. The trouble does not appear until the 
plants have begun to bloom. At this stage infected 
plants suddenly wilt and the foliage drops off (fig. 
54 a). On pulling out a diseased plant, we find that 
the trouble is localized at the crown and root of the 
plant. The infected surface is darkened, shrunken, 
but softened, so that the epidermis may be easily 
peeled off from the roots and crown of the plant. 
Occasionally, the diseased parts are covered with 



29^ Diseases of Truck Crops 

minute warts consisting of whitish to yellowish fun- 
gus threads. Very often in pulling out a plant 
which is partly infected, the young healthy rootlets 
or even those which are partly destroyed are found 
to be colored pinkish buff. 

The Organism. The organism which causes Texas 
root rot is, as far as we know, sterile. By this is 
meant that the fungus reproduces by division 
and further growth of its mycelium, but produces 
no fruit (fig. 28 q and r). Duggar' claims that the 
pink buff color mentioned above represents the 
colored spore masses of the fungus which he named 
Pliymatotrichum omnivorum (Shear) Dug. However 
no inoculation experiments have been carried out to 
prove that this fruiting stage is in any way connected 
with Ozonium. In establishing the relationship of 
various stages of apparently the same parasitic fun- 
gus, inoculation experiments alone should be the 
crucial test. 

Control. No definite methods of control are as 
yet known. Deep plowing undoubtedly retards the 
work of the disease, but it does not prevent it by any 
means. Crop rotation should be resorted to. In the 
system of rotation may be included sweet corn, cab- 
bage, radish, spinach, kale, mustard, lettuce, and 
cauliflower. Crops to be omitted from the rotation 
are beans, beets, cowpeas, sweet potatoes, eggplants, 
tomatoes, and peppers. The latter two are only 
partly susceptible to Texas root rot. 

Root Knot (fig. 54 b), see Nematode, p. 49. 

• Duggar, B. M., Ann. ISIissouri Bot. Gard., 3: 11-23, 1916. 



CHAPTER XX 

FAMILY PORTULACACEiE 

In this family the only plant which may interest 
the trucker is the purslane. The latter is grown as a 
pot herb ; but it is little known in the United States. 
It is comparatively free from diseases, only two of 
which need be mentioned. 

White Rust 

Caused by Cystopus portulacecB (D. C.) Kze. 

In appearance, this rust is not different from the 
white rust of the radish. However the causative 
fungus is not the same. White rust is not prevalent 
in the United States and is of no economic importance. 

Root Rot, see Rhizoctonia, p. 45. 

Weeds. There are no weeds of importance in the 
Portulacaceae family which carry diseases detrimental 
to truck crops. 



299 



CHAPTER XXI 

FAMILY SOLANACE^ 

In this great family the trucker possesses crops 
which are of great economic importance. Some of 
them are the eggplant, pepper, potato, and tomato. 
According to the Thirteenth Census of the United 
States, the total area devoted to eggplants in 1909 
was 895 acres, and the crop value was estimated at 
$154,643. The two States which supply nearly all 
the markets with eggplant are Florida and New 
Jersey. The total area in 1909 devoted to peppers 
was estimated at 3,483 acres and the crop valued 
at $408,741. Of the leading States producing this 
crop are New Jersey, California, Florida, New 
Mexico, Illinois, Texas, and Louisiana. The area in 
white potatoes in 1909 was estimated at 3,668,855 
acres, and the crop valued at $166,423,910. The 
leading potato States are New York and Michigan; 
the others following in their order are: Wisconsin, 
Pennsylvania, Minnesota, Ohio, Iowa, Illinois, Maine, 
Nebraska, Colorado, Indiana, Missouri, Virginia, 
New Jersey, Kansas, California, Washington, Ken- 
tucky, North Dakota, South Dakota, Oregon, West 
Virginia, Tennessee, Maryland, Texas, Oklahoma, 
300 



Family Solanaceae 301 

Arkansas, Idaho, Vermont, Massachusetts, Connec- 
ticut, Montana, Louisiana, New Hampshire, Ala- 
bama, Utah, Georgia, Delaware, South Carolina, 
Florida, Mississippi, Wyoming, New Mexico, Nevada, 
Rhode Island, and Arizona. The area in 1909 de- 
voted to tomatoes was estimated at 207,379 acres, 
and the crop valued at $13,707,929. The leading 
producing States are as follows: Maryland, New 
Jersey, Indiana, Delaware, Florida, Virginia, Mis- 
souri, New York, Ohio, Texas, California, Tennessee, 
Pennsylvania, Illinois, Mississippi, Kentucky, Michi- 
gan, Iowa, West Virginia, Arkansas, Colorado, Utah, 
Kansas, and Massachusetts. States with less than 
one thousand acres are omitted. 

DISEASES OF THE EGGPLANT {Solanum 
melongena) 

Southern Wilt, see Tomato, p. 342. 
Damping Off, see Pythium, p. 43. 

Fruit Rot 

Caused by Phomosis vexans (Sacc. and Syd.) Hart. 

The disease is quite common in New Jersey, and it 
undoubtedly occurs in the more southern States. 
The trouble has been recognized as serious, but the 
cause has been only recently worked out by Harter. ' 

Symptoms. Fruit rot attacks all parts of the plant 

' Harter, L. L., U, S. Dept. of Agr. Jour. Agr. Research, 2 : 331- 
338, 1914- 



302 Diseases of Truck Crops 

except the roots. On the seedlings it causes a damp- 
ing off. Young plants are attacked at the stem end 
or an inch or tv/o above the ground line as indicated 
by a constricted area at that place. On the leaves the 
trouble is manifested as large brown round spots 
which later become irregular and jagged (fig. 56 a). 
The older spots are light purple in the center and 
surrounded by a black margin. As they enlarge the 
spots also invade the veins, midribs, and petioles, 
forming depressions. Diseased fruits are at first 
soft and mushy, but later they become dry, shriveled, 
and mummified (fig. 56 b). 

The Organism. Pycnidia (fig. 56 f) are usually 
found on all parts of the plant attacked. Within 
the body of the pycnidia and intermixed with the 
conidiophores (fig. 56 c) and pycnospores (fig. 56 e), 
are found filiform hooked-shaped bodies termed stylo- 
spores (fig. 56 d). Phomosis vexans has been erroni- 
ously referred to as Phoma solani Hals; Phoma vexans 
Sacc. and Syd., and Aschochyta hortorum Speg. 

Control. The seedlings in the seed bed should be 
sprayed with Bordeaux at least once before trans- 
planting. The plant in the field should be sprayed 
from four to eight times with either Bordeaux mixture 
or ammoniacal copper carbonate. 

Anthracnose 

Caused by Gleosporium melongence E. and H. 

Anthracnose on the eggplant attacks only the 
fruit. The trouble is characterized by numerous 




Fig. 56. Egg-Plant Diseases. 

a. Phomopsis of leaf, 6. Phomopsis on fruit, c. conidiophores, rf. stylospores, e. 
pycnospores of Phomopsis vexans, f. photomicrograph of a cross section through an 
infected calyx of an egg plant showing pycnidia of P. vexans (c. to f. after Harter), 
g.. anthracnose on egg-plant fruit. 



Family Solanaceae 303 

deep pits which later become covered with salmon 
colored acervuli (fig. 56 g). The latter are made up 
of myriads of spores of the fungus. Spraying for 
fruit rot will also help to control anthracnose. 

Stem Anthracnose, see Potato, p. 324. 

Southern Blight, see Pepper, p. 305. 

Root Knot, see Nematode, p. 49. 

DISEASES OF THE PEP-pER {Capsicum annum) 

The pepper plant is considered comparatively 
hardy, and its few diseases usually become trouble- 
some only when the crop is grown too long on the 
same land. 

Anthracnose 

Caused by Glomerella piperata ( E. and E.) S. 

Anthracnose is a serious disease which is usually 
confined to the fruit only. Its symptoms are char- 
acterized by round, soft, sunken, pale spots (fig. 57 a). 
The summer or conidial stage is known as Gleospo- 
rium piperatum E. and E. and is found as salmon 
colored pustules abundantly scattered over the spots 
(fig. 57 b-f). The ascospore stage may develop in 
pure cultures of the fungus. 

Black Anthracnose 

Caused by Colletotrichum nigrum E. and H. 

This form of anthracnose differs from the disease 
described above only in that the spots turn jet black. 



304 Diseases of Truck Crops 

The trouble attacks the young as well as the mature 
fruit. The winter or ascospore stage of the causative 
fungus has not as yet been found. It is very prob- 
able that the fungus is carried over as viable myce- 
lium on the infected fruit left over in the field. Both 
forms of anthracnose may be controlled by spraying 
with Bordeaux mixture. 

Fruit Spot 

Caused by Macrosporium sp. 

This disease, which is as important as anthracnose, 
attacks the fruit at the blossom end. Attacked 
peppers are half rotted, black, and moldy. Little 
is known about the causative fungus. It is probable 
that the disease has the same origin as the blossom 
end rot of tomatoes, and that the Macrosporium 
fungus is only secondary. Spraying with Bordeaux 
is recommended. 

Leaf Spot 

Caused by Cercospora capsisi H. and W. 

This disease is prevalent on peppers in Texas. The 
same trouble may be found also in the more southern 
States. It is characterized by roundish raised spots 
on the upper surface, at first brown, later becoming 
gray brown. They are limited by a dark zone, be- 
yond which the leaf tissue is pale and chlorotic. 
Where the spots are abundant the leaves turn yellow, 
wilt, and fall off prematurely. 



"'II' Id'! 





Fig. 57. Diseases of the Pepper. 

a. Anthracnose on fruit, b. anthracnose spot showing acervuli, c. acervulus 
greatly magnified, d. section through acervulus of Glomerella piperata, showing seta?, 
conidiophores, and conidia, e. conidia, /. germinating conidium, g. Southern blight. 



Family Solanaceae 305 

The conidiophores of the fungus are formed in 
clusters on both surfaces of the spots. The conidia 
are dilutely brown, clavate, and several septate. 

Southern Blight 

Caused by Sclerotium Rolsfsii Sacc. 

Blight is a disease which is commonly met with in 
the Southern States. It often causes considerable 
losses, owing to the fact that a great percentage of the 
plants is killed at the bearing age. 

Symptoms. Affected plants become apparent by 
the drooping of the young leaves at the tips of the 
branches. At night the plant recovers and it appears 
normal the next morning. This, however, is a tem- 
porary condition. Wilting generally progresses, and 
after three to four days the leaves yellow completely, 
wilt, droop, and die. In another day the stem of the 
plant loses its green color, dries, and dies. On pull- 
ing out a plant freshly wilted, we find a shrunken 
discolored area at the foot of the stem, slightly be- 
low ground level. In more advanced stages, the 
shrunken area is covered by a delicate web of white 
mycelial threads (fig. 57 g), and after the death of 
the plant numerous brown mustardlike sclerotia are 
found on the surface of the affected tissue. 

The seriousness of blight is that it attacks not only 
the pepper but also the tomato, eggplant, Irish po- 
tato, sweet potato, beets, beans, cowpeas, cabbage, 
squash, watermelon, rhubarb, and numerous other 
plants. 



3o6 Diseases of Truck Crops 

Control. It may be controlled in a way similar to 
that recommended for lettuce drop, see p. 143. 

DISEASES OF THE POTATO {Solanum 
tuberosum) 

General Consideration. Potato diseases are caused 
for the most part by definite parasitic organisms. 
However, there are many indirect causes Vv^hich may 
predispose the plant to various diseases. 

Color. The shade of red or pink in the tuber is 
usually affected by the health of the plant and by its 
nutrition. Color is usually intensified in run out 
stock. The White Ohios, for instance, may show 
much red at the eyes and at the eye end under poor 
conditions, but are white under proper culture and 
climate. Deep eyed and poor shaped tubers are 
likely to be densely colored. The flesh of the Early 
Rose variety may become red under unfavorable 
conditions. Whiteness of flesh is also influenced by 
the degree of ripeness. The color therefore may 
often serve as a general indicator of the health of the 
tuber. Sharp and long eyed ends with numerous 
eyes usually indicate a weak and run out strain. 

Position of the Eyes. On examining a tuber, we 
find a cluster of well developed eyes at the blossom 
end, generally termed the "seed end. " The other is 
generally known as the "stem end" of the tuber and 
it contains but few if any of the eyes. Careful 
growers are in the habit of discarding the "stem 
ends. " Plants resulting from the stem ends develop 



Family Solanacese 307 

late and are poor yielders. On the other hand, plants 
resulting from the "seed ends" develop early, are 
much more prolific and vigorous, apparently more 
resistant to disease and less subject to running out. 
Market gardeners who aim at producing an early 
crop should depend on the "seed ends" for plant- 
ing, and should discard the "stem ends," and even 
those pieces which come from the middle of the seed 
tuber. 

It is common knowledge that potatoes soon run 
out when grown too long under Southern conditions. 
In the South, Northern grown seed must be de- 
pended upon, such seed being far superior to that 
grown in the South. The effect of one year's removal 
of the Northern seed to Southern conditions is notice- 
able in a decline in yield and vigor of the crop. 
Therefore except under favorable Northern latitudes, 
frequent changes of seed are necessary. 

Germination Troubles. Conditions of poor germi- 
nation are often met with. There may be several 
factors to account for this. When planting seed 
which is heavily infected with blackleg, wilt, or 
Rhizoctonia rot, a poor germination and stand should 
be expected. This is especially true in cool, damp 
springs. 

Cutting the seed ten or fifteen days before plant- 
ing, as is the custom with some growers, is a practice 
which may lead to much germination trouble. When 
this is done, the seed is held too long and is apt 
to undergo a heat. Frequently seed is cut too 
small and there are few or no eyes left to permit 



3o8 Diseases of Truck Crops 

germination. Poor sprouting may sometimes be 
attributed to shipping of seed in overheated cars. 
In this case the seed when cut open will be seen to be 
blackened at the heart, a trouble soon to be con- 
sidered. 

Leaf Roll 

Cause Unknown. 

Leaf roll is but an old disease with a new name. 
The trouble has been carefully studied by Orton. ^ 

Symptoms. As the name indicates, the charac- 
teristic symptom is a rolling of the leaves (fig. 58 a). 
The leaflets roll and curl upward on their midrib, 
often assimiing a tube shape. This condition may 
involve the upper leaves of a plant or in serious cases 
the entire foliage. Rolled leaflets assume a sickly 
yellow reddish to purplish color. This is especially 
apparent on affected plants grown from tubers of a 
previously infected crop. 

The effect of leaf roll is to interfere with proper 
growth. This generally results in a premature dying 
of the leaves. The effect of the disease on the tubers 
seems to be strongly marked. The tubers in the hill 
are small, unfit for market and the yield is often re- 
duced by about one half. The disease is not con- 
tagious in the sense that it can spread from plant to 
plant; but the inherent weakness is transmitted to 
the seed. This when sown again will show new out- 
breaks of leaf roll the following year. True leaf roll 

' Orton, W. A., U. S. Dept. of Agr. Bui. 64 : 1-48, 1914. 




Fig. 58. Potato Diseases. 

a. Leaf roll, 6. curly dwarf (a. and b. after Appel), c. net necrosis, d. spindly sprout, 
e. lilack heart, /. hollow heart {d. to /. after Stakman and Tolaas), g. mosaic, h. tip 
burn (c. g. and h. after W. A. Orton). 



Family Solanacese 309 

should not be mistaken for a temporary rolling of the 
leaves that may be brought about by excessive 
humidity in poorly drained lands. Heat, drought, 
and excessive use of fertilizers, especially potash, may 
bring about a temporary leaf rolling. Leaf roll is 
prevalent in Germany, Austria-Hungary, Switzer- 
land, the Netherlands, Denmark, and Sweden. In 
the United States it is found in Eastern Colorado, 
Western Nebraska, Virginia, and Maine. Since the 
trouble is carried with the seed, this should be 
secured from localities known to be free from the 
disease. 

Curly-Dwarf 

Cause Unknawn. 

This disease differs from leaf roll by a dwarfed 
development of the plant, and a wrinkled and down- 
ward curling of the leaves (fig. 58 b), resembling the 
natural curling of the foliage of kale or Savoy cab- 
bage. A peculiarity of this disease is that the mid- 
ribs, veins, and leaf petioles together with stems and 
branches are all dwarfed, giving the foliage a thickly 
clustered appearance. The foliage keeps its normal 
color and turgidity. There is also a tendency for the 
plant to send out numerous branches with brittle 
stems. The effect of the disease is to reduce the 
yield, and in severe cases there is an absence of tuber 
production altogether. Like leaf roll the disease 
is transmitted with the seed tubers, but it does not 
spread from plant to plant. The trouble is prevalent 



310 Diseases of Truck Crops 

in potato fields, but not to such an extent as to be 
noticed. It is always found scattered in individ- 
ual plants, indicating deterioration. Prevention of 
this trouble consists in careful selection of seed from 
unaffected hills. 

Spindling Sprout 

Cause Unknown. 

Spindling sprout is an abnormality common to 
Southern grown seed, which reduces the yield con- 
siderably. Instead of healthy sprouts, long, thin 
slender ones germinate (fig. 58 d) . No lesions of any 
kind are found on the sprouts or on the seed pieces. 
A weak tuber will produce only spindly sprouts. Both 
strong and spindly sprouts are never found on the 
same seed tuber. The character and the fertihty of 
the soil seem to have no influence whatsoever on this 
trouble. The only remedy known is the use of 
Northern grown seed. 

Internal Brown Spotting 

Cause U7iknown. 

This disease is pecuHar to the Early Maine and is 
found in New York, Maine, Connecticut, and Minne- 
sota. 

Symptoms. Usually the trouble is internal with- 
out any symptoms apparent on the outside of the 
tuber. But occasionally its presence is indicated by 



Family Solanaceae 311 

reddish discoloration on the skin. In cutting across 
an affected tuber, the flesh is found to be spotted 
reddish in isolated and scattered places. The 
trouble usually starts at the stem end and works 
toward the bud end and inwards. In severe cases, 
the trouble is indicated by a discolored band, the 
outside of which may easily be mistaken for late 
blight injuries, Phytophora infestans. 

Net Necrosis 

Cause Unknown. 

Tubers often show minute black areas (fig. 58 c) 
beginning near the stem end and extending about an 
inch inwards. It is not known whether the trouble, 
if such it may be called, has any influence in reducing 
the yield. However, it is safer not to use tuber 
seed which shows these minute internal browned 
specks. 

Black Heart 

Caused by Overheating. 

This trouble is often met on tubers kept in storage 
pits which are poorly ventilated. In this case the 
sweating and overheating will cause the tubers to 
turn black at the heart (fig. 58 e) . The same occurs 
when potatoes are shipped in overheated cars. The 
remedy is to keep the potatoes as cool as possible, 
and slightly above the freezing point. 



312 Diseases of Truck Crops 

Hollow Heart 

Cause Uneven Growth. 

When potatoes are overgrown or when quick growth 
results from dry spells followed by moist weather, 
the heart of the tuber tears and a hollow center is 
formed (fig. 58 f). The trouble does not injure the 
edible quaHty of the tuber. Varieties such as Rural 
New Yorker and King are especially susceptible to 
hollow heart. So far as possible these should be 
avoided on heavy soils. 

Tip Burn 

Caused by Unfavorable Soil and Weather. 

This trouble is prevalent in dry weather in mid- 
summer, when the leaves transpire water more 
rapidly than the roots can take it in from the soil. 
As a result the tips and margins of the leaves dry 
up and die (fig. 58 h) . The uproUing of the margins 
of the leaflets is a characteristic of tip burn, also 
distinguishing it from late bHght. The trouble may 
be considerably reduced by frequent shallow culti- 
vation, making a shallow surface mulch which will 
prevent excessive evaporation. Spraying will also 
protect the foliage from tip burn. 

Mosaic , 

Cause Unknown. 

Mosaic is a disease which is not confined to the 
tubers, but which also affects the parts of the plant 



Family Solanaceae 313 

above ground. It is characterized by a mottled ap- 
pearance of the leaves (fig. 58 g). The portions 
which are lighter in color seem to be thinner than 
those which are of a normal green. In advanced 
stages, brown spots of dead tissue may take the place 
of the light colored mottled leaf areas. 

Mosaic undoubtedly reduces the yield, the losses 
often amounting to twenty per cent. The Green 
Mountain seems to be very susceptible to mosaic, 
while the Irish Cobler seems to be especially resistant. 
It has been proven by Worthley^ that the disease is 
carried with the tubers from diseased vines. As a 
matter of precaution these tubers should not be used 
for seed. Long before digging, the field should be 
carefully inspected, and hills which show mosaic 
infection should be pulled out and removed. This 
will prevent tubers from diseased plants from being 
mixed with healthy ones. 

Arsenical Injury 

Potato foliage is often injured when the plants are 
sprayed with Paris green. Within a few days dead 
spots similar to those occurring in early blight ap- 
pear on the surface of the leaves. To obviate this, 
lime should be added to the Paris green. If the 
Paris green is used dry, one pound of powdered lime 
should be mixed with each half pound of Paris green. 
The same proportions are used when Paris green 
is applied as a spray. 

Pox or Pit (fig. 60) see Sweet Potato, p. 152. 

' Worthley, E. I., Science, N. S., 42 : 460-461, 1915. 



314 Diseases of Truck Crops 

Powdery Scab 
Caused by Spongospora suhterranea (Woll.) Johns. 

Powdery scab may justly be considered a danger- 
ous disease. The trouble has undoubtedly been of 
European origin. In the United States the disease 
is now found in Presque Isle, Me., Chateaugay, N. Y., 
Nehalem, Ore., Hastings, Fla., Inohomish, Wash., 
and Virginia, Minn. The trouble has been carefully 
investigated by Melhus and Rosenbaum.' 

Symptoms. Powdery scab attacks the young root- 
lets, forming galls resembling in size those of legume 
nodules (fig. 59 c, d). At this stage infection does not 
take place on the tubers. In fact it is not unusual 
to find the total root system affected with galls, while 
the tubers remain free. Thus if we look for the dis- 
ease in the field a search should be made for infection 
on the roots and rootlets. 

Infection on the tubers is evidenced at first by 
minute discolored areas on the epidermis. Six to 
eight days later, the spots increase in size, become 
raised and somewhat jelly like. Powdery scab on the 
tubers cannot easily be mistaken for common scab, 
Actinomyces chroma genus. In powdery scab the 
sori are more often circular and not as extended as in 
common scab. In powdery scab, the border of the 
pustules is virtually raised, forming a cuplike sorus 
or pit (fig. 59 a), and the pits are deeper and at matu- 

' Melhus, I. E., and Rosenbaum, J., U. S. Dept, of Agr. Jour. Agr. 
Research, 7 : 213-254, 1911. 




Fig. 59. Diseases of the Potato. 

a. Powdery scab, early stage, 6. powdery scab, advanced stage of rotting, c. and d. 
powdery scab, gall-forming stage on potato roots {c. and d. after Melhus and Rosen- 
baum), e. single potato cell showing spore balls of the powdery scab fungus (after 
Melhus), /.black leg, g. common scab, h. to i. drawings of the organism of common 
scab, showing branching of threads and groups of spores or conidia (after Lutman 
and Cunningham). 



i* 



v# •-.*.. 






Fig. 6o. Pox or Pit of the White Potato, Showing Different 
Stages of Infection. 



Family Solanaceae 315 

rity always filled with black spore balls. The sori 
of common scab are shallow and made up of corky 
compact tissue. After being handled or shipped long 
distances, potatoes infected with powdery scab can- 
not be distinguished from those suffering from com- 
mon scab. However, a microscopical examination 
of the sori will soon reveal the difference. 

In storage, potatoes infected with powdery scab 
will dry rot. This is but the final stage of the disease 
(fig. 59 b) . While it is not uncommon for the dry rot 
to invade the whole tuber, it generally extends only in 
spots. The effect of powdery scab on stored potatoes 
is a more rapid drying of the tubers and the opening 
of a way for the invasion of secondary infection. 

In the field, the disease is favored only by cool, 
damp, and rainy weather. Besides the potato, the 
tomato too is attacked by powdery scab. In this 
case, infection is confined to the root system, which 
is much more distorted than is the case with the po- 
tato. Of the other hosts affected may be mentioned 
Solanum warscewicii, S. hematoclodum, S. mammosum, 
S. marginatum, S. ciliatum, and S. commersoni. 

The Organism. The Plasmodium within the host 
ceills is irregular in shape. It is composed of proto- 
plasm within which are evenly distributed nuclei. 
Within the host cell the protoplasm of the plasmodium 
is closely applied to the host nucleus. Infection 
seems to take place by means of a plasmodium rather 
than by single amoebse. The parasite is confined to 
the phloem of the host. The invaded cells are not 
killed, but are stimulated to an abnormal cell division. 



3i6 Diseases of Truck Crops 

Germination of the spore balls may be effected in 
two ways: (i) the spore walls of the entire spore balls 
break down, liberating as many amoebae as there were 
cells within; (2) the amoebae may escape through 
openings in the wall of the spore ball and move about 
by means of pseudopodia. 

Control. Infected soils should never be limed, 
since the application of lime favors the disease. 
Rotation of crops is suggested. The land should be 
given a rest from potatoes, or tomatoes, for at least 
five years. Since infection of the tubers takes place 
late, early harvesting and the growing of early 
maturing varieties is advisable. Since the disease 
is carried with infected seed tubers, the latter should 
be disinfected. The use of mercuric chloride or 
formaldehyde, or both, is recommended. (See also 
P- 336.) No soil treatment will cure the trouble, but 
sulphur applied at the rate of nine hundred pounds 
per acre will reduce the amount of infection. 

Blackleg 

Caused by Bacillus phytopthorus Appel. 

Blackleg is a dangerous disease which may readily 
be introduced into new localities with the seed. The 
trouble has been well described by Morse. ' 

Symptoms. Blackleg does not manifest itself until 
the plants are about 7 to 10 inches high. Diseased 
plants are unthrifty, undersized, with the branches 

' Morse, W. J., Maine Agr. Expt. Sta. Bui. 174: 307-328, 1909. 



Family Solanaceae 317 

growing upward, forming a compact top. In severe 
cases, affected plants turn yellowish, topple over, and 
die. On pulling out a diseased hill, we find that the 
stem end near the seed potato is black (fig. 59 f). 
This blackness may extend even one or two inches on 
the stem above the ground. The seed pieces in this 
case soft rot. Occasionally the newly formed tubers 
become infected in the soil and rapidly soft rot. 
The disease is carried in the interior of the infected 
seed tubers, and in this way is distributed from one 
locality to another. Blackleg is now prevalent in 
Maine, South Carolina, Virginia, Maryland, Dela- 
ware, New Jersey, New York, Ohio, Oregon, and possi- 
bly also in Florida, Georgia, New Hampshire, North 
Carolina, Rhode Island, Vermont, and Wisconsin. 

The Organism. Bacillus phytopthorus is a rod- 
shaped organism, motile by means of peritrichiate 
flagella. It is an aerobe, non-sporiferous, liquefying 
gelatin slowly and producing no gas. On agar, the 
colonies are grayish white, round, and smooth. 

Control. Careful selection of the seed tubers is 
essential. Those which show evidence of internal 
discoloration or rot should be disinfected with 
formaldehyde, see p. 336. 

Southern Wilt, see Tomato, p. 342. 

Common Scab 

Caused by Actinomyces chroma genus Gasp. 

Common scab is a disease which is generally skin 
deep. The kind of injury and the severity of infec- 



31 8 Diseases of Truck Crops 

tion depends on the variety of tuber and the cultural 
conditions. Common scab may often be confused 
with powdery scab; but a careful examination will 
reveal striking differences. 

Symptoms. The disease attacks the tubers only. 
It begins as small surface spots or stains, which soon 
spread and increase in depth, penetrating to a depth 
of a half centimeter. The spots consist of accumu- 
lated corky tissue which may be readily removed 
(fig- 59 g)- The diseased cells lose their starch and 
are filled instead with what appears as fat globules. 
The scab spot is merely the result of the corky cam- 
bium cells which are formed to protect the inner 
starch-bearing parenchyma tissue from the irrita- 
tion of the parasite. Scab does not impair the germi- 
nation of the seed, but it reduces the yield as well as 
prejudicing the keeping qualities of the tubers. It 
does not in any way impair their edible quality. 

The Organism. The scab-causing organism was 
formerly beHeved to belong to the class of fungi and 
was originally named Oospora scabies Thaxter. But 
two American workers, Lutman and Cunningham,^ 
found that the scab organism is not a fungus, but 
belongs to the thread bacteria (fig. 59 h, i). A. 
chromogenus consists of long irregular filaments; the 
cross walls of the branches are scarcely visible. On 
agar, under lack of moisture conditions or concentra- 
tion of medium, the filaments grow out, and become 
closely segmented into short rods known as gonidia 

' Lutman, B. F., and Cunningham, G. C, Vermont Agr. Expt. Sta. 
Bui. 184 : 3-64, 1914. 



Family Solanaceae 319 

or spores. The filaments or gonidia are non-motile. 
It produces no gas, but is capable of producing a 
brown pigment which is soluble and diffuses through 
the medium. 

Control. The disease is carried about with infected 
tubers. The latter when fed to cattle will infect the 
manure. The scab organism can pass the digestive 
tract of the cows or horses without losing its vitality. 
Before planting, seed potatoes should be disinfected 
with corrosive sublimate or formaldehyde. See also 
p. 336. Fertilizers which tend to make the soil alka- 
line, such as barnyard manure, lime, wood ashes, or 
bone meal, all tend to increase scabby potatoes. The 
use of kainit, muriate of potash, sulphur, or acid 
phosphate as a fertilizer all tend to decrease scab. 

Black Wart 

Caused by Chrysophylyctis endohioticum (Schilb.) 
Perc. 

Black wart is perhaps one of the most dangerous of 
the potato diseases. The trouble is now prevalent 
in Germany, England, Upper Hungary, and in New- 
foundland. The disease has not as yet made its 
appearance in the United States, although it is 
beUeved that infected potatoes have been shipped in 
from Newfoundland. 

Symptoms. In early stages of infection, the eyes 
are first attacked, turning brown and later black. 
The disease then works down to the tuber, which 
is but slightly disfigured. In advanced stages, big 



320 Diseases of Truck Crops 

dark warts, sometimes as large as the tuber itself, 
appear on its sides or ends (fig. 6i a). The warty 
growth consists of a scabby gall-like formation, 
closely resembling the crown gall of the peach. The 
last stage of the disease is when the fungus has utilized 
all the food stored in the tuber and has reduced it to a 
brownish black, soft mass with a very offensive odor. 
At this stage the fungus consists almost entirely of a 
mass of spores which, when disturbed, scatter and 
spread all over the field. 

The Organism. Chrysophylyctis endohioticum has 
been investigated by Johnson^ and others. The 
vegetative parts of the fungus consist first of a naked 
mass of protoplasm which attacks and feeds on the 
protoplasm of the cells of the host. As this bores 
from cell to cell, it stimulates abnormal growth, which 
results in the warts or galls already mentioned. 
During the summer, the plasmodium rounds up, 
forming a thin smooth wall about itself. Later the 
contents of this body break up into numerous zoo- 
spores, which escape through a hole in the cell wall 
and attack healthy potato tissue. As the season 
advances, the fungus ceases to reproduce by means of 
zoosporangia and zoospores and forms a resting spo- 
rangium. This helps to carry the fungus over the 
winter, and the following spring it germinates by 
means of zoospores. 

Control. So far, there are no methods of control 
known. It is imperative that we prevent black wart 

' Johnson, T,, The Scientific Proceedings of the Royal Dublin Sac, 

Vol. 12, 1909. 



Family Solanaceae 321 

from getting a foothold in the United States. This 
can be accomplished only by strict quarantine laws 
prohibiting the importation of tubers from countries 
where wart is prevalent. 

Melters or Leak 

Caused by Pythium de Baryanum Hesse; Rhizo- 
pus nigricans Ehr. 

Melters is a common storage and shipping disease. 
The trouble is prevalent in the Delta region of San 
Joaquin River, CaHfornia. The rot is common 
during hot weather and begins to work soon after 
harvesting. 

Symptoms. The disease first appears as small dis- 
colorations at a cut or bruise made by an im- 
plement at harvesting. The rot does not affect 
unbruised tubers. Later the affected potatoes turn 
brown, become soft (fig. 61 g), and if pressure is 
applied a brownish watery liquid exudes, wetting the 
neighboring tubers. 

The Organism. Orton^ has shown that leak may 
be induced by the fungus Rhizopus nigricans. For 
a fuller description of this fungus, see soft rot of sweet 
potatoes, p. 156. Hawkins^ has further shown that 
leak may also be caused by the fungus Pythium de 
Baryanum. For a description of the latter, see also 
damping off, p. 43. 

' Orton, W. A., U. S. Dept. of Agr. Bur. PI. Ind. Circ. 23 : 1 1, 1909. 
^ Hawkins, L. A., U. S. Dept. Agr. Jour. Agr. Research, 7: 627-639, 
1916. 

21 



322 Diseases of Truck Crops 

Late Blight 
Caused by Phytophthora injestans (Mont.) De Bary. 

Late blight is a disease which is restricted to some 
parts of the United States. As it thrives best in 
States where the midsummers are moist and cool, 
it is common in the Northern States. Farther 
south or west, it is unknown or it occurs sporadically, 
causing little damage. 

Symptoms. Late blight attacks both the foliage 
and the tubers in the field, or the tubers alone in 
storage, the disease appearing when the plants have 
passed the flowering stage. 

On the leaves the trouble is first manifested as 
purplish black or brownish black areas on the lower 
side (fig. 6i b). It attracts attention only when the 
upper leaves are attacked and blackened. At first 
the infected leaves become watersoaked and pale, 
then they wilt and blacken. On examining an in- 
fected leaf during a dewy morning, a delicate growth 
of the fungus is perceptible as a fine powdery 
bloom on the under side. 

When the tops are badly blighted, the tubers too 
will show evidence of disease. In early stages the 
infection becomes perceptible as brownish to pur- 
plish discoloration of the skin with a softening of the 
inner tissue (fig. 6i c). In dry, well drained soils, 
the progress of the disease underground is slow, and 
at harvesting dry rot may be in evidence. Infected 
tubers when stored in cool, dry cellars may pass the 




Fig. 6i. Potato Diseases. 

a. Black wart (after Gussow), b. late blight on foliage, c. late blight on tuber, d. 
successive stages of the development of the conidia of Phyiophthora infestans (b. 
and d. after L. R. Jones), e. germination of conidia of Phytophlhora infestayis, bv 
means of zoopores (after Ward),/, mature oogonium of P. infestans (after Clinton)'. 
R. melters. surface view, early stage of infection, h. pycnidium of Phoma tuberose 
(after Melhus and Rosenbaum). 



Family Solanaceae 323 

winter unhurt, the rot being checked by the favorable 
storage conditions. 

The Organism. The mycelium of the fungus is 
hyaHne, non-septate. As shown by Melhus' and 
others, the mycelium may be carried from year to 
year within the infected tubers. In fact this is but 
one way late bhght is distributed. Through the 
stomata of the infected leaf emerge the slender coni- 
diophores (fig. 51 d), bearing the ovoid conidia. Ac- 
cording to Melhus, ^ the conidia of Phytophthora infes- 
tans may germinate either directly by a germ tube 
or by the production of zoospores (fig. 61 e) as in 
Pythium. The best germination occurs at the op- 
timum temperature, which lies between 10 and 13° C. 
(50-57° F.). The conidia may be killed by exposure 
for 6 to 24 hours to dry atmospheric conditions such 
as exist in an ordinary room. Frost which kills the 
top of the plants will also kill the conidia of Pytho- 
phthora. Light does not hinder germination and 
therefore has no inhibiting effect on infection. 
Phytophthora infestans does not seem to produce sex- 
ual spores or oospores within the affected tissue of 
the leaf or tuber. However, Clinton ^ succeeded in 
developing what appeared to be oospores of the 
fungus in pure culture on oat agar (fig. 61 f). The 
oogonia appear as swollen terminal heads, cut off 

' Melhus, I. E., U. S. Dept. of Agr. Jour. Agr. Research, 5 : 59-65, 

1915- 

' Melhus, I. E., Wisconsin Agr. Expt. Sta. Research Bui. 37 : 1-64, 

1915- 

3 Clinton, G. P., Connecticut Agr. Expt. Sta. Ann. Rept., 1909- 

1910:753-774- 



324 Diseases of Truck Crops 

from the main thread by a cross wall. The antherid- 
ium resembles that of P. phaseoli. IMature oospores 
have a medium thick, smooth, hyaline wall. It is 
not known how the oospores germinate. For meth- 
ods of control, see p. 337. 

Phoma Rot 

Caused by Phmna solani Mel., Rosen., and Sch. 

Phoma rot is found only on bruised tubers. It is 
also found following injuries produced by powder^' 
scab, Spongospora subterranea. The lesions of phoma 
rot are brownish dark to gray dark sunken pits with 
irregular and sharply defined margins. The black 
pycnidia (fig. 61 h) are found scattered over the entire 
surface of the lesions. The disease may cause con- 
siderable damage in storage. The remedy consists in 
careful handling of the tubers during digging and 
storing. 

Anthracnose 

Caused by Colletotrichum atramentarium (Berk. 
and Br.) Taub.^ 

Anthracnose was first described by O'Gara^ as 
a disease attacking the foot of the plant. The 
fungus was originally named Colletotrichum solani- 
colum O'Gara, but was later changed by the 
writer to C. atramentarium. It causes deep lesions 

' Taubenhaus, J. J., Mem. N. Y. Bot. Gard., 6 : 549-560, 1916. 
^ O'Gara, P. J., Mycologia, 7 : 38-41, 19 15. 








Fig. 62. Potato Diseases. 

a. Early blight (after L. R. Jonej). 6. spores of the early blight fungus, c. silver 
scurf, d. conidiophores and conidia of the silver scurf fungus, e. and /. Fttsarium 
oxysporum wilt in tubers, g. chlamydospores and one to several celled conidia of 
F. nxysponim. h. conidiophores of F. oxysporum (g. and /;. after Sherbakoff), i. Ver- 
ticillium wilt (after Orton). 



Family Solanaceae 325 

on the stems, usually attacking plants which are full 
grown. It is also found as a saprophyte in the soil, 
or growing on dead potato vines; or frequently 
associated with silver scurf on the tuber. It was 
previously thought to be a sclerotial stage of 
Spotidylocladium atrovirens Harz. Colletotrichum 
atramentarium differs from most CoUetotrichums in 
that it produces an abundance of sclerotia both 
on the host and in pure culture. It sporulates very 
poorly but otherwise possesses all the characteristics 
of the genus Colletotrichum. 

Early Blight 

Caused by Macrosporium solani E. and M. 

Early blight attacks the foliage only. Infection 
seems to follow injury from insects such as the potato 
beetle and the flea beetle. 

Symptoms. The disease is characterized by cir- 
cular or irregular brown dry spots made up of a suc- 
cession of rings (fig. 62 a). The spots may become so 
numerous as to involve the entire foliage and cause 
premature death of the tops. 

The Organism. The mycelium is brownish to olive 
in color. The conidiophores arise through the sto- 
mata of the leaf. The conidia are produced singly, 
the body of the spore has from 4 to 12 transverse 
septa, with few longitudinal cross walls (fig. 62 b). 
When germinating, a germ tube may be produced 
from each cell of the conidia. This penetrates the 



326 Diseases of Truck Crops 

leaf either through the stomata or by piercing through 
the cell wall of the epidermis. Early blight may be 
controlled by spraying, see p. 337. 

Silver Scurf 

Caused by Spondylocladium atrovirens Harz. 

Silver scurf is prevalent throughout the East. 
Fortunately the disease does not cause much direct 
damage, since it is confined only to the exterior of the 
epidermis. It is claimed that affected tubers are 
subject to more rapid shrinking and drying. The 
spots on the tubers are brown and turn silvery when 
moistened (fig. 62 c). 

The Organism. The conidiophores are borne either 
singly or in clusters, erect septate, with numerous 
sterigmata which bear the spores (fig. 62 d). The 
conidia are thick walled, elongate, many septate, apex 
narrowed and longer at the bottom. 

Control. Seed treatment does not seem to control 
the disease. Since silvery scurf is directly carried 
with the seed tubers, selection of clean seed is recom- 
mended. 

Verticillium Wilt 

Caused by Verticillium alho-atrum McA. 

Verticillium wilt is not a dangerous disease when 
compared with Fusarium wilt. It does not kill out 



Family Solanaceae 327 

entire fields but is generally confined to individual 
hills irregularly scattered in a field. In distribution, 
Verticillium wilt has been found only in the more 
northern States. 

Symptoms. The disease as described by Orton' is 
characterized by a sudden wilting of the foUage (fig. 
62 i) and the premature dying of the hill. In split- 
ting open a diseased stem, the browning of the vessels 
will be well marked. This will extend to the tips of 
the stems and into the leaf petioles, a symptom which 
distinguishes it from Fusarium wilt, since in the latter 
the browning of the vessels does not extend into the 
tips of the stalks. Moreover, in Verticillium wilt 
there is a production of conidia on the stalks long 
before they are entirely dead. In Fusarium wilt, 
the conidia appear only after the stem has been killed 
for some time. 

Control. Since the disease is carried internally in 
the seed tubers, control methods are the same as for 
Fusariiim wilt. 

Fusarium Wilt 

Caused by Fusarium oxysporum (Sch.) Sm. and Sw. 

Fusarium wilt is a disease which thrives best in 
warm climates. In CaHfornia, Arizona, Ohio, Mis- 
souri, and Nebraska the trouble is most prevalent. 
New England and New York are relatively free from 
Fusarium wilt. There, however, the VerticiUium 

' Orton, W. A., U. S. Dept. of Agr. Bal. 64 : 16-18, 1914. 



328 Diseases of Truck Crops 

wilt is prevalent. In Michigan, Illinois, Wisconsin, 
and Minnesota, Fusariiim wilt is found in the older 
potato districts. The trouble is also found in Colo- 
rado and Utah where it thrives on irrigated as well as 
on dry lands, on sandy loams as well as on the heavier 
clays. 

Symptoms. When infected seeds are planted, the 
result is a poor germination and uneven stand. The 
disease however does not attract attention until the 
plant attains a height of a foot or more. 

Wilt is characterized by a drooping of the lower 
leaves, which are first to die. This is followed by a 
v/ilting of the upper foliage and by a premature dying 
of the tops. The leaf roll that is noticed in Fusarium 
wilt differs from true leaf roll in that in the former 
the leaves lack the turgidity and soon die as a result 
of the infection. Wilted plants are at first light green, 
then yellow, finally drying up and dying. The disease 
first gains entrance through the tender rootlets in the 
soil, gradually working up into the main roots, stolons, 
tubers (fig. 62 e, f), and some way into the stem. In 
splitting open a diseased stem, the interior water 
vessels are found to be slightly browned. But few 
Fusarium spores are formed on the dead stems. In 
the tubers the presence of wilt is indicated by a 
browning of the vascular rings. 

The Organism. The microconidia are pedicellate, 
sporodochia and pseudopionnotes present, macro- 
conidia 4 to 5 septate, pinkish buff color in mass 
(fig. 62 g, h). Bluish black sclerotia are formed on 
potato plugs. For methods of control see p. 337. 



Family Solanaceae 329 

Black Rot or Jelly End Rot 
Caused by Fusarium radicicola Woll. 

This disease is seldom found in the field at digging 
but is usually manifested as a storage trouble. It is 
common in Idaho, Oregon, Washington, California, 
Nevada, Mississippi, New York, Virginia, District 
of Columbia, and certain parts of Pennsylvania. 

Symptoms. In the irrigated sections of California, 
Oregon, and Idaho the trouble is manifested as a soft 
rot termed "Jelly End Rot." The stem end soft 
rots, and the affected portion may be easily removed 
from the remainder of the tuber. The disease pro- 
gresses inwards until the entire tuber within the skin 
becomes soft and jellylil^e in consistency. If not 
disturbed, the inside tissue will dry, and the skin per- 
sist as a loose tunic, or it may shrivel and shrink, 
giving the appearance of a dry rot. 

In the non-irrigated potato districts, the symptoms 
of the disease are sunken, blackish, leathery areas on 
any part of the tubers. In Pennsylvania the disease 
is known as "black rot" or "black head." Micro- 
conidia of the fungus are the dominant type of 
spores. Chlamydospores are common and pseudo- 
pionnotes are absent, while sporodochia are usually 
present. 

Control. This disease does not make any progress 
in storage at or below fifty degrees F. The trouble 
is confined mostly to the Idaho, Rural, and Pearl. 
So far as possible, these should be avoided and re- 



330 Diseases of Truck Crops 

placed by the more resistant varieties best adapted to 
the infected localities. 

Stem End Rot 

Caused by Fusarium eumartii Carp. 

Although a storage trouble, stem end rot may cause 
a wilt in the field which may not be easily distin- 
guished from other Fusarium wilts. However, in 
the laboratory the causative organism may be readily 
determined by pure culture methods. 

Symptoms. The wilt produced on plants in the 
field resembles other wilts. On the tubers, decay 
starts at the stem end. The infected part slowly 
shrivels and becomes filled with a mass of a dried 
brown pulp, consisting mainly of dead tissue. In- 
fection usually takes place through a wound or even 
through a lenticel in the tuber. The fungus is char- 
acterized by its production of macroconidia which are 
4 to 6 septate, pionnotes are present, otherwise the 
organism resembles F. martii. 

For control, see p. 337. 

Powdery Dry Rot 

Caused by Fusarium trichothecioides Woll. 

Powdery dry rot is a storage trouble which is pre- 
valent in the arid and semi -arid sections of the 
western part of the United States. The disease was 




Fig. 63. Potato Diseases. 

a. Powdery dry rot, b. Rhizoctonia lesion on young potato sprouts (after W. A. 
Orton), c. Rhizoctonia sclerotia on seed potato tubers, d. melters, artificially in- 
duced by inoculating with a pure culture of Sderoltum Rolfsii. e. pure culture of 
5. Rolfsii. 



Family Solanacese 331 

first described by Jamieson and Wollenweber. ' The 
trouble is the same as that described by Wilcox^ 
and the causative organism was previously named 
Fusarium tuherivorum. In poorly ventilated storage 
houses, bruised potatoes dry rot (fig. 63 a), the entire 
content of the tuber turning into a powdery mass. 
The disease does not attack growing plants in the 
field nor unbruised tubers. 

There are numerous other species of Fusaria w^hich 
are capable of producing a rot on tubers through a 
wound. Sherbakoff 3 mentions twenty-eight of them 
which may produce a rot on stored potatoes. 

Rosette or Russet Scab 

Caused by Corticium vagum B. and C. var. solani 
Burt. 

Rosette, although generally distributed, is more 
prevalent in the Eastern States. The disease is 
often very serious, and causes great money losses. 
The trouble attacks the tuber as well as the foot of 
the stem. 

Symptoms. On the tubers the disease is recognized 
as superficial dark brown sclerotia varying in size from 
that of a mustard seed to that of a vetch (fig. 63 c) . 

' Jamieson, C. 0., and Wollenweber, H. W., Jour. Wash. Acad. 
Sci., 2 : 146-152, 1912. 

^ Wilcox, E. M., et al., Nebraska Agr. Expt. Sta. Research Bui. 
I : 1-88, 1913. 

3 Sherbakoff, C. D., New York (Ithaca) Agr. Expt. Sta. Mem., 
6:97-270, 1915. 



332 Diseases of Truck Crops 

In planting infected tubers, the sclerotia germinate 
and the growing fungus threads attack the young 
sprouts, causing lesions (fig, 63 b). These may be 
superficial or so deep as almost to girdle the stems. 
The lesions are usually numerous. Infected plants 
attempt to overcome the ill effect of the disease by 
sending out numerous sprouts above the injured 
parts, giving the appearance of a rosette. Diseased 
hills often produce aerial tubers. The disease is 
spread about by the use of the infected seed tubers. 
The causative fungus, once introduced into a field, 
will live in the soil on dead organic matter and attack 
numerous other crops. Rosette is worse on w^et, 
poorly drained soils, and during seasons of heavy 
rainfall. Recently Rosenbaum ' has found that there 
are variations in the strains of Rhizoctonia isolated 
from diseased potatoes. Some of the strains seem to 
be more virulent pathologically, and differ morpho- 
logically from others. For methods of control, see 

P- 336. 
Southern Blight (fig. 63 d-e), see Pepper p. 305. 

Root Knot 

Caused by Heterodera radicicola (Greef) Muller. 

Root knot on the potato may be easily overlooked. 
Usually there are no knots on the tubers, and the 
trouble is merely manifested by minute pimples on 
the surface of the potato, resembling the pimples 

' Rosenbaum, J., U. S. Dept. of Agr., Jour. Agr. Research, 9 : 413- 
419, 1917. 



Family Solanace^ 333 

induced by flea beetle injury. Small knots resem- 
bling legume nodules may occasionally be formed on 
the smaller rootlets of the plant. For a further de- 
scription of root knot, see Nematode, p. 49, 

Control of Potato Storage Rots 

As seen above, numerous fungi are capable of pro- 
ducing a rot on bruised potatoes. The greatest loss 
from this source occurs v/hen the tubers are held in 
storage. IMost of this loss, however, could be reduced 
to a minimum if more care were exercised at digging. 
Few realized the heavy losses from bruises and cuts 
and rough handling in the field. This could be best 
appreciated if we were to watch the storers sort out 
the tubers, to prepare them for the market. A visit 
to the retail stores where quantities of unsalable 
potatoes are dumped out will also convince us why 
the grower must exercise more care. 

Potatoes are usually stored in pits, in cellars or 
dug-outs, and in insulated frame structures. In the 
larger storage houses, conditions may be better regu- 
lated than in pits or cellars. No matter which 
method of storage we adopt, there are certain 
fundamental principles to observe. 

Temperature. Upon proper temperature usually 
depends success in storing. Careful investigations 
by the United States Department of Agriculture has 
shown that the freezing point of Irish potatoes lies 
between 26 and 28 degrees F. This means that po- 
tatoes can stand the low temperatures, which are 



334 Diseases of Truck Crops 

especially necessary for good keeping. A tempera- 
ture of about thirty-six degrees F. may be considered 
ideal for the best keeping. This temperature will 
keep the tubers in the best of condition and will also 
inhibit the work of decay organisms. It is claimed 
that when potatoes are stored at low temperatures 
they take on a sweetish taste when cooked. This 
may or may not be an objectionable feature. This 
objection, however, is of little significance, when we 
consider the fact that stored potatoes become normal 
in taste after being kept a week at the retailer's 
store at ordinary room temperature. 

Moisture. Little is known as to the amount of 
moisture necessary during potato storage. The 
object, however, should be to maintain sufficient 
moisture in the air to prevent excessive drying of the 
tubers, and at the same time to keep the moisture 
content low enough to prevent it from condensing and 
falling on the potatoes. Appleman' suggests that 
storage houses be maintained at 33 to 35 degrees F., 
and at a humidity of 85 to 90 per cent. 

Ventilation. Pure fresh air seems to be necessary 
to insure successful storage. This may be secured 
by top and side ventilators installed in the storage 
house. In pit or cellar storage, neither the tem- 
perature nor the relative humidity can be suc- 
cessfully controlled. Here the trucker is entirely 
dependent on the chances of natural weather con- 
ditions. 

Bins. It is bad practice to store in large bins or 

» Appleman, C. O., Maryland Agr. Expt. Sta. Bui. 167 : 330, 1912, 



Family Solanaceae 335 

piles, for the potatoes in them are aknost certain to 
undergo a heat which will destroy their keeping and 
germinating power. This is a serious matter in stor- 
ing seed potatoes. Bins should be small, provided 
with a false floor, and separated one from the other 
by a two-inch air space. Direct sunlight should be 
kept from the storage. Subdued light or electricity 
will not cause the tubers to turn green and unfit for 
cooking. Finally, only sound tubers should be stored. 
The storage house should be carefully cleaned out 
before the crop is brought in from the field and the 
interior walls and woodwork thoroughly disinfected 
by burning flowers of sulphur. 

Care in Shipping. In Florida potatoes are shipped 
in double-headed barrels, as is done for apples. No 
matter in what receptacles potatoes are shipped, it 
is imperative to avoid rough handling and to pack 
securely. This will prevent shaking and bruising of 
the tubers while in transit. The cars should be 
cleaned and protected from leakage. During ex- 
treme cold weather, the cars should be generously 
supplied with a layer of straw at the bottom and at 
the sides. 

Control of Potato Diseases in the Field 

It is fortunate that most of the potato troubles in 
the field maybe kept in check. Truckers, therefore, 
are no longer justified in allowing their potato crops 
to be carried off by disease. 

Seed Selection. Most of the potato diseases are 



336 Diseases of Truck Crops 

carried over with the seed. The importance of clean, 
carefully selected seed cannot be too strongly em- 
phasized. Selecting seed from resistant and highest 
yielding hills is preferable to selecting from the bin. 
In cutting the tuber into pieces for planting, none 
should be used that show the least blemish or rot 
on the outside, or decay or discoloration within. 
By observing this precaution carefully, we shall 
prevent our seed from carrying scab, rosette, and 
many of the blights and wilts. Selected clean seed 
alone will not give the desired result if it is planted 
on infected soil. Less disease may be expected 
when clean seed is planted on lands rotated with 
alfalfa or grain, than when it is planted on virgin 
land. 

Seed Disinfection. The object of disinfecting seed 
is to destroy disease-producing organisms which may 
be adhering to the exterior of the seed coat. After 
the seed pieces are cut, they should be soaked for one 
and a half hours in a solution made up of four ounces 
of corrosive sublimate dissolved in thirty gallons of 
water. It is desirable to disinfect the seed immedi- 
ately before planting. Doing it a week to ten days 
before planting leaves the risk of the seed undergo- 
ing heat and having its germination injured. For 
disinfecting large quantities of seed, the dipping 
process is too tedious, and a preferable method is 
that of the formaldehyde gas. This method re- 
quires care, or else we are apt to injure the seed 
badly. In this case, it is essential to have 167 
bushels of potatoes for each one thousand cubic feet 



Family Solanacese 337 

of space in the disinfecting room. With less quan- 
tities of potatoes in this space, the formaldehyde 
gas will injure the germination and produce a pitting 
on the tuber. A tight room is used for this purpose, 
and the seed potatoes are placed in open crates, or in 
layers in slated bins, or in small piles on the floor. 
For each one thousand cubic feet of space, three 
pints of formaldehyde (40%) pure and twenty-three 
ounces of potassium permanganate should be used. 
The latter is placed in deep wooden or earthen dishes, 
and the formaldehyde is poured on the salt crystals, 
the disinfector rushing out locking the door at once. 
The fumigated house is kept closed for twenty-four 
hours. 

Spraying. The field diseases such as early and late 
bHght, tip burn, and, in fact, all other foliage diseases 
except leaf roll and curly dwarf may be controlled by 
spraying. Lime sulphur in any form has failed to 
give satisfactory results. The spray recommended 
is 5-5-50 Bordeaux mixture. To each one hundred 
gallons of Bordeaux, add one pound of Paris green 
or six pounds of lead arsenate paste. Spraying 
should begin when the plants are about six inches 
high, and from 3 to 6 applications should be given, 
depending on the climatic conditions. To yield the 
desired result, spraying must be applied in a thorough 
manner. It is a good form of insurance, as has been 
demonstrated by many workers. Table 16 by Lut- 
man^ clearly shows the profits to be derived from 
spraying. 

' Lutman, B. F., Vermont Agr. Expt. Sta. Bui. 159 : 216, 296, 191 1. 



338 Diseases of Truck Crops 

Table i6 

Gains from the Use oj Bordeaux Mixture on Late Potatoes. 20 Years' 
Experiments. 







Yield Per 






Variety 
and Date 


Sprayed 


A 


ere 


Gain 


Prevalence 






per 


of Late 


0/ Planting 






Not 
Sprayed 


Acre 


Blight 






Sprayed 






White Star 




bu. 


bu. 


bu. % 




May, 1 89 1 


Aug, 26, Sept. 8 


313 


248 


65 26 


some 


May, 1893 


Aug. I, 16, 29 


291 


99 


192 194 


much 


May 20, 1893 


Aug. I, i6, 29 


338 


114 


224 196 


much 


Apr. 26, 1894 


Tune 16, July 17, Aug. 30 
July 25, Aug. 13, 31 


323 


251 


72 29 


none 


May 20, 1895 
Polaris 


389 


219 


170 78 


rot 


May 15, 1896 


Aug. 7, 21 


325 


267 


68 26 


none 


June I, 1897 


July 27, Aug. 17, 28 


151 


80 


71 89 


some 


White Star 












May 10, 1898 


July 21, Aug. 10 


238 


112 


126 112 


little 


Average (3 varie- 












ties) 












May 18, 1899 


July 26, Aug. 17, Sept. 8 


229 


161 


68 42 


little 


Delaware 












May 23, 1900 


Aug. 4, 23 


285 


225 


5o 27 


rot 


May 25, 1901 


July 20, Aug. 21 


170 


54 


116 215 


much 


May 15, 1902 


Aug. I, 20 


298 


164 


134 82 


severe 


Green Mountain 












May I, 1903 


Aug. 10 


361 


237 


124 52 


severe 


Delaware 












May 25, 1904 


Aug. I, Sept. I 


327 


193 


134 69 


some 


May 15, 1905 


Aug. 2, 21 


382 


221 


161 73 


severe 


Green Mountain 












May 27, 1906 


Aug. 13, 22 


133 


lOI 


32 32 


some 


May I, 1907 


July 16, 25, Aug. 8, 22 


171 


63 


108 175 


little 


May 15, 1908 


June 26, July 9, Aug. 6, 26 


156 


65 


91 140 


none 


May 28, 1909 


July 12, 23, Aug. 6, 27 


243 


188 


55 29 


none 


May 9, 1910 


July 1 1, 27, Aug. 15,23,30 


240 


202 


38 18 


none 




Average for 20 years 


268 


163 


105 64 





Family Solanaceae 339 

DISEASES OF THE TOMATO (Lycopersicum 
esculentum) 

Like potatoes, tomatoes are subject to numerous 
diseases which the trucker cannot afford to ignore if 
he is to reap the greatest profits from his crop. 

Hollow Stem 
Cause Physiological. 

Hollow stem is a trouble manifested on seedlings in 
the bed, or after transplanting. The central portion 
of the head of the plant remains green while the lower 
leaves turn yellow. In severe cases, affected plants 
fall over as in damping ofl, with the absence, however, 
of signs of rotting. Such plants when examined are 
found to have hollow stems and seem too weak to 
stand up. 

Cause. There are several causes, all of which 
when combined may lead up to the hollow stem. 
I. A highly nitrogenous fertilizer applied to the 
seed bed to force the seedlings. 2. An abundance 
of water supply to make the fertilizer quickly avail- 
able. 3. Sowing seeds of a rapid growing variety. 
4. Transplanting without hardening off. 5. Trans- 
planting into a dry soil. 

Control. It is evident from what has been said 
that the fertilizer in the seed bed should be well bal- 
anced. Care should be taken to prevent the seedling 
from becoming leggy, and to see that they are pro- 
perly hardened before transplanting. The Stone and 
its related varieties seem to be more resistant to hollow 



340 Diseases of Truck Crops 

stem. On the other hand, the Dwarf Champion 
seems to be especially susceptible to hollow stem. 

Blossom End Rot 

Cause Unknown. 

Blossom end rot, also known as point end rot, may 
be found wherever tomatoes are grown. It is a dis- 
ease of the fruit only. In some seasons fifty per cent. 
or more of the fruit crop is ruined by it. It seems 
to be more serious in dry weather and on light soils. 

Symptoms. Infection is manifested as a water- 
soaked spot at the blossom end of the fruit (fig. 64 
b-c) . The size of the spot may be that of a pin-head, 
or it may spread so rapidly as to involve half of the 
tomato. A few days later, the water-soaked spot 
becomes black and leathery and ceases to make fur- 
ther progress. Complete rotting of the fruit may be 
brought about by secondary invasions. 

Plants subject to frequent slight wilting produce a 
greater number of defective fruits. There seems no 
doubt but that the water supply in the soil is an 
important factor in limiting or increasing blossom end 
rot. The factors of drainage and cultivation are 
therefore important considerations. Although dry 
soils and drought favor the increase of the disease, yet 
the condition of health of the plant itself seems more 
important than the decrease of water supply. 

The use of fertilizers, too, seems to influence the 
trouble. Heavy applications of manure or of potash 
seem to increase the rot, as do fertilizers in the form of 




Fig. 64. Tomato Diseases. 

a. Various stages of mosaic on foliage, b. c. blossom end rot, d. downy mildew, 
Phytophlhora infestans, e. conidia of buck-eye rot Phylophthora terrestris, f. conidia 
of P. terrestris. germinating Viy means of zoospores, g. zoospores, h. mature oospores 
cf P. terrestris, i. Ijuck-eye rot (p. to /. after §h-erbakoff). 



Family Solanaceas 34^ 

ammonium compounds. This is especially true on 
sandy loams. On the other hand, nitrate of soda or 
lime seems to check blossom end rot. 

Sunburn 

Tomato fruits are often bumed while they are on 
the vines by strong sunlight beating on the exposed 
fruit. This results in a scalding of certain parts (fig. 
67 e),loss of color, and a local drying which produces 
white spots with a dry peppery appearance. Such 
fruit is unfit for the market. Sunburn may also 
result from other and indirect causes. In dry sea- 
sons the tomato cannot supply the necessary supply 
of moisture to the foliage and fruit. As a result, they 
become weakened and contain numerous starved 
areas which dry up when exposed to strong sunHght. 
The same result may also be brought about by the in- 
direct action of the numerous leaf and root diseases. 

Control. In sections where sunburn is prevalent, 
it is advisable to plant tomato varieties with dense 
foliage. The plants should be put out as early as 
possible so that the vines may attain their maximum 
before hot weather sets in. The soil should be prop- 
erly fertilized, and sufficient humus incorporated to 
hold the moisture during periods of high temperatures. 
Irrigation should be practiced wherever possible. 

Mosaic 
Cause Unknown. 

A lengthy discussion on mosaic has already been 
given on p. 83. Mosaic on tomato is a common field 



342 Diseases of Truck Crops 

trouble, conspicuous on stalks, fruit, and leaves. On 
the leaves it is manifested as a mottling of yellow 
areas on the tissue between the veins. The unequal 
growth of tissue causes the leaves to warp and grow 
unevenly. In severe cases the normal leaflets are 
replaced by a filform or fern -like structure (fig. 64 a), 
with a striking dissected form. The blossom of the 
diseased plant usually drops off, and the few setting 
fruits are small and deformed. 

Southern Wilt 

Caused by Pseudomonas solanacearum Ew. Sm. 

Southern wilt has a wide distribution. As its 
name indicates, it is generally found in the more 
southern States. It is generally severe in Texas, 
Alabama, Georgia, Mississippi, North and South 
Carolina, Florida, Maryland, Virginia, New York, 
and Connecticut. 

Symptoms. Infected plants usually wilt rapidly 
without losing their green color. In large leaves, the 
main axis is bent downward in a drooping way. 
With the young plants the stems and foliage also 
droop and shrivel. The vascular system of such 
plants is browned, indicating the presence of the 
causative organism within. In cutting across a 
freshly wilted stem, a dirty white to brownish white 
slime that is not sticky is seen to ooze out. In soft 
and rapidly growing plants, the whole pith is often 
converted into a watery slime. In tomato and egg- 
plants the disease seldom attacks the fruit but is 



Family Solanacese 343 

localized to the vegetative parts. With the Irish 
potato, the disease works underground where it also 
penetrates the tubers. These show a yellowing and 
blackening of the veins, finally giving way to a soft 
rot. On squeezing, a creamy exudate oozes out from 
the diseased veins. 

Southern wilt attacks not only the tomato, potato, 
and eggplant, but it also causes a serious disease on 
the tobacco, peanut, nasturtium, ragweed, im- 
patience, verbena, — plants which belong to families 
other than the Solanacese. 

The Organism. Pseudomonas solanacearum is a 
mediimi-sized rod, with rounded ends and motile 
by means of polar flagella. Pseudo-zoogloeae are 
common in old cultures. No spores are formed; 
on agaragar, colonies are white, then dirty white, 
afterv^^ards becoming brown w^th age. The or- 
ganism does not liquefy gelatin and produces no 
gas. 

Control. Crop rotation is the safest method of con- 
trol. All crops subject to wilt, such as potato and 
eggplant should be left out from the rotation 
system. 

Damping off, see Pythium, p. 43. 

Late Blight 

Caused by Phytophthora injestans (Mont.) De By. 

Late blight usually attacks the fall tomato crop. 
It is especially prevalent during rainy weather, where 
it may even be found in the seed bed. The trouble 



344 Diseases of Truck Crops 

may be found wherever Irish potatoes are known to 
stiff er from late blight, since the tomato and potato 
blight are caused by the same fungus. 

Symptoms. Affected plants appear as though 
killed by frost. The disease first shows itself as small 
blackened areas on the leaves (fig. 64 d), stems, and 
fruits. These rapidly increase in size and cause pre- 
mature death of the affected host. Fruits which may 
not show signs of disease will develop the trouble in 
transit if coming from infected fields. For a de- 
scription of the causative fungus, see late blight of 
potato, p. 322. Late blight of tomatoes may be con- 
trolled by spraying. The best results are obtained 
by using 5-5-50 Bordeaux. Spraying should begin 
with the rainy season. The ripe fruit should be 
cleaned by wiping off the Bordeaux stains with a 
dry cloth. 

Buckeye Rot 

Caused by Phytophthora terrestria Sherb. 

"Buckeye rot is a disease which attacks the fruit. 
The trouble seems to be new and has been recently 
described by Sherbakoff.^ So far as is known the 
disease has appeared only in Florida. 

Symptoms. The disease, as the name indicates, 
appears as a pale to dark greenish -brown zonate spots 
on the fruit (fig. 64 i) . The rot is hard and somewhat 
dry when the fruit is green, but becomes softer as the 

' Sherbakoflf, C. D., Phytopath. 7 : 1 19-129, 1917. 



Family Solanaceae 345 

tomato ripens. It usually begins at a point where the 
fruit touches the ground, which is most commonly 
at the blossom end, and might be mistaken for 
blossom end rot were it not for the characteristic 
zonations. 

The Organisms. The mycelium is at first continu- 
ous, then septate. Conidia (fig. 64 e-g) germinate by 
means of swarm spores. Chlamydospores are com- 
mon, oospores (fig. 64 h) common on commeal agar. 
Besides tomato fruit, P. terrestria causes a foot rot of 
citrus trees and a stem rot of lupines. 

Control. Tomato plants, as far as possible, should 
be staked. By preventing the fruit from coming 
into direct contact with the soil, infection will be 
avoided. Fruit destined for distant markets should 
not be packed as soon as it is brought in from the 
field. If possible it should be kept a few days to 
allow for possible rot to develop so that the affected 
ones may be culled out and destroyed. 

Yeast Rot 

Caused by Nematospora lycopersici Sch. 

Yeast rot, as the name indicates, is induced by a 
parasitic yeast. This little known trouble has been 
investigated by Schneider. ' 

Symptoms. The disease is indicated by a slightly 
depressed reddish-brown spot. The epidermal area 
of the affected spot becomes indurated and shriveled. 

' Schneider, A., Phytopath. 6 : 395-399, 1916; and in Phytopath. 
7 : 52-53. 1917. 



34^ Diseases of Truck Crops 

The greatest amount of rotting occurs within the 
fruit. 

The Organism. The parasite is a typical yeast. 
It produces arthrospores of non-gametic origin, asci 
of gametic origin (fig. 65 a-c). The ascospores are 
formed in two groups of four each, slender, one- 
septate, and each containing a motionless flagellum. 
Little is known about the control of this disease. 

Fruit Rot 

Caused by Phoma destructiva Plowr. 

Fruit rot is found in Cuba, Florida, South Carolina, 
Kansas, and New York. If not checked, it will no 
doubt spread rapidly and add to the burdens of losses 
from other troubles. 

Symptoms. On the fruit the disease is charac- 
terized by conspicuous dark spots (fig. 65 e) on the 
side and at the stem end of both green and mature 
fruit. On the surface of the largest spots numerous 
dark pycnidia may be seen. Besides attacking the 
fruit, the disease may also attack the foliage, causing 
dark spots which resemble those on the fruit (fig. 
65 d). Affected leaves shrivel, droop, and sometimes 
drop off. The disease seems to be unable to attack 
potatoes or peppers. 

The Organism. The mycelium (fig. 65 h) forms a 
dense network of fungal threads within the host 
tissue. The pycnidia (fig. 65 g) are subglobose, car- 
bonaceous, smooth, slightly papillate, and with a dis- 
tinct central pore. The pycnidia are scattered and 








Fig. 65. Tomato Diseases. 

a. Various forms of vegetative cells of the yeast rot fungus, 6. ascus, .-. ascosporet 
of the yeast rot fungus (a. to c. after Schneider), d. Phoma rot on foliage, c. Phoma 
rot on fruit,/, pycnidium of the Phoma rot organism, g. cross-section of a pycnidium 
of the Phoma fungus, h. mycelium, «. pycnospores of same {d. to i. after Jamieson). 




Fig. 66. TOxMato Diseases. 

a. Septoria leaf spot, b. section through a pycnidium of Septoria lycopersici 
(after Levin), c. section through acervulus of Colletolrichum phomoides (after Venus 
Pool), d. anil e. Melanconium rot, /. section through an acervulus of the Melan- 
conium fungus {d. to f. after Tisdale). 



Family Solanaceae 347 

possess a thin wall; the pycnospores (fig. 65 i) are 
hyalin and one-celled. Jamieson' failed to find an 
ascus or winter stage. Should the disease become 
serious, spraying with Bordeaux is recommended. 

Leaf Spot 

Caused by Septoria ly coper sici Speg. 

The disease is generally known as late bHght, or 
blight, both of which names are misleading. Recent 
investigations by Levin'' confirm the belief that leaf 
spot is widely distributed. It is found in Alabama, 
California, Connecticut, Delaware, Illinois, Louisiana, 
Massachusetts, Maryland, Michigan, Missouri, New 
Jersey, New York, North Carolina, Ohio, Penn- 
sylvania, Virginia, Tennessee, Texas, and Wisconsin. 

Symptoms. The first indications of the disease 
are minute water-soaked spots on the underside of the 
leaves. With time these increase in size and become 
circular in outline with a definite margin (fig. 66 a) . 
The spots become hard, dry, dark, and shrunken, and 
when numerous they coalesce into large blotches, in- 
volving the entire leaflets and leaves ; the latter soon 
droop, dry, and cling to the stalk, until broken off by 
the wind or by any other jar. Within the spots are 
formed minute black glistening pycnidia and the 
spores exude as yellowish mucilaginous drops. 

On the stems the spots are similar to those on the 
leaves, although they are not so clearly defined, nor 

" Jamieson, C. O., U. S. Dept. Agr. Research, 4 : 1-20, 1915. 

^ Levin, E., Michigan Agr. Expt. Sta. Tech. Bui. 25 : 7-51, 1916. 



348 Diseases of Truck Crops 

do they work in deep to form cankers. Spots may 
also occur on the calyx and on the fruit. The dis- 
ease, however, is usually a foliage trouble. Of the 
more resistant varieties maybe mentioned Mikado, 
King Humbert, Wonder of the Market, and Up to 
Date. Of the medium resistant varieties may be 
mentioned Alice Roosevelt, President Garfield, Pre- 
lude, Ponderosa, and Magnum Bonum. The Trophy 
and Ficarazzi are very susceptible varieties. 

The Organism. The mycelium of Septoria ly co- 
per sici is hyalin, septate. The pycnidia are globose 
(fig. 66 b) ; the pycnospores are hyalin, needle-shaped, 
many-septate, and lose their vitality when exposed to 
ordinary room temperature for about four days. 

Control. The disease often starts on the seedlings 
in the seed bed. It is important therefore to start 
with a clean seed bed soil. Seedlings should be 
sprayed with 4-4-50 Bordeaux before being trans- 
planted. In the field the plant should not be worked 
in wet weather, or when covered with dew. Spraying 
with 4-4-50 Bordeaux is recommended, especially in 
wet weather. Since the causative fungus is carried 
over in pycnidia on dead leaves or stems, the burn- 
ing of all trash becomes necessary. 

Anthracnose 

Caused by Colletotrichum phomoides (Sacc.) Chester. 

Anthracnose is a disease to which ripe tomatoes 
are especially subject. The losses are often consid- 
erable both in the field and in transit. 



Family Solanaceae 349 

Symptoms. The spots are at first small, but they 
soon enlarge. They are discolored, sunken, wrinkled, 
with distinct central zones, closely resembling the 
anthracnose of apple. In moist weather the spots 
become coated with a salmon-colored layer which 
consists of the spores of the fungus. 

The Organism. In structure C. phomoides is little 
different from other Colletotrichums. The setas of 
the fungus are very numerous, thus giving the acer- 
viili a black appearance. The conidiophores are 
short, and the conidia, oblong, hyalin, and one-celled 
(fig. 66 c). 

Control. Anthracnose depends upon wet weather 
for its activity. Spraying with Bordeaux is recom- 
mended. 

Melanconium Rot 

Caused by Melanconium Tisdale Taub. 

Melanconium rot is a disease which attacks tomato 
fruit. Tisdale^ was the first to call attention to this 
trouble which he attributed to a species of Melan- 
conium- The writer has often had occasion to col- 
lect this disease on tomatoes in the Bryan (Texas) 
market. The origin of the fruits could not be exactly 
ascertained, but they were supposed to come from 
Florida, while others were home-grown. 

Infection experiments by the author affirm the 
parasitic nature of the organism, which is tempor- 
arily named Melanconium Tisdale Taubenhaus. 

' Tisdale, W. H., Phytopath. 6 : 390-394, 1916. 



350 Diseases of Truck Crops 

Symptoms. The disease is found both on partly 
green and on ripe fruit. The spots are brown to 
black, small, irregular, somewhat sunken, dry, and 
superficial, with the centers slightly raised (fig. 66 
d-e). 

The Organism. The mycelium is white, much 
branched, and closely septate, the septation however 
being largely influenced by food supply. The co- 
nidiophores are straight, short, closely packed to- 
gether, arising from a basal pseudostroma (fig. 66 f). 
The conidia are borne singly at the apex of each co- 
nidiophore. The conidia are Phoma-like, minute, 
cylindrical, slightly rounded at both ends, greenish 
white in color, and germinate by means of a single 
germ tube produced at either end. 

Control. Nothing seems to be known of the control 
of this trouble. Little is known of its distribution. 
But since it has been found in Wisconsin by Tisdale, 
and in Texas by the writer, it seems to be of wider 
distribution than is generally recognized. Possibly 
it is usually mistaken for other tomato troubles. 

Leaf Mold 
Caused by Cladosporium fulvum Cke. 

Leaf mold is a tomato trouble which is very 
troublesome under greenhouse conditions. In some 
of the Southern States, however, it is found on field 
tomatoes. The disease is favored by damp, muggy 
weather. 

Symptoms. The mold appears as rusty cinnamon, 




Fig. 67, Tomato Diseases. 

a. Cladosporium leaf mold, 6. conidiophores of Cladosporium fulvum. c. conidia of 
C. juhmm, (6. and c. after Southworth), d. two plants artificially infected with 
iicUrolium Rolfsii, e. sunburn, /. Macrosporium rot. 



Family Solanaccae 351 

irregiilar, feltlike spots on the underside of the leaf 
(fig. 67 a), the upper part of which turns brown, then 
black, and the affected foliage finally curls and dies. 
Control. Careful spraying with Bordeaux mixture 
will help to keep it in check. 

Black Rot 

Caused by Macrosporium solani E. and M. 

Black rot is a fruit trouble commonly found in dry 
weather and generally attacking ripe tomatoes. 
The spots are black, dry, slightly wrinkled, and ex- 
tending deep into the interior tissue (fig. 67 f). 

The mycelium of the fungus is at first hyalin to 
brown, then black. The conidiophores and conidia 
are dark, with three to six transverse and one to two 
longitudinal septa. 

Sleeping Sickness 

Caused by Fusarium lycopersici Sacc. 

Sleeping sickness is one of the most serious of 
tomato troubles. It is prevalent in New Jersey, 
Delaware, Maryland, Virginia, and in nearly every 
Southern State. 

Symptoms. Infected plants become pale, the 
leaves wilt and droop and never recover (fig. 68). 
The droopiness of a diseased plant gives it a sleepy 
appearance, hence the name of the disease. On 
splitting open a diseased root or stem, the interior 
vascular bundles will be found to be brown. 



352 Diseases of Truck Crops 

The Organism. F. ly coper sici is a soil fungus 
which may be introduced with infected manure or 
seedlings. The fungus greatly resembles F. oxy- 
sporum. The conidia are hyalin to yellowish, fal- 
cate, acute. 

Control. Spraying will not control this malady 
since the parasite lives internally and cannot be 
reached by external applications. Long rotations 
in which the land is given a rest from tomatoes are 
recommended for at least ten years. The selection 
of resistant varieties may offer a means of conquering 
this trouble. 

Yellow Blight 

Caused by Fusarium orthoceras App. and WolL; 
Fusarium oxysporum Schl. 

This disease is common on tomatoes in the Pacific 
Northwest. It has been investigated b}^ Humphrey^ 
and found by him to be caused by the two species of 
Fusaria above mentioned. 

Symptoms. It does not usually manifest itself 
until late, when the plants are blooming, or even 
when the fruits are partly formed. At first there is 
a slight twisting of the entire leaf, accompanied by a 
purpling of the veins. This is also followed by a 
rolling inward, and by drooping, but not wilting, of 
the leaflets and leaves. The foliage then take on 
glaucous greenish color, the fruit ripen prematurely, 

' Humphrey, H. B., Washington Agr. Expt. Sta. Bui. 115 : 1-22, 
19 1 4. 






Fig. 68. Sleeping .Sickness of Tomato. 



Family Solanacese 353 

but the pulp lacks in flavor and taste. Affected 
plants cease growing, exhibit a thin, spindly growth, 
and cease producing. The disease is confined to the 
root system, which is slowly destroyed; it becomes 
most virulent with the high temperatures. Both 
Fusarium orthoceras and F. oxysporum also induce 
a disease on the potato, see p. 327. 

Control. Both Fusaria produce an abundance of 
chlamydospores in the soil, thus making the eradica- 
tion of the disease very difficult. Long rotations 
seem to have no effect in controlling the trouble. 
Injuring the rootlets at transplanting seems to in- 
crease the amount of diseased plants. Definite 
methods of control are as yet lacking. 

Rhizoctonia Fruit Rot 

Caused by Corticium vagum B. and C. var. sdani 
Burt. 

This form of rot makes its appearance at the place 
where the fruit touches the ground. The diseased 
area becomes chocolate-colored, and the epidermis 
slightly wrinkled. The rot extends into the interior 
pulp turning it brown and dry. For further descrip- 
tion of the causative fungus, see p. 45. 

Southern Blight (fig. 67 d), see Pepper, p. 305. 

Root Knot, see Nematode, p. 49. 



CHAPTER XXII 

FAMILY UMBELLIFEILE 

This family contains trucking crops which are of 
considerable economic importance. Of these may 
be mentioned the carrot, celery, parsley, and parsnip. 
According to the Thirteenth census of the United 
States, the area devoted to carrots in the United 
States in 1909 was 3764 acres, and the total crop was 
valued at $473,499, with New York leading in acreage. 
The area devoted to celery in 1909 was 15,863 acres, 
and the total crop estimated at $3,922,848. Of the 
leading celery States may be mentioned New York, 
California, Michigan, Ohio, Massachusetts, and 
Pennsylvania. The area in parsley in 1909 was 192 
acres, and the crop estimated at $27, 1 8 1 . This crop is 
largely grown in Louisiana. The area in parsnip in 
1909 was 722 acres, and the crop estimated at $102,- 
674. Parsnip is grown mainly in New York, Massa- 
chusetts, Illinois, and Michigan. 

DISEASES 01^ THE CARROT {Daucus carota) 

Soft Rot, see Cabbage, p. 192. 
Root Rot, see Rhizoctonia, p. 45. 
354 



Family Umbelliferae 355 

DISEASES OF THE CELERY (Apium graveolens) 
Soft Rot, see Cabbage, p. 192. 
Rust 

Caused by Puccinia hullata (Pers.) Schr. 

This rust resembles the rust of asparagus. The 
disease is unimportant, and is seldom met with in 
the United States. 

Leaf Spot 
« 

Caused by Pliyllosticta apii Hals. 

Leaf spot is a disease of minor importance. The 
trouble is characterized by dull brown patches on any 
part of the leaf. Spraying for late blight will also 
control leaf spot. 

Late Blight 

Caused by Septoria petroselini Desm. var. apii 
Br. and Cav. 

Late blight is perhaps one of the worst diseases of 
celery. It may be found wherever celery is grown. 
In California, the greatest money losses to this crop 
are attributed to late blight. 

Symptoms. The disease first attacks the lower 



356 Diseases of Truck Crops 

leaves of the stalk, producing irregtdar spots without 
a definite boundary line. When the spots become 
numerous the foliage withers and dries up (fig. 69 a, 
b, c, d). The disease attacks the leaves as well as 
the stalks, rendering the affected plants useless so far 
as market is concerned. In storage, plants affected 
with late blight will keep very poorly or rot alto- 
gether. 

The Organism. The fungus mycelium is hyalin, 
septate. The pycnidia (fig. 69 e) are olivaceous, 
prominent, and abundant in the spots. The pycnidia 
are filifom, straight or curved, hyalin, and many 
septate. 

Control. According to Rogers,^ late blight may 
be controlled by spraying with 5-6-50 Bordeaux. 

The first two applications should be given the 
seedlings in the seed bed. In the field the first 
spraying should be given about six weeks after trans- 
planting and continued once a month until the rain}'' 
season is over. With the advent of heavy rains, 
spraying should be done once every two weeks. 
Besides spraying, shading also seems to keep the 
disease in check. In spraying celery great care 
should be exercised to use a sprayer which is operated 
by a pressure of not less than 1 50 pounds. Where this 
is overlooked, large drops of the Bordeaux mixture 
may be deposited on the leaves and stalks, which upon 
drying may deposit copper salt sufficient to harm 
the consumer. Sprayed celery should be carefully 
washed and dried before shipping. 

' Rogers, S. S., California Agr. Expt. Stat. Bui. 208 : 83-115, 191 1. 




A" 



-^r, 
^^~-~ 





Fig. 69. Celery Diseases. 

a. Septoria leaf spot on leaf, b. Septoria leaf spot on leaflet, c. Septoria lesions on 
celery seed, d. Septoria spots showing pycnidial bodies, e. cross section showing 
pyncidium and pycnospores of Septoria pelroselini (a, c, and e after Coons and 
Levin). 






Fig. 70. Celery Diseases. 

a. Cercospora leaf spot, h. conidiophores and conidia of Cercospo 
(afterDuggar and Baily), c. Rhizoctonia root rot. 



Family Umbelliferae 357 

Early Blight 
Caused by Cercospora apii Fr. 

Early blif-ht is as common a disease as the late 
blight. In some seasons of heavy rains it is very 
destructive. It appears early and affected plants 
have little value for market purposes. 

Symptoms. The trouble first appears on the outer 
leaves as pale blotches visible on both sides of the 
affected parts. The spots are irregular, angular in 
outline, limited apparently by the leaf veins, with 
slightly raised borders (fig, 70 a-b). The spots later 
turn brown to ashy white. 

Control. Early blight may be controlled by spray- 
ing with Bordeaux mixture as with late blight. The 
Boston Market and Gold Heart should be avoided 
because of their susceptibility to the disease. The 
White Plume seems to be resistant. 

DISEASES OF PARSLEY {Carum petroseUnum) 

Drop, see Lettuce, p. 143. 

Late Blight, see Celery, p. 355. 

DISEASES OF THE PARSNIP {Pastinaca sativa) 

Early Blight, see Celery, p. 357. 

Root Rot (fig. 70 c), see Rhizoctonia, p. 45. 

Weeds 

Of the more important Umbelliferous weeds which 
truckers have to contend with may be mentioned 



35^ Diseases of Truck Crops 

Wild Carrot {Daucus carsta) , wild parsnip {Pastinaca 
sativa), and poison hemlock {Cornium maculatum). 
All of these weeds should be eradicated by clean ciil- 
ture. The first two especially help to carry the 
fungus of early blight, Cercospora apii. 



PART IV 



359 



CHAPTER XXIII 

METHODS OF CONTROL 

From the preceding chapters the trucker will be 
made well aware of the many crop diseases he has to 
deal with and of the numerous methods at hand to 
help him to control or keep in check most of the 
troubles. The methods of control may be classified 
as follows: 

(i) Soil sterilization. This method has been dis- 
cussed under Chapter IV, page 53. 

(2) Seed treatment taken up in Chapter VII. 

(3) Spraying. ^ 

(4) Crop rotation. 

(5) Development of resistant varieties. 

Spraying 

While the orchardist has learned the necessity of 
spraying, it is doubtful whether truckers have suf- 
ficiently realized its value. Spraying has two aims: 
to kill the insect and animal pests, and to con- 
trol fungous diseases. The substances which are 
used for the one purpose are without effect on the 
other. 

361 



362 Diseases of Truck Crops 

Insecticides 

All animal and insect pests are best controlled by 
the use of poisonous mixtures applied in the form of 
liquid sprays or of powders. Insecticides may be 
classified as internal or stomach poisons, and external 
or contact poisons. 

(a) Stomach Poisons. Paris green is one of the 
oldest of stomach poisons. When chemically pure, 
it is composed of copper oxide, acetic acid, and arseni- 
ous acid. It destroys cutworms, caterpillars, beetles, 
grubs, slugs, etc. It should be applied preferably as 
a liquid, using one pound of the poison and two 
pounds of lime to two hundred gallons of water. It 
tends to sink to the bottom of this mixture, unless 
constantly stirred while being applied. This chemi- 
cal is often adulterated with white arsenic, causing 
it to scorch the treated plants badly. Therefore 
for truck crops the use of arsenate of lead is to be 
preferred, since it is less liable to scorch the foliage, 
and it adheres better. Its chemical composition 
consists of acetate of lead and arsenate of soda. It 
is applied to the best advantage as a liquid, using 
about three pounds of powdered arsenate or five 
pounds of paste arsenate to one hundred gallons of 
water. 

Arsenite of zinc may also be used. It is a very 
finely divided fluffy white powder which distributes 
and adheres well to the foliage. It is intermediate 
between Paris green and lead arsenate in strength, 
and it costs less than either. 



Methods of Control 363 

It is essential when arsenicals are used to see that 
they are correctly labeled, and kept under lock and key, 
as they are poisonous to man and animals. 

Hellebore or white hellebore Is somewhat less 
dangerous than the arsenicals. However, it loses 
its insecticidal value by being exposed to the air. 
It is a specific against slugs. 

(b) Contact Poisons. All the tobacco or nicotine 
products sold principally as extracts or powders be- 
long to this class. A common brand much used is 
the preparation known as "Black leaf 40," diluted 
I part to 700 or 800 of water. An addition of 
ivory soap at the rate of two bars to each 100 
gallons of the solution increases its effectiveness 
by making it spread out better. Aphine, sulpho 
tobacco, and a number of other products found on 
the market are usually valuable as contact poisons 
if properl}^ tested out and guaranteed by the deal- 
ers. Ordinary laundry soap, one pound to seven 
gallons of water, is very effective against all soft- 
bodied sucking insects. 

Fungicides 

These are poisons used to control fungous diseases. 
As previously stated, some parasitic fungi live on the 
surface of the leaves and stems and are therefore 
easily controlled. An example of this Is the powdery 
mildew. Other fungi, and these are in the larger 
majority, are those which live parasltically within 
the tissue of the host, and therefore cannot be reached 



364 Diseases of Truck Crops 

by any spray. Fungicides are helpful only in pre- 
venting entrance of the parasite in the host. They 
are as ineffective in controlling insect pests, as are 
insecticides in controlling fungous diseases. 

(a) Bordeaux Mixtures. This is the standard 
fungicide. The strength used for tender plants is 
three pounds of copper sulphate — also known as blue 
stone, — six pounds of lime, and fifty gallons of water. 
The easiest way to prepare it is to dissolve the blue 
stone thoroughly in twenty-five gallons of water. 
The best quality of unslaked lime should be used 
and slaked in a little hot water, care being taken, 
however, not to flood it while slaking, nor to let it 
become too dry. When the slaking is completed, 
enough water is added to make twenty-five gallons. 
The limewater and the blue stone solution are 
then mixed, pouring first one part of lime water, then 
another part of the blue stone; the mixture is then 
strained and used at once. With crops with delicate 
foliage, such as watermelon, weak Bordeaux must be 
used to prevent burning of foliage (see page 243) . 

For truck crops with less delicate foliage, the stand- 
ard Bordeaux mixture is 4-4-50 — that is, four pounds 
copper sulphate, four pounds unslaked lime, and 
fifty gallons of water. 

Stock Solutions. In spraying large areas, it is not 
always practical to weigh out and prepare the in- 
gredients at short notice. The trucker will therefore 
find it ad'/antageous to prepare stock solutions so 
that large quantities of both dissolved copper sul- 



Methods of Control 365 

phate and of lime may be ready for instant use. A 
stock solution of blue stone may be prepared as 
follows: Forty gallons of water are put into a 
fifty-gallon barrel; forty pounds of blue stone are 
placed in a basket and hung up so that the basket is 
half covered by the water in the barrel. As the blue 
stone is dissolved, each gallon of the water contains 
one pound of the chemical. In another barrel may 
be slaked forty pounds of fresh lime. Each gallon of 
that will contain one pound of lime. By keeping the 
slaked lime in the barrel covered with water and pre- 
venting it from evaporating, and also keeping the 
barrel v/itli the blue stone solution covered to prevent 
evaporation, we shall have stock solutions ready for 
instant use. To make a 4-4-50 Bordeaux from stock 
solutions, for instance, it is necessary to take four 
gallons from the stock solution barrel with blue 
stone, and add this to twenty-one gallons of water. 
Four gallons are also taken from the stock solution 
barrel of slaked lime and added to twenty-one gal- 
lons of water. The two solutions of twenty-five 
gallons each are now added together, thus making a 
4-4-50 Bordeaux. In this way it is easy to prepare 
any formula from the stock solutions. To determine 
if the Bordeaux contains sufficient lime, the following 
test may be carried out. A few drops of potassium 
ferrocyanide are added to the Bordeaux mixture. 
If sufficient lime is present, no change will take place, 
but if the mixture is deficient in lime, a dark reddish 
brown color will appear where the drop strikes the 
liquid. This testing fluid is easily prepared by dis- 



366 Diseases of Truck Crops 

solving one ounce of potassium ferrocyanide in about 
eight ounces of water. This chemical costs but a few 
cents in any drug store and will last a long time if 
kept in a tightly sealed bottle. 

Points to be Remembered 

In preparing Bordeaux the following points should 
be kept in mind : 

(i) Copper sulphate solutions must be kept only in 
vessels of wood, fiber, brass, bronze, or copper. They 
must not be kept in iron or tin vessels, as they will 
corrode them. 

(2) It is necessary to use fresh stone lime, as air- 
slaked lime is useless. 

(3) Bordeaux mixture can be used only when 
freshly mixed. If allowed to stand twelve hours after 
making, it loses all fungicidal value. 

(4) Bordeaux mixture or lime should never be 
strained through burlap. The lint of the burlap is 
likely to work up into the nozzles and clog them. 

(5) Undiluted solutions of copper sulphate or lime 
should never be mixed together. 

(6) Bordeaux mixture should not be prepared with 
hot water. 

{h) Ammoniacal Copper Carbonate. The objection 
to the use of Bordeaux is that it stains the leaves 
and foliage. 

To avoid staining, colorless ammoniacal copper 
carbonate may take the place of Bordeaux. It is 
prepared as follows ; 



Methods of Control 367 

Copper carbonate 5 ounces 

Ammonia (26 Baume) 3 pints 

Water 50 gallons 

The best results are obtained when the copper car- 
bonate is first made into a paste with a little water. 
It is then dissolved by adding the ammonia, which is 
diluted with four quarts of water. If three pints 
of ammonia fail to dissolve all the copper carbonate, 
more may be used. Ammoniacal copper carbonate 
is only effective when used fresh. It loses its fungi- 
cidal value by standing, as the annnonia evaporates 
quickly. 

(c) Sulphur. Flowers of sulphur are often used to 
control powdery mildew or asparagus rust. It may 
be applied either by hand or with a duster. There 
are a number of other fungicides on the market which 
are not mentioned here. They should be thoroughly 
tested before they are used. Considerable discretion 
should be exercised before using a new fungicide 
which claims to be a " Cure all. " 

Combination Sprays 

In the foregoing chapters on diseases, it was seen 
that truck crops are subject to the attacks of more 
than one malady. Moreover, truck crops are also 
subject to the attacks of insect pests. It is therefore 
advisable to control both insect pests and fungous 
diseases at the same time. Spraying, if properly 



Tobacco 


Bordeaux 


extracts 


mixture 


yes 


yes 


yes 


yes 


yes 


no 


yes 


yes 



368 Diseases of Truck Crops 

done, is effective in controlling or in keeping in check 
all the pests which attack truck crops. In combining 
a fungicide with an insecticide, we may accomplish 
two aims in one operation. The various spray mix- 
tures which may or may not be combined are in- 
dicated by Cooley and Swingle' as follows: 



Paris green 
Arsenate of lead 
Arsenite of zinc (ortho) 
Arsenite of lime 

Each of these preparations is mixed and applied just 
as if it were used alone. A combination of the am- 
moniacal copper carbonate with an arsenate would be 
unsafe, since the ammonia renders the arsenic more 
soluble, and hence may result in the burning of the 
foliage. However, it may be safely mixed with the 
tobacco products. 

Recent investigations by Professor Safro, Entomo- 
logist to the Kentucky Tobacco Products Co., indi- 
cate that ' ' Black leaf 40 " may be used in combination 
with such spray chemicals as lime-sulphur, arsenate 
of lead, arsenite of zinc, and iron sulphate, for con- 
trolHng sucking and chewing insects and fungous dis- 
eases, the soap in this case being omitted. Professor 
Safro's work further claims that "Black leaf 40" may 

' Cooley, B. A , and Swingle, D. B., Montana Agr. Expt. Sta. Circ, 
17: 119-151, 1912. 



Methods of Control 369 

be safely combined with Bordeaux, and the desired 
results obtained. He writes as follows: "For pur- 
poses of spraying, add to every one hundred gallons of 
Bordeaux three fourths of a pint of 'Black leaf 40.' 
As far as safety to the foliage is concerned, much 
greater strengths of nicotine may be added to the 
Bordeaux, but no additional effectiveness will be 
given to the mixture as an insecticide. Any nicotine 
solution which contains four hundredths of one per 
cent, nicotine will be effective in controlling plant lice, 
provided, however, the work is thoroughly done. " 

Proportions of Combined Sprays 

Bordeaux and Paris Green 

Paris Green y^ pound 

Bordeaux mixture 50 gallons 

Bordeaux and Ar senile of Soda 

Arsenite of Soda i quart 

Bordeaux mixture 50 gallons 

Bordeaux mixture must never be combined with 
kerosene emulsion, carbolic acid emulsion, and mis- 
cible oils. 

(d) Potassium Sulphide. Like sulphur this is a 
valuable fungicide for the control of the powdery 
mildew. The following strength is recommended: 

Potassium Sulphide 4 oz. 

Water 10 gallons 

24 



370 Diseases of Truck Crops 

Potassium sulphide is effective only if used imme- 
diately it is prepared. It loses its value by being 
exposed for any length of time. 

Stickers 

It is well known that with some plants, such as 
cabbage, spray mixtures cannot be made to stick. 
The use of a sticker added to the spray mixture will 
largely overcome this difficulty. A sticker may be 
prepared as follows : 

Resin 2 pounds 

Sal Soda (crystals). . . i pound 
Water i gallon 

The resin and the sal soda should be added to one 
gallon of water and boiled in an iron kettle for one 
and a half hours until clear. For plants which are 
hard to wet, such as cabbage, or onions, the amount 
of the sticker given above should be used for each 
fifty gallons of Bordeaux or ammoniacal copper car- 
bonate. For other plants, this amount is added to 
each one hundred gallons of the spray mixture. 

Principles Involved in Spraying 

It should be remembered that to destroy chewing 
insects, such as caterpillars, etc., the stomach poison 
must be evenly distributed all over the plant. This 
thorough spraying should be done as soon as the 
presence of the pest is suspected. Intelligent and 
observant growers will remember the time of ap- 



Methods of Control 371 

pearance of the pest every year, although this date 
depends somewhat on the climate of each season. 
In destroying the green aphids, the contact poison 
should be distributed as evenly as possible on the 
insect itself. It is, therefore, best to spray for aphids 
when they are actually found working on the plants. 
To check chewing insects and fungous pests, however, 
the applications are made before the parasites appear. 
Before spraying it is necessary to have well in mind 
which organism is to be destroyed, and the proper 
ingredients to be used. To keep fungous pests in 
check it is necessar}'- to have the plant covered with 
the fungicide all the time infection is feared or sus- 
pected. This spraying is preventive, protecting the 
plant from becoming infected. When the parasite 
has penetrated the host, spraying is of little value in 
saving the infected plant, although it will protect 
others which are as yet healthy. It is essential that 
the trucker be always ready to spray. Sometimes 
retardation for even a day may prevent the attain- 
ment of positive results. The timely destruction of 
one insect, or of one spore, means the destruction of 
countless generations of these pests. 

Thoroughness is as important in spraying as it is in 
everything else in life. Especially is this true for the 
control of fungous diseases. 

Spraying Machines 

Success in spraying often depends on the sprayer, 
and especially on the nozzle. In small scale garden- 



372 Diseases of Truck Crops 

ing, an ordinary knapsack or barrel sprayer (fig. 71a) 
will answer the purpose. For trucking on large 
areas the use of power sprayers (fig. 71 b) becomes 
necessary. It is difficult to recommend the use of 
any one type when there are so many models on the 
market. After consulting various catalogues and 
examining types of spray machines at the county 
fairs and other exhibits, the grower will be in a posi- 
tion to determine the kind of apparatus best adapted 
for his conditions. A good power sprayer should be 
capable of maintaining a pressure of at least one 
hundred pounds while the nozzles are open. The 
sprayer should also have a convenient attachment for 
spraying four rows or more, and should also possess 
a device by which each row can be sprayed with 
either single or double nozzles. Moreover, all the 
working parts must be easily accessible, simple, and 
solidly built. 

Care of the Spraying Machine 

After each spraying the outfit should be emptied 
and carefully cleansed with water. Failure to do 
this will result in the corroding of the tank, rods, and 
nozzles. 

Crop Rotation 

Many of the soil diseases, such as root knot, Fusar- 
itim wilts, etc., may be economically controlled by 
crop rotation. If a certain disease gains a foothold 
in the soil, it is likely to become progressively serious, 





Fig. 71. Spray Machinery. 

a. A hand power pump, b. a power machine, rear view, showing 
arrangement for spraying three rows of cucumbers (after W. A. Orton). 



Methods of Control 373 

as the particular crop which the disease attacks is 
grown for a number of years on the same field, the 
soil becoming thoroughly permeated by the mycelium 
and spores of the parasitic organism. If the infected 
land is planted with crops not subject to the disease, 
the parasitic organism will sooner or later die for 
want of a suitable host to live upon. For this reason 
crop rotation plays an important part in the control 
of numerous truck crops. To meet with success 
in rotation, the trucker must know what crops are 
subject to the disease to be controlled, so as to avoid 
them temporarily in the sick land. Weeds, too, are 
often subject to the same diseases as the cultivated 
crops. Crop rotation often fails if we overlook the 
importance of clean culture. 

Varieties Resistant to Disease 

It is a well-known fact that not all varieties of 
plants are alike subject to the same disease. In 
going over a diseased field, we find that while a large 
percentage of the plants may be dying, some few 
individuals will stand up and thrive in spite of the 
disease. If these individual plants are perpetuated 
in the same sick field, we may succeed in developing 
a strain or variety of plant which will produce one 
hundred per cent, healthy individuals in the same sick 
soil. On this principle are based the selection and 
development of resistant varieties. Much has al- 
ready been accomplished in this direction and still 
more is to be expected in the future. 



374 Diseases of Truck Crops 

How to Develop a Resistant Variety 

This may be accomplished by selecting, from the 
sickest piece of land on which the crop is growing, the 
healthiest individuals, and taking the seed from them. 
The following year the selected seeds are again 
planted on the same infected land. The best in- 
dividual plants from this sowing are selected and their 
seeds saved. By continuing this method of selection 
for a number of years it may be possible to develop 
a strain which will yield one hundred per cent, of 
healthy plants in a sick soil. To maintain the purity 
of the selected strain as well as its resistance, it is 
necessary to reserve a plot of the sick soil, upon which 
the selected strain is grown for seed purposes. Care 
must be taken toward carrying any of the sick soil 
of this plot to other parts of the field. 

Drawbacks. With some crops and with certain 
diseases it seems hopeless to try to develop a resist- 
ant strain. If a variety is resistant to one disease 
it may be susceptible to several others, which are 
perhaps more serious. The resistance may often be 
local, in which case it becomes necessary to develop 
resistant types for each local condition. Resistant 
varieties often may not embody the requirements of 
the market. Nevertheless, the development of re- 
sistant strains should be tried wherever it gives 
any promise of success. 



CHAPTER XXIV 

CONTROL OF INSECT PESTS BY NATURAL FACTORS 

In this discussion we shall consider very briefly 
the natural factors which help in the control of 
parasitic insects. 

(a) Beneficial Predacious Insects. It is fortunate 
that nature always provides its own remedies. If 
insect pests were not kept in check by natural enemies 
the trucker who does not spray would be faced by 
tremendous odds in attempting to raise crops. The 
natural and beneficial enemies may be grouped, first, 
into parasites which develop within the body of the 
host, and second, predacious or those which feed 
externally. 

I. Of the first group may be mentioned a small 
wasp-like insect, Lysiphlebus testaceipes. This is no 
doubt an important parasite, which greatly helps to 
keep the green Aphis in check. Its life history was 
originally worked out by Webster, ^ and may be briefly 
summarized as follows : 

A mature female thrusts her ovipositor into the 
upper side of the Aphis and deposits a single egg 

' U. S. Dept. of Agr. Bur. of Entomology Bui., i lo, 1912. 
375 



376 Diseases of Truck Crops 

within its body (fig. 72 c-d) . The egg of Lysiphlebus 
hatches and soon begins to feed on the vital parts of 
the Aphis. The latter gradually ceases activity and 
finally dies and becomes mummified. When the 
larva of Lysiphlebus reaches maturity and pupates, it 
emerges through a circular lid cut on the back of the 
dead Aphis. Lysiphlebus is not active at tempera- 
tures below 56 degrees F. 

2. Of the parasites which feed externally on 
Aphids may be mentioned the lady-bird beetle, of 
which there are several species. These actually de- 
vour great numbers of plant lice. Lady beetles 
need no description, as they are well known to all 
truckers. There are, of course, other important 
beneficial insects such as the Syrphid and the lace- 
winged flies. For a further description of these the 
reader should consult Webster's original publication 
already cited. 

(b) Beneficial Fungus Parasites. There are numer- 
ous species of fungi which from an economic consider- 
ation are very important. These live parasitically 
on numerous insect pests and undoubtedly greatly 
help in keeping them in check. Of these may be 
mentioned species of Empusa, and of Acrostalagmus, 
which live on Aphids or plant lice. Fungi which 
belong to species of Aschersonia are parasitic on the 
white fly. The fungus Botrytis rileyi is parasitic on 
numerous caterpillars. The fungus Cordyceps (fig. 
72 a-b) contains some important species which are 
parasitic on the Harlequin bugs and other insect 
pests. The green muscardine fungus Metarrhizium 




Pig. 72. Parasitized Insects. Tri:atmi:\t of Pi;xci: Posib. 

a. Cabbage bug parasitized by Cordyteps nutans, b. cabbage bug parasitized by 
(\irdyceps sobolifera {a. and 6. after Lloyd), c. watermelon aphids parasitized by 
Lysiphlebus testaceipes, showing circular holes on the backs of the aphids through 
which parasite emerged, d. a female of L. testaceipes in the act of laying her eggs in 
the back of a green aphis (after Webster) , e. Creosoted post after a period of service, 
/. a willow post treated 4 hours in hot creosote and 10 hours in cold; set June 13, 
1005, examined November i, 1914, and showing practically no deterioration after 
9}^ years' service. 2. A split soft maple post treated 4 hours in hot creosote and 
10 hours in cold; set in 190S and examined November is, 1914. The post was set 
below the creosote line and some decay has entered beneath the creosote shell, j. 
A 5-inch split Cottonwood post given a creosote bath treatment, set in 1905 and 
examined in 1914. The post shows practically no decomposition in either top or 
bottom. 4. An 8-inch ash post split in half, given butt creosote treatment of 6 
hours in hot and 12 hours in cold, set 1905 and examined in November, 1914. The 
creosoted bottom is sound, penetration on the heart wood surface was less than in 
the sap wood. The heart wood portion of this post will undoubtedly give away first. 
The untreated top is in excellent condition. 5. A 4^-inch untreated white cedar 
post after standing 9}^ years. /. A small treating tank in operation, {e. and /. 
after McDonald). 



Natural Factors Controlling Pests 377 

anisoplicB is parasitic on numerous grubs and beetles. 
Most of these fungi, however, are only active during 
warm moist weather and cannot always be depended 
upon with certainty. 



CHAPTER XXV 

TREATMENT OF FENCE POSTS 

Whether trucking on a large or small scale, fence 
posts are always used to protect the crops from pas- 
turing animals or undesirable marauders. In buy- 
ing fence posts, the aim should be to seciure those 
which naturally last longest. Posts of willow, 
Cottonwood, or soft maple will last far less than those 
of red cedar, osage orange, or the mulberry. Posts 
made largely of sapwood will rot much faster than 
those made of heartwood. All posts, before being 
used, should be rid of all their bark. The latter usually 
harbors insect and fungi which when active hasten 
destruction or decay. In order to preserve the life 
of fence posts longest, they should be treated with 
some good standard preservative. Creosote is the 
most important preservative for fence posts (fig. 72 e, 
I to 5). On a moderate scale, tanks (fig. 72 f) 
four feet high, three feet in diameter, and capable 
of holding thirty-five 4>^-inch posts should be 
used. The tank is raised about one foot above the 
ground to provide room for the fire box. The creo- 
sote is poured in the tank and the posts are allowed 
to remain in the hot preservative for a period of from 
two to six hours. The posts may then be allowed to 
378 



Treatment of Fence Posts 379 

remain in the tank until the preservative cools off, 
or it is immediately transferred to another tank which 
contains cold creosote. This cooling off is necessary, 
as it causes a contraction of the remaining air and 
moisture in the wood structure. This causes addi- 
tional preservative to be drawn into the wood. 

Fence posts may be treated at any time of the year. 
The time of the year posts are cut affects only the 
seasoning, but not its durability. Posts cut in the 
winter are more difficult to peel. Contrary to general 
belief, winter cut posts contain more moisture and 
hence require longer seasoning. All posts to be 
treated must have all the bark removed. If the 
posts are cut in the spring, the peeling of the bark 
is very easy. Beveling the tops of treated posts 
is also recommended. This is especially necessary 
when the posts are treated at the butt end which 
is stuck in the ground. 



GLOSSARY 
A 

ACERVULi. Small groups of mycelial tufts upon which 
fungus spores are formed. 

.ECiDiosPORES. Spores of the rust family formed in an 
ascidium. 

^CIDIUM (ascium). A cup -shaped body in which are 
formed the spring spores of certain rust fungi. 

AEROBE. Organism requiring air, more especially oxygen. 

AMMONiFiCATiON. The formation of ammonia at the 
expense of other forms of nitrogen compounds, by 
the action of microorganisms upon organic sub- 
stances. 

AMMONIFIER3. Microorganisms capable of transforming 
nitrogen compounds into ammonia. 

AMffiBOiD. Like an amoeba, the creeping movement 
of which is made possible by appendage-like bodies. 

ANTHERIDIUM. The male sexual organ in fungi. 

APICAL. Terminal formation at the point of any struc- 
ture. 

ARTHROSPORES. Whole vegetative cells of either bac- 
teria or fungi, which by a thickening of their walls 
become resting spores. 

AscospoRES. Spores formed in an ascus. 

Ascus. A sac-like structure in which the winter spores 
of certain fungi are formed. 
381 



382 Glossary 

B 

BASIDIOSPORES. Spores formed on basidia. 
BASIDIUM. A Straight stick- like spore bearing fungal 
thread. 

C 

CANKER. Definite dead area in the bark of stems or 

roots of plants. 
CAPITATE. Possessing a head. 
CARBONACEOUS. Dark to black colored. 
CHLAMYDOSPORES. Resting spores with very thick 

walls, formed within mycelial cells. 
CHLOROPHYLL. Green coloring matter in leaves of the 

higher plants. 
CHROMOGENic. Producing color. 
CILIATE. Fringed with hairs. 
COLUMELLA. Sterile axle of a pillar-like structure within 

a sporangium. 
CONIDIA. Spores formed asexually. 
CONIDIOPHORE. A spore-beaiing fungal stalk. 
CONSTRICTED. Drawn together or contracted. 
CORTEX. Outer bark. 
CUTICLE. The outermost skin of plants. 
CYST. Sac or cavity. 

D 

DELIQUESCENT. Dissolving or melting. 
DIFFUSE. Loosely spread. 
DILATED. Enlarged. 

E 

ENDOSPORE. Spore formed within another cell. 
ENTOMOGENOUS. Living on insects. 



Glossary 383 

ENZYME. An organic chemical product capable of 
bringing about chemical changes, but without itself 
undergoing any change, or entering into the final 
product. 

EXOSPORE. Outer covering of a spore. 

F 

FALCATE. Sickle shaped. 

FLAGELLA. Whip-like appendage of protoplasm of bac- 
teria and swarm spores. 

FUNGUS. A plant of very lovv^ order. Its mycelium corre- 
sponds to roots and reproduces by means of spores. 



GLAUCUS. Sea green. 
GONIDIA. Algas-like cells. 
GUTTULATE. Drop-Hke. 

H 

HAUSTORIA. Special organs of a fungus used for attach- 
ment or for obtaining food. 

HOST. Any plant which nourishes a parasite. 

HYALINE. Translucent or colorless. 

HYPERTROPHiED. Part of diseased plant abnormally 
enlarged. 

HYPH^. Thread-like vegetative part of a fungus. 

I 

INDURATED. Hardened. 

INFECT. To cause disease. 

INTERCELLULAR. Growing between the host cells. 

INTRACELLULAR. Growing inside the host cells. 



384 Glossary 



LENTICEL. A special loose corky structure in plants 
intended for the exchange of gases of the air and the 
interior of the plant. 

LESIONS. A definite diseased area. 



M 



MACROCONiDiA. Large conidia. 
MiCROCONiDiA. Very small conidia. 
MIDDLE LAMELLA. The Connecting or cementing mem- 
brane between any two cells of a plant. 
MYCELIUM. Vegetative threads or hyphae of a fungus. 
MYCOLOGY. The study of fungi. 



OMNIVOROUS. Attacking a large variety of plants. 
OOGONIUM. Female sexual organ of fungi, containing 

one or more oospheres. 
OOSPHERE. Naked mass of protoplasm developing into 

oospores after fertilization. 
OOSPORE. Fertilized oosphere. 



PAPILLATE. Having wing-like structures. 

PARAPHYSES. Sterile filaments found in some fruiting 

forms of fungi. 
PARASITE. An organism living at the expense of another 

(the host) . 
PATHOGENE. A disease-producing organism, 
PEDiciLLATE. Borne on a stalk. 



Glossary 385 

PERiTHECiUM. A flask-shaped or globose sexual fruiting 
<. body containing asci. 

PERITRICHIATE. Flagella all over the surface. 

piONNOTES. An effuse conidial stage containing a maxi- 
mum of conidia and a minimum of aerial mycelium. 

PLASMODIUM. A mass of naked protoplasm with numer- 
ous nuclei and capable of amoeboid motion. 

POLAR FLAGELLA. Flagella borne at the polar ends of an 
organism. 

PROTOPLASM. The living substance of any plant cell. 

PSEUDOPiONNOTES. False pionnotes. 

PSEUDOSTROMA. False stroma. 

PUSTULE. A blister or pimple. 

PYCNIDIA. Sac-shaped fruiting bodies of a fungus in 
which the pycnospores or summer spores are formed. 

PYCNOSPORES. Siunmer spores of certain fungi which 
are formed in pycnidia. 



SCLEROTIA. Compact masses of mycelium in a dormant 
state. These help to carry the fungus over un- 
favorable weather conditions. 

SEPTUM. Any partition between two cells in the same 
fungus filament. 

SET^. Bristle-shaped bodies. 

SOIL FLORA. Bacterial or fungus growth in a soil. 

SORUS. Heap of spores. 

SPORANGIOPHORE. Stalk-bearing sporangium. 

SPORANGIOSPORES. Spores formed in a sporangitim. 

SPORANGIUM. Free non-sexual bearing spore sac. 

SPORES. Seed of bacteria or fungi. 

STOMATA. Minute openings in the stems, leaves, or fruits 
of plants which serve as a medium of exchange of 
gases. 

25 



386 Glossary 

STROMA. A spore-bearing cushion composed of mycelium 

and sometimes of host tissue. 
SWARM SPORES. Sporcs possessed with the power of 

motility. 



TELEUTOSPORES (teliospores) . Resting or winter spores 
of certain rust fungi. 

U 

uredospores. Summer spores of certain rust fungi. 



VESICULAR. Composed of vessels. 
VISCID. Sticky. 



zooGLE/E. Colony embedded in a gelatinous bed. 
ZOOSPORANGIA. Sporangia which produce zoospores. 
ZOOSPORE. A motile spore. 



I 



INDEX 



Abbot, J. B., 30. 
Acid sick soils, 25 et seq. 
Acrostalagmus panax, 113. 
Actinomyces, 6. 

chromogenus, 317. 

attacking beets, 120. 

attacking radish, 209. 

Alkali sick soils, 34 ei seq. 
AUard, H. A., 84. 
Allium cepa, 285. 

schoenoporasum, 2S4. 

Alphano Humus Co., 20. 
Alternaria brassiccs, 196. 

var. nigresccjis, 223. 

;— panax, 114. 

Ammoniacal copper carbonate, 

366. 
Ammonification, 14. 
Antheridium, 11. 
Aphis gossypii, 233. 
Apium graveolens, 355. 
Arthur, J. C, 117, 138. 
Artichoke, Globe, diseases of, 
139 et seq. 

■ Leaf spot, 139. 

Jerusalem, diseases of, 137 

et seq. 

Downy mildew, 138. 

Leaf blotch, 138 e/ seq. 

Rust, 138. 

Ascochyta armor acice, 205. 

hortorwn, 302. 

pisi, 277. 

Asparagus (officinalis), 280. 
diseases, 279 et seq. 

Leopard spot, 280. 

Rust, 280. 



Asparagus, resistant to rust, 283. 

rust, natural enemies, 283. 

Atkinson, G., 43. 
Available nitrogen, elaboration 
of, 13. 



B 



Bacillus, 4. 

Bacillus carotovorus, 192, 

attacking onions, 285. 

attacking salsify, 146. 

fiuorescens liquefaciens, 14. 

putridus, 14. 

lathyri, 261. 

on cowpea, 270. 

phytopthorus, 316. 

7nelonis, 221. 

mesentericus vulgatus, 14,23. 

mycoides, 14, 23. 

pestifer, 23. 

proteus vulgaris, 14. 

ramosus, 23. 

subtilis, 23. 

tracheiphillus , attaching cu- 
cumber, 229. 

Bacteria, distribution in soil, 6. 

forms, 4. 

influence of depth of cul- 
tivation, 8. 

number influenced by man- 
ure, 9. 

relationship to function of 

soil, 5. 

Bacterium teutlium, 118. 

Balm diseases, 256. 
Leaf spot, 256. 
Rust, 256. 

Barus, M. F., 265. 



3^7 



388 



Index 



Bean diseases, 260 et seq. 

Anthracnose, 263. 

Blight, 260. 

Damping off, 261. 

Downy mildew, 261. 

Powdery mildew, 262. 

Rust, 262. 

Sclerotinia rot, 263. 

Stem anthracnose, 263. 

Streak, 261. 
Beattie, W. R., 293. 
Beet diseases, 117 e/ seq. 

Crown gall, 118, 119. 

Damping off and root rot, 
122, 123. 

Downy mildew, 123, 

Drop, 124. 

Leaf spot, 126, 127. 

Leaf spot and heart rot, 
125, 126. 

Root knot, 129, 130. 

Root rot, 128. 

Root tumor, 121, 122. 

Scab, 120-12 1. 

Soft rot, 118. 

Tuberculosis, 120. 

Water core spots, 117, 

White rust, 123. 
Beneficial fungi, 376. 
Bessey, E. A., 51. 
Beta vulgaris, 117. 
"Black leaf 40," 368. 
Blinn, P. K., 224. 
Blossom drop, 82, 83. 
Bordeaux mixture, 364. 
Branch, G. V., 226. 
Brassica Japonica, 208. 

olemcea, 186. 

var. acephala, 207. 

var. hotrytis, 202. 

rapa, 214. 

Bremia laducce, 141. 
Brown, N. A., 140. 



Cabbage diseases, 186 et seq. 
Black leg or foot rot, 195. 
Black mold, 196. 
Black rot, 190. 



Club root, 186. 
Damping off, 193. 
Downy mildew, 194. 
Drop, 194. 
Leaf spot, 196. 
Root knot, 199. 
Soft rot, 192. 
White rust, 193. 
Wilt or yellows, 197. 

storage decays, 199 et seq. 

Cantaloupe, 225. 

blight resistant, 225. 

care in shipping, 225 et seq. 

diseases, 219 et seq. 

Anthracnose, 223. 
Bacterial wilt, 219. 
Cercospora leaf spot, 224. 
Cladosporium mold, 224. 
Dowmy mildew, 221. 
Leaf blight, 223. _ 
Mycosphserella wilt, 222. 
Phyllosticta leaf spot, 224. 
Powdery mildew, 222. 
Root knot, 225. 
Soft rot, 221. 
Southern blight, 225. 

spraying, 232. 

Capnodium, 238. 
Carbon, transformation of, 13. 
Carrot diseases, 354. 
Root rot, 354. 
Soft rot, 354. 
Carum petrosclinum, 357. 
Catnip diseases, 257. 
Leaf spot, 257. 
Stem rot, 257. 
Cauliflower diseases, 202 et seq. 
Bacterial leaf spot, 202. 
Ring spot, 204. 
Causes of diseases in crops, 7 1 

et seq. 
Celery diseases, 355 et seq. 
Early blight, 357. 
Late blight, 355. 
Leaf spot, 355. 
Rust, 355. 
Soft rot, 355. 
Cercospora apii, 357, 358- 

armoracicB, 207. 

canescens, 269. 



Index 



389 



Cercospora capsisi, 304. 

citrullina, 243. 

cruenta, 2^1. 

cuciirbitcB, 224. 

dolichi, 2'ji. 

hibisci, 295. 

Chive diseases, 284. 
Choanophora cucurbitarum, 235. 
Chrysophylyctis endobioticum, 

Citron diseases, 234. 
Cilrullus vulgaris, 234 et seq. 
Cladosporitim Julvum, 350. 

macrocarpum, 134. 

sp., 284. 

Liinton, G, P., 122, 124, 14;, 

215,284,323. 
Coccus, 4. 

Cochleaia armoracia, 204. 
Colletotrichum atramentariu::i, 
325, 326 

caulicoliim, 266. 

Higginsianum, 214. 

nigrum, 303. 

phomoides, 348. 

Combination sprays, 367. 
Conidia, 12, 
Conn, J. H., 6. 
Contact poisons, 363. 
Convulvuhis batatas, 151. 
Cooley, B. A.,368. 
Corticiufti vagiim, 128. 
Cowpea diseases, 270 et seq. 

Angular leaf spot, 271. 

Powdery mildew, 271. 

Rust, 271. 

Streak, 270. 

Wilt or Yellows, 270, 
Crop rotation, 272. 
Cucumber diseases, 228 et seq. 

Angular leaf spot, 229. 

Anthracnose, 232. 

Bacterial wilt, 229. 

Damping off, 230. 

Downy mildew, 230. 

Mosaic, 228. 

Powdery mildew, 230. 

Root knot, 232. 

spraying, 232. 

Cucumis sativus, 228. 



Cucumis melo, 2ig. 
Cucurbita maxima, 234. 

moschata, 234. 

pepo, 234. 

Cutworms, 52. 

Cystopus candidus ,a.tta.c'^mg rad- 
ish, 211. 

— — -; on horseradish, 205. 

ipomoeoR-pandurarKE, 155. 

portulacecz, 299. 

Cyslospora batatas, 152, 



Damping off, 42 et seq. 

Darluca filum, 284. 

Dauctis carota, 354. 

Denitrification, 24. 

Denitrified soils, 23. 

Diabrotica vittata, 220. 

Diaporthe battis, 157, 159. 

Didlake, M., 20. 

Didymella catarie, 257. 

Diplodia herbarum, 258. 

herbicola, 257. 

— tubericola, 165. 

, attacking watermel- 
on, 239. . 

Diseases of a mechanical nature, 
72 et seq. 

— — of an unknown origin, 83 
et seq. 

' due to bacteria or fungi, 

86 et seq. 

Dodder, 90, 91. 

Doryland Ch., 8. 

Drought injury, 78. 

Duggar, B. M., 128, 298. 

Durst, C. E., 233. 



Edgerton, C. A., 264. 
Edson, H. A., 209, 
Eggplant diseases, 300 et seq. 

Anthracnose, 302. 

Damping off, 301. 

Fruit rot, 301. 

Root knot, 303. 

Southern blight, 303. 



390 



Index 



Eggplant diseases — Continued 
Southern wilt, 301. 
Stem anthracnose, 303. 

EUiottJ.A., 154. 

Enlows, E. M., 229, 

Entyloma Ellisii, 133. 

Erysiphe cichoracearum, 232. 

galeopsidis, 258. 

polygoni, 216. 

, on bpan, 262. 

, on cantaloupe, 222. 



Family Agaricaccce, 103 et seq. 

Araliaceas, 108 et seq. 

Chenopodiacese, 1 16 et seq. 

Compositce, 137 et seq. 

Convolvulaces, 151 et seq. 

Cruciferse, 185 el seq. 

Cucurbitaceas, 218 et seq 

Graminece, 250 et seq. 

Labiatae., 255. 

Liliaceffi, 279 et seq. 

Malvace^, 295 et sen. 

Portulacacece, 299. 

Solanaceae, 300 et seq. 

Umbelliferas, 254 et seq. 

Fence post treatment, 378. 
Fertility of soil, 16, 17 

Fisher, O.S., 31- 
Fleet, W. v., 255. 
Formaldehyde, treatment of soil, 

53, 54- 
Freiberg, G. W., 84. 
Frost injury, 74, 75. 

prediction, 76, "/"/. 

protection, 77, 78. 

Fuligo violacea, 152. 

Fungicides, 363. 

Fungi, structure and life history, 

10. 
Fusarium hatatatis, 47, 157, 170. 

citrulU, 244. 

conghitinans, 197. 

cucurbitce, 237. 

eumartii, 330. 

hyperoxyspornm, 47 et seq. 

lycopersici, 351. 

niveum, 244. 



Fusarium orthoceras, 352. 

oxysporum, 327, 352. 

Poolensis, 244. 

radicicola, 329. 

trichothecioides , 330. 

tuberivorum, 331. 



Garden pea, 275. 

diseases, 273 et seq. 

Pod spot, 276. 

Root knot, 278. 

Root rot, 278. 

Septoria leaf spot, 278. 

Stem blight, 273. 

Thielavia root rot, 275. 
Garman, H., 20. 
Gilbert, W. W., 74. 
Gilman, J. C., 198. 
Ginseng, no, in, 113. 
diseases, 108 et seq. 

Acrostalagmus wilt, 113, 114 

Altemaha blight, 114. 

Black rot, no, in. 

Bordeaux injury, 115. 

Damping off, 108. 

Downy mildew, 108, 109. 

Fiber rot, in, 112. 

Leaf anthracnose, 113. 

Papery leaf spot, 115. 

Root knot, 115. 

Stem anthracnose, 112. 

White rot, no. 
Gleosporium melongcnce, 302. 
Glomerella piperata, 303. 
Grossenbacher, J. G., 222. 

H 

Hail storm, 73, 74. 
Halstead, B. D., 125. 
Harding, H. A., 191. 
Harris, F. S., 35. 
Harter, L. L., 199, 301. 
Hawkins, 321. 
Headen, W. P., 16, 24. 
Heald, F. D., 139, 266. 
Healthy host and its require- 
ments, 63 el seq. 



Index 



391 



Healthy soil flora, nature and 

function, 12. 
Helianthus aiuiuus, 148. 

tuherosiis, 137. 

Heterodera radicicola, 48, 52, 332. 
attacking cabbage, 

199. 

attacking beets, 129. 

attacking lettuce, 146. 

attacking sweet pota- 
to, 176. 
Heterosporium variabile, 134. 
Hibiscus esculentus, 295. 
Hicks, G. A., 96. 
Higgins, B. B., 214. 
Hopkins, G. G., 31. 
Horehound diseases, 258. 

Leaf spot, 258. 

Powdery mildew, 258. 
Horseradish diseases, 204 et seq. 

Leaf spot, 207. 

Macrosporium black mold, 
206. 

Root rot, 205. 

Shot hole, 206. 

White mold, 206. 
Humbert, J. G., 55. 
Humphrey, J. E., 232. 



Insecticides, 362. 
Iron, changes of, 15. 
Irrigation, methods of, 67 et seq. 
Isariopsis griseola, 269. 
Istvanfli, G. De, 143. 



Jamieson, C. O., 331. 
Johnson, J., 57, 276. 

T., 320, 347. 

Jones, L. R., 74. 

K 



Kale diseases, 207, 208. 
Koch, Robert, 4. 



Lactuca sativa, 140. 
Lady beetles, 376. 
Leeuwenhoek, Anton van, 4. 
Lettuce diseases, 140 ei seq. 

Bacterial blight, 140. 

Cercospora leaf spot, 145. 

Downy mildew, 141. 

Gray mold, 142. 

Leaf spot, 144. 

Lettuce drop, 143. 

Root knot, 146. 

Rosette, 146. 

Shot hole, 145. 
Levine, E., 347. 
Lightning injury, 74, 75. 
Lima bean diseases, 267 et seq. 

Blight, 267. 

Downy mildew, 267. 

Leaf blotch, 269. 

Leaf spot, 269. 

Pod blight, 268. 

Powdery mildew, 268. 

Root rot, 269. 

Rust, 268. 

Texas root rot, 269. 
Lutman, B. F., 318. 
Lycopersicum esculentum, 339. 
Lysiphlebus testaceipes, 375. 

M 

McClintock, J. A., 263. 
McCuUoch, L., 202. 
McKay, M. B., 127. 
Macrosporium herculeum, 2C 
217. 

parasiticum, 290. 

porri, 290. 

solani, 325. 

sp., 304. 

Malnutrition, 80 et seq. 
Manns, T. F., 99, 195. 
Marrubium vulgare, 258. 
Marsonia perforans, 145. 
Meier, F. C., 239. 
Melanconium Tisdale, 349. 
Melhus, T. E., 212, 323. 
Meliotus alba, 20. 



392 



Index 



Meliotus denliculata, 20. 

lupulina, 20. 

Melissa officinalis, 256. 
Mentha virides, 258. 
Merrill, L. A., 65. 
Methods of control, 361. 
Mint diseases, 258. 
Monilochcetes infuscans, iGS. 
More, C. T., 226. 
Morse, W. J., 316. 
Mosaic, 83 el seq. 
Muck or peat soils, 34 ei seq. 
Mushroom diseases, 103 el seq. 

Bacterial spot, 103, 104. 

The Mycogone disease, 103 

el seq. 
Mustard diseases, 208. 
Mycogone peniiciosa, 104, 105. 
MycosphcBrella brassicola, 204. 
citrulina, 22. 

N 

Nemalospora lycopersici, 345. 
Nepela cataria, 257. 
Niter-sick soils, 24. 
Nitrification, 14. 
Nitrobacter, 14. 
Nitrogen fixation from air, iS. 

maintaining supply, 17. 

Nitrosococcus, 14. 
Nitrosomonas, 14. 



O'Gara, P. J., 324. 

Okra diseases, 295 el seq. 

Leaf spot, 295. 

Root knot, 298. 

Root rot, 297. 

Texas root rot, 297. 

Wilt, 296. 
Olpidium brassicce, 193. 
Onion diseases, 285 el seq. 

Anthracnose, 289. 

Black mold, 290. 

Black neck, 290. 

Blight, 286. 

Bulb rot, 290. 

Damping off, 2S6. 



Downy mildew, 286. 

Pink root, 291. 

Rust, 2S9. 

Sclerotium rot or black 
neck, 290. 

Smut, 288. 

Soft rot, 285. 

storage, 292 el seq. 

Oogonia, 43. 

Oogonium, 11, 43. 

Orton, W. A., 232, 273, 327. 

Ozonititn omnivoriuni attacking 

okra, 297. 
■ attacking sweet pota- 
to, 175- 



Pammel, L. H., 46, 123. 
Parasitic fungi, 10. 

soil Fusaria, 46, 47. 

Parsley diseases, 357. 

Drop, 357. 

Late blight, 357. 
Parsnip diseases, 357. 

Early blight, 357. 

Root rot, 357. 
Paslinaca saliva, 357, 
Penicillium expansuin, 11. 
Pepper diseases, 303 el seq. 

Anthracnose, 303. 

Black anthracnose, 303. 

Fruit rot, 304. 

Leaf spot, 304. 

Southern blight, 305. 
Peppermint diseases, 258. 
Perithecium, 12. 
Peronospora effiisa, 131, 132. 
parasitica attacking cab- 
bage, 194. 

sckachlii, 123. 

schleideni, 286. 

Pestalozziafunerea attacking gin- 
seng, 113. 
Phaseolus vulgaris, 260. 
Phonia belce, 125. 

deslrucliva, 346. 

napobrassiccB, 215. 

oleracea, 195. 

solani, 324. 



Index 



393 



Phoma subcircinata, 268. 


Root knot, 332. 


Phomosis vexans, 301. 


Rosette, 331. 


Phosphates, changes of, 15. 


Silver scurf, 326. 


Phyliosticta apii, 355. 


Southern blight, 332. 


batatas, 164. 


Southern wilt, 317. 


chenopodii, 133, 134. 


Spindling sprout, 310. 


cucurbitaceai'um, 224. 


Stem end rot, 329. 


Physiological diseases, 80 et seq. 


Tip burn, 312. 


Phythium de Baryanum, 42, 44, 


diseases, field control, 335. 


193- 


storage rots control, 333. 


attacking beet, 122. 


Predacious insects, beneficial, 


Phytophthom cactorum, 108. 


375- 


infestans, late blight of 


Psciidomonas beticola, 120. 


Irish potato, 322. 


campestris, 190, 191, 205. 


late blight of tomato, 


attacking radish, 208. 


343- 




phaseoh, 267. 


fliiorescens, 103, 104. 


terrestria, 344. 


lachrymans, 229. 


Pisiim sativum, 273. 


maculicola, 202, 203. 


Plasmopora Halstedii, 13S, 148. 


pisi, 273. 

radicicola, 18 et seq. 


Plenodomus destruens, 159. 


Points to remember, 366. 


solanacearum, attacking to- 


Pool Venus, 127. 


mato, 342. 


Poor seed, 92, 97. 


Stewarti, 251. 


Potassium, changes of, 15. 


tumefaciens, a.tta.c]di\g beets 


sulphide of, 369. 


118. 


Potato diseases, 306 et seq. 


viridilividum, 140. 


Anthracnose, 324. 


Pseudoperonospora cubensis, 230 


Arsenical injury, 313. 


Puccinia alii, 289. 


Black heart, 311. 


asparagi, 280. 


Black leg, 316. 


bullata, 355. 


Black rot or jelly end rot. 


helianthi, 149. 


329- 


attacking Jerusalem 


Black wart, 319. 
Common scab, 317. 


artichoke, 138. 




Curly dwarf, 309. 


Purslane diseases, 299. 


Early blight, 322. 


Pycnidium, 12. 


Fusarium wilt, 327. 




Hollow heart, 312. 


R 


Internal brown spotting. 




310. 


Radish diseases, 208 et seq. 


Late blight, 322. 


Black rot, 208. 


Leaf roll, 308. 


Club root, 208. 


Melters or leak, 321. 


Damping oflf, 209. 


Mosaic, 312. 


Downy mildew, 211. 


Net necrosis, 311. 


Root knot, 214. 


Phoma rot, 324. 


Root rot, 214. 


Powdery dry rot, 330. 


Scab, 209. 


Powdery scab, 314. 


White rust, 211. 


Pox or pit, 313. 


Rainstorms, 73. 



394 



Index 



Ramularia armoracicB, 206. 

cynarce, 138. 

Rand, F. V., 229. 
Rankin, W. H., no. 
Raphanus sativiis, 208, 
Readliimer, J. E., 31. 
Reid, H. L., 134, 138. 
Resin, 370. 

Resistant varieties, 373. 
Rheosporangium ap'.ianiderma- 

tuin, 209. 
Rhizoclonia solani, 44. 
Rhizopus nigricans, 156, 158. 

attacking squash, 2,36. 

the cause of leak, 321. 

Roasting or pan firing, 56. 

Rogers, S. S., 356. 

Root knot, 48 et seq. 

Root rot, caused by Rhizoclonia 

solani, 45, 46. 
Rosenbaum, J., 109, no, 314. 



Sackett, W. G., 24. 
Salsify diseases, 146 et seq. 

Rust, 148. 

Soft rot, 146. 

Southern blight, 148. 

White rust, 147. 
Sal soda, 370. 

Sanitary environment, 69, 70. 
Sarcina lutea, 14. 
Schneider, A., 345. 
Schrenk, H. von, 203. 
Sclerotinia libertiana, 45. 

attacking bean, 263. 

attacking beet, 



124. 



attacking cabbage, 



[94- 



■ attacking ginseng, 1 10. 

panacis, no. 

Sclerotium hataticola, 157, 173, 

174. 

cepivorum, 290. 

Rolfsii, 44. 

attacking cantaloupes, 

225. 
attacking peppers, 

305- 



Sclerotium Rolfsii, attacking 
sweet potatoes, 174. 

attacking watermelon, 

247. 

Seed, age of, 92. 

cultural conditions, 92, 93 . 

fertilizer effect, 95, 97. 

storage conditions, 94. 

testing, 95. 

treatment against insects, 

97- 

treatment with formalde- 
hyde, 99, 

weight and color, 93, 94. 

Selby, A. D., 55, 291. 

Septoria hataticola, 165. 

consimilis, 144. 

lactucce, 144. 

lycopersici, 347. 

melisscs, 256. 

nepetcB, 257. 

pisi, 278. 

Shamel, A. D., 54. 

Sherbakoff, C. D., 331, 344. 

Sick soil, treatment, 53. 

Sirrine, F. A., 282. 

Smith, E. F., 119, 190, 251. 

E, W., 230. 

R.E.,281. 

Smoke injury, 78 et seq. 

Soft rot, 236._ 

Soil flora, action on mineral sub- 
stances, 14. 

Solonum tuberosum, 306. 

Spearmint diseases, 258. 

Spharella pinodes, 276. 

Sphdronema fimbriatum, 160, 

173- . 
Spinach diseases, 130 et seq. 
Anthracnose, 132. 
Black mold, 134. 
Downy mildew, 131, 132. 
Leaf spot, 134, 136. 
Malnutrition, 130, 131. 
Phyllosticta leaf blight, 133, 

134- 
White smut, 133. 
Spinacia oleracea, 130. 
Spondylocladium atrovirens, 224, 
326. 



Index 



395 



Spraying, 361. 

machines, 370. 

principles involved, 370. 

Squash diseases, 234 et seq. 
Anthracnose, 237. 
Bacterial wilt, 234. 
Fruit rot, 235. 
Leaf spot, 237. 
Powdery mildew, 237. 
Root knot, 238. 

Root rot, 238. 
Soft rot, 236. 

Wilt or yellov/s, 2^J. 
Steaming sick soil, 54. 
Stevenson, J. A., 146. 
Stewart, F. C, 12S, 285. 
— F.G.,251. 
Stickers, 370. 
Stock solutions, 364. 
Stomach poisons, 362. 
Stone, G. E., 93. 

R.E., 277. 

Subirrigation, 67, 68. 
Sulphur, 367. 
Sunflower diseases, 148. 

Downy mildew, 148. 

Rust, 149. 
Surface or spray irrigation, 68, 

69. 
Sweet potato diseases, 151 ei scg^. 

Black rot, 160. 

Charcoal rot, 173. 

Cottony rot, 174. 

Dry rot, 159. 

Foot rot, 159. 

Java black rot, 165. 

Phyllosticta leaf blight, 164. 

Ring rot, 158. 

Root knot, 176. 

Septoria leaf spot, 165. 

Slime mold, 152. 

Soft rot, 156. 

Soil rot, 152. 

Soil stain or scurf, 16S. 

Texas root rot, 175. 

Trichoderma rot, 167. 

Vine wilt or yellows, 170. 

White rust, 155. 

methods of control, 

176 ei seq. 



Taubenhaus, J. J., 160 et scg. 

Temple, J. C., 9. 

Thick sowing, effect on dampinp- 

off, 57. 
Thielavia basicola attacking gar- 
den pea, 275. 

attacking ginseng, 1 1 1 . 

attacking horseradish, 

205. 
Tinslev, J. D., 37. 
Tolaas, A._ S., 103. 
Tomato diseases, 339 et seq. 

Anthracnose, 348. 

Blossom end rot, 340. 

Buckeye rot, 344. 

Damping off, 343. 

Fruit rot, 346. 

Hollow stem, 339. 

Late blight, 343. 

Leaf spot, 347. 

Melanconium rot, 349. 

Mosaic, 341. 

Rhizoctonia fruit rot, 353. 

Southern wilt, 342. 

Sunburn, 341. 

Yeast rot, 345. 

Yellow blight, 352. 
Tragopogon porrijolms, 146. 
Trichoderma koningi, 167. 

lignorum, 167. 

Tubercularia persicina, 284. 
Turnip diseases, 214 c/ seq. 

Anthracnose, 214. 

Black rot, 214. 

Club root, 214. 

Macrosporium leaf spot, 2 1 7. 

Phoma rot, 215. 

Powdery mildew, 216. 



Uredinales, 10. 
Urocystis cepulce, 288. 
Uromyces apperidiculatiis, 262. 
Urophlyctis leproides, 121. 



396 



Index 



V 

Veihmeyer, F. J., 105. 
Vermicularia circinans, 2S9. 

dematium, 112. 

Verticillium albo-atrum, 326. 

W 



Ward, M., 43. 

Water, need of plants, 64, 67. 

Watermelon diseases, 238 et seq. 

Anthracnose, 240. 

Bacterial wilt, 238. 

Blossom end rot, 247. 

Cercospora leaf spot, 243. 

Downy mildew, 238. 

Fruit rot, 247. 



Honey dew or sooty mold, 
238. 

Malnutrition, 238. 

Mycosphasrella wilt, 239. 

Powdery mildew, 238. 

Root knot, 246. 

Stem end rot, 239. 

Vine wilt or yellows, 244. 
Whetzel, H. H., no, 287. 
White grubs, 52. 
Whitney, M., 64. 
Widtsoe, J. A., 65. 
Wind storms, 72, 73. 
Wire worms, 52. 
Wolf, F. A., 139, 235. 
WoUenweber, H. W., 331. 



Zea mays, 250. 



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