AGRIC.
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DISEASES OF TRUCK CROPS
AND THEIR CONTROL
OTHER WORKS
BY THE SAME AUTHOR
The Culture and Diseases of
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
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. BUTTON & COMPANY
681 FIFTH AVENUE
V
tf
Copyright, 1918
By E. P. DUTTON & COMPANY
PRINTED IN THE UNITED STATES OF AMERICA
TO MY FRIEND
B. KACZER
425501
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
vii
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 1915, 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 1915
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 1915 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. P. 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, TEXAS
January 22, ipi8.
PREFATORY NOTE
WITH the greater specialization along all lines of
industry the problems that confront such a specialist
as the author of this 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
xiii
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
pathologist s 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.
PAGE
CONTENTS
PART I
CHAPTER I
T* TV T JfAUS
IHE NORMAL SOIL AND ITS REQUIREMENTS . 3
CHAPTER II
SICK SOILS NOT INFLUENCED BY PARASITES . 23
CHAPTER III
SOIL SICKNESS DUE TO THE PRESENCE OF PARA-
SITES HARMFUL TO PLANTS . 4!
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
XVll
xviii Contents
PAGE
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^: . . . .103
Diseases of the Mushroom
CHAPTER IX
FAMILY ARALIACE.E . . . . . 108
Diseases of the Ginseng
CHAPTER X
FAMILY CHENOPODIACE^E 116
Diseases of the Beet
Diseases of the Spinach
CHAPTER XI
FAMILY COMPOSITE 137
Diseases of the Artichoke (Jerusalem)
Diseases of the Artichoke (Globe)
Diseases of the Lettuce
Diseases of the Salsify
Diseases of the Sunflower
Contents xix
CHAPTER XII
PAGE
FAMILY CONVOLVULACE^E . . . . .151
Diseases of the Sweet Potato
CHAPTER XIII
FAMILY CRUCIFEILE . ." . . . i%$
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 CUCURBITACLE . . . . .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^E . • • 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
FAMILY 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^E 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
FIG. PAGB
1. BACTERIA ...... 4
2. STRUCTURE OF FUNGI . . . .11
3. NITRE-SICK BEET FIELD, SHOWING BARREN
SPOTS 25
4. EFFECT OF LIME . . . . . 27
5. PYTHIUM DEBARYANUM . . . . 43
6. RHIZOCTONIA 45
7. FUSARIUM WILT . . . . - 47
8. NEMATODE ROOT KNOT .... 49
9. INVERTED PAN FOR STEAM STERILIZATION 55
10. 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
xxiv Illustrations
FIG. PAGE
15. MOSAIC 84
1 6. BEAN SEEDS AFFECTED WITH ANTHRACNOSE,
Colletotrichum lindemuthianum ... 84
17. DODDER 90
18. 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
OTG. 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 BEAN. 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
FIG. PAGE
58. POTATO DISEASES 308
59. DISEASES OF THE POTATO . . • 3J4
60. POX OR PIT OF THE WHITE POTATO, SHOWING
DIFFERENT STAGES OF INFECTION . .315
61. POTATO DISEASES . . . . 322
62. POTATO DISEASES . . . . 325
63. POTATO DISEASES . . . . • 331
64. TOMATO DISEASES 34°
65. TOMATO DISEASES ... . 346
66. TOMATO DISEASES . . . . . 347
67. TOMATO DISEASES 35 1
68. SLEEPING SICKNESS OF TOMATO . . 352
69. CELERY DISEASES 356
70. CELERY DISEASES 357
71. SPRAY MACHINERY ... . 372
72. PARASITIZED INSECTS. TREATMENT OF FENCE
POSTS . 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
CHAPTER I
THE NORMAL SOIL AND ITS REQUIREMENTS
THE aim of this chapter is to study the conditions
under which a healthy plant lives and grows. Such
knowledge will prepare us to consider the causes or
factors which are responsible for abnormalities and
diseases. Plants are endowed with life, and to live
they must have food. Part of the. food is derived
from the air, but they cannot subsist on air alone.
The sustenance of plants is also derived from the
soil.
It is to be regretted that laymen often regard the
soil as merely a conglomeration of inert particles of
dead rock. If this were true, plant life would be an
impossibility. It is because soils are teeming with
various forms of organisms beneficial to them that
plant life is made possible therein. The science of
Soil Bacteriology, though still in its infancy, has
already taught us much to help make the trucking
business much more profitable and successful than
it has been hitherto.
Indeed we may judge a soil by the kind of flora
which predominates there, and call it fertile and
healthy when this germ life helps to make it a f avor-
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. BACTERIA.
a. Rod shaped, b. coccus, c. spirillum, d. plate culture, showing bacterial colonies
isolated from soil.
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 x 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-
1 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. Brown1 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 -
Plot
No.'
Lab.
No.
Depth of
Sampling
Bacteria per Gram of Air-Dry Soil
I
II
III
IV
Average
601
A
4 in.
2033000
1627000
1793000
1555000
1752000
B
8 in.
1437000
I2IIOOO
I24IOOO
1104000
1248250
C
12 in.
541000
567000
559000
525000
546000
D
i6in.
287000
292OOO
3I2OOO
302000
298250
E
20 in.
147000
154000
159000
154000
153500
F
24 in.
92300
96500
95100
91500
93850
G
30 in.
49900
46300
50900
46900
48500
H
36 in.
32900
30000
33100
30400
31600
602
A
4 in.
3102000
287OOOO
29I7OOO
2947000
2959000
B
8 in.
2238000
2I77OOO
2105000
2258000
2194500
(J
12 in.
498000
531000
531000
528000
522000
D
i6in.
255000
328000
316000
314000
304250
E
20 in.
182000
I92OOO
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
42IOOOO
3932000
4164000
B
8 in.
3132000
2834OOO
2976OOO
2793000
2943750
C
12 in.
1016000
882OOO
901000
831000
907500
D
i6in.
320000
309000
3IIOOO
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.
35ioo
36600
34900
32600
34800
1 Brown,P. E., Iowa Agr. Expt.Sta. Research Bui. 8 : 283-321, 1912.
3 Plot No. 601. — Continuous corn. 602. — 2-year rotation, corn
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 Doryland1 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 of Depth of Cultivation on Soil Bacteria
Silt-
plowed 4 inches deep increases the number of bacteria. . 1546%
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%
1 King, W. E., and Doryland, Ch., Kansas Agr. Expt. Sta. Bui.
161 1211-242, 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 i o 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 Temple1 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
Soil No. 326
Soil No. 3260,
Date
March 26, 1909
No Manure
1,220,000
With Manure
1,220,000
April i, 1909
1.633 ooo
4..3OO.OOO
April Q, IQOQ .
6,120,000
I4,OOO,OOO
April 15, IQOQ..
3.780.000
IO,6lO,OOO
April 22, 1909
2.730.000
5,860 ooo
April 29, 1909 ... .
2. 77O.OOO
3,34.0.000
May 6, 1909
s.sio.ooo
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:
1 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
Plat No. i
Plat No. 4
Plat No. 5
Plat No. 6
Dec. 9, 1910
March 30, 1911
May 26, 1911
28,230,000
18,500,000
20,200,000
11,430,000
9,150,000
4,850,000
19,850,000
8,040,000
6,720,000
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 Penicillium, showing
conidiophores and conidia, b. mycelium
of Penicillium, c. an individual conidiopnore
and chain of conidia of Penicillium, d. two
conidia of Penicillium, showing attachment
of spores in the chain, e. fertilization ot
female oogonium by male anthendium, /.
mature oospore, g. fruiting stalks of Rn}zo-
pus, h, individual fruiting head of Rhizo-
pus showing spores, *. sexual fertilization
and k. zygospore of Rhizopus showing spores,
/. perithecium, showing asci and ascospores,
or winter spores, m. Pycnidium or sac in
which the summer spores are borne.
Normal Soil and Its Requirements 11
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 function of a normal soil is to provide avail-
able plant food. About 95 per cent, of the com-
bustible weight of a growing 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 place, 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 Sackett1 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 subtilis, 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 Nitrobacter. 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-
1 6 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. Headen1 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;
1 60 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
1 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. Schlosing1 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,2 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.
1 Schlosing, Compt. Rend. Acad. Sci. Paris, Ixxvii, 203-253.
» Chester, F. D., Pa. State Dept. of Agr. Bid. 98: 9-88, 1912.
1 8 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 necessary 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, Pseudomonas
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 Station1 has found that
an acre of soy beans for instance may fix about
I OCX) 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
1 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. Garman and
Didlake1 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
1 Garman, H. and Didlake, Mary, Kentucky Agr. Expt. Sta. Bui.
184: 343-363, I9H.
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 with 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. NlTRE-SlCK SOILS
This form of sickness, peculiar to certain Colorado
soils, was carefully studied by Headen x and Sackett. 2
Nitre-sick soils are those which contain such large
quantities of nitrates that they inhibit plant growth.
1 Headen, W. P., Colorado Agr. Expt. Sta. Bui. 155.
2 Sackett, W. G., Colorado Agr. Expt. Sta. Bui. 196:3-39, 1914.
FIG. 3. NITRE-SICK BEET FIELD, SHOWING BARREN SPOTS.
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 cornmeal or ashes.
The accumulation of excessive amounts of nitrates
in the soil is due to the activity of a bacterial soil
organism, Azotobacter 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., <?. 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
Damon1*.
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 J 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 lime
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 (o), cress
(o), cucumber (i), eggplant (2), endive (3), okra (3),
horseradish (2), kale (i), kohlrabi (i), leek (3), lettuce
(3), mustard (2), muskmelon (o), onion (3), parsley (o),
parsnip (3), pea, garden (i), pepper (3), potato (o),
radish (i), rape (2), rhubarb (3), sorrel ( - 1), spinach
(3) (fig- 4& to h), turnip (o), watermelon ( — i).
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 Blair2 a loamy to a clay loam will require
1 Hartwell, B. L., and Damon, S. C., Rhode Island Agr. Expt.
Sta. Bui., 160: 408-446, 1914.
"Blair, A. W., New Jersey Agr. Expt. Sta. Cir., 54: 3-11, 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 1120 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 flat 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-
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,1 may be seen in Table 5.
TABLE 5
Chemical Analyses of Different Types of Unproductive
Black Soils.
Kind of
Soil
Substance determined
Add
peat
Neutral
peat
Acid
peaty
sand
Neutral
peaty
sand
Insoluble & soluble silica, etc.
Potash (K2O)
10.40
.2^
9-OO
.12
88.63
.14
71-47
.28
Lime (CaO)
1.86
^.89
.08
S.QI
Magnesia (MgO).
.26
.52
.11
1. 71
Iron oxide (Fe2O3) ........
Aluminum oxide (AlzOa)
Phosphoric acid (P3Os)
Sulphur trioxide (SO3)
Carbon dioxide (C02)
2.87
•36
.49
.20
4-27
.40
.28
63
3-25
.08
.04
IO
5-03
.21
4.42
22
Volatile matter.
8^.16
81.16
8.16
12 l6
Total nitrogen
"O'i(-
1.82
-i.ci
.28
cy
Total potash (K2O)
Phosphoric acid soluble in
N/SHC1 . .
•34
.032
.26
.0506
1.62
.OO S8
1-25
.0^7
Total humus. . .
^0.68
2S-55
4.86
4.72
Acid humus..
27.74
1.22
4.64
none
Acidity in pounds calcium car-
bonate (CaCOa) Per acre foot
Hygroscopic moisture
I94O.OO
11.82
360.00
18.57
3500.00
1.65
none
•1.1O
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
1 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
Fisher1 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 of Peat Soil: Burning. The mistake is
1 Hopkins, C. G., Readhimer, J. E., and Fisher, O. S., Illinois Agr.
Expt. Sta. Bui. 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 burn 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-
Pounds
Average
Increase in bushels per acre
ment
fertil-
unfer-
izer
tilized
No.
per acre
yield
4-8-10 I
o-8-io
4-0-10
4-8-0
4-3i
IOOO
606.9
113.0
124.2
76.3
75-5
43-n
IOOO
79.1
I33-I
58.0
49.6
57-1
92-21
IOOO
307-0
130.0
240.0
145.0
2O.O
37-H
IOOO
234.0
332.0
285.0
I2O.O
89.0
1 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
No.
Pounds
fertil-
izer
per acre
Average
unfer-
tilized
yield
Increase in bushels per acre
4-8-10
o-8-i o
4-0-10
4-8-0
-64.6
25.0
47.6
145.5
49.0
$12.28
12.22
37-15
43-21
57-n
57-1 la
Average
1000
1000
1000
500
613.0
628.0
394-2
372.8
404.4
73-7
o.o
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
Cost of fertilizer
Average profit pe
$17.34
$ 9.56
51.84
$12.84
29.16
r acre. 47-8 1
We have as yet no definite data on the effect of lime
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, x 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
Total
Counties
Soluble
Chlorides
Carbonates
Sulphates
Salts
Boxelder
4,806
1,485
1,983
711
Salt Lake
2,440
545
858
2,334
Millard
10,852
640
1,418
9,795
Cache
5,792
i,573
1,515
2,539
•x Harris, F. S., Utah Agr. Expt. Sta. Bui., 145 13-21, 1916.
Diseases of Truck Crops
TABLE 7 — (Continued)
Parts of field producing medium crop
Total
Counties
Soluble
Chlorides
Carbonates
Sulphates
Salts
Boxelder
Salt Lake
7,075
4,228
3,021
875
1,727
792
543
i, 812
Millard
Cache
18,325
17,218
3,077
2,541
1,271
888
13,238
13,126
Parts of field where no crop would grow
Boxelder
Salt Lake
10,079
6,938
6,767
2,045
1,874
689
i,i54
3,636
Millard
21,488
6,289
1,875
13,304
Cache
30,148
3,585
795
23,027
Origin of 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, Tinsley1 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 alkali 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.
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
Fungi 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.
. Mycelium, 6. conidiophore bearing con-
idia, c. germinating conidium, d. fertil-
ized pogonium 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. Ward1
found it to be a very prevalent parasite in the garden
soils of Europe. In America the fungus was first
recognized by Atkinson2 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 hyphae. These swellings readily break
off 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-
1 Ward, M., Quart. Jour. Micros. Soc., New Ser. 22 : 487, 1883.
a 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 Pythium 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 other fungi which are capable of producing a
damping off in seedlings may be mentioned; Sdero-
tinia liber tiana Fckl., Phoma solani Halst., Colle-
totrichum sp., Fusarium sp.; Sderotium Rolfsii Sacc.,
and Rhizoctonia solani Kiihn. 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. RHIZOCTONIA.
a. Rhizoctpnia cankers on stems of young bean plants, b. young growing hyphae
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 Peltier1
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. x 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 hyphae 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 alrhost 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 (fig. 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 effect 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-
1 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, b. sweet potato hill killed
by Fusarium wilt, c. spores of Fusarium batatatis, d. spores of Fusarium hyper*
oxysporum, 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 batatatis 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 many
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. 7 e). 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 KNOT
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
numbers 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. 8. 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, ». matured female worm (d. to *. 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 semi transparent, 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), semi transparent
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 larvse, 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 of 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 Bessey1 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.
b. Garden Weeds. Birdsfoot trefoil, burdock, car-
petweed, dandelion, dead nettle, Florida beggarweed,
horse nettle, lamb's-quarters, mayweed, milkweed,
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.
1 Bessey, E. A., U. S. Dept. Agr. Bureau PI. Ind. Bui. 217 :
7-89, 1911.
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
resowings 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.), (Lycophotiasp.), (Peridroma
sp.), wire worms (Melanotus sp.), and white grubs
(Phyllophaga sp.).
CHAPTER IV
METHODS OF TREATING SICK SOILS
^ DAMPING OFF, whether induced by Pythium, Rhi-
zoctonia, or any other 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 injthe 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 evenly 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 may 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 SELBY.)
FIG. 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 Humbert1 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>£ x 8 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
of i% 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 of fig. Q) or may enter from the top as per illus-
1 Selby, A. D., and Humbert, J. G., Ohio Agr. Expt. Sta. Circ. 151 :
65-74, 1915.
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 of 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, Johnson1 presents some interesting data on
the effect of thick sowing on damping off.
y TABLE 8
Effect of Thick Sowing on Percentage of Diseased Plants.
Flat No.
Weight of seed sown
Plants Diseased
per flat
per JOO sq. ft.
i.
Grams
O.I
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
i. 60
Per cent.
o
o
8
15
35
&
80
92
96
2
3~
6
7
8
9,
10
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
1 Johnson, James, Wisconsin Agr. Expt. Sta. Research Bui. 31:
31-61, 1914.
58 Diseases of Truck Crops
should be taken to prevent the seedlings 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 may 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 larvae 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
61
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 micro6rganisms
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, x 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,
1 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.
1 Widtsoe, J. A.f and Merrill, L. A., Utah Agr. Expt. Sta. Bui. 117:
69-119, 1912.
51
66
Diseases of Truck Crops
TABLE 9
The Yields of Truck Crops as Harvested, with Different
Quantities of Water
Yield of crops is expressed in Ibs. per acre; quantities of water used
are expressed in acre-inches.*
CARROTS
i. Irrigation water supplied
2. Rainfall and soil water . .
3. Total water for use of
crop . . .
3-75
10.25
14.00
7.50
10.25
I7.7S
15.00
10.25
2S-2S
25.00
10.25
35.25
35-°°
10.25
45.25
60.00
10.25
70.2 <S
4. Total yield of carrots
(Ibs per acre)
^4S77
3^223
49SO7
467 SS
56930
68420
5. Yield per inch of irriga-
tion water. .
Q22I
441O
3106
1871
1627
1129
6. Yield per inch of total
water.
246Q
1872
1963
1326
1258
974
CABBAGE
I. Irrigation water supplied
2. Rainfall and soil water
3. Total water for use of crop. . . .
4. Total yield of cabbage (Ibs. per
acre) .
12.50
5-54
18.04
18400
20.00
5-54
25-54
18524
25.00
5-54
30-54
16310
40.00
5-54
45-54
20432
70.00
5-54
75-54
23098
5. Yield per inch of irrigation
water.
1479
926
652
511
33°
6. Yield per inch of total water.. .
1025
725
534
449
306
ONIONS
I Irrigation water supplied. . . ...
15.00
20.00
3O.OO
65.00
2 Rainfall and soil water ....
5-54
5.54
5.54
5.54
3 Total water for use of crop
20.54
25.54
35-54
70.54
4. Total yield of onions (Ibs. per acre).. .
5. Yield per inch of irrigation water
6. Yield per inch of total water
21471
1432
1045
22038
1 102
863
32437
1098
913
34I7I
526
484
1 The term acre-inch means the quantity ttfet 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) Subirrigation. As this implies, the water is
applied underground and through perforated pipes.
The conditions necessary for subirrigation 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, subirrigation
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
7O 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- vary ing 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
72 Diseases of Truck Crops
ing here, or wobbling there, to the great danger of its
stability. 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 winds 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. n). 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 Gilbert1 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
1 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 which 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 temperature is reached,
the fires may be started. Smudging and heating are
extensively 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, b.
drought injury of sweet corn (a. 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 trucker 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 somewhat with
FIG. 13. MALNUTRITION, SHOWING A
CABBAGE LEAF AFFECTED BY THE
DISEASE. (AFTER HARTER.)
Causes of Diseases in Crops 81
the crop, the nature of the soil, and the fertilizer
applied. 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 Stone1 and
Harter2 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,
1 Stone, G. E., Massachusetts Agr. Expt. Sta., Ann. Rept., 5-13,
1910.
2 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 1000 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 Allard1
and Freiberg2 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 100, 200, 400,
600, 800, 1000, 1200, and 1500
parts of virus solution.
1 Allard, H. A., "Some properties of the virus of the mosaic
disease of tobacco," Jour. Agr. Research, 6 : 649-674, 1916.
3 Freiberg, G. W., "Studies in the mosaic diseases of plants,"
Ann. Missouri Bot. Card., 4 : I75-232,
FIG. 15. MOSAIC, SHOWING AFFECTED PEA LEAF
^ *•
r
FIG. 16. BEAN SEEDS AFFECTED
WITH ANTHRACNOSE, Colletotri-
chum lindemuthianum.
Causes of Diseases in Crops
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 of Infection and Period of Incubation. Mosaic
may be readily transmitted from plant to plant.
The easiest way to prove this is to rub with the rin-
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 (Peronosporaceae). Late blight
of potatoes (Phytophthora infestans), downy mil-
dew of lima beans (Phytophthora 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. 16), 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
r61e 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 Hkely 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.
a. Dodder on Tomato plant, b. 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 many
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, Stone1
has shown that the heavy sinking seed give a higher
per cent, of germination than the lighter (see Tables IO
and n).
TABLE 10
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
100
117
17-
Onion
38
85
142.
Lettuce
44
88
100.
Onion
50
58
17.
Average
60
87
61.
1 Stone, G. E., Massachusetts Agr. Expt. Sta. Bui. 121 :3-i4, 1908.
94
Diseases of Truck Crops
TABLE n
Showing Results of Seed Separation by the Water Method
on Germination and Growth of Seeds of Onions.
Total of 400 Seeds Used
Per Cent, of Germination
No. of
Plants
Wt. of Plants
(grams)
Per Cent, of Increase
of Heavy over
Light
Total
Average
Heavy (sank)
Light (floated)
45-5
19-5
85
38
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 Hicks1 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 of Curled
Simpson Lettuce Seed
Fertilizer Used
How Applied
First
Sprouts
Per Cent.
Germinated
Fourth Day
Per Cent.
Germinated
Twelfth Day
Potash
In the rows
No sprouts
No sprouts
Mixed with the soil
«i «<
«« «
Phosphoric
In the rows
May 26
« <i
2-5
acid
Mixed with the soil
" 21
2-5
45.25
Nitrogen
In the rows
No sprouts
No sprouts
Mixed with the soil
«« «i
(i «
Lime
In the rows
May 23
o-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
u ««
(i «
Check,
no fertilizer
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
i-5
i-5
IO.O
95-0
1 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
44 26
May 24
May 25
24
May 24
2.O
6-5
37-5
93-0
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.
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. Manns1 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,
1 Manns, T. F.f Ohio Agr. Expt. Sta. Bui. 228 : 255-297, 1911.
PART III
101
CHAPTER VIII
SPECIFIC DISEASES OF TRUCK CROPS
FAMILY AGARICACE^E
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. r
Symptoms. It is characterized by an unsightly
' Tolaas, A. S., Phytopath. 5 : 51-53, 1915.
103
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 fluorescens is a
small rod rounded at both ends and motile by means
of polar flagella. 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. 18. MYCOGONE 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,1 there are no
evidences that tend to show that the Mycogone
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
1 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^E
THE ginseng is the only plant in this family which
is of 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
quinguefolium)
Ginseng is subject to numerous diseases, most of
which may be kept in check.
DAMPING OFF (Fie. 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 infected with Acrostalagmus showing diseased condition of nbro-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-
ing cup of Sclerotinia 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. 19 c).
The Organism. The mycelium (fig. 19 d) of Phy-
tophthora 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 Rosenbaum1
may germinate by means of a germ tube or by
swarm spores. The conidia germinate 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.
1 10 Diseases of Truck Crops
WHITE ROT
Caused by Sclerotinia liber tiana Fckl.
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 Rosenbaum1 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.2
1 Whetzel, H. H., and Rosenbaum, J., U. S. Dept. of Agr., Bur,
of PI. Ind., Bui. 250 : 7-44, 1912.
3 Rankin, W. H., Phytopath. 2 : 28-31, 1912.
Family Araliaceae in
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 panaois greatly
resembles S. liber tiana (fig. 19 p).
Control. Remove the diseased plants and the sur-
rounding healthy ones on a strip a foot wide. Drench
the soil with a heavy application 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 on a purple bronze color. In wet weather the
ii2 Diseases of iruck Crops
wilting is more sudden, and the stems bend into a
curve. In this case affected seedlings 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 Pestalozzi a 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 WlLT
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 1).
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 sclerotial like bodies (fig.
19 k) which apparently serve in tiding it over un-
favorable weather conditions. The fungus has been
identified by Rankin1 as Acrostalagmus panax. So
1 Rankin, W. H., Spec. Crops. U. S., 9 : 349, 1910.
ii4 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 Alter naria 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 Organism. 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^E
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 market. 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 Chcnopodiaceae 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 vulgar is)
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.
Arthur1 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.
n8 Diseases of Truck Crops
SOFT ROT
Caused by Bacterium teutlium Met.
This disease was originally described by Metcalf . x
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 which 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.
1 Metcalf, Haven, Nebraska Agr. Expt. Sta. iyth Ann. Rept.: 69-
112, 1904.
FIG. 20. BEET DISEASES.
a. Crown gall, b. scab, c. downy mildew, d. Conidiophore of Peronospora schachlii
arising from a stomate of an infected beet leaf, e. germinating zoospore of P. schach-
tii,f. oospore of P. schachtii, g. Cercospora leaf spot (after Halsted), h. conidiophore
and conidia of Cercospora beticola (after Duggar), i. Phoma leaf spot (after Pool and
McKay), k. pycnidium of Phoma beta (after T. Johnson) (d.-f. after Prillieux).
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 tumefaciens 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. tumefaciens 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. Smith1 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. P., et. al., " Crown Gall of Plants," U. S. Dept. Agr.,
Bur. PI. Ind., Bui. 213 : 13-200, 1911.
ri2o 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, smootji 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 Urophlyctis 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, r
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-
1 Clinton, G. P., Connecticut Agr. Expt. Sta. 39th. Ann. Rept. :
433-436,
Family Chenopodiaceae 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 Cystopus bliti (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. J In appear-
ance, infected leaves show white raised pustules or
sori 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 winter
(fig. 20C-f).
1 Pammel, L. H., Iowa Agr. Expt. Sta. Bui. 15 : 234-254, 1891.
124 Diseases of Truck Crops
DROP
Caused by Sclerotinia libertiana Fckl.
Drop on beets, which attacks young seedlings, but
not older plants, is otherwise not very different from
a similar trouble on lettuce. Clinton1 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 beta, 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
1 Clinton, G. P., Report of the Botanist for 1915, Connecticut
Agr. Expt. Sta. 39th Ann. Rept. : 433-436, 1915.
Family Chenopodiaceae 125
by means of a germ tube which enters the beet leaf
again. -2. Uredo 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
liberate 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 Phoma betes 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 Halsted1 as root rot of beet which he
attributed to a species of Phyllosticta.
1 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
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
McKay1 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
1 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 Stewart1 and by others. It produces
1 Duggar, B. M., and Stewart, F. C., New York (Cornell) Agr.
Expt. Sta. Bui. 1 86 : 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 Khizoctonia 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) Muller.
This disease is different from crown gall or tuber-
culosis. Although the symptoms are sometimes
manifested as knots or outgrowths on the main
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
9
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 okracea)
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. 21. SPINACH DISEASES.
a. Downy mildew, b. 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 Colletolri-
chum spinacice, f. leaf spot, g. spores of the leaf spot fungus Heterosporium variabile-
(b. c. e. after Halsted, d. after Reed).
^Family 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. 21 b) 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 spinacia 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 setae (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 133
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 variabile 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, z 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
1 Reed, H. L., and Cooley, J. S., Virginia Agr. Expt. Sta. Ann.
Rept. 1909 and 1910.
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
var labile, 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, Peronospom 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 Arthur1 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 cynarcz 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-
1 Arthur, J. C., Mycologia, 11 153, 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 obscura H. and W.
Heald and Wolf1 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 -sept ate,
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
1 Heald, F. D., and Wolf, F. A., Mycologia, 3 : 5-22, 1911.
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 cynarcz) . In damp weather it may be necessary
to spray from three to four times during the season.
DISEASES OF LETTUCE (Lactuca saliva)
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
Brown1 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 was 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
1 Brown, Nellie A., U. S. Dept. of Agr. Jour. Agr. Research, 4 :
417-478, 1915. ,,:>-
Family Composite 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
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 Composite.
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
FIG. 22. LETTUCE DROP.
To the right, artificially inoculated plant; to the left, healthy.
Family Composite 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
Istvanffi1 was able to confirm the work of De Bary,
who first indicated the relationshp of Botrytis cinerea
with Sclerotinia Fuckeliana.
LETTUCE DROP
Caused by Sclerotinia 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.
1 Istvanffi, G. De, Ann. de 1'institut central ampel. roy. Hongnois:
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 r 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 lactuccz Pass, and Septoria
consimilis E. and M.
1 Stevens, F. L., North Carolina Agr. Expt. Sta. Bui. 217 : 7-21,
1917.
FIG. 23. LETTUCE DISEASES.
a Germinating sclerotium of Sclerotinia libertiana
the 'cause of lettuce drop, b. section of fruiting cup
(apothecium) showing asci, ascospores and parapnyses
of S. libertiana, c. section through sclerotium of A.
libertiana, d. germinating ascospore of .S .libertiana (a.
to d. after F. S. Stevens), e. Cercospora leaf spot.
Family Composite 145
This disease is induced by two species of Septoria
fungi. The symptoms produced by both are -so
nearly alike 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,
10
146 Diseases of Truck Crops
where it has been recently described by Stevenson. x
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
porrtfolius)
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
1 Stevenson, J. A., Journal Department of Porto Rico, I : 93-
117, 1917.
Family Composites 147
Soft rot of salsify is more a storage trouble than a
field trouble. The disease, as it has been studied by
Clinton, T 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-
1 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
(Helianihus 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. v
FIG. 24. SOUTHERN BLIGHT OF THE SALSIFY.
the right healthy plant, to the left diseased plant, with root rotted off.
Family Composite 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 Composite contains a large number of
weeds. The following are often troublesome: rag-
weed (Ambrosia artemisifolia), great ragweed (Am-
brosia trifida), Mayweed (Anthemis cotula), burdock
(Arctium minus), ox-eye daisy (Chrysanthemum
leucanthemum pinnatifidum) , blue sailors (Cicorum
intybus), 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
qfficinale), 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, Puccinia 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
(Convolvulus batatas)
Sweet potatoes are subject to numerous field and
storage diseases, many of which may be controlled.
152 Diseases of Truck Crops
SLIME MOLD
Caused by Fuligo molacea Pers. and Physarum
plumbeum Fries.
Very often the plants in the seed beds are covered
with white, yellowish, 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 powder. The growth, which
is a slime mold, .has been determined as Fuligo
molacea 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 violaced), b. slime mold (Physarum plumbeum), c. pox or
pit, d. formation of a cyst and liberation of spores of Cystospora batata (after Elliot),
e. white rust, /. oospore of the white rust fungus, g. soft rot, h. ring rot, i. fruiting
stalks of Rhizopus nigricans.
Family Convolvulaceae 153
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 I 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.
1 Elliot, J. A., Delaware Agr. Expt. Sta. Bui. 114 : 3-25, 1916.
Family Convolvulaceae 155
WHITE RUST
Caused by Cystopus ipomcece-pandMaruz 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 with 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.
Symptoms. 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 liquid 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 vitality 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.
t
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, b. black shank, c. showing a pycnidium of the
black rot fungus, d. dry rot, e. cross section through /, 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 batatis (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.
160 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 Rox1
Caused by Sph&ronemafimbriatum (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
1 Material drawn from the author's work. Taubenhaus, J. J.,
Delaware Agr. Expt. Sta. Bui. 109 : 3-56, 1915.
Family Convolvulaceae 161
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 y£ 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
K
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 growers 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-
1 64 Diseases of Truck Crops
tive portion known as "mycelium*1 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.t
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 are found
Family Convolvulaceae 165
protruding. The fungus, so far as is known, lives
only on sweet potato foliage.
SEPTORIA LEAF SPOT
Caused by Septoria bataticola 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. 27 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 bataticola 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 tubericola (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
166 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 tubericola. 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 born singly or in groups
FIG. 27. SWEET POTATO DISEASES.
a. Trichoderma rot, b. Septoria leaf spot, c. soil stain, J. Charcoal rot, e. Texas
root rot: notice the center of the hill is dead, while the side shoots are alive as they
are supported by the secondary roots formed at the nodes of the vines, /. sweet
potato artificially inoculated with Sclerolium Rolfsii, g. net necrosis.
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. x
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
1 For further details of this fungus see Taubenhaus, J. J., Ameri-
can Jour, of Bot., 2 : 324-3-31, 1915.
1 68 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 infuscans 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
170 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 100 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 born 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 batatatis Woll. Fusarium
hyperoxysporum Woll.
The terms "stem wilt," "vine wilt," or "yellows"
are commonly used to describe this disease, and
a
FIG. 28. SWEET POTATO DISEASES.
a. and i. Chains of conidia of the soil stain fungus Monilochceles infuscans,
b. to I. 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 Phymatotrichum omnivorum, r. mycelial strands
of the Texas root rot fungus, Ozonium omnivorum from dead cotton plant (q.
and r. after Duggar), m. sclerotia of Sderotium bataticola.
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. 27 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^e 173
three quarters of a million for the entire sweet potato
crop of the United States. >
CHARCOAL ROT
Caused by Sclerotium bataticola 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 1913, 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, Sph&ronema 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 5. 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 hyphas. 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 175
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.
Sclerotium Rolfsii 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) Mull.
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 Convolvulaceae 177
from the mother cuttings. However the growing of
slip seed every year is a tedious process. To im-
prove the strain and avoid disease slip 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,
12
1 78 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 clipped.
To obviate this possibility 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 Convolvulaceae 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, 3-3-5°-
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 i% 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,
1913, 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
1 4th of November. Rainy days and damp weather
Family Convolvulacese
181
offer no opportunity for the lowering of the moisture,
as will be seen on November i6th, when opening the
LTABLE 14
Storage Temperature and Moisture Reading for November, 1909, for
1st and jd Floors.
Thermometer Reading
First Floor
Ther.
Moist.
Moist.
Read.
Read.
Read.
Outdoor
Date
East Side
West
Third
Floor
First
Floor
Third
Floor
Temp.
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 53
50 58
57 62
65 55
6? 57
38 54
Pair
3
42 S3
45 60
55 60
67 46
70 42
33 52
Fair
4
52 56
56 63
57 62
68 54
65 50
54 60
Fair
5
6
46 52
41 S3
48 57
44 60
56 60
52 62
63 52
67 60
65 48
68 47
37 54
30 60
Fair
Fair
7
43 54
49 60
54 64
68 72
67 60
35 64
Fair
8
S3 58
58 64
59 66
80 77
70 67
54 60
Fair and cloudy
9
5« 54
65 57
62 54
70 71
72 60
63 50
Rain
10
50 50
54 54
45 52
70 55
60 52
38 45
Cloudy and fair
II
45 47
50 51
Si 50
65 54
62 48
33 38
Fair and windy
12
45 SO
49 SS
50 54
65 56
63 55
36 42
Fair
13
48 SS
54 60
52 62
71 55
64 42
45 62
Fair
14
54 58
50 64
57 63
70 62
65 56
52 63
Cloudy
IS
46 50
4« 52
54 56
61 62
65 62
38 43
Cloudy and rainy
16
52 54
56 58
56 58
75 79
68 70
50 52
Rainy
17
50 50
56 55
54 56
72 62
68 60
42 48
Fair
18
19
47 55
SS 60
50 6l
58 68
54 60
58 68
72 50
71 59
63 45
66 49
37 62
42 67
Fair
Fair
20
58 63
62 70
58 72
68 65
63 55
55 70
Fair
21
58 65
.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
Fair
24
23
26
50 58
47 55
50 55
56 62
52 59
55 58
64 72
62 60
60 60
59 46
64 64
63 44
54 55
56 62
SO 73
38 50
34 46
Fair and windy
Fair and cloudy
Cloudy and rainy
•27
23
52 54
57 58
60 60
62 62
58 63
60 55
62 65
72 75
65 65
70 70
45 50
46 45
Cloudy
Rainy and cloudy
?9
60 68
62 62
58 60
75 74
70 74
SO 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 1 6 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 1 6 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% feet wide. Large houses should have their
main aisle along the side walls. These should be at
least 3>2 feet wide. A center aisle between the two
rows of bins should be three feet wide. All these
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 ijA 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
184 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 (Ipomcea pur pur ea), the
wild sweet potato (Ipomosa pandurata) , and the
small and great bindweed (Convolvulus arvensis and
C. sepium) are all subject to black rot, Sph&ronema
fimbriatum. All these weeds are also attacked by
white rust, Cystopus ipomcece-pandurancB. 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 CRUCIFER^E
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
1 86 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 Plasmodiophora brassicce 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), e. individual black rot germs of
Pseudomonas campestris, /. 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. pycnospores of P. oleracece (i. and.;', after Manns).
.Family Cruciferae 187
per cent, of the crop, although most of it may be
prevented.
Symptoms. Affected plants show a wilting of the
foliage 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 seedlings 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,1 the first signs of germination
are a swelling of the spores, followed later by
a bulging at one side. The inner pressure exerted
splits 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
1 Chupp, Charles, New York (Cornell) Agr. Expt. Sta. Bul.t
387:421-452, 1917.
1 88 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,1 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
1 Cunningham, L. C., Vermont Agr. Expt. Sta. Bui., 185 : 67-96,
1914.
Family Cruciferae
189
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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. Smith1
1 Smith, E. F., U. S, Dept. of Agr. Farmers Bui., 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 broccoli, Brussels sprouts, cauliflower, char-
lock, collard, kale, kohlrabi, black mustard, rape,
rutabaga, radish, sweede, and turnip.
The Organism. 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 Harding1 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
1 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.
1 The Organism. The Bacillus is rod- shaped, long
or short, and usually formed in chains. It moves
about by peritrichous flagella. 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.
13
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
shrunken. 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
application should be given as soon as the disease
makes its appearance. Later the application will
be governed by weather conditions.
DROP
Caused by Sclerotinia libertiana Fckl.
Drop is a disease fairly common on cabbage. The
trouble may be recognized by a drooping and wilting
Family Cruciferae 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
Manns1 in Ohio, 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 seedlings 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.
1 Manns, T. P., 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 applied 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 Alternaria brassica (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. 31 a).
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
FIG. 3i. 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,
e. conidia of Fusarium conglulinans, 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.
Symptoms. 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
conglutinans Woll. is given by Gilman.1 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 Gilman2
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
1 Oilman, J. C.f Annals Missouri Bot. Garden, 3 : 2-84, 1916.
2 Jones, L. R., and Gilman, J. C., Wisconsin Agr. Expt. Sta. Bui.,
38 : 1-69, 1915.
FIG. 32. 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 199
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 Harter1 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
1 Harter, L. L., U. S. Dept. Agr.'Bur. PI. Ind. Circ., 39: 3-8, 1909.
2oo 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. botrytis)
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. 1 86, and drop, p. 143.
BACTERIAL LEAF SPOT
Caused by Pseudomonas maculicola McC.
Bacterial leaf spot was first studied and described
by McCulloch1 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.
1 McCulloch, Lucia, U. S. Dept. of Agr. Bur. PI. lad. Bui. 225 : 7-
15, 1911.
FIG. 33. DISEASES OF THE CAULIFLOWER AND RADISH.
a. Spot disease of cauliflower (after McCulloch), 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 Mycosphcerclla brassicicola, i.
ascospores of Mycosphcerella brassicicola (g. to ». 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-zoogloese 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 x 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
1 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 Mycosphczrella brassicola (Duby) Lind.
The exact distribution of this disease is as yet un-
known. The trouble was studied by Osmun and
Anderson1 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 (Cochkaria
armoracia)
The horseradish is generally considered a hardy
plant. However, it is subject to numerous diseases.
1 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 armor aci<R 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.
206 Diseases of Truck Crops
SHOT HOLE
Caused by Septoria armoracice, Sacc.
Shot hole is a very serious disease which attacks
the foliage 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 brassica
(Berk.) Sacc., see p. 196.
WHITE MOLD
Caused by Ramularia armor acicB Fckl.
White mold is frequently met with on foliage of
the horseradish. The spots are indefinite, irregular,
PIG. 34. CERCOSPORA LEAF SPOT
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 armoracicB 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
fertilized in order to maintain their vigor, thereby
also preventing the leaf diseases from getting
troublesome.
DISEASES OF THE KALE (Brassica okracea
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,
208 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 brassica Wor., see p. 1 86.
DISEASES OF THE MUSTARD (Brassica
Japonicd)
Garden mustard Brassica Japonica is cultivated
for its foliage. It is used as a green, relished for its
edible qualities, 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
Caused by Pseudomonascampestris (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-
vasculaf 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,
seep. 317.
DAMPING OFF
Caused by Rheosporangium aphanidermatum Ed.
This disease, which was studied and described by
Edson,1 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.
1 Edson, H. A., U. S. Dept. of Agr., Jour. Agr. Research, 4: 279-
292,
210 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 hyphae. 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, b. presporangium
C. mycelium of Rheosporangium aphanidermatum , d. fertilization of the female
oogonium by the male antheridium, e. mature oospore, /. root knot (b to e afler
Edson).
Family Cruciferae 211
With the maturity 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. Melhus1
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
1 Melhus, T. E., Wisconsin Agr. Expt. Sta. Research Bui., 15: 25-
83,1911.
Pamily Cruciferae 213
turnips (Brassica rapa), black mustard (Brassica
nigrd), rutabaga (Brassica campestris), shepherd's
purse (Capsella bursa-pastoris) , garden cress (Le-
pidium sativum), wild pepper grass (Lepidiumvirgini-
cum), hedge mustard (Sisymbrium officinale and S.
altissimum), candy- tuft (Iberis umbellata), water cress
(Nasturtium officinale), and wall flower (Cheiranihus
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.
Fertilization 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.
BLA^K ROT
Caused by Pseudomonas 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 Higgins1 in Georgia.
1 Higgins, B. B., U. S. Dept. of Agr., Jour, of Agr. Research, 10:
157-161, 1917.
FIG. 36. TURNIP DISEASES.
a. and b. Anthracnose, c. cross section through acervulus, d. anthracnose spores
e. Cylindrosporium leaf spot, /. Phoma rot, g. Sclerotinia rot (c. and d pfter
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 brassiccz 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 bmssictz
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 Clinton1 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., 36th. Ann.Rept. :
355-353, 1912.
216 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, b. Macrosporium herculeum, showing
conidiophores and conidia, c. individual conidium of M . herculeum
(a. to c. after F. C. Stewart).
Family Crucifcrae 217
MACROSPORIUM LEAF SPOT
Caused by Macrosporium herculeum 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 (Lepidium 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^E
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.
218
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 cerifera, Cucurbita fcetidissima, C. call-
fornica, 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 vittatd).
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 Mycosphaerella wilt, d. section through
a perithecium of Mycospharella citrullina, showing immature asci, e. ascospores of
M. citrullina (c. to e. after Grossenbacher),/. Alternaria leaf blight, g. Conidiophores
and spore of Macros porium 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 when 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
flagella. 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 Mycosph&rella 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. Grossenbacher1
found that infection is localized at the nodes and not
at the internodes (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
1 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 Alternaria brassica 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
earliness in maturing; (3), resistant qualities; (4),
form, size, and netting; (5), texture and edible quali-
ties; (6), shipping qualities. Blinn x 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 cucurbits E. and E.
This disease behaves very much like leaf blight.
In the former, however, the spots are usually of a
1 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 Rolfsii 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
is
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.1
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
1 More, C. T., and Branch, G. V., U. S. Dept. of Agr. Farm. Bui.
707 : 1-23, 1916.
Family Cucurbitacese 227
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-
FIG. 39. RESISTANT CANTALOUP STRAIN.
a. Cantaloup hill, destroyed by Alternaria leaf blight, b. cantaloup hill resistant
to Alternaria blight, a. and b. same variety (Rockyford) growing in same field
under equal conditions.
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,
Didbrotica 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 Enlows1
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
1 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, x 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 Pseudoperono spora cubensis (B. and C.)
Rost.
Downy mildew is prevalent in New Jersey, New
York, Florida, Texas, and possibly other States. It
1 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), c. individual germs of
Fseudomonas 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
mycelium is hyaline, 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, x 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 Orton2 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.
1 Humphrey, J. E., Massachusetts Agr. Expt. Sta. loth Ann.
Rept.: 225-226, 1892. fcj
2 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. Durst1 recommends spraying with " Black
1 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 OF THE CITRON (Citrullus 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 few 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 cucurbitarum,
b. squash entirely rotted by the Choanophora fungus, c. young conidiophore or
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 (a, c. to h. after
Wolf), *. Fusarium wilt of young squash plants, j. 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, Massachusetts, 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 growth 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. Wolf1 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.
1 Wolf, F. 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
with 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 cucurbitarum
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 alike. 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 cucurbitcz Taub. x
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. cucurbitcE 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
1 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 cucurbita of the squash.
ROOT ROT, see RHIZOCTONIA, p. 45.
ROOT KNOT, see NEMATODE, p. 49.
DISEASES OF THE WATERMELON (Citrullus
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. blossom end rot.
Family Cucurbitaceae 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 Meier1 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 a). 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
1 Meier, F.C., U.S.Dept. of Agr., Journal ofAgr. 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 catfses stem
end rot of watermelon 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 tubericola 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 Cottetotrichum 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
FIG. 43. WATERMELON ANTHRACNOSE.
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-
16
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
setse 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
fungicide 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 burn the
foliage.
CERCOSPORA LEAF SPOT, see CANTALOUPE, p. 224.
CERCOSPORA LEAF SPOT
Caused by Cercospora citrulUna 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.1; Fusarium Poolensis Taub.a
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
1 From unpublished data by the writer, the organism was carried
as Fusarium No. 106.
2 The organism was carried as Fusarium No. 116.
FIG. 44. WATERMELON DISEASES.
a Wilt (Fusarium niveuni), b. Bordeaux injury, c. Tom Watson,
an ideal shipping melon, d. macroconidia of Fusarium niveum.
Family Cucurbitaceae 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 citrulli 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 cucurbita, 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 Cucurbitaceae 247
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 Cucurbitaceae 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 cucurbit weeds are
subject to the diseases which attack the cultivated
species.
CHAPTER XV
FAMILY GRAMINE^E
OF this great family the only crop that concerns
the trucker and gardener is sweet corn. This is
grown to a great extent in the more northern States.
In the South, the ordinary field corn is grown instead
of sweet corn and is sold for "roasting ears" or on the
cob in the milky stage. The present discussion will
limit itself to sweet corn only. It is estimated in the
Thirteenth United States Census that the total area
of sweet corn 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
FIG. 45. SWEET CORN DISEASES.
a. Bacterial blight, b. individual blight organisms (a. to b. after F. C. Stewart),
c. smut, d. smut spores, e. and/, germinating spores of Ustilago zece(d. to/, after J. B.
S. Norton).
Family Gramineae 251
sweet corn 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.1 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 P. Smith, 2 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 affected 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
1 Stewart, F. G.-, New York (Geneva) Agr. Expt. Sta. Bui. 130 :
424-439, 1897.
2 Smith, E. P., Bacteria in 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 bundles 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 Gramincae 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
aecidium of this rust occurs on oxalis and is known as
jEcidium oxalidis Thum. The uredo and puccinia
stages both occur on the corn.
WEEDS
So far as is known, none of the Graminaceous
weeds are subject to the three diseases of the sweet
corn 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 Labiatae: 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 x has estimated
1 Fleet, W. V., U. S. Dcpt. 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 menihcB Pers.
The disease attacks about thirty-five members of
the mint family. All the three stages i. e., secidio-
spores, uredospores, and teleutospores, occur on the
same host. The disease is characterized by brown
sori 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 melisscz Desm.
The disease is characterized by numerous brownish
spots which are angular and apparently limited by the
Family Labiatae £57
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 cataria (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 nepeta 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 (Marrubium
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^E
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 7°>487 acres, yielding a crop valued at
$2,785,502. The States ranked according to largest
area devoted to peas x were as follows : South Carolina,
Georgia, North Carolina, Michigan, Alabama, Wis-
consin, Mississippi, Arkansas, Texas, Illinois, Tennes-
1 In the Thirteenth Census, no distinction is made between the
garden pea and the cowpea.
259
260 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 in j ured
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,
FIG. 46. 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 Leguminosse 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, J 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 lathy ri 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.
1 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.
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 (c. d. and /. after Whetzel), g. Cercospora leaf spot, h. Isariopsis griseola leaf
spot, *. conidiophores and conidia of Isariopsis.
Family Leguminosae 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 libertiana 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. x 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 lindemuthianum (Sacc.
& Magn.) B. and C.
Anthracnose may be considered one of the most
destructive bean diseases. However the trouble
1 McClintock, J. A., Phytopath. 6 : 436-441 , 19 16.
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
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 Edgerton1 that from one
1 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, Barrus1 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
x Barrus, 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. lindemuihianum,
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 Wolf1
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.
1 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. b. c. different stages of downy mildew on pods, d. tuft of conidiophores and
conidia of Phythophthora 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, I. 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
dry 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
Pythium (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 subcircinata 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.
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.
270 Diseases of Truck Crops
DISEASES OP THE COWPEA~(Vigna 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 lathyri 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 lathy ri as worked out by
Manns, x 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
angularrrusty 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. P., Delaware Agr. Expt. Sta. Bui. 108 : 3-44, 1915.
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. Fusarium wilt, b. field of cow peas killed by Texas root rot, c. root knot, d.
row of iron cow pea resistant to Fusarium wilt in sick field where other varieties of
peas have died (a. and d. after W. A. Orton).
Family Lcguminosae 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. Orton1 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 Pseudomonas pisi Sack.
Blight is a new disease recently found by Sackett2
in the pea fields of Colorado. So far as is known, the
1 Orton, W. A., U. S. Dept. of Agr. Bur. PI. Ind. Bui. 17 : 9-36,
1902.
2 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 Pseudomonas pisi, c. Sclerotinia libertiana
rot on bean pods, d. endospore of Thielavia basicola, e. chlamydospores of T. basicola.
Family Leguminosae 275
THIELAVIA ROOT ROT
Caused by Thielavia basicola 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 course out of the question. The method of control
suggested is crop rotation. Investigations by John-
son1 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
Caused by Spharella 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.
1 Johnson, J.f 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.
The 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 localities
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.
1 Stone, R. E., Annales Mycol., 10 : 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 sori 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
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 (b. 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 effect 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 x 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 aecidiospores 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
1 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 branch
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
life 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. Sirrine1 has
1 Sirrine, F. A.. N. Y. (Geneva) Agr. Expt. Sta. Bui. 188 : 122-
166, 1 900.
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 Ibs. resin, I Ib. 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-like 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. Tubercularia 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 schoenopo-
rasum)
RUST
Caused by Pucdnia porri (Sow.) Wint.
This rust, though prevalent in Europe, has been
reported but once in the United States by Clinton1
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
1 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, p.. interior of storage
house, showing method of stacking 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,
1 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 stand to the en tire 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, b. mature conidiophore and conidia of Peronospora schleideni,
c. fertilization of the female oogonium by the male antheridium, d. oospore (a. to
d. after Whotzel), e. onion smut, /. spore ball of the smut fungus, g. spore germina-
tion, formation of sporidia at x, h. Vermicularia anthracnose, *. section through
acervulis of Vermicularia circinans, j. setae and spore formation in V. circinans (e.
to g., i. and j. after Thaxter), k. pink root of onion, healthy and diseased bulbs, I.
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 Liliaceas 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 blight 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
Whetzel1 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
1 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
corn smut, p. 252.
Family Liliaceae 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 circinans 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).
19
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 Macro sporium 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). Selby1 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
1 Selby, A. D., Ohio Agr. Expt. Sta. Bui. 214 : 414, 1910.
3 Investigations by the author seem to show that pink root is
paused 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 Beattie1 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
1 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 100 to 300 bushels each. However,
neither bags nor bins are satisfactory. The best
method is storing in crates.
Of the Liliacese weeds, the only one of importance
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.E
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
295
296 Diseases of Truck Crops
States. According to Stevenson1 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.2
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
1 Stevenson, J. A., Jour. Dept. Agr. of Porto Rico, 1 : 93-117, 1917.
2 From unpublished work by the writer.
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
298 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). Duggar1 claims that the
pink buff color mentioned above represents the
colored spore masses of the fungus which he named
Phymatotrichum 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.
1 Duggar, B. M., Ann. Missouri Bot. Gard., 3: 11-23, 1916.
CHAPTER XX
FAMILY PORTULACACE^:
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 portulacece (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^E
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
1 Harter, L. L., U. S. Dept. of Agr. Jour. Agr. Research, 2 : 331-
338.
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 two 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, b. Phomopsis on fruit, c. conidiophores, d. 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/, after Harter),
t>. 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 PEPPER (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 piper ata ( 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 piper alum 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.
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 setae,
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 Rolsfsu 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.
306 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 which 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
308 Diseases of Truck Crops
germination. Poor sprouting may sometimes be
attributed to shipping of seed in overheated cars.
In this ease 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. x
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 assuming 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, b. curly dwarf (a. and 6. after Appel), c. net necrosis, d. spindly sprout,
e. black 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 Unknown.
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
3io 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 fertility 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 Unknown.
This disease is peculiar 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 quality 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 uprolling of the margins
of the leaflets is a characteristic of tip burn, also
distinguishing it from late blight. 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 Solanaceac 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 Worthley1 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.
1 Worthley, E. I., Science, N. S., 42 : 460-461, 1915.
314 Diseases of Truck Crops
POWDERY SCAB
Caused by Spongospora subterranea (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.1
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 chromo 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-
1 Melhus, I. E., and Rosenbaum, J., U. S. Dept. of Agr. Jour. Agr.
Research, 7 : 213-254, 1911.
a
g
FIG. 59. DISEASES OF THE POTATO.
a. Powdery scab, early stage, b. 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 «** %• -
*
FIG. 60. 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
cells 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 amoebae. The parasite is confined to
the phloem of the host. The invaded cells are not
killed, but are stimulated to an abnormal cell division.
316 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.1
Symptoms. Blackleg does not manifest itself until
the plants are about 7 to 10 inches high. Diseased
plants are unthrifty, undersized, with the branches
1 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 chromo genus Gasp.
Common scab is a disease which is generally skin
deep. The kind of injury and the severity of infeo
3i 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 believed to belong to the class of fungi and
was originally named Oospora scabies Thaxter. But
two American workers, Lutman and Cunningham,1
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
1 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 endobioticum (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
believed 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. 61 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 endobioticum has
been investigated by Johnson1 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 Soc.,
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, California. 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. Or ton1 has shown that leak may
be induced by the fungus Kkizopus nigricans. For
a fuller description of this fungus, see soft rot of sweet
potatoes, p. 156. Hawkins2 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.
1 Orton, W. A., U. S. Dept. of Agr. Bur. PI. Ind. Circ. 23 : 1 1, 1909.
3 Hawkins, L. A., U. S. Dept. Agr. Jour. Agr. Research, 7: 627-639,
1916.
81
322 Diseases of Truck Crops
LATE BLIGHT
Caused by Phytophthora infestans (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. 6 1 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. 61 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. 61. POTATO DISEASES.
a. Black wart (after Giissow), &. 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 Phyiophihora infestans, by
means of zoopores (after Ward),/, mature oogpnium of P. infestans (after Clinton),
/?. melters, surface view, early stage of infection, h. pycnidium of Phoma tuberosa
(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
hyaline, non-septate. As shown by Melhus1 and
others, the mycelium may be carried from year to
year within the infected tubers. In fact this is but
one way late blight 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, a 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° P.). 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, Clinton3 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
1 Melhus, I. E., U. S. Dept. of Agr. Jour. Agr. Research, 5 : 59-65,
15-
a Melhus, I. E.f Wisconsin Agr. Expt. Sta. Research Bui. 37 : 1-64,
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. Mature 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 Phoma solani Mel., Rosen., and Sch.
Phoma rot is found only on bruised tubers. It is
also found following injuries produced by powdery
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.1
Anthracnose was first described by O'Gara2 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
1 Taubenhaus, J. J., Mem. N. Y. Bot. Card., 6 : 549-560, 1916.
2 O'Gara, P. J., Mycologia, 7 : 38-41, 1915.
FIG. 62. POTATO DISEASES.
c. Early blight (after L. R. Jone^), b. spores of the early blight fungus, c. silver
scurf, d. conidiophores and conidia of the silver scurf fungus, e. and /. Fusarium
oxysporum wilt in tubers, g. chlamydospores and one to several celled conidia of
F. oxysporum, h. conidiophores of F. oxysporum (g. and h. after Sherbakoff) , *. 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
Spondylocladium atrovirens Harz. Colletotrichum
atramentarium differs from most Colletotrichums 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 byVerticillium albo-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 Orton1 is
characterized by a sudden wilting of the foliage (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
Fusarium wilt.
FUSARIUM WILT
Caused by Fusarium oxysporum (Sch.) Sm. and Sw.
Fusarium wilt is a disease which thrives best in
warm climates. In California, 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 Verticillium
1 Orton, W. A., U. S. Dept. of Agr. Bui. 64 : 16-18, 1914.
328 Diseases of Truck Crops
wilt is prevalent. In Michigan, Illinois, Wisconsin,
and Minnesota, Fusarium 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
wilting 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 Solanaceas 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 jelly like 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 trichoihecioides 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 Sclerotium Roljsii. e. pure culture of
5. Rolfsii.
Family Solanaceae 331
first described by Jamieson and Wollenweber. x The
trouble is the same as that described by Wilcox2
and the causative organism was previously named
Fusarium tuberivorum. 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 which
are capable of producing a rot on tubers through a
wound. Sherbakoff3 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. 630).
1 Jamieson, C. O., and Wollenweber, H. W., Jour. Wash. Acad.
Sci., 2 : 146-152, 1912.
2 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 wet,
poorly drained soils, and during seasons of heavy
rainfall. Recently Rosenbaum x 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
1 Rosenbaum, J., U. S. Dept. of Agr., Jour. Agr. Research, 9 : 413-
419, 1917.
Family Solanacese 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 when the tubers are held in
storage. Most 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. Appleman1 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
1 Appleman, C. O., Maryland Agr. Expt. Sta. Bui. 167 : 330, 1912.
Family Solanaceae 335
piles, for the potatoes in them are almost 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 may be 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 Solanaceae 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
blight, 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-
man1 clearly shows the profits to be derived from
spraying.
1 Lutman, B. F.,Vennont Agr. Expt. Sta. Bui. 159 : 216, 296, 1911.
Diseases of Truck Crops
TABLE 16
Gains from the Use of Bordeaux Mixture on Late Potatoes. 20 Years'
Experiments.
Yield per
Acre
Variety
Gain
Prevalence
and Date
Sprayed
Per
of Late
of Planting
Nnt
Acre
Blight
Sprayed
IV (/*•
Sprayed
White Star
bu.
bu.
bu. %
May, 1891
Aug. 26, Sept. 8
313
248
65 26
some
May, 1893
Aug. i, 1 6, 29
291
99
192 194
much
May 20, 1893
Aug. i, 16, 29
338
114
224 196
much
Apr. 26, 1894
May 20, 1895
June 16, July 17, Aug. 30
July 25, Aug. 13, 31
323
389
251
219
72 29
170 78
none
rot
Polaris
May 15, 1896
Aug. 7, 21
325
267
68 26
none
June i, 1897
White Star
July 27, Aug. 17, 28
151
80
71 89
some
May 10, 1898
July 21, Aug. 10
238
112
126 112
little
Average (3 varie-
ties)
May 1 8, 1899
July 26, Aug. 17, Sept. 8
229
161
68 42
little
Delaware
May 23, 1900
Aug. 4, 23
285
225
60 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, 1963
Aug. 10
36i
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
May i, 1907
Aug. 13, 22
July 16, 25, Aug. 8, 22
133
171
IOI
63
32 32
108 175
some
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. 15,23,3°
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 off, 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,
Phytophthora infestans, e. conidia of buck-eye rot Phytophthora terrestris, f. conidia
of P. terrestris, germinating by means of zoospores, g. zoospores, h. mature oospores
of P. terrestris, i. buck-eye rot (e. to i. after Sherbakoff).
Family Solanaceae 341
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 burned 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 sunlight.
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 Solanaceae 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 Solanaceae.
The Organism. Pseudomonas solanacearum is a
medium-sized rod, with rounded ends and motile
by means of polar flagella. Pseudo-zoogloese are
common in old cultures. No spores are formed;
on agaragar, colonies are white, then dirty white,
afterwards becoming brown with 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 infestans (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
suffer 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.1 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
1 Sherbakoff, C. D., Phytopath. 7 : 119-129, 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 cornmeal 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
iield. 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. x
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 1395-399, 1916; and in Phytopath.
7 : 52-53,
346 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 destructives 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
- <•;>
*v <Cw:''
Wv.,
FIG. 65. TOMATO DISEASES.
a. Various forms of vegetative cells of the yeast rot fungus, b. ascus, j. ascosporeh
of the yeast rot fungus (a. to c. after Schneider), d. Phoma rot on foliage, e. 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. TOMATO DISEASES.
a. Septoria leaf spot, b. section through a pycnidium of Septoria lycopersici
(after Levin), c. section through acervulus of Colletotrichum phomoides (after Venus
Pool), d. and e. Melanconium rot, /. section through an acervulus of the Melan-
conium fungus (d. to/, after Tisdale).
Family Solanaceae 347
possess a thin wall; the pycnospores (fig. 65 i) are
hyalin and one-celled. Jamieson1 failed to find an
ascus or winter stage. Should the disease become
serious, spraying with Bordeaux is recommended.
LEAF SPOT
Caused by Septoria lycopersici Speg.
The disease is generally known as late blight, or
blight, both of which names are misleading. Recent
investigations by Levin2 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
1 Jamieson, C. O., U. S. Dept. Agr. Research, 4 : 1-20, 1915.
2 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 lyco-
persici 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 setae of
the fungus are very numerous, thus giving the acer-
vuli 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. Tisdale1 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.
35° 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, b. conidiophores of Cladosporiunt fulvum, c. conidia of
C. fulvum, (b. and c. after Southworth)', d. two plants artificially infected with
Sclerotium Rolfsii, e. sunburn, /. Macrosporium rot.
Family Solanaceae 351
irregular, 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 orihoceras App. and WolL;
Fusarium oxysporum Schl.
This disease is common on tomatoes in the Pacific
Northwest. It has been investigated by Humphrey1
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,
1 Humphrey, H. B., Washington Agr. Expt. Sta. Bui. 115 : 1-22,
1914.
FIG. 68. vSLEEPiNG SICKNESS OF TOMATO.
Family Solanaceae 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. solani
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.
23
CHAPTER XXII
FAMILY UMBELLIFER.E
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 $2 7 , 1 8 1 . Thi s 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 OF 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 bullata (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 Phyllosticta 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 irregular 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,1 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 rainy
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
maybe 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.
1 Rogers, S. S., California Agr. Expt. Stat. Bui. 208 : 83-115, 1911.
i
FIG. 69. CELERY DISEASES.
a. Septoria leaf spot on leaf, b. Septoria leaf spot on leaflet, c. Septoria lesions on
relery seed, d. Septoria spots showing pycnidial bodies, e. cross section showing
Eyncidium and pycnospores of Seploria petroselini (a, c, and e after Coons and
evin).
FIG. 70. CELERY DISEASES.
a. Cercospora leaf spot, 6. conidiophores and conidia of Cercospora apii
(afterDuggar and Baily), c. Rhizoctonia root rot.
Family Umbelliferae 357
EARLY BLIGHT
Caused by Cercospora apii Fr.
Early blight 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 petroseHnum)
DROP, see LETTUCE, p. 143.
LATE BLIGHT, see CELERY, p. 355.
DISEASES OF THE PARSNIP (Pastinaca sativd)
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 cul-
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:
(1) 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
// 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 properly 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 parasitically 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 advantageous 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 with 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 :
(1) 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.
(b) 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 ammonia 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
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 Swingle1 as follows:
Tobacco Bordeaux
extracts mixture
Paris green yes yes
Arsenate of lead yes yes
Arsenite of zinc (ortho) yes no
Arsenite of lime yes yes
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-
trolling 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
1 Cooley, B. A , and Swingle, D. B., Montana Agr. Expt. Sta. Circ.
17:
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 37 *
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 necessary 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. 71 a)
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-
ium 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, r 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
1 U. S. Dept. of Agr. Bur. of Entomology Bui., no, 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
FIG. 72. PARASITIZED INSECTS. TREATMENT OF FENCE POSTS.
a. Cabbage bug parasitized by Cordyceps nutans, b. cabbage bug parasitized by
Cordyceps sobolifera (a. and b. 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,
i. a willow post treated 4 hours in hot creosote and iq hours in cold; set June 13,
1005, examined November I, 1914, and showing practically no deterioration after
9/12 years' service. 2. A split soft maple post treated 4 hours in hot creosote and
10 hours in cold; set in 1905 and examined November 15, 1914.- The post was set
below the creosote line and some decay has entered beneath the creosote shell, j.
A s-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
anisoplice 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 secure 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.
^CIDIOSPORES. Spores of the rust family formed in an
ascidium.
^CIDIUM (secium). 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.
AMMONIFIERS. Micro6rganisms capable of transforming
nitrogen compounds into ammonia.
AMCEBOID. 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.
382 Glossary
B
BASIDIOSPORES. Spores formed on basidia.
BASIDIUM. A straight stick- like spore bearing fungal
thread.
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-bearing fungal stalk.
CONSTRICTED. Drawn together or contracted.
CORTEX. Outer bark.
CUTICLE. The outermost skin of plants.
CYST. Sac or cavity.
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.
FALCATE. Sickle shaped.
FLAGELLA. Whip-like appendage of protoplasm of bac-
teria and swarm spores.
FUNGUS. A plant of very low order. Its mycelium corre-
sponds to roots and reproduces by means of spores.
GLAUCUS. Sea green.
GONIDIA. Algae-like cells.
GUTTULATE. Drop-like.
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^E. Thread-like vegetative part of a fungus.
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 hyphse of a fungus.
MYCOLOGY. The study of fungi.
O
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. Summer 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^E. 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 sporangium.
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.
386 Glossary
STROMA. A spore-bearing cushion composed of mycelium
and sometimes of host tissue.
SWARM SPORES. Spores possessed with the power of
motility.
TELEUTOSPORES (xELio SPORE s) . Resting or winter spores
of certain rust fungi.
U
UREDOSPORES. Summer spores of certain rust fungi.
V
VESICULAR, Composed of vessels.
VISCID. Sticky.
ZOOGLE^. Colony embedded in a gelatinous bed.
ZOOSPORANGIA. Sporangia which produce zoospores.
ZOOSPORE. A motile spore.
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 et seq.
Allard, H. A., 84.
Allium cepa, 285.
schoenoporasum, 284.
Alphano Humus Co., 20.
Alternaria brassica, 196.
var. nigrescens, 2,23.
-— panaXj 1 14.
Ammoniacal copper carbonate,
366.
Ammonification, 14.
AnthericUum, n.
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 et seq.
Rust, 138.
Ascochyta armor aci&, 205.
hortprum, 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.
fluorescens liquefaciens, 14.
putridus, 14.
lathy 'ri, 261.
on cowpea, 270.
phytopthorus, 316.
melonis, 221.
mesentericusvulgatus, 14,23.
mycoides, 14, 23.
pestifer, 23.
pro tens 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.
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 et 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, 120-121.
Soft rot, 1 1 8.
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.
oleracea, 186.
var. acephala, 207.
var. botrytis, 202.
rapa, 214.
Bremia lactuc®, 141.
Brown, N. A., 140.
Cabbage diseases, 186 et seq.
Black leg or foot rot, 195.
Black mold, 196.
Black rot, 190.
Club root, 1 86.
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.
Downy mildew, 221.
Leaf blight, 223.
Mycosphaerella 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 petroselinum, 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, 71
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, 271.
cucurbitce, 224.
dolichi, 271.
hibisci, 295.
Chive diseases, 284.
Choanophora cucurbitarum, 235.
Chrysophylyctis endobioticum,
319.
Citron diseases, 234.
Citrullus vulgaris, 234 et seq.
Cladosporium fulvum, 350.
macrocarpum, 134.
sp.f 284.
Clinton, G. P., 122, 124, 147,
215, 284, 323.
Coccus, 4.
Cochleaia armor acia, 204.
Colletotrichum atramentarium,
325, 326
caulicolum, 266.
Higginsianum, 214.
nigrum, 303.
phomoides, 348.
Combination sprays, 367.
Conidia, 12.
Conn, J. H., 6.
Contact poisons, 363.
Convulvulus batatas, 151.
Cooley, B. A., 368.
Corticium vagum, 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.
Ciicumis melo, 219.
Cucurbita maxima, 234.
moschata, 234.
pepo, 234.
Cutworms, 52.
Cystopus candidus, attacking rad-
ish, 211.
on horseradish, 205.
ipom<z<z-panduran<z, 155.
portulacecz, 299.
Cystospora batatas, 152.
D
Damping off, 42 et seq.
Darluca filum, 284.
Daucus carota, 354.
Denitrification, 24.
Denitrified soils, 23.
Diabrotica vittata, 220.
Diaporthe battis, 157, 159.
Didlake, M., 20.
Didymella catarice, 257.
Diplodia herbarum, 258.
herbicola, 257.
tubericola, 16=5.
, 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.
Elliott, J. A., 154.
Enlows, E. M., 229.
Entyloma Ellisii, 133.
Erysiphe cichoracearum, 232.
galeopsidis, 258.
polygoni, 216.
, on bean, 262.
, on cantaloupe, 222.
Family Agaricaceae, 103 et seq.
Araliaceffi, 108 et seq.
Chenopodiaceae, 1 16 et seq.
Composite, 137 et seq.
Convolvulaceae, 151 et seq.
Cruciferae, 185 et seq.
Cucurbitaceae, 218 et seq
Gramineas, 250 et seq.
Labiatae, 255.
Liliaceae, 279 et seq.
Malvaceae, 295 et seq.
Portulacaceae, 299.
Solanaceae, 300 et seq.
Umbelliferae, 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, 77.
protection, 77, 78.
Fuligo violacea, 152.
Fungicides, 363.
Fungi, structure and life history,
10.
Fusarium batatatis, 47, 157, 170.
citrulli, 244.
conglutinans, 197.
cucurbittz, 237.
eumartii, 330.
hyperoxysporum, 47 et seq.
ly coper sici, 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
Alternaria blight, 114.
Black rot, 110, in.
Bordeaux injury, 115.
Damping off, 108.
Downy mildew, ro8, 109.
Fiber rot, in, 112.
Leaf anthracnose, 113.
Papery leaf spot, 115.
Root knot, 115.
Stem anthracnose, 112.
White rot, 1 10.
Gleosporium melongena, 302.
Glomerella piper ata, 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 et seq.
Index
Healthy soil flora, nature and
function, 12.
Helianthus annuus, 148.
tuber osus, 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. BM 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.
Istvanffi, G. De, 143.
J
Jamieson, C. O., 331.
Johnson, J., 57,276.
T., 320, 347.
Jones, L. R., 74.
Kale diseases, 207, 208.
Koch, Robert, 4.
Lactuca saliva, 140.
Lady beetles, 376.
Leeuwenhoek, Anton van, 4.
Lettuce diseases, 140 et 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.
McCulloch, L., 202.
McKay, M. B., 127.
Macrosporium herculeum, 206,
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 denticulata, 20.
lupulina, 20.
Melissa officinalis, 256.
Mentha virides, 258.
Merrill, L. A., 65.
Methods of control, 361.
Mint diseases, 258.
Monilochates infuscans, 168.
More, C. T., 226.
Morse, W. J., 316.
Mosaic, 83 et seq.
Muck or peat soils, 34 et seq.
Mushroom diseases, 103 et seq.
Bacterial spot, 103, 104.
The Mycogone disease, 103
et seq.
Mustard diseases, 208.
Mycogone perniciosa, 104, 105.
Mycospharella brassicola, 204.
citrulina, 22.
N
Nematospora lycopersici, 345.
Nepeta cataria, 257.
Niter-sick soils, 24.
Nitrification, 14.
Nitrobacter, 14.
Nitrogen fixation from air, 18.
— — maintaining supply, 17.
Nitrosococcus, 14.
Nitrosomonas, 14.
O
O'Gara, P. J., 324.
Okra diseases, 295 et seq.
Leaf spot, 295.
Root knot, 298.
Root rot, 297.
Texas root rot, 297.
Wilt, 296.
Olpidium bras sices, 193.
Onion diseases, 285 et seq.
Anthracnose, 289.
Black mold, 290.
Black neck, 290.
Blight, 286.
Bulb rot, 290.
Damping off, 286.
Downy mildew, 286.
Pink root, 291.
Rust, 289.
Sclerotium rot or black
neck, 290.
Smut, 288.
Soft rot, 285.
storage, 292 et seq.
Oogonia, 43.
Oogonium, n, 43.
Orton, W. A., 232, 273, 327.
Ozonium omnivorium 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.
Pastinaca sativa, 357.
Penicillium expansum, n.
Pepper diseases, 303 et seq.
Anthracnose, 303.
Black anthracnose, 303.
Fruit rot, 304.
Leaf spot, 304.
Southern blight, 305.
Peppermint diseases, 258.
Perithecium, 12.
Peronflsporaeffusa, 131, 132.
parasitica attacking cab-
bage, 194.
schachtii, 123.
schleideni, 286.
Pestalozziafunerea attacking gin-
seng, 113.
Phaseolus vulgaris, 260.
Phoma beta, 125.
destruction. 346.
napobrassiccc, 215.
oleracea, 195.
solani, 324.
Index
393
Phoma subcircinata, 268.
Phomosis vexans, 301.
Phosphates, changes of, 15.
Phyllosticta apii, 355.
batatas, 164.
chenopodii, 133, 134.
cucurbitacearum, 224.
Physiological diseases, 80 et seq.
Phythium de Baryanum, 42, 44,
193-
attacking beet, 122.
Phytophthora cactorum, 108.
infestans, late blight of
Irish potato, 322.
late blight of tomato,
343-
phaseoh, 267.
terrestria, 344.
Pisum sativum, 273.
Plasmopora Halstedii, 138, 148.
Plenodomus destruens, 159.
Points to remember, 366.
Pool Venus, 127.
Poor seed, 92, 97.
Potassium, changes of, 15.
sulphide of, 369.
Potato diseases, 306 et seq.
Anthracnose, 324.
Arsenical injury, 313.
Black heart, 311.
Black leg, 316.
Black rot or jelly end rot,
329-
Black wart, 319.
Common scab, 317.
Curly dwarf, 309.
Early blight, 322.
Fusarium wilt, 327.
Hollow heart, 312.
Internal brown spotting,
310.
Late blight, 322.
Leaf roll, 308.
Melters or leak, 321.
Mosaic, 312.
Net necrosis, 311.
Phoma rot, 324.
Powdery dry rot, 330.
Powdery scab, 314.
Pox or pit, 313.
Root knot, 332.
Rosette, 331.
Silver scurf, 326.
Southern blight, 332.
Southern wilt, 317.
Spindling sprout, 310.
Stem end rot, 329.
Tip burn, 312.
- diseases, field control, 335.
-- storage rots control, 333.
Predacious insects, beneficial,
375-
Pseudomonas beticola, 120.
-- campestris, 190, 191, 205.
-- attacking radish, 208.
--- attacking turnip, 214.
- fluorescens, 103, 104.
- lachrymans, 229.
-- maculicola, 202, 203.
- pisi, 273.
-- radicicola, 18 et seq.
-- solanacearum, attacking to-
mato, 342.
- Stewarti, 251.
- tumefaciens, attacking beets,
118.
- viridilividum, 140.
Pseudoperonospora cubensis, 230.
Puccinia alii, 289.
- asparagi, 280.
- helwnthi, 149.
-- attacking Jerusalem
artichoke, 138.
- tragopogoni, 148.
Purslane diseases, 299.
Pycnidium, 12.
Radish diseases, 208 et seq.
Black rot, 208.
Club root, 208.
Damping off, 209.
Downy mildew, 211.
Root knot, 214.
Root rot, 214.
Scab, 209.
White rust, 211.
Rainstorms, 73.
394
Index
Ramularia armoracia, 206.
cynarce, 138.
Rand, F. V., 229.
Rankin, W. H., no.
Raphanus sativus, 208.
Readhimer, J. E., 31.
Reid, H. L., 134, 138.
Resin, 370.
Resistant varieties, 373.
Rheosporangium aplianiderma-
tum, 209.
Rhizoctonia solani, 44.
Rhizopus nigricans, 156, 158.
attacking squash, 236.
the cause of leak, 32 1 .
Roasting or pan firing, 56.
Rogers, S. S., 356.
Root knot, 48 et seq.
Root rot, caused by Rhizoctonia
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,
194-
attacking ginseng, 1 10.
— — panacis, no.
Sclerotium bataticola, 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 bataticola, 165.
consimilis, 144.
lactucce, 144.
lycopersici, 347.
melissa, 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.
Sphcsrella pinodes, 276.
Spharonema 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, 324,
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 yellows, 237.
Steaming sick soil, 54.
Stevenson, J. A., 146.
Stewart, F. C., 128, 285.
-F.G.,25i.
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 et seq.
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, 168.
Texas root rot, 175.
Trichoderma rot, 167.
Vine wilt or yellows, 170.
White rust, 155.
methods of control,
176 et seq.
Taubenhaus, J. J., 160 et sea.
Temple, J. C., 9.
Thick sowing, effect on damping
off, 57.
Thielavia basicola attacking gar-
den pea, 275.
attacking ginseng, 1 1 1 .
attacking horseradish,
205.
Tmsley, 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 spotf> 347.
Melanconium rot, 349.
Mosaic, 3^1.
Rhizoctonia fruit rot, 353.
Southern wilt, 342.
Sunburn, 341.
Yeast rot, 345.
Yellow blight, 352.
Tragopogon porrifolius, 146.
Trichoderma koningi, 167.
lignorum, 167.
Tubercularia persicina, 284.
Turnip diseases, 214 et seq.
Anthracnose, 214.
Black rot, 214.
Club root, 214.
Macrosporiumleaf spot, 217.
Phoma rot, 215.
Powdery mildew, 216.
U
Uredinales, 10.
Urocystis cepulce, 288.
Uromyces appendiculatus, 262.
Urophlyctis leproides, 121.
396
Index
Veihmeyer, F. J., 105.
Vermicular ia circinans, 289.
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.
Mycosphaerella 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.
Wollenweber, H. W., 331.
Zea mays, 250.
f ~
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