• TABLE OF CONTENTS
HIDE
 Title Page
 Credits
 Table of Contents
 Introduction
 Anthracnose
 Wilt
 Southern wilt
 Gummy-stem blight
 Stem-end rot
 Blossom-end rot
 Downy mildew
 Powdery mildew
 Cercospora leaf spot
 Macrosporium leaf spot
 Ground rot
 Speckle
 Minor diseases not found in...
 Cold, wind, and sand injury
 Handling
 Seed disinfection
 Fungicides and their applicati...














Group Title: Bulletin - University of Florida. Agricultural Experiment Station ; no. 225
Title: Diseases of watermelons in Florida
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00027380/00001
 Material Information
Title: Diseases of watermelons in Florida
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 52 p. : ill. ; 23 cm.
Language: English
Creator: Walker, M. N ( Marion Newman ), 1900-
Weber, George F ( George Frederick ), b. 1894
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1931
 Subjects
Subject: Watermelons -- Diseases and pests -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by M.N. Walker and George F. Weber.
General Note: Cover title.
Funding: Bulletin (University of Florida. Agricultural Experiment Station)
 Record Information
Bibliographic ID: UF00027380
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000924072
oclc - 18175910
notis - AEN4676

Table of Contents
    Title Page
        Page 1
    Credits
        Page 2
    Table of Contents
        Page 3
        Page 4
    Introduction
        Page 5
    Anthracnose
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
    Wilt
        Page 12
        Page 13
        Page 14
        Page 15
    Southern wilt
        Page 16
        Page 17
    Gummy-stem blight
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
    Stem-end rot
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
    Blossom-end rot
        Page 29
        Page 30
        Page 31
    Downy mildew
        Page 32
        Page 33
    Powdery mildew
        Page 34
    Cercospora leaf spot
        Page 35
    Macrosporium leaf spot
        Page 36
    Ground rot
        Page 37
    Speckle
        Page 37
    Minor diseases not found in Florida
        Page 38
        Page 39
    Cold, wind, and sand injury
        Page 40
        Page 41
    Handling
        Page 42
        Page 43
    Seed disinfection
        Page 44
    Fungicides and their application
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
        Page 52
Full Text


February, 1931


UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
Wilmon Newell, Director


DISEASES OF WATERMELONS

IN FLORIDA

By

M. N. WALKER AND GEORGE F. WEBER


C-,

g U
I f3 "'z P, ~


Fig. 1.-Watermelon showing anthracnose lesions resulting from
natural infection.


Bulletins will be sent free upon application to the
Agricultural Experiment Station
GAINESVILLE, FLORIDA


Bulletin 225







BOARD OF CONTROL
P. K. YONGE, Chairman, Pensacola RAYMER F. MAGUIRE, Orlando
A. H. BLENDING, Leesburg FRANK J. WIDEMAN, West Palm Beach
W. B. DAVIS, Perry J. T. DIAMOND, Secretary. Tallahassee

STATION EXECUTIVE STAFF


JOHN J. TIGERT, M.A., LL.D., President
WILMON NEWELL, D.Sc., Director
S. T. FLEMING, A.B., Asst. Director
J. FRANCIS COOPER, M.S.A., Editor
R. M. FULGHUM, B.S.A., Asst. Editor


IDA KEELING CRESAP, Librarian
RUBY NEWHALL, Secretary
K. H. GRAHAM, Business Manager
RACHEL McQUARRIE. Accountant


MAIN STATION-DEPARTMENTS AND INVESTIGATORS


AGRONOMY
W. E. STOKES, M.S., Agronomist
W. A. LEUKEL, Ph.D., Associate
G. E. RITCHEY, M.S.A., Assistant*
FRED H. HULL, M.S., Assistant
J. D. WARNER, M.S., Assistant
JOHN P. CAMP, M.S.A., Assistant
ANIMAL HUSBANDRY
A. L. SHEALY, D.V.M., Veterinarian in
Charge
E. F. THOMAS, D.V.M., Asst. Veterinarian
R. B. BECKER, Ph.D., Associate in Dairy
Husbandry.
W. M. NEAL, Ph.D., Assistant in Animal
Nutrition
C. R. DAWSON, B.S.A., Assistant Dairy
Investigations
CHEMISTRY
R. W. RUPRECHT, Ph.D., Chemist
R. M. BARNETTE, Ph.D., Associate
C. E. BELL, M.S., Assistant
J. M. COLEMAN, B.S., Assistant
H. W. WINSOR, B.S.A., Assistant
H. W. JONES, B.S., Assistant
COTTON INVESTIGATIONS
W. A. CARVER, Ph.D., Assistant
E. F. GROSSMAN, M.A., Assistant
PAUL W. CALHOUN, B.S., Assistant
RAYMOND CROWN, B.S.A., Field Assistant


ECONOMICS, AGRICULTURAL
C. V. NOBLE, Ph.D., Agricultural Economist
BRUCE McKINLEY, A.B., B.S.A., Associate
M. A. BROOKER, M.S.A., Assistant
ECONOMICS, HOME
OUIDA DAVIS ABBOTT, Ph.D., Head
L. W. GADDUM, Ph.D., Biochemist
C. F. AHMANN, Ph.D., Physiologist
ENTOMOLOGY
J. R. WATSON, A. M., Entomologist
A. N. TISSOT, M.S., Assistant
H. E. BRATLEY, M.S.A., Assistant
L. W. ZIEGLER, B.S., Assistant
HORTICULTURE
A. F. CAMP, Ph.D., Horticulturist
HAROLD MOWRY, B.S.A., Associate
M. R. ENSIGN, M.S., Assistant
A. L. STAHL, Ph.D., Assistant
G. H. BLACKMON, M.S.A., Pecan Culturist
C. B. VAN CLEEF, M.S.A., Greenhouse
Foreman
PLANT PATHOLOGY
W. B. TISDALE, Ph.D., Plant Pathologist
G. F. WEBER, Ph.D., Associate
A. H. EDDINS, Ph.D., Assistant
K. W. LOUCKS, M.S., Assistant
ERDMAN WEST, B.S., Mycologist


BRANCH STATION AND FIELD WORKERS
L. O. GRATZ, Ph.D., Asso. Plant Pathologist in charge, Tobacco Exp. Sta. (Quincy)
R. R. KINCAID, M.S., Assistant Plant Pathologist (Quincy)
JESSE REEVES, Farm Superintendent, Tobacco Experiment Station (Quincy)
J. H. JEFFERIES, Superintendent, Citrus Experiment Station (Lake Alfred)
GEO. D. RUEHLE, Ph.D., Assistant Plant Pathologist (Lake Alfred)
W. A. KUNTZ, A.M., Assistant Plant Pathologist (Lake Alfred)
B. R. FUDGE, Ph.D., Assistant Chemist (Lake Alfred)
W. L. THOMPSON, B.S., Assistant Entomologist (Lake Alfred)
R. V. ALLISON, Ph.D., Soils Specialist in charge Everglades Experiment Sta. (Belle Glade)
R. W. KIDDER, B.S., Foreman, Everglades Experiment Station (Belle Glade)
R. N. LOBDELL, M.S., Assistant Entomologist (Belle Glade)
F. D. STEVENS, B.S., Sugarcane Agronomist (Belle Glade)
H. H. WEDGEWORTH, M.S., Associate Plant Pathologist (Belle Glade)
B. A. BOURNE, M.S., Associate Plant Physiologist (Belle Glade)
J. R. NELLER, Ph.D., Associate Biochemist (Belle Glade)
A. DAANE, Ph.D., Associate Agronomist (Belle Glade)
FRED YOUNT, Office Assistant (Belle Glade)
M. R. BEDSOLE, M.S.A., Assistant Chemist (Belle Glade)
A. N. BROOKS, Ph.D., Associate Plant Pathologist (Plant City)
R. E. NOLEN, M.S.A., Field Assistant in Plant Pathology (Plant City)
A. S. RHOADS, Ph.D., Associate Plant Pathologist (Cocoa)
C. M. TUCKER, Ph.D., Associate Plant Pathologist (Hastings)
H. S. WOLFE, Ph.D., Associate Horticulturist (Homestead)
L. R. TOY, B.S.A., Assistant Horticulturist (Homestead)
STACY 0. HAWKINS, M.A., Field Assistant in Plant Pathology (Homestead)
D. G. A. KELBERT, Field Assistant in Plant Pathology (Bradenton)
FRED W. WALKER, Assistant Entomologist (Monticello)
D. A. SANDERS, D.V.M., Associate Veterinarian (West Palm Beach)
M. N. WALKER, Ph.D., Associate Plant Pathologist (Leesburg)
W. B. SHIPPY, Ph.D., Assistant Plant Pathologist (Leesburg)
C. C. GOFF, M.S., Assistant Entomologist (Leesburg)
J. W. WILSON, Ph.D., Assistant Entomologist (Pierson)

*In cooperation with U. S. Department of Agriculture.

















CONTENTS

PAGE

INTRODUCTION 5

ANTHRACNOSE-Colletotrichumn lageawrium (PASS.) ELL. & HALS. 5

WILT-Fusarium niveum E.F.S....... 12

SOUTHERN WILT-Sclerotiu9i rolfsii SACC .. ............... 16

GUMMY-STEM BLIGHT-Mycosphaerella citrullina (C.O. SM.) GROS.. 18

STEM-END ROT-Diplodia PP ....... ........ 23

BLOSSOM-END ROT-Pythitum de baryanum HESSE .................. 29

DOWNY MILDEw-Pseudoperonospora cubensis (B. & C.) ROST. 32

POWDERY MILDEW-Erysiphe cichoracearum E. & E..... .. 34

LEAF SPOT-Cercospora citrullina CKE. .... 35

LEAF SPOT-Macrosporium cucumerinum E. & E... 36

GROUND ROT-Corticium vagum B. & C. ........ 37

SPECKLE ..... ....... .......--. 37

DISEASES WHICH ARE NOT FOUND IN FLORIDA .. .. ... 38

COLD, WIND, AND SAND INJURY ..... ..40

HANDLING .............. 42

SEED DISINFECTION .. ..... ........44

FUNGICIDES AND THEIR APPLICATION ..... ... 45

Stem-end treatment .... ...... .. ... 27

Copper sulfate paste 28












DISEASES OF WATERMELONS

IN FLORIDA
By
M. N. WALKER AND GEORGE F. WEBER

INTRODUCTION

Watermelons are produced in commercial quantities in al-
most every county in Florida, but the bulk of the crop is pro-
duced in comparatively a few of them. Between 25,000 and 35,-
000 acres are planted to the crop every year, and approximately
9,000 carloads, averaging about 15% of the watermelon crop
of the United States, are produced. The returns to growers
amount to from $500,000 to $2,000,000 a year.
It is impossible to give an accurate estimate of the financial
loss incident to watermelon diseases, but they are often an im-
portant factor, especially in wet seasons, in determining the suc-
cess or failure of the crop. It is obvious that anything that re-
duces the quantity or quality of a crop increases the cost of
production, and with a low priced crop, such as watermelons,
this is especially serious. Certain of the diseases of watermelons
may entirely destroy the crop under conditions favorable for
their development, and it is seldom that a field is observed in
which one or more of the several diseases of watermelons are
not doing some damage.
The area planted to watermelons every year is largely de-
pendent on the financial success of the preceding melon crop.
Although there are a number of important factors besides dis-
eases which determine the success of the crop, it is the purpose
of this bulletin to discuss only the diseases, to give descriptions
of them, and to outline means for their prevention and control.
ANTHRACNOSE
The cause of the anthracnose disease of watermelons is a
fungus, Colletotrichum lagenarium (Pass.) Ell. & Hals. An-
thracnose is the worst disease of watermelons in the United
States, and is found almost everywhere that melons are grown. It
is especially severe and destructive in the more extensive water-
melon growing sections of the southern states, and in Florida
it causes more loss than all other diseases of watermelons com-









DISEASES OF WATERMELONS

IN FLORIDA
By
M. N. WALKER AND GEORGE F. WEBER

INTRODUCTION

Watermelons are produced in commercial quantities in al-
most every county in Florida, but the bulk of the crop is pro-
duced in comparatively a few of them. Between 25,000 and 35,-
000 acres are planted to the crop every year, and approximately
9,000 carloads, averaging about 15% of the watermelon crop
of the United States, are produced. The returns to growers
amount to from $500,000 to $2,000,000 a year.
It is impossible to give an accurate estimate of the financial
loss incident to watermelon diseases, but they are often an im-
portant factor, especially in wet seasons, in determining the suc-
cess or failure of the crop. It is obvious that anything that re-
duces the quantity or quality of a crop increases the cost of
production, and with a low priced crop, such as watermelons,
this is especially serious. Certain of the diseases of watermelons
may entirely destroy the crop under conditions favorable for
their development, and it is seldom that a field is observed in
which one or more of the several diseases of watermelons are
not doing some damage.
The area planted to watermelons every year is largely de-
pendent on the financial success of the preceding melon crop.
Although there are a number of important factors besides dis-
eases which determine the success of the crop, it is the purpose
of this bulletin to discuss only the diseases, to give descriptions
of them, and to outline means for their prevention and control.
ANTHRACNOSE
The cause of the anthracnose disease of watermelons is a
fungus, Colletotrichum lagenarium (Pass.) Ell. & Hals. An-
thracnose is the worst disease of watermelons in the United
States, and is found almost everywhere that melons are grown. It
is especially severe and destructive in the more extensive water-
melon growing sections of the southern states, and in Florida
it causes more loss than all other diseases of watermelons com-






Florida Agricultural Experiment Station


bined. Seldom a season passes without this disease being a con-
trolling factor in production. Anthracnose is especially severe
during the latter part of the season when there is a combination
of high temperatures and heavy rainfall which makes the spread
of the disease extremely difficult to control. It is not limited
in its attacks to watermelons, but also attacks cucumbers, can-
taloupes, and a number of other related plants. The seriousness
of anthracnose on watermelons may be realized from the annual
losses of from 20 to 30 percent of the crop reported in some
states.
The losses caused by this disease may be divided into those
occurring in the field and those occurring in transit. The grower
should be primarily concerned with the disease in the field, as
it will not occur in transit if it has been controlled in the field.
Losses from anthracnose in the field are due to the defoliation
of the plants, which results in the production of immature and
sunburned melons, and the direct infection of the melons them-
selves, which causes them to be refused at the car or to rot
while in transit. When the foliage has been killed the melons
that are well developed are exposed to the hot sun and are burn-
ed. A large number of the official inspection reports on car-
loads of melons originating in Florida and inspected at their
destination show some sunburned melons in almost every car,
and the worst reports show as high as 30 percent sunburned
melons.
The lesions on the melons caused by the parasite are a more
common and severe form of the disease. These lesions may vary
considerably in size, depth, and number, and a few spots on the
melon may be overlooked, especially if they are small. When
such melons are loaded, heavy losses at destination are experi-
enced. In this respect the transportation loss from anthrac-
nose is second only to that caused by stem-end rot.
The fungus causing anthracnose is carried over winter in de-
caying plant material in the field, on the seed, and on other culti-
vated host plants, such as cantaloupe and cucumber. From
these sources of initial infection the spores of the fungus are
spread widely by wind, rain, cultural implements, animals, and
laborers. It is often observed that shortly after the first picking
a severe outbreak of anthracnose occurs which is probably due
to workmen walking through the wet vines, and many of the
later melons may be sunburned as a result of the defoliation of
the plants. Also many of the melons will show the character-





Bulletin 225, Watermelon Diseases in Florida


istic pitted appearance of anthracnose. Such melons, if shipped,
are liable to rot in transit.
The disease in the field occurs first on the oldest leaves around
the center of the hill (Fig. 2). This infection is usually
the result of planting infected seed that were not treated. The
disease develops on the cotyledons, or seed leaves, from the fun-
gus spores on the seed coat, and from there spreads to the first
true leaves, which at later periods, when the vines are running,
are considered the oldest leaves. Under average conditions it
takes about 10 days for the fungus to complete its life cycle;
that is, the period of time from the germination of the spore
and its infection of the plant to the production of mature spores.


Fig. 2.-Watermelon leaves around the center of the hill killed by an-
thracnose. The arrow indicates the base of the plant.

During dry, cool periods this time may be considerably pro-
longed, but, on the other hand, several wet, warm days may
reduce it to six or seven days. Thus, it is easily understood why
the disease usually develops slowly early in the season during
the cool weather, and why, with the advent of warm, wet weather
whole fields may become diseased in less than a week.
DESCRIPTION
The anthracnose fungus attacks all parts of watermelon plants
above ground in all stages of their development, though con-





Florida Agricultural Experiment Station


editions in the field are such that the disease is usually first
noticed on the central leaves of plants that have attained some
size. In rainy, warm weather the fungus spreads to other near-
by leaves and plants by means of spores, which are borne in
great number on anthracnose lesions. The leaves show small
black spots (Fig. 3) which may enlarge until the whole leaf


Fig. 3.-Anthracnose of watermelon showing typical lesions on leaf blade.





Bulletin 225, Watermelon Diseases in Florida


becomes black and shriveled. During periods of weather favor-
able to the disease a whole field may show these blackened leaves
in the course of a few days, and is often described by the grower
as having been "burned over." (Fig. 4.) This form of the dis-
ease is also spoken of as the "June or July frost," depending on
the month of occurrence. Often, under less favorable conditions
for the disease, only the leaves at the center of the plant are
killed, leaving the stem and a portion of the runners bare. Heavy
defoliation caused by attacks of anthracnose results in the oc-
currence of many immature and sunburned melons.
During wet weather a close examination of the spots will
show the presence of small, orange-pink, oily masses of the
spores of the fungus, which serve to spread the disease to other

















Fig. 4.-Watermelon plant showing most of the leaves killed by
anthracnose. (Courtesy USDA.)

plants. In dry weather, however, the spore masses are of a
grayish, less conspicuous appearance. The stems and runners
also may be attacked and killed by the fungus. The lesions on
the stems are rather long and narrow in the direction of the
stem, and in the early stages of infection appear as small, water-
soaked areas which later become sunken and tan to black in
color. The spore masses also appear abundantly in these lesions,
being especially noticeable during wet weather. Both the leaf
and stem lesions serve as sources of infection to the melons
that develop later. When young melons are infected, black spots





Florida Agricultural Experiment Station


appear which are similar to those on the leaves, and the melons
are often malformed or distorted. On the older melons the dis-
ease causes small, water-soaked spots with greasy, yellowish
centers, which become somewhat elevated above the surface of
the melon, giving it a bumpy appearance (Fig. 1, cover). These
raised areas later become sunken and pitted and of a creamy to
black color and are covered with the pink spore masses of the
fungus (Fig. 5). These lesions enlarge slowly, but may finally
attain an inch or more in diameter. By the coalescence of sev-
eral of these spots a large part of the surface of the melon may
be involved.






l
'. r .
'U












Fig. 5.-Anthracnose of watermelon, slightly enlarged to show character-
istic lesions and masses of spores.

Melons showing this pimply, bumpy surface when loaded on
the car, rot badly in transit, both from the continued growth
of the anthracnose fungus and from other rot-producing fungi
that enter through the anthracnose lesions.
CONTROL
One of the first steps to take in controlling the anthracnose
disease of watermelons is the proper disinfection or sterilization
of the seed. This may be done by dipping the seed in a 1:1,000






Bulletin 225, Watermelon Diseases in Florida


solution of bichloride of mercury (corrosive sublimate) for 10
minutes, and then thoroughly rinsing them in fresh water. A
more detailed account of the method of treating watermelon
seed is given on page 44.
The later development of the disease can be greatly reduced
by thoroughly spraying the vines with 4-4-50 bordeaux mixture,
or by dusting with 20-80 copper-lime dust. It must be remem-
bered that any spray serves as a preventive and not as a cure;
it is, therefore, necessary to keep the plants covered with the
fungicide, for after the leaves show the disease it is impossible
to save them. These infected and killed leaves not only reduce
the total leaf surface of the plant and thus indirectly reduce the
production of melons, but also allow the melons to become sun-
burned, and, in addition, serve as a source of inoculum for the
further spread of the disease. Spraying or dusting must be
considered as insurance and a regular schedule of sprays should
be applied whether any disease has been noticed or not, for it
is safe to assume that the disease is present, but has not reached
serious enough proportions to call attention to it. The follow-
ing schedule of spraying or dusting is given after calling atten-
tion again to the fact that a coating of the spray material should
be kept on the vines at all times and that frequent rains may
make it necessary to make additional applications.
Make a thorough application of bordeaux spray or copper-
lime dust when the first two or three leaves have developed, and
another when the vines are just beginning to run. (Details as
to the mixing and application of these fungicides are given in
a later section.) These applications are especially important
because they prevent infection of the first leaves and thereby
reduce the source of infection later in the season.
The third application should be made about a week after the
crop has set.
The fourth application should be made about two weeks after
the third one.
Where infection is heavy, spraying or dusting during the load-
ing season is often advisable to prevent the formation of the
pimples on the melons and the consequent rotting in shipment.
Much anthracnose infection can be avoided by not disturbing
the vines any more than is absolutely necessary, especially when
they are wet, while cultivating, spraying or dusting, and har-
vesting.





Florida Agricultural Experiment Station


WILT
The wilt disease of watermelons is caused by a soil-inhabit-
ing fungus, Fusarium niveum E. F. S., and has been recognized
as a serious disease of watermelons for many years. It is large-
ly on account of this disease that watermelon growers have
found from experience that it is inadvisable to grow water-
melons on the same piece of ground without a long interval of
time between crops. The disease is widely distributed, and is
known in practically every melon-growing area of the United
States. However, it is on the lighter, sandier soils that the dis-
ease does the most damage. Where a field is heavily infested
with the causal fungus a total loss of the crop may result. Or-
dinarily in commercial practice where the same ground is rarely
planted to watermelons two years in succession the disease is
not especially serious, but in escaping the disease by rotation
there is the additional expense of changing to new land every
year. In small home plantings, however, or in new fields located
close to older fields that have shown the presence of the disease,
wilt is often the cause of heavy losses. Some watermelon-grow-
ing areas have been abandoned on account of this disease, and
the acreage is being reduced in other sections because of the dif-
ficulty in finding new, uninfested ground for planting.
The fungus causing the wilt disease is capable of living in the
soil for as much as 16 years, though it gradually becomes less
abundant if melons are not planted. It is spread in a number
of ways, and may be introduced into new areas on the feet of
men or animals, and by cultivation implements, drainage water,
infested manure, wind-blown spores, soil, or plant debris. It is a
common practice to turn cattle into an abandoned field, and this
often results in the spread of the disease to the surrounding
territory. After once being introduced the parasite is capable
of living in the soil on decaying organic matter. The disease
is apparently limited in its attack to watermelons alone, not
even attacking such closely related crops as cucumbers and
squashes.
The wilt fungus grows best at a temperature around 800F.,
which fact probably explains the late appearance of the disease
in the field. Even under favorable conditions there appears to
be a considerable variation in the susceptibility to the disease
of different strains and varieties of watermelons. While there
is no strain or variety of watermelons that appears to be com-
pletely immune to the disease, certain ones appear to be less






Bulletin 225, Watermelon Diseases in Florida


rapidly killed by wilt than others, with the result that more
plants of these strains survive and produce fruit. There is,
however, a high degree of resistance to the disease in many
kinds of citrons. By selecting and propagating the more resist-
ant and vigorous strains of watermelons or the progeny of
watermelon-citron crosses which produce melons of high qual-
ity, good market type, and with the ability to stand shipment,
the prospect for the future control of wilt seems to be very good.
DESCRIPTION
The name wilt accurately describes the appearance of dis-
eased plants, as wilting is one of the most noticeable symptoms
of the disease (Fig. 6). Wilt may attack watermelon plants in
any stage of their development, though its injuries are more ap-
parent after the plants have attained some size. The disease
may occur as a general rot of the seedlings before they reach
the surface of the ground, or as a damping-off of seedlings after








4 1









Fig. 6.-Watermelon plants in the field killed by Fusarium wilt.

they are well out of the ground. This latter type of injury is
characterized by a dull green color of the cotyledons and small
leaves which soon droop and become completely dry and withered
after a day or so. The stems of such plants when pulled up are
found to be girdled by a soft rot just at or below the soil level,
and often the stems appear to be water-soaked for some distance
above the rotted area. After the plants are killed the fungus






Florida Agricultural Experiment Station


grows out over the surface and produces spores in great num-
bers. Another type of injury caused by the wilt organism on
seedling plants is a stunting of plants not immediately killed.
Wilt is more commonly observed, however, in older plants,
where the disease causes the leaves to wilt and shrivel, starting
at the tips of the runners. Such plants may appear healthy
in the mornings and wilted by noon, and this alternate wilting
and recovery may continue for several days, but the plant never
permanently recovers after it is once attacked. The plants are
eventually killed and dry up. Melon plants in the later stages
of the disease often show just above the ground the light colored
cottony growth of the fungus on which are borne large numbers
of spores. If the stem of a wilted vine is cut, the water-carry-
ing vessels of the plant will be found to appear yellow or brown,
or in some cases a large part of the stem will be browned (Fig.
7). This browned condition of the vessels of the plant is very
characteristic of the wilt disease, and has led to the disease being
called "black root" in some sections.
CONTROL
Where wilt occurs the safest means of avoiding the disease
is never to plant watermelons on land that has produced a water-
melon crop before. Different growers have different ideas as to
the length of time the land must be used for other crops before
it is again used for watermelons, but it is known that the disease
is capable of living for 16 years in the soil. Consequently, it
is dangerous to plant melons on large areas of land that have
once shown heavy infestation. In general, however, five years
or longer has been found sufficient to reduce somewhat the
amount of the disease in the soil, and for small plantings on land
which showed only a small amount of disease the chance may
be taken.
There is always danger of wilt occurring on new land where
drainage water from a diseased field flows over the new field, or
where cattle have had access to both fields. It is also dangerous
to use manure in an area where wilt is present, for the fungus
is capable of maintaining itself in manure for long periods of
time; and the opportunity for it to establish itself in manure
piles is very great, either through the animals having access to
diseased fields, or through vines being included in the hay cut
from old melon fields.
The most hopeful means of combatting the wilt disease in the






Bulletin 225, Watermelon Diseases in Florida


Fig. 7.-Longitudinal sections of watermelon stems show-
ing darkened areas caused by Fusarium wilt. A healthy
plant is shown on left.






Florida Agricultural Experiment Station


future is through the development of varieties or strains resist-
ant to the disease. At present, however, none of the standard
commercial varieties are highly resistant to wilt. A resistant
melon, the Conqueror, was developed several years ago by the
United States Department of Agriculture, but it has never come
into common use on account of its being an undesirable market
type, and because it has shown a tendency toward variation
when grown in other localities than that in which it was develop-
ed. A number of experiment stations, however, are working on
the development of varieties of watermelons resistant to wilt,
and it is possible that within a few years a larger selection of
resistant varieties will be available.
SOUTHERN WILT
Southern wilt is caused by the fungus Sclerotium rolfsii Sacc.
This fungus is very common in the southeastern and south cen-
tral portions of the United
f States, the northern limit ap-
proximating the Ohio River.
: This area also coincides with the
,great watermelon producing
B area of this country. This fun-
gus causes a wilt of water-
melons, and, in addition, has
been found on more than 180
,. other species of plants. The
S: diseases resulting from attacks
-. of Sclerotium rolfsii on various
hosts are primarily the same
and result in a wilting and dy-
S ing of the plant, because of the
girdling of the main stem at or
Near the soil line. On water-
melons this disease has not been
of much importance during past
seasons, except in occasional
fields where melons followed
some other crop, such as sweet
potatoes or peanuts, which was
Fig. 8.-Sclerotium rolfsi on a gir- very susceptible to attacks of
died and killed watermelon this fungus. The fungus lives
plant (after 72 hours in moist
chamber), in the soil from season to season






Bulletin 225, Watermelon Diseases in Florida


in the form of sclerotia, which are hard, brown, round structures
of fungus growth about the size of mustard seed (Fig. 8). These
sclerotia develop in large numbers on plant parts that are kill-
ed and overgrown by the fungus. When an attacked melon rots
and dries these sclerotia are scattered by wind, water and culti-
vation, and remain in the soil until the next crop is developing.
When warm, wet periods prevail, the sclerotia germinate and


Fig. 9.-Young melon killed by southern blight. The fungus is fruiting
on one side of it.

produce the fungus mycelia which attack the stems of the plants
in their immediate vicinity. After the stems are girdled and
killed, numerous sclerotia are again produced.
DESCRIPTION
When the fungus has attacked the main stem of the melon
plant at the soil line, the first indication of disease to the casual
observer is a slight lack of turgidity or wilting of some of the
younger leaves near the growing tips of the runners. The dis-
ease has seldom been found attacking melon vines before runners
have started to cover the ground. This wilting gradually be-
comes more pronounced and involves more and more of the plant
until complete collapse takes place and the plant quickly dies.





Florida Agricultural Experiment Station


Often the fungus will attack only a single runner at some dis-
tance from the main root and in such an instance only the one
member is killed. The fungus also attacks the melons them-
selves from the lower surface where they are in contact with the
soil (Fig. 9). The fungus hyphae penetrate the rind, causing
it to turn brown. The watery content of the cells in this area
escapes through the rind and collects on its surface in droplets
resembling sweat. The fungus rapidly overgrows the attacked
areas and produces an abundance of white mycelium. Gradu-
ally the fungus invades the whole melon which collapses, shriv-
els, and dries, leaving the innumerable newly-developed sclerotia.
CONTROL
Methods advocated to control other important watermelon
diseases should control this one in most cases. Rotation and
sanitation are of most importance. All infected melons should
be removed from the field or buried a foot deep.

GUMMY-STEM BLIGHT
Gummy-stem blight is caused by the fungus Mycosphaerella
citrullina (C.O. Sm.) Gros., and is widely distributed over the
eastern and central United States and has been reported from as
far west as Arizona. The disease is capable of causing con-






f









Fig. 10.-Spots of gummy-stem blight on cotyledons of watermelon plants.

siderable losses through defoliation and killing of runners under
weather conditions favorable to the fungus, but, though very
prevalent in Florida, the disease is ordinarily of secondary im-






Bulletin 225, Watermelon Diseases in Florida


portance. Its wide distribution can be accounted for by its in-
troduction on the seed, from which it attacks cotyledons (Fig.


Fig. 11.-Gummy-stem disease on blade and petiole of watermelon leaf.






Florida Agricultural Experiment Station


10), leaves, and runners as they develop. Later the fungus
forms great quantities of spores on the attacked parts, which
serve for its further dissemination by wind and water, or other
agencies such as cultural implements and animals. After es-
tablishing itself in a field, the fungus is capable of living for
several years on the decaying plant material in the soil.


Fig. 12.-Gummy-stem blight affecting crown of melon plant. The point
of attack is indicated by point of knife.

DESCRIPTION
The spots on the cotyledons and primary stems of young
plants are often the first symptoms of the disease. These spots
are usually circular, sunken, blackish, and wrinkled. Pycnidia
containing spores are produced in abundance on these spots.
When these spots are located on the portion of the cotyledon






Bulletin 225, Watermelon Diseases in Florida


close to the petiole, the whole blade is often killed, and the axil-
lary bud or the whole growing tip may be destroyed by the en-
largement of the primary lesion. The first true leaves are in-
fected by spores from the spots on the cotyledons, and girdling
and death of the growing tip may result in the same manner as
described for the cotyledon infections. (Fig. 11.) The disease
may also attack and girdle the stem below the cotyledons. Gum-
my-stem blight spreads from the center of the hill outward as
the season advances, attacking both leaves and stems. On the
leaves the disease is characterized by light brown spots, in the
centers of which the minute, black fruiting bodies-pycnidia-

















Fig. 13.-Typical lesions on watermelon stem caused by gummy-stem blight.

of the fungus develop. On the stems the disease appears as
elongate, water-soaked areas that later become light brown to
whitish in color (Fig. 12). The fruiting bodies, in which are
formed great quantities of spores, appear abundantly in these
cankered areas, sometimes in numbers sufficient to give the
lesion a black appearance. The cankers often crack open and
exude a reddish-amber gum, and it is this characteristic of the
disease that gives it its name. The lesions on the stem or run-
ners persist until the end of the season, if the plant is not killed
and, late in the season, they may become continuous and the
stem and all the runners appear bleached, often cracked (Fig.
13), and sometimes blackened with the dried gum and the masses
of fruiting bodies of the fungus. In some instances the cankered




Florida Agricultural Experiment Station


stem enlarges to two or three times its normal size as shown
in Fig. 13. The gummy-stem blight fungus also occurs on the
melons, though to no great extent.


Fig. 14.-Taproot of watermelon showing injury caused by
gummy-stem disease.


r-*41






Bulletin 225, Watermelon Diseases in Florida


CONTROL
Gummy-stem blight usually does not become serious enough
to warrant special control measures; seed treatment and the ap-
plication of fungicides as recommended for anthracnose will les-
sen the amount of gummy-stem blight present.
STEM-END ROT
Stem-end rot of watermelons is primarily a transit disease,
and is caused by fungi of the genus Diplodia. The principal spe-
cies capable of causing this decay are Diplodia tubericola (E. &
E.) Taub., Diplodia frumenti E. & E., Diplodia gossypina Cke.,
and Diplodia natalensis Ev. These organisms also cause diseases




4 AA


Ip I



A B C D
Fig. 15.-Photomicrographs of pycnidiospores of Diplodia spp. that are
capable of causing stem-end rot of watermelon. A-Diplodia frumenti;
B-Diplodia gossypina; C-Diplodia tubericola.

of sweet potatoes, an ear and stalk rot of corn, boll rot of cotton,
and gumming of citrus. The cotton and citrus organisms are
probably the same. All of the above mentioned organisms pro-
duce pycnidiospores that are indistinguishable (Fig. 15), and
artificial inoculations have shown that each of them can cause
stem-end rot of watermelon.
The disease is common and destructive in most of the water-
melon-growing regions of the United States, and is especially
prevalent in the Southern states, because of the long time the
fruit is in transit to Northern markets. In Florida the disease
is almost wholly a transportation problem. The melons are loaded
at the local shipping points in a healthy, sound condition as far
as can be determined and when they arrive at their destination






Florida Agricultural Experiment Station


from four to eight days later
10% (Fig. 16).


the decay is evident, usually about


Fig. 16.-Interior of railroad car at destination after sound melons were
removed. Loss caused principally by stem-end rot and anthracnose.
(Courtesy USDA.)

This disease seldom develops in the field, but if the melons
are picked and left in the field for a day or two before being
loaded and shipped, they may show a very high percentage of
stem-end rot upon arrival at their destination a week or ten
days later. The exact source of the inoculum is not definitely






Bulletin 225, Watermelon Diseases in Florida


known, but since it has been proved that the organisms affecting
citrus, sweet potatoes, corn, and cotton will also cause the dis-
ease, it can be readily understood where some of the fungus
spores originate. Records of collection in Florida for the past
10 years show that Diplodia spp., producing spores very much
like those found on diseased watermelons, have been found nat-
urally infecting more than 40 different kinds of plants.
The disease causes serious loss to watermelon shippers in all
parts of this State during the shipping season. Reports of in-
spectors made at the destination of shipments of Florida melens
have shown as high as 40% stem-end rot. In every instance
where more than 12-15 % decay occurred the stems had not been
treated. The average of several hundred reports was 8-10 %.















Fig. 17.-Stem-end rot of watermelon caused by Diplodia frumenti.

Such losses are entirely too high when the disease can be so
easily controlled. The uninjured melon on the vine is entirely
resistant to the disease. When it is injured or cut from the vine
these unprotected areas are exposed to infection by spores of
the fungus. Where the skin is broken or where the stem is cut,
a watery exudate appears and persists for considerable time.
This makes a very suitable medium for the germination of the
spores and growth of the fungus which later advances into the
melon and causes decay. The percent of decayed melons in-
creases with the length of time these injured places are exposed.
Melons should be handled carefully and removed from the field
to loading points as soon as possible. The spores of the fungus
germinate in a very few hours and in less than 12 hours may






Florida Agricultural Experiment Station


infect the cut stem and later grow into the fruit, causing the
rot typical of the disease. The development of the disease in
transit is favored by high temperatures, high humidity, and
lack of ventilation in the cars, along with the constant jarring
while traveling. All commercial varieties of melons are subject
to the disease to about the same extent.
DESCRIPTION
The first symptom of the disease is the browning and shrivel-
ing of the stem; which may be observed before the melon shows
any indication of infection. The first decay of the fruit takes
place around the stem where the rind becomes slightly darkened,
taking on a water-soaked appearance which is later followed by
a light tan or brown color (Fig. 17). After the decay first shows
on the rind the advance of the line of demarcation between in-
vaded and sound tissue is exceedingly rapid and can be readily
observed from day to
day. After one-third
or more of the melon
has been invaded the
stem-end portion be-
comes dark colored
and wrinkled and
gradually shrinks as
evaporation continues
(Fig. 18). The outer
rind becomes over-
grown with a dense
greenish- or grayish-
black mold, or under
certain conditions the
mold may be light
gray or whitish,
speckled with black.
The spores of the fun-
gus are produced in
abundance on the old-
er decayed areas. An
Fig. 18.-Stem-end view of watermelon indication of decay
showing development of stem-end rot.
can often be detected
before any discoloration appears by the softness of the rind
around the stem end as determined by light pressure of the
thumb.






Bulletin 225, Watermelon Diseases in Florida


CONTROL
The control of this disease should begin in the field at harvest
time. Instructions should be given and harvesting operations
closely supervised to guard against injury to the fruit by rough
and careless handling. The stems should be clipped as long as
possible so as to permit a second clipping after the melons are
loaded in the railroad car. The truck or wagon bodies used in
collecting melons in the field should be free from gravel, sand,
splinters, nails, etc., and should be lined with soft material such
as burlap. The melons should be loaded carefully and gently
placed in position in the car. They should be loaded a tier at
a time in alternate ends of the car so that the stems can be clip-


Fig. 19.-Clipping stems of tier of watermelons after loading in railroad
car and preparatory to treating to prevent stem-end rot. (Courtesy USDA.)

ped a second time and the cut end disinfected with copper sul-
phate paste in one end of the car while the melons are being
loaded in the opposite end (Fig. 19). The stems can be cut off
with an ordinary knife, but thin-bladed, sharp clippers are to
be preferred. Immediately following the clipping process the
stem should be painted. The cutting in the field should leave the
stems about 2 to 3 inches long and when the melons are loaded





Florida Agricultural Experiment Station


the stems should be cut to about an inch long. The portions cut
off should be carefully collected and removed from the car. An
additional precaution would be the occasional disinfection of the
clippers. The paste used to paint the clipped stems should be
about as thick as ordinary paint and is easily applied with an
ordinary cheap paint brush of small size. The paste should be
held in a container that is easily handled while being used and
one that will not easily be tipped over (Fig. 20). The disin-
fecting paste is made up according to the following recipe:
Place 31 quarts of water in an enamel-ware kettle and
add 8 ounces of bluestone and bring to a boil. As soon as the
bluestone is dissolved and while boiling add the starch mixture,


Fig. 20.-Painting the clipped stem ends with copper sulphate paste for
the prevention of stem-end rot. (Courtesy USDA.)

slowly stirring the concoction all the time. The starch mixture
is made by mixing four ounces of either laundry or corn starch
with a pint of cold water, stirring until a milky mixture is ob-
tained. Continue the boiling and stirring of the mixture until it
thickens into an even paste, but the boiling should last only one
or two minutes after the starch is added as the paste must not
become too thick to be easily applied with a brush. It should
have the consistency of thick paint. A paste made from com-






Bulletin 225, Watermelon Diseases in Florida


mercial dry bordeaux will do if not too thick. This paste serves
as a disinfectant and kills the germinating spores, if they are
present. It has been proved that this paste enables the melons
to arrive in the market without stem-end decay.
Recutting of the stems and the application of the paste by
means of a small, long-handled brush is the most important part
of this control measure. Consequently the operation should not
be left to careless individuals or small boys as is often the case.
The owner or a reliable workman should do this particular job,
making certain that there are no bruises on the stem when it
is recut. If bruised, the stem should be recut closer to the melon.
BLOSSOM-END ROT
Blossom-end rot is the name applied to a group of abnormal-
ities either parasitic or physiological, which affect the end of the
melon opposite the stem. All the causes have not been definitely
decided upon by investigators. Some attribute the cause
to deranged nutrition, closely associated with moisture supply
and high temperatures. Others contend that parasitic organ-
isms, principally Pythium de baryanum Hesse and P. aphani-
dermatum (Eds.) Fitz., are the cause of the decay, or at least
inaugurate the infection (Fig. 21). A large number of organ-
isms, both fungi and bacteria, either saprophytic or parasitic,
have been isolated from diseased melons. Those who favor the
physiological theory consider this influx of organisms a natural
result of the breaking down of the tissue and the destruction
of any vestige of protection or resistance. This condition can be
applied equally as well to melons attacked by parasitic fungi such
as Pythium sp. These parasites break down the protection or
resistance of the host by their invasion, leaving the tissue sub-
ject to the inroads of the multitude of secondary invaders.
A large number of organisms have been isolated from these
decaying blossom ends, but the greater portion of them are un-
doubtedly secondary. Pythium de baryanum has been definite-
ly determined to be the cause of blossom-end rot of citrons.
Other organisms found associated with blossom-end rot are My-
cosphaerella citrullina (Sm.) Gross, Colletotrichum lagenarium
(Pass) E. & H., Cladosporium sp., Fusarium sp., Alternaria sp.,
and Diplodia spp.
Blossom-end rot is exceedingly common in melon fields
throughout the country, especially in the South. In Florida it
can be found in almost any field after the first fruit sets. The






Florida Agricultural Experiment Station


disease has been found on fruits of all sizes and ages, but it
appears to be more common on melons approximately one-fourth
grown, or melons measuring 6 to 10 inches by 4 to 6 inches. The
affected ones are more conspicuous at this stage of development
because of the contrasting black color of the diseased area and


Fig. 21.-Blossom-end rot of citron caused by Pythium de baryanum. The
fungus has advanced from the blossom-end toward the stem-end and
caused a decay of all the melon except the light colored area around
the stem.

because a large percent of the melons are also "crooks" or are
malformed. Whether the "crooks" are a result of invasion by
the parasite or whether they were mechanically injured, thus
permitting the entrance of the fungi, is a matter of opinion.
Either may be a possible explanation of the trouble until further
information is available.






Bulletin 225, Watermelon Diseases in Florida


SYMPTOMS
The first indication of blossom-end rot is the water-soaked-
appearing tissue at the blossom end, which gradually becomes
darker in color. As the spot enlarges and involves more tissue,
the center of the spot changes from green to a tannish brown
and becomes soft. It is at this stage of the development of the
spot, which may be one to three inches in diameter, that second-
ary invasion is most common and the spots become almost black
(Fig. 22). Often there is no secondary invasion and the whole
melon becomes involved, turns brown, and collapses. This is
also true when Pythium spp. are involved in the decay. Other


Fig. 22.-Blossom-end rot of melon caused by the gummy-stem blight
organism.

instances occur where the progress of the rot is arrested and
only a portion of the fruit becomes decayed. This decayed por-
tion usually shrinks and becomes wrinkled and black, while the
remainder of the melon is of a normal green color.
CONTROL
No control methods are known, although the "crooks" and
malformed fruits should be removed from the vines and field
to prevent the development of parasitic organisms on them that
may possibly infect other fruits and portions of the vine.






Florida Agricultural Experiment Station


DOWNY MILDEW

Downy mildew is caused by the parasitic fungus Peronoplas-
mopara cubensis (B. & C.) Rostow. This disease has been found
on watermelons in most of the Gulf and Atlantic states and in
a few of the interior ones that produce watermelons. It is not


Fig. 23.-Spotting of citron leaf caused by downy mildew.






Bulletin 225, Watermelon Diseases in Florida


of first rank as a disease of this plant, although it is common
year after year, and is widespread in Florida. The fungus has
been collected on most of the cucurbits, such as cucumber, can-
taloupe, squash, pumpkin, and gourd. It is the worst disease
of cucumbers in the State, and, since cucumbers are widely
grown during most of the year, there is an abundant source of
inoculum for watermelons. The disease does not usually become
of serious consequence until after the middle of the growing
season. It attacks only the leaf blades of the watermelon, where
it causes lesions that eventually kill them. The spores are pro-
duced on the diseased spots, most plentifully on the lower sur-
faces, and are easily detached and disseminated by rain and wind.
The fruiting structures of the fungus are often difficult to de-
tect even with a good hand lens, consequently the spots caused
by the fungus are generally mistaken for those of anthracnose,
which has been previously described. The fungus can be de-
tected easily in the early morning before the dew has disap-
peared.
DESCRIPTION
The first symptom of infection by the downy mildew fungus
is the appearance of a slightly yellowish spot on the blade of
the leaf. This yellowing becomes more pronounced and about
two days later the fruiting fungus can be observed. This is
usually about eight or 10 days after infection has taken place.
These yellow spots are more or less circular or oval in outline
and blend gradually into the green color of the leaf (Fig. 23).
Later, however, the tissue is killed and turns brown or blackish.
These spots are more or less angular in outline, and often may be
confused with leaf spots caused by other parasites. The spots
may be few or many on a single leaf, depending on the abundance
of primary infection, and may coalesce when in close proximity
and thus rapidly involve the entire leaf blade which then turns
black, dries, and disintegrates. These spots vary in size from
several millimeters to a centimeter or more in diameter. The
spores of the fungus are visible on the lower surfaces of the
leaves immediately beneath the yellow spots which are conspic-
uous on the upper surface (Fig. 24). They are easily blown
or washed from the leaf, and are capable of causing infection
when they come in contact with other watermelon leaves. The
life cycle, that is, the period from infection to spore production,
varies from eight to 12 days under average conditions.






Florida Agricultural Experiment Station


Fig. 24.-Branched conidiophore of downy mil-
dew fungus and spores that grow upon its
branches (highly magnified).


CONTROL
The control of
this disease is
best accomplish-
ed by the applica-
tion of bordeaux
mixture or cop-
per-lime dust.
The liquid spray
is probably more
efficient than the
dust. Thorough
applications of
the fungicide
should be made
at weekly inter-
vals. These ap-
plications can be
included with the
control methods
recommended for
other, more im-
portant, diseases
of the host pre-
viously discussed.


POWDERY MILDEW
The fungus Erysiphe cichoracearum DC., has been found at-
tacking watermelon leaves and fruits, causing a disease known
as powdery mildew. This disease has been reported from various
foreign countries and the watermelon-growing sections of the
United States. In Florida it is common on the leaves, but very
seldom becomes serious, as it develops most rapidly in warm,
moist weather which usually occurs in Florida toward the end
of the growing season. This disease has been found on all of
the cucurbits, including the cantaloupe, cucumber, squash, gourd,
and pumpkin. The spores are produced on both surfaces of the
leaves, but they are more plentiful on the upper surface. The
fungus very seldom kills the leaves quickly, but overgrows them
without causing much loss of turgidity until they appear gray
or whitish. When this stage is reached brownish spots begin






Bulletin 225, Watermelon Diseases in Florida


to develop, which gradually involve the whole leaf, causing it to
dry and die.
The early symptoms appear on the leaf surfaces as small,
superficial, circular spots of a white, powdery nature which is
the vegetative growth of the fungus. The spots enlarge and the
white coating of fungus growth becomes more dense with the in-
creased production of the spores. These spores give the spot
its powdery appearance and serve to disseminate the disease.
CONTROL
Methods of control have not been worked out, but the regular
spray schedule followed for the control of other melon diseases
should be sufficient to hold this disease in check.
CERCOSPORA LEAF SPOT

This characteristic spot of watermelon leaves is caused by
Cercospora citrullina Cke. The disease has been reported from
most of the watermelon growing sections of the United States.
In Florida it has been found widespread, but has not been com-
mon or of any economic importance until toward the end of the
season. The disease is usually first observed on the leaves
around the center of the hill, but as the season advances it in-
volves all of the leaves toward the growing tip of the runners.
The spotted leaves turn yellow, wilt, and die.
DESCRIPTION
The first symptom of the disease is the appearance of small,
water-soaked spots scattered over the surface of the leaf. These
spots enlarge up to several millimeters in diameter, become sun-
ken, and dry out in the center (Fig. 25). The tissue in the cen-
ter of the spots changes from green to light tan and finally to
a dull white. The whitish centers are separated from the green
tissue by a dark brown to black ring which is very characteristic.
Often these spots are so close together that they coalesce, form-
ing larger brown areas that may include several of the individual
spots. The spots are often invaded by other parasitic fungi,
such as Colletotrichum and Alternaria, which hasten the death
of the leaf. The fungus may be detected with a hand lens on
either surface of the leaf, but it is usually more prominent on
the lower surface where it occurs in the form of dark, hairy
specks. The spores are long and thin and are easily detached
and distributed by wind or water.





Florida Agricultural Experiment Station


.- V- ~^,




~ I







Fig. 25.-Cercospora leaf spot of watermelon.
CONTROL
This disease has never been important enough to warrant
specific control experiments; consequently definite methods can
not be given. However, the use of fungicides for the control of
other diseases should control this leaf spot.
MACROSPORIUM LEAF SPOT
A leaf spot caused by Macrosporium cucumerinum E. & E. is a
very widely distributed disease of watermelons and other related






Bulletin 225, Watermelon Diseases in Florida


plants, especially cantaloupe. It usually causes little damage
and is seldom observed, except during warm, wet seasons. Such
conditions favor the development of the fungus. The disease
attacks the leaves around the center of the hill and causes brown,
concentrically ringed spots to develop, on which the spores are
borne in black tufts. These spots may enlarge, and when num-
erous coalesce to involve the whole leaf and cause it to shrivel
and die. Occasionally in warm, moist weather the disease may
cause considerable defoliation. The disease is often confused
with anthracnose, but the lighter colored, and concentrically
zoned spots serve to distinguish it from anthracnose spots which
are black in color. The application of fungicides recommended
for anthracnose also serves to reduce the amount of leaf spot
present.
GROUND ROT

Ground rot, caused by Corticium vagum B. & C., has not been
of any importance in Florida or the United States as a whole up
to the present time. Occasionally, however, a watermelon will
show lesions on the side in contact with the soil, but these are
usually small and insignificant. The spots at first appear almost
superficial, and are slightly tan colored in contrast to the sur-
rounding green. In the more advanced stages the spots are
sunken and the brown color may cover an area several inches in
diameter. This disease is most troublesome during wet seasons,
or when the melons continually rest on wet soil. The disease
may occur in any field, as the causal organism is considered to
be present in practically all Florida soils, and is capable of caus-
ing infection whenever favorable conditions develop.
SPECKLE

Speckle is an abnormal condition of the rind of watermelons,
the cause of which is not known. The disease is characterized
by the appearance of numerous yellow or whitish spots scattered
over the surface of the melon, principally on the upper half
(Fig. 26). The spots are usually more or less circular in shape,
and vary in size from those barely visible to those almost a cen-
timeter in diameter. The surface of the melon is smooth, and
the epidermis appears to be normal except in color. The spec-
kled melons show no apparent ill effects other than their poor ap-
pearance. The cause of the condition is apparently not parasitic






Bulletin 225, Watermelon Diseases in Florida


plants, especially cantaloupe. It usually causes little damage
and is seldom observed, except during warm, wet seasons. Such
conditions favor the development of the fungus. The disease
attacks the leaves around the center of the hill and causes brown,
concentrically ringed spots to develop, on which the spores are
borne in black tufts. These spots may enlarge, and when num-
erous coalesce to involve the whole leaf and cause it to shrivel
and die. Occasionally in warm, moist weather the disease may
cause considerable defoliation. The disease is often confused
with anthracnose, but the lighter colored, and concentrically
zoned spots serve to distinguish it from anthracnose spots which
are black in color. The application of fungicides recommended
for anthracnose also serves to reduce the amount of leaf spot
present.
GROUND ROT

Ground rot, caused by Corticium vagum B. & C., has not been
of any importance in Florida or the United States as a whole up
to the present time. Occasionally, however, a watermelon will
show lesions on the side in contact with the soil, but these are
usually small and insignificant. The spots at first appear almost
superficial, and are slightly tan colored in contrast to the sur-
rounding green. In the more advanced stages the spots are
sunken and the brown color may cover an area several inches in
diameter. This disease is most troublesome during wet seasons,
or when the melons continually rest on wet soil. The disease
may occur in any field, as the causal organism is considered to
be present in practically all Florida soils, and is capable of caus-
ing infection whenever favorable conditions develop.
SPECKLE

Speckle is an abnormal condition of the rind of watermelons,
the cause of which is not known. The disease is characterized
by the appearance of numerous yellow or whitish spots scattered
over the surface of the melon, principally on the upper half
(Fig. 26). The spots are usually more or less circular in shape,
and vary in size from those barely visible to those almost a cen-
timeter in diameter. The surface of the melon is smooth, and
the epidermis appears to be normal except in color. The spec-
kled melons show no apparent ill effects other than their poor ap-
pearance. The cause of the condition is apparently not parasitic





Florida Agricultural Experiment Station


Fig. 26.Speckle of watermelon (cause unknown).
Fig. 26.--Speckle of watermelon (cause unknown).


in nature, and is due to some abnormal condition in the plant
or its environment.

MINOR DISEASES NOT FOUND IN FLORIDA
Bacterial wilt, caused by Bacillus tracheiphilus E. F. S., has
been reported on watermelons but a few times, and watermelons
are considered as practically immune to the disease, although
other cucurbits are susceptible in the following order: squash,
cantaloupe, and cucumber.
Bacterial leaf spot, caused by Bacterium cucurbitae Bry., has
been found on squash in South Carolina and Georgia, but there
are no authentic reports of its occurrence on watermelons, al-
though artificial inoculations have shown them to be susceptible.
Black root rot, caused by Thielavia basicola (B. & B.) Zopf.,
has been reported on watermelons in the northwestern part of
the United States on only two different occasions. Rather seri-
ous losses were reported in one of these cases, however.
Watery soft rot, caused by Sclerotinia sclerotiorum (Lib.)
Mass., has been reported as causing damage to melons in transit.
Mosaic, which is a serious disease on other cucurbits, and
which is thought to be caused by an infectious, filterable virus,
apparently does not occur on watermelons, though there are oc-
casional notes reporting its natural occurrence on citrons.






Bulletin 225, Watermelon Diseases in Florida


Fig. 27.-Watermelon leaf showing inter-mixed spots caused by Cercospora
citrullina, Peronoplasmopora cubensis, Macrosporium cucumerinum,
Colletotrichum lagenarium, and Mycosphaerella c;, .,il,,,,m.





Florida Agricultural Experiment Station


Other parasites and diseases reported on watermelons are
Phytophthora citrophthora, Corticium. centrifugus, Pestolotia
torulosa, and the curly top disease of sugar beets.

COLD, WIND, AND SAND INJURY
During the early part of the watermelon growing season in
Florida the young plants are often exposed to temperatures
considerably below the optimum for the growth and development
of the crop. Besides the actual freezing of the young plants,
which results in their immediate death, temperatures below 40
often cause severe damage by stunting the young plants to such
an extent that further growth is very slow. Such plants appear
yellow, oftentimes with the tips and margins of the cotyledons
browned and shriveled. The browning, however, is of a lighter
color than that caused by the attacks of various fungi, and can
be quite easily distinguished on most specimens. The older
leaves, which are even more sensitive than the cotyledons, when
subjected to very cool weather, assume a bronzed, glazed ap-
pearance, particularly on the higher portions of the leaf surface
(Fig. 28). These areas are not clearly defined as in the case of
fungus spots, though they are somewhat restricted to the areas
between the larger veins. Leaves showing these discolored
areas feel hard and brittle to the touch. Further growth is al-
most entirely stopped, and where further growth occurs it is
often in an irregular manner, causing the curling of the leaf.
Plants or leaves showing cold injury are more susceptible to the
attacks of various fungi than those in a more normal condition
of growth, and are often wholly destroyed by them.
Strong winds often occur during the growing season of water-
melons, and may whip the leaves so as to tear them. This in-
jury at times is severe and the leaves are almost entirely shred-
ded. Such leaves dry out on the torn edges, and become hard
and brittle, and very susceptible to the attacks of various fungi
such as Macrosporium and Colletotrichum. The most serious
type of wind injury, however, occurs during the period of fruit
setting, and may prevent the setting of early melons by whip-
ping off the blossoms and young melons.
Heavy winds during dry weather often result in sand burn,
which is characterized by the almost white areas that appear
on the leaves and stems. These areas of the leaves are rough
and brittle, and are often torn by the wind. Wind-blown sand






Bulletin 225, Watermelon Diseases in Florida


Fig. 28.-Cold injury to watermelon leaf.


often injures the epidermis and cortex of the main stems and
runners to such an extent as to cause them to form thick calluses
over the injured areas.





Florida Agricultural Experiment Station


HANDLING
The profits in watermelon growing may be lost or at least
greatly reduced by growers who consider their work finished
when the melon is cut from the vine. There are too many grow-
ers with this erroneous idea. In reality, some of the most care-
ful work just begins at this time.
Melons, although they have thick rinds, have thin skins and
are tender. They should be handled with this in mind so as to
prevent abrasions, bruises, cuts, gouges, or cracks. Any blemish
of a melon that causes the skin to be broken, opens a way for
the invasion of the melon by any of a large number of organisms
that cause it to rot while in transit. Help used in the harvest of
melons should be carefully and thoroughly instructed before they
are sent into the fields. The cutting and windrowing should
be done with care. The rack or box of the wagon or truck used
for transporting the melons from the field should be free of all
sand, gravel, splinters, nails, and sharp corners, and the inside
walls and bottom should be covered with several layers of burlap
or some other soft lining. Too much speed in handling and haul-
ing is often a detriment.














Fig. 29.-Injury of watermelon caused by contact with chemicals or fer-
tilizer on floor of uncleaned railroad cars.

Strict attention should be given the railroad car into which the
melons are loaded, being sure first that it is in good order. See
that a good, solid false lining is present. Clean the car carefully,
removing all traces of foreign material, especially fertilizers,
which have been found to burn the melons and thus allow rot
fungi to enter (Fig. 29). Smooth out all obstructions such as






Bulletin 225, Watermelon Diseases in Florida


splinters and nails. After the car has been cleaned a washing
with formaldehyde is beneficial, but the car should be aired
thoroughly afterward. Unless diseased melons have been in the
car this treatment may be dispensed with. The material used
for bedding should be according to law (in certain counties local
materials such as hay, straw, moss, and pine straw, cannot be
used on account of tick eradication regulations). Any bedding
used should be perfectly dry, as moist conditions are especially
favorable to diseases. Excelsior is being used more and more,
and is very satisfactory, as it is clean, soft, and cheap. It should
be carefully pulled apart as it is put into place. The melons
should not be walked upon, even with bare feet, during any of


















Fig. 30.-Watermelon harvest. The truck body is well lined.

the loading operations; the weight causes the melons to crack
internally and deteriorate much faster than sound melons. They
should be handed from the truck to helpers in the car who take
them to their places, and place them gently in the tiers. While
melons may be pitched from one worker to another, they should
not be tossed or too roughly forced into place in packing, though
no spaces should be left. Lay the melons with the stems toward
the middle of the car in rows and tiers, alternating between the
two ends of the car, in order that the stems can be cut and
treated in one end while the other is being loaded.





Florida Agricultural Experiment Station


SEED DISINFECTION
Watermelon seeds should be disinfected before they are plant-
ed, to prevent seed-borne diseases, such as anthracnose and gum-
my-stem blight, from developing on the seedlings. The best dis-
infectant to use for this purpose is corrosive sublimate, which
can be purchased at any local drug store. It should be dissolved
in water to make a solution of the strength of 1:1000 and the
seed should be soaked in this solution for 10 minutes. They
should then be thoroughly rinsed in clear water and spread out
to dry before being planted.
Corrosive sublimate is a deadly poison and should be handled
accordingly. It can be purchased either in the form of crystals
or in tablet form. If a large quantity of seed is to be treated
it would be well to purchase the poison in the crystal form. One
ounce of crystals dissolved in 71/2 gallons of water will make a
solution of the strength of 1:1000. As the corrosive sublimate
crystals dissolve more quickly in hot water, it will facilitate the
process to use a small quantity of hot water and dilute it after-
wards. If only small quantities of the disinfectant are desired,
it is best to purchase the tablets, which, dissolved at the rate of
one tablet to one pint of water, give a 1:1000 solution. The dis-
infecting solution should be made up in crocks or wooden con-
tainers and never in metal containers. If mixed in metal con-
tainers the solution will be weakened by the disinfecting agent
combining with the metal.
The seed to be treated should be tied loosely in porous cloth
bags and submerged in the solution. Stir the seed occasionally
with a stick to loosen all air bubbles that may be clinging to
them. Soak for 10 minutes, at the end of which time remove
them from the disinfectant, rinse in several changes of clear
water, making sure that they are thoroughly washed, then
spread out to dry in the shade. As soon as they are dry,
they are ready to plant. It is best to use a fresh solution after
two or three batches of seed have been treated.
In measuring the amount of solution to treat a required
amount of seed it is well to make up about three times the volume
of disinfectant compared with the volume of seed to be treated.
After the disinfectant is used it should be disposed of care-
fully because it is a deadly poison and will kill anything that
drinks it. It is also well to take particular care of the treated





Bulletin 225, Watermelon Diseases in Florida


seed because there is also some danger of these being fatal should
they be eaten.
When the seed are spread out to dry one should be careful not
to place them where there is danger of re-infection by common
parasites that may cause damage in the field. Newspapers are
very convenient to spread the seeds on. If the seed are dried
on a floor, it should be washed with the corrosive sublimate so-
lution. Experiments have shown that watermelon seed are very
resistant to injury from corrosive sublimate and for this reason
the immersion period has been lengthened to 10 minutes so as
to be sure that all fungus spores and bacteria adhering to their
coats are killed. Seed may be treated several days before plant-
ing but longer periods are not advisable on account of the pos-
sibility of re-infection.
Organic mercury compounds may be preferred by some grow-
ers for a dust treatment of seed. This type of seed treatment has
proved to be beneficial and is probably as efficient as the corro-
sive sublimate treatment. The dust disinfectants can usually
be purchased from the leading seed dealers or from drug stores
in the watermelon growing sections of Florida. The directions
for the use of the organic mercury dusts as disinfectants are
given on the container. They can be purchased for about 25
cents per ounce or $2.75 to $3.00 per pound.
FUNGICIDES AND THEIR APPLICATION
Fungicides such as bordeaux mixture, copper-lime dusts, and
sulphur are applied to plants in order to prevent infection by
some of the parasitic organisms that are common and destructive
to watermelons. The essential items to be considered carefully
in the application of fungicides are: 1.-Kind and cost of the
fungicide, 2.-Time of applications, 3.-Thoroughness of ap-
plications. In relation to the first point it should be known to the
grower just what the fungicide is supposed to do in the way of
preventing the occurrence of diseases and how it is supposed
to do it. There may be a difference of opinion among growers
as to the merits of liquid or dust fungicides on watermelons.
Both of these are used successfully by Florida growers.
In the matter of effectiveness in the control of diseases on
watermelons, spray seems to be somewhat better than dust, par-
ticularly in regard to the disease on the leaves, though both are
about equal in preventing the formation of bumps or lesions on





Florida Agricultural Experiment Station


the melons themselves, and with neither is there danger of suf-
ficient defoliation to occasion much loss from sunburned melons.
In no case, however, can either be considered as an absolute
preventive of anthracnose, for on an average 80% control seems
about the best one can expect, though in dry seasons the per-
centage may be somewhat higher. On the whole, though, both
may be considered about equal in effectiveness and the selection
of one or the other can be based on other factors, all of which
have a direct bearing on the cost. The more important of these
factors are: the cost of materials, the cost of labor for apply-
ing, the equipment available, the size, location, and condition of
the field.
Dust vs. Spray: Conclusions after several years of the use of
both spray and dust have shown that the bordeaux spray is
one-fourth more efficient than copper-lime dust. In other words
the dust is 75-80% as effective as the home-made liquid bor-
deaux. There have been some seasons and some experiments in
which the dust has been better than the spray, but on the av-
erage over a number of years, the spray has given better results.
This does not mean, however, that all dusting should cease. Some
growers are equipped to do dusting, having done it for a num-
ber of years, and have undoubtedly developed their methods in
a careful way so that they actually get better results from their
dusting operations than their neighbors who use liquid spray for
their melon crops, but apply it in a haphazard, inexperienced
way.
The use of fungicides requires careful consideration by the
grower, since the benefits derived from their application are
often lost by using the wrong fungicide and by having it applied
in a careless manner or at the wrong time. The copper fungi-
cides such as 4-4-50 bordeaux mixture and copper-lime dusts
are to be recommended for use on watermelons for the control
of diseases such as anthracnose and mildew. The dusts should
be fresh, and should be a guaranteed, labeled mixture. The con-
tainers should be kept tightly covered, when one is not actually
extracting the dust.
Cost of Fungicides: About 50 gallons of a 4-4-50 bordeaux
mixture or 30 pounds of 20-80 copper-lime dust are needed for
one application on one acre of melons that meet between rows,
though the amount may be greater or less depending on the den-
sity of the vines, the type of machine used, and the quality of
the labor. The cost of preparing 50 gallons of a 4-4-50 bordeaux






Bulletin 225, Watermelon Diseases in Florida


mixture on the farm is about 50 cents, with lime at 1 cent a
pound and copper sulphate or bluestone at 7 cents. This cost
may be increased by the labor necessary to provide water, if it
is not available in quantities. The cost of a commercial bor-
deaux, which may be obtained in dust or paste form, is about
three times this sum.
A 20-80 copper-lime dust may be prepared on the farm for
about $4.00 a hundred pounds or about $1.33 for the 30 pounds
necessary- for one application. The same dust bought ready
mixed costs about $7.00 a hundred pounds or $2.33 for enough
for one application to one acre.
The cost of applying the spray varies with the equipment,
but will usually equal the cost of preparing the spray; that is,
the cost of a single application of spray to one acre totals from
a dollar to a dollar and a quarter. The time required will vary
with the equipment and the quality of the labor and will be dis-
cussed later.
The cost of applying the dust is usually about one-half that
required to spray the same area, or about 25 cents, though this,
too, varies with the equipment and the labor.
The usual number of applications of spray or dust necessary
to protect an acre of watermelons for the season is four to five.
From the above figures the approximate total costs of protection
with the various fungicides are:
Home mixed bordeaux mixture, 4-4-50, $4.00 to $5.00
Home mixed copper-lime dust, 20-80, $6.32 to $7.90
Commercial copper-lime dust, 20-80, $10.32 to $12.40
The proper use of any of these materials will show consider-
able increase in the yield of mature melons free from sunburn-
ing as a result of defoliation and from pitting by anthracnose.
Considering the costs of materials and application alone,
spraying is seen to be at least 30% cheaper than using home-
mixed dust and 60% cheaper than the use of commercial dusts.
All of the figures are considered as average and the costs of each
may be considerably increased by wasteful and inefficient labor
or machines, or in the case of spraying, the necessity of hauling
water long distances. On the other hand, efficient handling
might lead to considerable savings.
Home-made Dust: A satisfactory 20-80 copper-lime dust can
be cheaply prepared on the farm by carefully weighing out 20
pounds of monohydrated copper sulphate and 80 pounds of a






Florida Agricultural Experiment Station


good grade of hydrated lime, and thoroughly mixing them. This
can be done by placing the two dusts into an empty, dry metal
drum with a few smooth stones and rolling the drum about for
at least five minutes. Where large quantities of material are
to be mixed a mixer can be cheaply made of a wooden barrel
fitted with pipe fittings to revolve on an axle in the same manner
as a barrel churn. After the dust is mixed, it should be sifted
through a 20-mesh brass or copper screen, and if stored it should
be in a dry, air-tight container.
Copper-lime dusts of other proportions, such as 25-75 and
15-85, are sometimes used, but have not generally appeared so
satisfactory as the 20-80 mixture.
Home-made Bordeaux Mixture:* Bordeaux mixture is a
liquid spray made from bluestone (copper sulphate) and either
rock or hydrated lime. This spray must not be made in metal
containers. Use wooden pails or barrels, or earthenware crocks
instead. Never mix the concentrated (stock) solutions and
never use bordeaux mixture that is more than 12 hours old.
Home-made bordeaux mixture, 4-4-50 formula, is a most valu-
able spray for the control of plant diseases. Altho not used ex-
clusively by melon growers, it is probably used more than all
other fungicides combined. When weather conditions are nor-
mal it gives good control if properly made and applied.
If a large amount of spraying is to be done, it is most con-
venient to make up stock solutions of bluestone and lime in such
proportions that one pound of either bluestone or lime is con-
tained in each gallon of water. These stock solutions will keep
indefinitely provided they are not allowed to dry out. When
a stock solution is once made the surface level should be marked
on the inside of the container so that water lost by evaporation
can be replaced and the whole thoroughly stirred before any of
the materials are used. Keep stock solutions covered.
Mixing Platform: If many acres are to be sprayed during the
season, it would be advisable to construct a mixing platform
where the bordeaux can be conveniently made. The first thing
to consider is the water supply. Build the platform in a place
convenient to both the water supply and the field to be sprayed.
"So-called "instant" bordeaux may be made in the spray tank by adding
the required number of pounds of chemical hydrated lime to half a tank of
water and after it is well mixed, add the remaining water through the tank
screen upon which has been placed the required amount of powdered cop-
per sulphate. Usually the copper sulphate has been dissolved before the
tank is filled and with the agitator in motion the spray mixture is obtained.






Bulletin 225, Watermelon Diseases in Florida


The platform should be well built and high enough to permit
the solutions to flow by gravity into the spray tank. Upon this
platform should be built a second, smaller platform upon which
the stock solutions are made. The smaller platform should be
elevated enough so that the stock solutions can flow by gravity
into the barrels on the main platform.
Stock Solution A, Bluestone: Dissolve at the rate of 1 pound
of bluestone to 1 gallon of water: put 50 pounds of bluestone
into a clean bag and suspend it in the top of a 50-gallon barrel
of water. It will dissolve over night. Never use a metal con-
tainer for this purpose. Always stir the stock solution before
taking any out.
Stock Solution B, Lime: Slake 50 pounds of rock lime and
dilute it in 50 gallons of water. Be careful not to drown or burn
the lime while slaking.
Using Stock Solutions: Always stir the stock solutions be-
fore taking any out. Do not stir the two stock solutions with the
same stick.
Hydrated lime may be used in place of rock lime. If hydrated
lime is used, it is necessary to use one-half again as much as
rock lime. Thus 75 pounds rather than 50 pounds should be used
in 50 gallons of water.
In making bordeaux mixture, observe the following directions:
Dilute the required amount of bluestone to half the amount of
spray to be made. Dilute the required amount of lime in a sep-
arate container to half the amount of spray to be made. Then
pour the contents of the two containers at the same time into a
third container or spray tank, stirring the combined mixture as
the two are poured together. Be sure to place a fine strainer
either over the faucets on the barrels or on top of the spray tank
so that all of the liquid will be well strained; this will prevent
nozzle trouble in the field.
If it is impractical to use the above method of mixing the
bordeaux, the following method may be used: Pour the diluted
lime solution into the spray tank, set the agitator going and add
slowly the diluted bluestone solution.
Different Amounts of 4-4-50 Bordeaux Mixture: In making
50 gallons of the mixture use 4 gallons of stock A, diluted to 25
gallons, and 4 gallons of stock B, diluted to 25 gallons. Run both
of these into the sprayer at the same time with the agitator go-
ing. For larger amounts, use the same proportions. For in-
stance, to make 100 gallons of spray, use 8 gallons of stock A,






Florida Agricultural Experiment Station


diluted to 50 gallons, and 8 gallons of stock B, diluted to 50 gal-
lons. Mix as above.
Time of Application: The first application should be made to
watermelon plants when the first and second true leaves have
developed. A few days earlier is to be preferred to a few days
later. All experienced watermelon growers know that anthrac-
nose in the field is first detected by the appearance of yellowing
of the older leaves around the hill. The early application of fun-
gicides is made to prevent this early infection and thus prevent
or delay the advent of the disease in destructive form in the
field. All schedules should call for applications at weekly inter-
vals, or more carefully interpreted, often enough to keep the new
growth covered and thus protected from the parasitic fungi and
bacteria. The applications should continue up to the picking
season or longer if desirable. The liquid sprays can be applied
to the plants at any time of day after the dew has disappeared.
The dusts should be applied preferably when the plants are
wet; this naturally requires operations in the early morning
and late evening or even during the night if lights can be used
to see the plants. Another advantage of these times of day for
dust applications is the usual lack of wind or strong air -cur-
rents. Dust should not be applied during the day when there
is more than an 8- or 10-mile wind, particularly if the plants
do not cover the ground. Under such conditions there is an un-
warranted waste of material.
Thoroughness of Applications: Great care should be taken to
insure the utmost efficiency of machinery used to apply fungi-
cides. Power sprayers and dusters should be carefully over-
hauled and put in first class condition before their use is requir-
ed. Particular attention should be given to the pumps and fans
so that the required pressure is assured and likewise the hose
connections and distributing nozzles should be cleaned and ad-
justed. Delays in the field caused by faulty equipment result in
loss, which can usually be prevented. Thoroughness of the ap-
plications depends on the kind and care of machinery, the kind of
labor used, and first hand knowledge of the grower on what fun-
gicides are, how they are made, and why they are applied. Fun-
gicides on watermelons are preventive and not cures. In bor-
deaux mixture and copper dusts, metallic copper is the toxic
agent. In making applications be certain that all the leaves
are well covered.
Machinery: In the use of sprays a power outfit of the truck





Bulletin 225, Watermelon Diseases in Florida


or orchard type delivering at least 10 gallons of spray per minute
to two or three leads of hose under 150 to 200 pounds of pres-
sure is the most satisfactory, as the spray can be applied quicker
and with less waste than with lower powered or hand pumps.
The type of machine used, however, will be governed by the size
of the field, the freedom from stumps, and whether it can be
used with other crops. With a machine of the type described
above it is possible to spray an acre of melons in 30 minutes.
The sprayer should be fitted with long arms or booms to prevent
the hose dragging over and injuring vines. Boys also may be
used to keep the hoses up off the ground. A decided disadvan-
tage in the use of spray machines is their great weight, which
sometimes makes it difficult to use them in a wet field. On the
other hand, the application of spray is less affected by wind than
is the application of dusts.
Dusting has an advantage over spraying in that the dust can
be applied somewhat more quickly than the spray, with less
labor, if power dusters are used. The dusters commonly in use
are of the hand operated puff type. This type of duster saves
somewhat in the amount of dust used on small vines, but should
be discarded in favor of the continuous dusters, preferably of
the power type, after the vines have begun to run. A power
duster of the truck or orchard type, delivering sufficient blast to
supply two 3-inch or three 23/4-inch pipes can be used to cover
three to five rows on each side of the duster, and can cover more
acreage with less dust than the hand dusters. On an average
about an hour and a half is required for dusting an acre with
a hand duster whereas with a power duster an acre can be cov-
ered in less than 15 minutes. A power duster, when filled, has
the advantage of being of less weight than an empty power
sprayer.
Growers have objected to the use of power dusters or sprayers
on the grounds that they cannot get them into the fields on ac-
count of stumps. It is true that watermelon fields are often cov-
ered with stumps because melons are usually the first crop to be
planted on newly cleared land, but the roadways left for harvest-
ing can be used for the sprayer or duster as well as for the ve-
hicles used in hauling the melons from the field, and the ef-
ficiency and speed of power outfits make them highly desirable.
Hand sprayers and dusters are often used in small fields by
many successful growers with good results. In such instances
one hand machine usually takes care of eight to 10 acres as a





52 Florida Agricultural Experiment Station

maximum load; five or six would be better. The early applica-
tions are relatively easy because of the spacing of the hills but
as the vines begin to run the task increases and a thorough job
requires considerable labor. The grower should exercise care
in the selection of hand machinery, since there is considerable
variation in the efficiency of the various machines. A knapsack
sprayer of about three gallons capacity, that will develop con-
siderable pressure, is to be recommended. Likewise, a duster
should be used that is light, easily handled, comfortable to wear
and operate, and that will hold 10 or 15 pounds of dust.
The preparation, necessity and use of copper sulphate paste
for the control of stem-end rot of watermelons during transit
is given under control methods of that disease on page 27.




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