• TABLE OF CONTENTS
HIDE
 Front Cover
 Credits
 Table of Contents
 Introduction
 Downy mildew of cucumbers
 Anthracnose
 Angular leaf spot and fruit...
 Mosaic
 Bacterial wilt
 Black rot
 Stem rot of cucumbers
 Powdery mildew
 Southern blight
 Fusarium wilt
 Macrosporium blight of cucumbe...
 White of albino cucumbers
 Ring spot
 Snakehead
 Leaf spot
 Bordeaux injury
 Seed disinfection
 Fungicides and their applicati...
 Thoroughness in spraying neces...
 Copper-lime dust














Group Title: Bulletin - University of Florida. Agricultural Experiment Station ; no. 208
Title: Cucumber diseases in Florida
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00027283/00001
 Material Information
Title: Cucumber diseases in Florida
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 48 p. : ill. ; 23 cm.
Language: English
Creator: Weber, George F ( George Frederick ), b. 1894
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1929
 Subjects
Subject: Cucumbers -- Diseases and pests -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by G.F. Weber.
General Note: Cover title.
General Note: "Revision of Bulletin 177"--T.p.
Funding: Bulletin (University of Florida. Agricultural Experiment Station)
 Record Information
Bibliographic ID: UF00027283
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000923515
oclc - 18173281
notis - AEN4066

Table of Contents
    Front Cover
        Page 1
    Credits
        Page 2
    Table of Contents
        Page 3
        Page 4
    Introduction
        Page 5
    Downy mildew of cucumbers
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
    Anthracnose
        Page 11
        Page 12
        Page 13
        Page 14
    Angular leaf spot and fruit rot
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
    Mosaic
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
    Bacterial wilt
        Page 27
    Black rot
        Page 28
    Stem rot of cucumbers
        Page 29
        Page 30
    Powdery mildew
        Page 31
        Page 32
    Southern blight
        Page 33
    Fusarium wilt
        Page 34
    Macrosporium blight of cucumbers
        Page 34
        Page 35
    White of albino cucumbers
        Page 36
    Ring spot
        Page 36
        Page 37
    Snakehead
        Page 38
    Leaf spot
        Page 39
    Bordeaux injury
        Page 40
        Page 41
    Seed disinfection
        Page 42
    Fungicides and their application
        Page 43
        Page 44
    Thoroughness in spraying necessary
        Page 45
        Page 46
    Copper-lime dust
        Page 47
        Page 48
Full Text



(Revision of Bulletin 177)


UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
Wilmon Newell, Director



CUCUMBER DISEASES
IN FLORIDA
BY G. F. WEBER


Fig. 1.-Typical downy mildew spotting of a cucumber leaf.

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


Bulletin 208


November, 1929








BOARD OF CONTROL


P. K. YONGE, Chairman, Pensacola
A. H. BLENDING, Leesburg
W. B. DAVIS, Perry
RAYMER F. MAGUIRE, Orlando


FRANK J. WIDEMAN, West Palm Beach
J. T. DIAMOND, Secretary, Tallahassee
J. G. KELLUM, Auditor, 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.A., Assistant
J. D. WARNER, M.S., 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
H. L. MARSHALL, M.S., Assistant
J. M. COLEMAN, B.S.. Assistant
J. B. HESTER, B.S., Assistant

COTTON INVESTIGATIONS
W. A. CARVER, Ph.D., Assistant
E. F. GROSSMAN. M.A., 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**
JOHN L. WANN, B.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-'
HORTICULTURE
A. F. CAMP, Ph.D., Horticulturist"
M. R. ENSIGN, M.S.. Assistant
HAROLD MOWRY, B.S.A., Assistant**
G. H. BLACKMON, M.S.A., Pecan Culturist**

PLANT PATHOLOGY
W. B. TISDALE, Ph.D., Plant Pathologist
G. F. WEBER, Ph.D., Associate
A. H. EDDINS, Ph.D., Assistant
W. B. SHIPPY, Ph.D., Assistant
K. W. LOUCKS. M.S., Assistant
ERDMAN WEST, B.S., Myco'ogist**


BRANCH STATION AND FIELD WORKERS

R. R. KINCAID, M.S., Assistant Plant Pathologist (Quincy)
JESSE REEVES, Foreman, Tobacco Experiment Station (Quincy)
J. H. JEFFERIES, Superintendent, Citrus Experiment Station (Lake Alfred)
W. A. KUNTZ, A.M., Assistant Plant Pathologist (Lake Alfred)
B. R. FUDGE, Ph.D., Assistant Chemist (Lake Alfred)
GEO. E. TEDDER, Foreman, Everglades Experiment Station (Belle Glade)
R. V. ALLISON, Ph.D., Soils Specialist in charge Everglades Experiment Station (Belle Glade)
L. O. GRATZ, Ph.D., Associate Plant Pathologist (Hastings)
A. N. BROOKS, Ph.D., Associate Plant Pathologist (Plant City)
A. S. RHOADS, Ph.D., Associate Plant Pathologist (Cocoa)
STACY O. HAWKINS, M.A., Field Assistant in Plant Pathology (Homestead)
D. G. A. KELBERT, Field Assistant in Plant Pathology (Bradenton)
R. E. NOLEN, M.S.A., Field Assistant in Plant Pathology (Monticello)
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)
*In cooperation with U. S. Department of Agriculture.
**On leave of absence.












CONTENTS

Page
INTRODUCTION ....................................... ........ 5
DOWNY MILDEW OF CUCUMBERS .................................... 5
Sym ptom s ................................................... 6
C control ..................................................... 8
ANTHRACNOSE ............ ....................................... 11
Description .................................................. 12
C control ..................................................... 14
ANGULAR LEAF SPOT AND FRUIT ROT ............................... 15
D description .................................................. 17
Control ..................................................... 19
M OSAIC ........................................................ 21
D description .................................................. 26
C control ..................................................... 26
BACTERIAL WILT ................................................. 27
D description .................................................. 27
Control...................................................... 28
BLACK ROT ..................................................... 28
D description .................................................. 29
C control ..................................................... 29
STEM ROT OF CUCUMBERS ......................................... 29
D description .................................................. 30
C control ..................................................... 30
POWDERY M ILDEW ................................................ 31
Description ................................................... 32
C control ..................................................... 33
SOUTHERN BLIGHT ............................................... 33
D description .................................................. 34
C control ..................................................... 34
FUSARIUM W ILT ................................................. 34
MACROSPORIUM BLIGHT OF CUCUMBERS .............................. 34
Description and Control ...................................... 35
WHITE OR ALBINO CUCUMBERS ...................................... 36
RING SPOT ................. ....................... ............ 36
SNAKEHEAD ...................................................... 38
LEAF SPOTS (Misc.) ............................................ 39
BORDEAUX INJURY ............................................... 40
SEED DISINFECTION ............................................. .42
FUNGICIDES AND THEIR APPLICATION ............................... 43
BORDEAUX MIXTURE .............................................. 43
THOROUGHNESS IN SPRAYING NECESSARY ............................ 45
COPPER-LIME DUST ............................................... 47













DISEASES OF CUCUMBERS
BY G. F. WEBER

Cucumbers have been profitably grown in Florida for years.
The quantity of production has steadily increased until at present
this crop is one of the leading truck crops of the state, returning
to the growers millions of dollars each year. The plant has been
successfully cultivated in nearly-every section of the state at
some season of the year.
During certain seasons the yields are reduced because of the
prevalence of diseases. There are a number of these diseases
attacking the cucumber plant, but it is seldom that more than
one particular disease is important in a single season.
This bulletin contains information concerning the diseases
that may attack the cucumber plant. Their occurrence and sea-
sonal development are discussed. A detailed description of each
disease is given, followed by control methods in each case. Certain
information previously published in Experiment Station Bulle-
tins 121, 139 and 177 is contained herein.

DOWNY MILDEW OF CUCUMBERS
One of the most destructive diseases of cucumbers in Florida,
commonly called "downy mildew," is caused by the fungus
Pseudoperonospora cubensis (B. & C.) Rostow. The disease has
been found in the different countries of the world.
In the United States the disease has been collected in almost
all of the states east of the Mississippi River; it is scarce in the
western part of the country. It is more serious in the southeast-
ern states than in the northern states. In Florida the disease has
been found in every county and has been collected by the writer
during every month of the year. Between November and March
it is common in the southern counties. During the past several
seasons it has been more destructive than all other cucumber
diseases combined.
This disease has been known to exist in Florida for the past 40
years and has been a factor in the production of cucumbers during
this time. The disease appears on young plants before the
runners develop but usually not in destructive form until about
picking time. Often the lack of rain accompanied by continued
high temperatures holds it in check. However, under favorable
conditions, the disease will show up on the host plant at any time










DISEASES OF CUCUMBERS
BY G. F. WEBER

Cucumbers have been profitably grown in Florida for years.
The quantity of production has steadily increased until at present
this crop is one of the leading truck crops of the state, returning
to the growers millions of dollars each year. The plant has been
successfully cultivated in nearly-every section of the state at
some season of the year.
During certain seasons the yields are reduced because of the
prevalence of diseases. There are a number of these diseases
attacking the cucumber plant, but it is seldom that more than
one particular disease is important in a single season.
This bulletin contains information concerning the diseases
that may attack the cucumber plant. Their occurrence and sea-
sonal development are discussed. A detailed description of each
disease is given, followed by control methods in each case. Certain
information previously published in Experiment Station Bulle-
tins 121, 139 and 177 is contained herein.

DOWNY MILDEW OF CUCUMBERS
One of the most destructive diseases of cucumbers in Florida,
commonly called "downy mildew," is caused by the fungus
Pseudoperonospora cubensis (B. & C.) Rostow. The disease has
been found in the different countries of the world.
In the United States the disease has been collected in almost
all of the states east of the Mississippi River; it is scarce in the
western part of the country. It is more serious in the southeast-
ern states than in the northern states. In Florida the disease has
been found in every county and has been collected by the writer
during every month of the year. Between November and March
it is common in the southern counties. During the past several
seasons it has been more destructive than all other cucumber
diseases combined.
This disease has been known to exist in Florida for the past 40
years and has been a factor in the production of cucumbers during
this time. The disease appears on young plants before the
runners develop but usually not in destructive form until about
picking time. Often the lack of rain accompanied by continued
high temperatures holds it in check. However, under favorable
conditions, the disease will show up on the host plant at any time







Florida Agricultural Experiment Station


during the year. In addition to cucumbers, the fungus also at-
tacks watermelons, cantaloupes, gourds, pumpkins, squashes and
gherkins, but none of these plants suffers from the disease as
much as cucumbers.
The fungus attacks severely only the leaves, rapidly killing
them. Spores are produced by the fungus a few days after it is
evident that the leaves are diseased. These spores are scattered
far and wide by the wind. They settle on the cucumber leaves and
germinate in the moisture supplied by the dew and infect the
plant. After three or four days the infection can be detected by















Fig. 2. Downy mildew on plants in field, early stage.

the appearance of yellow spots. (Fig. 2.) The disease spreads
most rapidly during periods of comparatively low temperature,
heavy dews and rains and windy days.
Symptoms: Because of the similarity of the several leaf spots
caused by different organisms on the leaves of cucumbers, it is
often difficult to determine with certainty the disease at first
glance. The earliest evidence of infection with downy mildew is
a slight yellowing of small areas of the leaf blade. This yellow-
ing appears several days after infection. When the yellow areas
appear it is possible in the early morning before the dew has
disappeared to detect them in a water-soaked condition. This is
the result of water soaking into the plant tissue among the cells
which are invaded by the fungus. The cells that have not been
attacked by the fungus will not appear water-soaked. During the
middle of the day this condition disappears but will again become
evident with dew or rain. These spots are more or less angular in







Bulletin 208, Cucumber Diseases in Florida


outline and are delimited by the veins of the leaf blade. (Fig. 1,
cover.)
The spots may be few or many on a single leaf, depending upon
the number and distribution of spores causing the different in-
fections. A single spot seldom develops to more than a centimeter
in diameter. However, if the spots are numerous enough on a
leaf they will coalesce and in a day or two kill the whole leaf,
which will dry out and turn brown. The dead leaves remain
erect and the edges of the blade curl inward very characteristical-
ly. (Fig. 3.) A few days after the yellow spots become visible on
















Fig. 3. Downy mildew killing the leaves of cucumber
plants, last stage.

the leaves a careful examination of one of these spots on the lower
surface will reveal a fine, white downy growth. Under certain
conditions the growth is seen with difficulty, even with the aid of
a good hand lens. The spores of the fungus are borne on the
tips of this downy growth. (Fig. 4.) These spores are usually
dark colored and give the areas of the leaf which they occupy a
grayish color. Upon closer examination, the spots appear to be
covered with very fine earth particles which are sticking to the
surface among the hairs of the leaf. These small particles are the
spores. They are barely distinguishable without the aid of a
lens. These spores are easily detached and because of their light
weight and small size are carried considerable distances by the
wind. They may cause additional infections on the same leaf or
adjacent healthy plants in the next 24 hours, should temperature
and moisture conditions be favorable for their germination.







Florida Agricultural Experiment Station


Control: A knowledge of the methods for control of downy
mildew is necessary before a grower can feel safe in risking the
growing of a field of cucumbers, because the disease usually
appears every year in certain localities, and none of the commer-
cial varieties are immune. An experimental plot containing 37
varieties of cucumbers was grown in an effort to determine
whether or not any differences in susceptibility would be evident.
The seeds of these varieties were northern grown. They were


Fig. 4. Branched conidiophore of downy mildew fun-
gus and spores that grow upon its branches.
Highly magnified.

planted and cared for as an ordinary crop, but were not sprayed.
The downy mildew showed up in the plot the same week it did in
the fields and within three to four weeks the plants were killed.
All varieties were attacked by the disease and there was no ap-
parent difference in degree of resistance among the varieties.
The following varieties were grown: Kirby Staygreen, Vickers
Forcing, Earligreen, Davis Perfect, Long Green, Extra Early
Green Prolific, Arlington Whitespine, Extra Long Whitespine,
Early Cluster, Improved Long Green, Everbearing, Shamrock,
Improved Arlington Whitespine, Panmure Long White, 40 Day,







Bulletin 208, Cucumber Diseases in Florida


Cool and Crisp, Fordhook, Snow's Pickling, Henderson, Ever-
bearing, Livingston Evergreen, Livingston Emerald, Klondike,
Early Fortune, Thorburns, Black Diamond, Chicago Pickling,
Prolific Pickle, Green Prolific, Jersey Pickling, Early Cyclone,
Cumberland, Japanese Climbing, Early Green Cluster, Short
Green Gherkin, Extra Early Whitespine, Early Whitespine.
Sanitation and rotation are good farming practices from the
viewpoint of soil fertility and general disease control, but it is
doubtful whether either of these practices will have much effect
upon the prevalence of downy mildew.


















Fig. 5. Portion of experimental plot showing dusted plants on right and
undusted (check) plants on left.

Experimental plots were sprayed and dusted during several
seasons to determine the advisability of using fungicides, their
benefit, if any, and the cost. (Fig. 5.) The spraying was done
with a hand sprayer of the knapsack type (Fig. 36), and the dust-
ing was done with a hand dusting machine (Fig. 37.)
The liquid sprays applied consisted of commercial copper-lime
mixture. The dusts applied were copper-lime mixtures and sul-
phur dusts. The dusts were always applied in the early morning
when the dew was on the plants.
The data collected in these experiments show that the plots
which received the application of certain fungicides gave a larger
profit per acre than the untreated plots after all costs were paid.
It showed that the cost of the dust was almost twice the cost of







Florida Agricultural Experiment Station


home-made Bordeaux mixture. However, the latter is more
expensive to apply so that unless large acreages are to be sprayed
there may be very little difference in actual cost when cost of
materials and cost of application are carefully considered. Bor-
deaux mixture 4-6-50 (using hydrated lime) has given the best
control of the disease. Other fungicides applied in both the wet
and dry form have given various degrees of control. As a general
rule, however, the copper fungicides have been most successful,
the spray usually being more effective than the dusts. The vari-












N:iO


Fig. 6. Portion of experimental plot showing sprayed plants on left and
unsprayed (check) plants on right.

ous forms of sulphur used proved less effective for the control of
downy mildew than the copper containing kinds.
Few of the growers seem to be thoroughly convinced that a
fungicide should be applied. However, the growers who practice
spraying or dusting and seed treatment are usually successful
with their crops. When applications are made they should be
thorough and often. Light applications should be made as soon as
the young plants show two true leaves and should be repeated at
least once a week thereafter until the beginning of picking
season.
The greatest mistake made by most cucumber growers who
apply fungicides is that they wait too long after the seedlings are
up before making the first application. One is waging a losing
fight if applications are not made before the first symptoms of the
disease are evident in the field. Liquid sprays may be applied at
any time; the copper dusts should be applied when the plants are







Bulletin 208, Cucumber Diseases in Florida


wet with dew. Fungicides are not cures but rather preventive
and should be used accordingly. Begin applications early, repeat
them often, do a thorough job each time and it will be found
profitable.

ANTHRACNOSE
The disease known as anthracnose is caused by the fungus
Colletotrichum lagernarium (Pass.) Ell. & Hals. This disease
has been known to occur on the cucumber for more than half a
century and has been found in both Europe and America. In the
United States the disease has been reported most common in the
states east of the Mississippi River and rare in the western
states. In Florida the disease is common and often severe. It
has been found almost everywhere the host plant is grown and
has been known to the growers since the early cultivation of the
plant. The same fungus causes anthracnose of muskmelons,
watermelons and some varieties of gourds.
The disease is favored by high temperature and high humidity,
heavy dews being the most important factor in Florida. It has
caused considerable losses in Florida in certain localities where
the growing of cucumbers is concentrated. The fall crop of
cucumbers, as a rule, suffers more from this disease than the
spring crop. It has been observed that cucumbers planted in the
fall in old watermelon fields Were total losses due to the fungus
spreading to the cucumbers from the old infected melon vines and
fruit. The fungus will spread from watermelons to watermelons,
cucumbers, cantaloupes and gourds and from each of these hosts
to the others.
The fungus lives during the growing season on the numerous
host plants and when they die it remains in the old vines and
fruits left in the fields. The climate of Florida is such that the
fungus easily lives the year around and when a new crop is
planted, if weather conditions are favorable, the first leaves in-
variably become infected.
Ten days to two weeks are required for the fungus to produce
dead areas in the leaves, although some yellowing is often visible
after one week. (Fig. 7.) Because of this early infection first
signs of the disease may be observed on the leaves in the immedi-
ate vicinity of the hill. These infected leaves produce the spores
for general infection of the crop later in the season. It is at this
time that the grower begins to find that the disease is giving him
trouble.







Florida Agricultural Experiment Station


Fig. 7. Cucumber leaf showing anthracnose spots.


This disease causes considerable loss in transit. Early infec-
tions on fruits being packed for market are often overlooked or
even not possible to detect. Should these shipments be delayed in
transit the disease develops and results in unmarketable fruit at
the destination.
The spores of the fungus are spread in the field by rain, wind,
running water, pickers, cultivators and insects, named in order
of their relative importance. The spores are washed from dis-
eased plants and spattered upon healthy plants. Heavy dews so
common in Florida offer the proper conditions for infection.
Description: All parts of the host plant above ground are sub-
ject to attack by anthracnose. The disease has not been observed







Bulletin 208, Cucumber Diseases in Florida


on the roots. The vines seldom show lesions, whereas the leaf
petioles and blades are the most severely attacked. The disease on
the fruits is more or less sporadic. Under certain conditions it
causes severe infections and serious losses; whereas in other
instances when the leaves are almost killed the fruit still remains
free from the disease. (Fig. 8.)
The first symptoms of the disease are slightly yellowish areas
on the leaf blades. This yellow color rapidly spreads in the central



-












Fig. 8. The general effect of anthracnose on a cucumber plant.

portion, becomes darker and in a short time turns black. The
spots gradually enlarge in a more or less circular manner. If the
infection is severe these spots coalesce and cause the premature
death of the leaf.
Anthracnose can be distinguished from other important leaf
spots of cucumber by the more or less circular spots that are not
delimited by the veins. (See Fig. 7.)
The spores develop on the spots and are readily scattered to
other plants by the many disseminating agents. On the petioles
and stems the lesions are usually sunken and linear in outline.
(See Fig. 9 B.) The tissue is killed and in many instances the
stem is completely girdled and the portion beyond the spot dies.
Spores form on these lesions in a very short time and can be seen
in the form of small groups of pinkish bead-like masses in the
central portion of the lesions.
On the fruits the infections first appear as more or less circular
or oval water-soaked spots. As the lesion enlarges the central






Florida Agricultural Experiment Station


portion becomes sunken and the sunken area becomes covered
with the pinkish spore masses as described on the stems. (Fig.
9 A.) These spore masses can be found readily on the lesion in
the morning before the dew has disappeared.
Control: Experimental data on the use of fungicides for the
control of anthracnose in the field are not sufficient to warrant
definite conclusions. However, the data obtained indicate that


Fig. 9. Anthracnose lesions (spots) on the fruit and stems
of cucumbers. (Courtesy U. S. D. A.)


Fig. 10. Portion of large field completely killed by anthracnose.


MOI


P~E~fE~.h~%I







Bulletin 208, Cucumber Diseases in Florida


fungicides properly applied will check the disease and give a
commercial control but will not, without some burdensome ex-
pense, absolutely control the disease. (Fig. 10.) Four-four-fifty
(4-4-50) Bordeaux mixture, or 4-6-50 if hydrated lime is used,
applied to both surfaces of the leaf once a week will give good
control under average weather conditions. Copper-lime dust is
also very good in controlling this disease but costs considerably
more and gives less satisfactory results than liquid Bordeaux.
Always apply the dust early in the morning before there is
much wind and before the dew has disappeared. Make certain
that the plants are well covered. Vines covering the ground
require about 30 pounds per acre per application.

ANGULAR LEAF SPOT AND FRUIT ROT
The diseases of cucumbers known as angular leaf spot and
fruit rot are caused by the same bacterial organism, Bacterium
lachrymans E. F. S. & Bryan. They have been found on the
cucumbers almost every season and, although not always of
serious economic importance, cause considerable damage. These
diseases have been known to the Florida trucker for the past 15
years and are quite generally distributed over the state. They
have been reported also from most of the states north of the Ohio
River but probably are not as severe in these states as in Florida.












Fig. 11. Pile of cull cucumbers discarded because of infections of the angular
leaf spot organism.

In Florida the greatest damage has been reported from sections
in the north central counties. Accurate surveys conducted in
these areas showed as much as 50 percent diseased fruits in
certain fields in 1924, 1925-26and 1928 which were unmarketable.
(Fig. 11.) The disease was not severe during 1927 or 1929. This







Florida Agricultural Experiment Station


loss, however, does not include the reduction in stand in the field
due to seedling infection, nor does it take into consideration
possible losses in production due to the reduction in leaf surface
during the growing season.
Another result of severe infections on the fruits is the usual
heavy loss in transit. At the time fruits are packed, preparatory
for shipment, infections may be overlooked and as a result the
rot develops in transit. The fruit arrives on the market badly
scarred by lesions, making it unsightly to the consumer, or it
may even become soft and mushy when the period in transit has
been extensive and refrigeration has not been good.


Fig. 12. Angular leaf spot (both surfaces) of cucumber leaf caused by
Bacterium lachrymans isolated from infected fruit.







Bulletin 208, Cucumber Diseases in Florida


The organism causing this disease (on leaf and fruit) has been
found on a large number of the commercial varieties of cucum-
bers, and several species of gourd which are closely related to the
cucumber. To judge from observations made in Florida the dis-
ease is favored in its spread and destructiveness by cool, rainy
weather. High temperatures tend to check the development of the
disease and during continued periods of warm weather the plants
grow away from the disease. The rain aids in the dissemination
of the organism by washing the bacterial ooze from the infected
areas on the leaves to the ground where it is carried by running
surface water and splashed upon other plants by the rain drops.
The organism enters the leaves and fruits through the stomata
and results in the formation of the spots that are known to
cucumber growers. Wind, insects and pickers are also carriers
of the organism and are instrumental in the spread of the disease.
The organism is brought into the field primarily with the seed, on
which it will live for a considerable length of time. Since most
of the northern states have
reported the occurrence of
the disease it is logical to
suppose it has come from
that source, as very little
seed is raised in Florida.
Description: It is impos-
sible to look at cucumber
seed and tell whether they
are infected with the angu-
lar leaf spot organism.
When the young plants
emerge the first indications
of the disease may be found
by the appearance of spots
on the cotyledons of a few
seedlings. It may be so se-
vere as to kill the seedlings
or it may not be serious at
all except that the infected
seedlings serve as a source
of infection for healthy
plants. The lesions appear Fig. 13. Typical angular leaf spot le-
plants. sions on cucumber leaves.







Florida Agricultural Experiment Station


anywhere on the cotyledons and are usually not fatal to the plant
unless they are located at the base of the cotyledon. From here
it readily attacks the bud, killing the seedling.
The lesions on the cotyledons are small, sunken, circular to oval
and at first darker in color than the surrounding tissue. Later the
tissue dies and becomes brown. As soon as the true leaves develop
they are subject to infection and the spots appear upon them
when about a week old. At first only a small water-soaked, circu-
lar area is evident. The spot enlarges and becomes limited in
extent by the veins of the leaf. (Fig. 13.) It varies in size from
1/16 to 1/2 inch in diameter. It is very seldom circular or oval but
rather angular in outline, being three-, four-, or five-sided depend-
ing on the surrounding veins.
The spots are most easily detected in the morning when the
dew is still on the plants. They are water-soaked and of a darker
green color than the remainder of the leaf and are practically the
same on each side of the leaf. If one examines these spots at this
time there can be found milky white ooze in the form of small
drops around the spots. This ooze, known as exudate, is liquid
from the leaf teeming with bacteria and appears whitish be-
cause of their presence. As the leaves grow older the spots do not
enlarge to any great extent and after several days the central
areas become dry and fall out or are knocked out by rains, leaving
the leaves in a ragged condition. (Fig. 14.) For this reason the
disease is often referred to as the shotholee" disease.
On the fruit the first indication of infection is the appearance
of small circular water-soaked spots, 1/16 of an inch or smaller
in diameter. (Fig. 15.)
They are found on any
part of the fruit but
most commonly on the
upper surface. A lesion
of this sort several days
old enlarges slightly and
a resinous formation ap-
pears on its surface.
There is very little out-
ward development from
this stage; instead the
fruit begins to decay on
the inside. From the
Fig. 14. General effect of angular leaf spot
disease on the foliage of cucumbers. lesion on the surface a








Bulletin 208, Cucumber Diseases in Florida


Fig. 15. Infection of cucumbers caused by the angular leaf spot organism.

brownish path leads directly into the interior until it comes in
contact with the vascular tissues. Once in these tissues the decay
develops lengthwise of the fruit, entering the three placentas and
causing the tissue to break down and result in a soft mushy mass.
(Fig. 16.) It is the fruit infection that causes the largest amount
of loss in Florida.
Control: It has been found that practically all commercial
varieties of cucumbers are subject to the disease, and consequent-
ly the possibility of securing resistant plants of the right market-
able qualities would require considerable time if it were possible
at all.
Spraying with Bordeaux, 4-4-50, or dusting with copper-lime
dust (80-20 formula) is of considerable importance in controlling
the disease after it makes its appearance in the field. The matter
of fungicides is fully discussed under the disease known as downy
mildew. Angular leaf spot can be controlled by the same applica-
tion of spray or dust used to control the mildew. (See page 8.)
The most effective method, however, of combating the disease
is by the treatment, or disinfection, of the seed. Tie the seed








Florida Agricultural Experiment Station


Fig. 16. Internal effect of the angular leaf spot disease.


loosely in a cloth bag and soak them for 10 minutes in a 1:1,000
solution of corrosive sublimate, rinse them in several changes of
fresh water, dry them and they are ready to plant. (See "Seed
Treatment," page 42, for details of this operation.)
During the season of 1924 some valuable data were obtained
under field conditions concerning seed treatment and its effect.
The early season was cold and wet. The first plantings failed to
come up and rotted because of excessive moisture and cold. In
many instances it was necessary to make second and third plant-
ings to obtain a stand. Seed treatment was advocated and
generally practiced by a large number of the growers. Ninety
percent of all the seed of the first planting was carefully treated.
But as later plantings had to be made to obtain a stand in the
field, fewer growers treated their seed. As a result only 12 per-
cent of the third and fourth plantings weretreated. Many growers
blamed the treatment for the rotting of the seed but check plots,








Bulletin 208, Cucumber Diseases in Florida


WNW


Fig. 17. Above: Cucumber fwuit showing surface lesions caused by
Bacterium lachrymans isolated from infected cucumber leaf. Lower: Same
fruit cut lengthwise through lesions, showing decay of interior parts caused
by this organism.

which were untreated, failed to germinate the same as the treated
seed.
After the plants had developed several true leaves a survey was
made of 26 cucumber fields and the occurrence or absence of
angular leaf spot was recorded. In 18 of these fields the disease
was found. A closer check and interview with the growers re-
vealed the fact that none of the seed in these fields had been
treated. Of the eight fields found free of the disease, six had been
treated and two had not been treated. These data show the
wisdom of seed treatment for the control of this disease, and this
method of control is efficient, cheap, simple and quickly done.
MOSAIC
The true and exact cause of the mosaic disease is not definitely
known at the present time. It is known, however, that the infec-








Florida Agricultural Experiment Station


tious substance is contained in diseased plants and is known as
"virus." Extensive research work has been conducted in various
places in an effort to isolate from the plant the principle causing
mosaic. This work has not yet been successful.
In the United States the disease is widespread and may occur
wherever cucumbers are grown. Although it is generally distrib-
uted over the cucumber area of the United States, mosaic has
been severe in relatively few states and these instances have been
in the north. The disease appears to be becoming relatively more
important in Florida. Several years ago its occurrence was rela-
tively rare but during the past year or two it has become more
common and certain fields during the past season showed losses.
A specific six-acre field showed 18 percent infected plants by
actual count and about 20 percent of the picked fruits were dis-
carded as culls because of the mottling and wartiness of their
surfaces. Cull piles of mosaic fruit (Fig. 18) are quite unique and
seldom seen. There appears to be a higher percentage of mottled
fruit in Florida fields than in northern fields when the numbers
of infected plants are about equal.


Fig. 18. Cucumber cull pile made up of mottled, warty fruit resulting
from the mosaic disease.







Bulletin 208, Cucumber Diseases in Florida


The disease is infectious and will spread from one plant to
another; further than this very little is known as to the nature of
the cause. No fungus or bacterial organism has been consistently
associated with the disease. The disease can be artificially
produced, however, by rubbing leaves of healthy and diseased
plants together. In this process there is an exchange of sap of
the two plants and the sap from the diseased plant has the ability
to produce the disease in the healthy plant. The symptoms of the
disease will show up on the inoculated plant after five or six days.
This process is carried on in nature with the assistance of in-
sects, principally the aphid and common cucumber beetle. The
former is by far the more important in spreading the disease. It
is a sucking insect and after feeding on a diseased plant it may
feed upon a healthy plant, in this way transmitting the disease.
Cultivators and pickers also transmit the disease in the field by
stepping on or brushing first diseased plants and then healthy
plants.
It has been found that a large number of plants closely related
to the cucumber are susceptible to the disease. There are also a


Fig. 19. Typical mosaic symptoms on growing cucumber runner, namely
short internodes, small, mottled deeply-notched leaves.







Florida Agricultural Experiment Station


Fig. 20. Pointed, mottled cucumber leaf, symptoms of mosaic.

number of plants of families other than those related to the
cucumber which have been found harboring the disease, the sap
of which, if transmitted to healthy cucumbers, will produce the
disease. Recent experiments' have shown that mosaic can be
transmitted from cucumber to muskmelon, pepper, ground cher-
ry, tomato, potato, tobacco, martynia, horseweed, catnip, poke-
weed, milkweed and pigweed. If these weeds have mosaic and
grow around the edges of the cucumber fields, insects can
transmit the disease to the cucumbers. In Florida, mosaic has
been found on weeds on the borders of fields every month of the
"'Further Studies on the Overwintering and Dissemination of Cucurbit
Mosaic." S. P. Doolittle and M. N. Walker. Jour. Agr. Res. 31:1925.








Bulletin 208, Cucumber Diseases in Florida


Fig. 21. Cucumber plant affected with mosaic. It shows small mottled
leaves at growing tips and mottled warty fruit.


Fig. 22. The warty, mottled effect of mosaic on the fruits.







Florida Agricultural Experiment Station


year so that the possible source of inoculum is always present and
all that is necessary for its spread is carrying agents.
Description: In general the two characteristic symptoms of
mosaic are a definite green mottling of leaves and fruit and a
marked stunting of the vines. These symptoms vary somewhat
according to the age of the plant at the time of infection. The
disease is not often found on the cucumber in the extreme early
stages of its development. In Florida the disease has manifested
itself about the time four or six true leaves are formed. The
younger leaves show a distinct mottling of dark and light green
color, a sort of patchwork over the leaf. In other respects the
leaf appears quite normal, except that it is reduced in size.
As the plant grows older the new growth at the ends of the
runners does not develop normally but rather appears rosetted
and stunted, the internodes are shortened and the leaves are
much smaller and more deeply notched. The older leaves near
the base of the vine begin to yellow and droop, gradually dying,
in the last stages there remain only a few small green leaves at
the extreme growing tips of the runners. (Fig. 21.) The dis-
ease shows up early on the fruit of mosaic plants. The mottling
is quite similar to that described on the leaves and in severe in-
stances the fruits become distorted, rough and warty. These
fruits are not marketable because of their appearance. (Fig. 22.)
Control: Attempts at breeding or selection of resistant plants
have been unsuccessful. Eleven genera and 26 species of plants
closely related to cucumbers have been found susceptible to
mosaic.
Field sanitation has been successfully practiced in certain dis-
tricts by cutting all weeds showing the symptoms of mosaic, thus
removing the source of infection. This practice has given good
results and will probably prove to be the only way to control the
disease in Florida should it become severe.
Whenever mosaic plants are found they should be pulled up
carefully and removed from the field. The hands should be
washed thoroughly in a disinfectant before healthy vines are
again touched. Pickers should be cautioned about the danger of
spread of the disease and be taught to avoid the diseased plants
in the field.
Another method of control is the elimination of insects that
transmit the disease. This can be done on a small scale but is an
expensive operation and would probably not be profitable in large
fields. The disease is not carried on or in the seed and no evi-







Bulletin 208, Cucumber Diseases in Florida


dence is available to show that it survives in the soil from one
season to the next.

BACTERIAL WILT
This wilt disease of cucumbers is caused by a bacterial organ-
ism, Bacillus tracheiphilus E. F. S. The disease is very common
and destructive in the northern cucumber districts but in the
south it is of less importance. In Florida, only isolated cases
have been observed and in these instances the economic impor-















Fig. 23. Cucumbers affected with bacterial wilt.

tance of the disease was negligible. It has been known in Florida
for probably 15 years. During the last two seasons it has been
occasionally observed in the field in commercial plantings. The
probable reason for the scarcity of the disease may be the limited
areas infested by the striped cucumber beetle, Diabrotica vittata
Fab. This insect has been found in two small isolated sections of
the state. In northern sections this insect has been found to be
most important in the spread of the disease. It has also been
demonstrated2 that the organism is not carried on the seed. The
conditions in Florida are such that the organism might survive
on wild host plants during the period when cucumbers are not
grown. This has not been thoroughly investigated, nevertheless
There may be possibilities of the survival of the organism in this
way.
Description: The first symptom of bacterial wilt is a gradual
progressive wilting of the plant, the earliest evidences of which
2Rand, F. V. & Enlows, E. M. A. Bacterial Wilt of Cucurbits. U. S. D. A.
Bul. 828:21, 1920.







Florida Agricultural Experiment Station


are at the extreme tips of the runners. If the plant is infected
upon the main stem all the tips wilt, but if the infection is on a
single runner some distance from the main stem, the wilting
gradually works back toward the base of the plant and then all
runners are affected and show the wilt, which becomes more
severe each day until the plant is unable to recover and soon dies.
(Fig. 23.)
Control: It is necessary to control the insects in the field, espe-
cially the striped beetle if present in a field showing wilt. If they
are not present, then the plants showing the symptoms of the
disease should be rogued out and removed from the field. The
disease is transmitted primarily by the injury and inoculation of
plants by biting insects that have fed previously on wilt-diseased
plants.
BLACK ROT
This disease, caused by the fungus Mycosphaerella citrullina
(Sm.) Gross, is found on the fruits, and causes a wilt of the
young seedlings. It also causes a leaf spot, especially on the coty-


Fig. 24. Cotyledons attacked by black rot.







Bulletin 208, Cucumber Diseases in Florida


ledons of seedlings and occasionally kills the young plants soon
after they are out of the ground. (Fig. 24.) The disease causes
severe losses in transit. The rot develops rapidly and can be
easily distinguished from the soft bacterial rots, since it is rather
firm and of a darker color. The rotted areas are also speckled
with the pycnidia and perithecia (spore-bearing parts of the
fungus) which are buried in the tissue just under the epidermis.
The disease is spread by wind and rain and is favored in its
development by warm, moist weather conditions.
Description: The spots on the leaves are usually of a brownish
black color, circular, and often are 1/4 inch in diameter. The
tissue rapidly dries out and becomes wrinkled or cracks and falls
away. When an infection is located near the petiole of a cotyle-
don the whole cotyledon is killed. In a particular field 18 per-
cent of the seedlings were killed before they developed any true
leaves. The wilt has not been observed as important in Florida.
The lesions of the fruit are at first oval to circular and are
greasy-green in color, later becoming dark brown. The rot de-
velops within the fruit and the whole fruit becomes darker col-
ored and soft but not of a slimy consistency. On this rotted fruit
the spores of the fungus are developed in small black structures,
pycnidia and perithecia.
Control: Seed treatment should be practiced to kill the black
rot organism on the seed.
Bordeaux spray, 4-4-50, or copper-lime dust, 80-20, will control
the disease in the field and careful handling during picking and
packing so as not to bruise the fruit will help materially in con-
trolling the disease in transit.

STEM ROT OF CUCUMBERS
This disease is caused by the fungus Sclerotinia sclerotiorum
(Lib.) Massee. It is not a common disease, having been found
only in scattered fields over the state during the past few years.
It was found both in the field and in greenhouses.
Plants are attacked at any stage of development, usually on the
stem near the soil line of the younger plants and on the fruits of
the older plants. The principal damage is done in transit when
diseased fruits are packed for shipment. The fungus develops
rapidly in transit, resulting in a watery soft rot.
This is the same fungus which causes a common disease of let-
tuce known as drop, and the destructive disease of celery known







Florida Agricultural Experiment Station


as pink rot. It is also known to attack a large number of the
other common truck crops grown in the state.
The white cottony growth on the main stem is typical of the
disease in its early development. Later large irregular black
sclerotia are formed either imbedded in the tissue or clinging to
the outside of the stem among the dense mycelia. These sclerotia
tide the fungus over unfavorable periods of the year and when
conditions are again favorable for its growth they germinate,
produce spores and spread the fungus over large areas.
Description: The plants are attacked near or at the soil line.
At first there is very little effect shown on the plant even though
the white growth of the fungus is conspicuously evident. Grad-
ually the stem begins to turn yellow and shrivel. The decay is
comparatively dry. The softer tissue is rapidly disintegrated,
leaving only the vascular
tissue (veins) connecting
the roots and top. (Fig. 25.)
The plant soon dies after
this stage is reached. When
the parasite attacks the
fruit a soft waterly rot is
S3produced that involves the
whole fruit in a very short
time. This condition of the
product in transit is readily
detected because of the
leaking container.

I Control: There is no in-
expensive way to control
S stem rot in the field. The
best way to combat it is to
rotate the crop, growing a
field or forage crop on the
land for two or three years
..- before planting cucumbers
** on it again. If the disease
/ occurs in the greenhouse
it would be necessary to
Fig. 25. Stem rot of cucumbers on ma- sterilize the soil with for-
ture plants.








Bulletin 208, Cucumber Diseases in Florida


maldehyde or steam. If this cannot be done it would be necessary
to use new soil in the benches. Spraying or dusting will have
very little effect on the disease, but considerable benefit is derived
from field applications as preventive.

POWDERY MILDEW
Powdery mildew, caused by Erysiphe cichoracearum D. C., ap-
pears upon the leaves of the host plant in all sections of the state,
but its severity depends upon the time of year the plants are
grown. It is much worse during late spring and summer than at
any other times of the year. It is widespread in the United
States and occasionally does considerable damage, although in
Florida it is of very little importance, since the cucumber crop is
produced before June 1. Some trouble has been noted in the
greenhouses in the state.
The disease is found on all members of the cucumber family
and is severe on squashes. Spores of the fungus are produced in
abundance on the leaves, mostly on the upper surface and are
easily scattered when the leaves are moved. They are carried
considerable distances by the wind and rain. The fungus lives
on wild plants along the fences, woods and roadsides during the
period cucumbers are not growing.


Fig. 26. Cucumber plants severely infected with powdery mildew.








32 Florida Agricultural Experiment Sttiv;'

Description: The fungus does not kill the tissue of the host
plant at first but rather grows superficially, covering areas a
centimeter in diameter with a white powdery growth usually
circular in outline. The developing spores give it the powdery


Fig. 27. Powdery mildew on cucumber leaves, early primary infection
above.








Bulletin 208, Cucumber Diseases in Florida


appearance. The fungus penetrates the epidermis only slightly to
obtain its nourishment. As the fungus requires more food, the
leaf begins to turn yellow and a few brown specks can be seen
near the center of the white fungus growth. These spots enlarge
and when very many of them occupy a single leaf it is rapidly
killed.
Control: In greenhouses it is recommended that the plants be
dusted with flowers of sulphur. In the field the spraying with
Bordeaux mixture or dusting with copper-lime dust for the
control of other diseases is sufficient to control the powdery
mildew.

SOUTHERN BLIGHT lB


Southern blight is caused by the
fungus Sclerotium rolfsii Sacc. Al-
though the fungus is very common in
Florida and has been found to be a
serious factor on a large number of
the cultivated and wild plants in the
State, it has not been important on
cucumbers. Its occurrence and de-
structiveness are variable and spo-
radic, depending principally on
weather conditions, being worse dur-
ing the rainy period of the summer
months. A plant once attacked by the
fungus is always killed, as it is usually
girdled at the surface of the soil.
Numerous sclerotia are developed
which are white when young, gradu-
ally turning light brown and finally
dark brown. They vary somewhat in
size, averaging about the size of mus-
tard seed. (Fig. 28.) These sclerotia
are easily scattered in tilling the soil,
also by rain and running water. They
germinate quickly in a moist atmos-
phere and infect other plants. Once
the fungus is established only a few
days are required to kill the plants.


Fig. 28. Southern blight on
main steam, showing white
mycelia and small brown
sclerotia.







Florida Agricultural Experiment Station


Description: Southern blight is usually not detected until a
wilting of the growing tips is observed. The wilting takes place
during the middle of the day at first but a day or two later the
whole plant wilts and fails to revive at night and then dries out
rapidly. When such a plant is found in the field it is well to
examine the main root near the soil surface. There the fungus
causing the death of the plant will be readily seen and can be
definitely identified by the presence of the small, mustard-seed-
like, brown sclerotia clustered on the stem at the soil line.
Control: The only control practicable is the careful removal of
the diseased plants with the sclerotia from the field wherever
found. If severe in the whole field, rotate with a forage crop.

FUSARIUM WILT
This wilt of cucumbers is caused by the fungus Fusarium
cucurbitae Taube. The disease is not common in Florida and
has been found in only a few scattered places. In the greenhouses,
however, it has at times become a serious factor and has caused
considerable loss. The organism causing this disease lives from
one season to the next in the soil and plants set in infected soil or
seed planted on it are liable to become diseased. The spores of
the fungus are formed on the roots and stems of the plants that
are killed and it lives over unfavorable seasons in this way and
by the infection of wild host plants. The disease is most easily
detected during hot weather before the summer rains.
Description: The only symptoms of Fusarium wilt are the wilt-
ing of the growing tips, followed by the wilting of the whole
plant. After wilting, the plant rapidly dries up and dies. This
disease is often confused with southern wilt but southern wilt
can be readily distinguished from Fusarium wilt by the presence
of the sclerotia.
Control: The only control in the field is rotation of crops.
When the disease appears in the greenhouse it is necessary to
remove the diseased plants and either remove the soil or sterilize
it. Soil used in greenhouses should always be sterilized before seed
are planted. Sterilize it with either live steam or formaldehyde.

MACROSPORIUM BLIGHT OF CUCUMBERS
This leaf blight is caused by the fungus Macrosporium cucum-
erinum E. & C. It is not found commonly on cucumbers in Flor-
ida, although it may be considered common on cantaloupe and
watermelon. The disease has not been of economic importance







Florida Agricultural Experiment Station


Description: Southern blight is usually not detected until a
wilting of the growing tips is observed. The wilting takes place
during the middle of the day at first but a day or two later the
whole plant wilts and fails to revive at night and then dries out
rapidly. When such a plant is found in the field it is well to
examine the main root near the soil surface. There the fungus
causing the death of the plant will be readily seen and can be
definitely identified by the presence of the small, mustard-seed-
like, brown sclerotia clustered on the stem at the soil line.
Control: The only control practicable is the careful removal of
the diseased plants with the sclerotia from the field wherever
found. If severe in the whole field, rotate with a forage crop.

FUSARIUM WILT
This wilt of cucumbers is caused by the fungus Fusarium
cucurbitae Taube. The disease is not common in Florida and
has been found in only a few scattered places. In the greenhouses,
however, it has at times become a serious factor and has caused
considerable loss. The organism causing this disease lives from
one season to the next in the soil and plants set in infected soil or
seed planted on it are liable to become diseased. The spores of
the fungus are formed on the roots and stems of the plants that
are killed and it lives over unfavorable seasons in this way and
by the infection of wild host plants. The disease is most easily
detected during hot weather before the summer rains.
Description: The only symptoms of Fusarium wilt are the wilt-
ing of the growing tips, followed by the wilting of the whole
plant. After wilting, the plant rapidly dries up and dies. This
disease is often confused with southern wilt but southern wilt
can be readily distinguished from Fusarium wilt by the presence
of the sclerotia.
Control: The only control in the field is rotation of crops.
When the disease appears in the greenhouse it is necessary to
remove the diseased plants and either remove the soil or sterilize
it. Soil used in greenhouses should always be sterilized before seed
are planted. Sterilize it with either live steam or formaldehyde.

MACROSPORIUM BLIGHT OF CUCUMBERS
This leaf blight is caused by the fungus Macrosporium cucum-
erinum E. & C. It is not found commonly on cucumbers in Flor-
ida, although it may be considered common on cantaloupe and
watermelon. The disease has not been of economic importance







Bulletin 208, Cucumber Diseases in Florida


up to the present time in Florida except in small late summer
garden patches.
The fungus lives from one season to the next on wild host plants
and on old leaves and vines that have not been destroyed. The
spores are scattered by the wind and rain and germinate quickly
in water from rain or heavy dew.
Description: The first noticeable evidence of macrosporium
blight on the cucumber is a small brownish spot. These spots
enlarge and become dark brown, showing concentric zoning as
they develop, often enlarging to almost a centimeter in diameter.
At this time the brown, dried central portions often crack and
fall away, leaving holes in the leaves. When there are numerous
spots on the leaves they coalesce and quickly kill the whole leaf.
The disease has not been observed on the stems but has caused
some infections on the fruits, especially those sunburned or
otherwise injured. It has not been important, however, on the
fruits.


Fig. 29. Albino cucumber fruits probably the result from reversion to
white spine types.







Florida Agricultural Experiment Station


Control: This blight can be controlled by the application of
Bordeaux mixture or copper-lime dust.
WHITE OR ALBINO CUCUMBERS
The occurrence of white or albino cucumber fruits has been
reported during the past season with considerable regularity.
They can be found in almost every field visited. The percent of
such fruits is always too small to be considered of any economic
importance. These fruits are never packed and shipped because
they do not sell as well as the green fruit. Most growers cut
such plants at the soil line when found in the field. They can be
distinguished somewhat before any fruit develops because of
their lighter green color and general appearance. Few growers
recognize them, however, before the fruit sets and often such
plants are not killed until picking time. Other than as just
mentioned the plants appear and develop quite normally. -This
condition is not contagious in any way and there is no remedy
for it. Since the yellow-white fruits are not marketable, the
product of these plants is a total loss to the grower and were the
percentage of their occurrence large, it would be necessary to
recognize certain losses. These white fruited plants have been
found in several different varieties and it appears to be connected
with the white spine strain.
Control: There is no artificial control for this condition other
than the destruction of these plants. It is a constitutional trouble,
probably a reversion to some impurity in the seed stock or to white
spine parentage.
None of the generally practiced control methods such as sanita-
tion, rotation or application of fungicides can possibly change the
situation. However, care should be exercised in the selection of
seed in an attempt to avoid the trouble as much as possible.
RING SPOT
Ring spot of cucumber has been found only on the leaves. Only
circumstantial evidence is at hand in attributing this trouble to
physiological causes. Close observations have been continuously
made during the growing season on cucumber fields in the vicinity
of Gainesville. A specific inspection trip revealed the fact that
all fields visited on that date showed leaves spotted as in Fig. 30.
None was previously found and none has been observed since.
The young leaves at the extreme tips of the runners were not
spotted. The first spots showed on leaves about three-fourths
developed and included all leaves older than these. Closer ex-







Florida Agricultural Experiment Station


Control: This blight can be controlled by the application of
Bordeaux mixture or copper-lime dust.
WHITE OR ALBINO CUCUMBERS
The occurrence of white or albino cucumber fruits has been
reported during the past season with considerable regularity.
They can be found in almost every field visited. The percent of
such fruits is always too small to be considered of any economic
importance. These fruits are never packed and shipped because
they do not sell as well as the green fruit. Most growers cut
such plants at the soil line when found in the field. They can be
distinguished somewhat before any fruit develops because of
their lighter green color and general appearance. Few growers
recognize them, however, before the fruit sets and often such
plants are not killed until picking time. Other than as just
mentioned the plants appear and develop quite normally. -This
condition is not contagious in any way and there is no remedy
for it. Since the yellow-white fruits are not marketable, the
product of these plants is a total loss to the grower and were the
percentage of their occurrence large, it would be necessary to
recognize certain losses. These white fruited plants have been
found in several different varieties and it appears to be connected
with the white spine strain.
Control: There is no artificial control for this condition other
than the destruction of these plants. It is a constitutional trouble,
probably a reversion to some impurity in the seed stock or to white
spine parentage.
None of the generally practiced control methods such as sanita-
tion, rotation or application of fungicides can possibly change the
situation. However, care should be exercised in the selection of
seed in an attempt to avoid the trouble as much as possible.
RING SPOT
Ring spot of cucumber has been found only on the leaves. Only
circumstantial evidence is at hand in attributing this trouble to
physiological causes. Close observations have been continuously
made during the growing season on cucumber fields in the vicinity
of Gainesville. A specific inspection trip revealed the fact that
all fields visited on that date showed leaves spotted as in Fig. 30.
None was previously found and none has been observed since.
The young leaves at the extreme tips of the runners were not
spotted. The first spots showed on leaves about three-fourths
developed and included all leaves older than these. Closer ex-







Bulletin 208, Cucumber Diseases in Florida


Fig. 30. Ring spot of cucumber leaf, produced by sunburning through
water drops.
amination showed that this spotting was more prevalent on ex-
posed leaves. Whereas leaves partially covered showed spots on
only the exposed area. Leaves fully protected though mature
showed no spots. It was first thought that overhead irrigation
was responsible but this theory was disproved, as non-irrigated
fields showed the same spotting. All fields in the vicinity of
Gainesville were affected.
A search of the rainfall records showed that one-tenth of an
inch of precipitation was recorded at 2 o'clock in the afternoon
of a slightly cloudy day with maximum temperature of 87
degrees. This occurred four days prior to these observations. To
judge from these circumstances it seems quite probable that the
spots were caused by the sunshine following the rain, the rain
drops acting as lenses, killing the host cells in specific lines,
making this characteristic marking on the leaves. All the various







Florida Agricultural Experiment Station


stages or degrees were observed from leaves showing only a few
spots to those almost completely killed and shrivelled. Fig. 30
shows one of the slightly affected leaves.
The spots were generally circular in outline, although the lines
were somewhat irregular both as to density and contour. The
blade of the leaf was a normal green in color, while the margins
of the spots were decidedly yellow, grading into brown, apparent-
ly depending upon the intensity of the burning action. The tissue
in the interior of the circles was a normal green in color. Leaves
badly affected dried out rapidly in the following day or two and
became brown. The edges curled upward very much like leaves
affected with downy mildew.
The picking season was past its height at this time so that little
or no damage was caused.

SNAKEHEAD
Occasionally cucumber seedlings are found that make no
growth or abnormal growth after the cotyledons appear above
ground. Closer examination shows the growing tip entirely
lacking or suffering from severe injury. The name "snakehead"


Fig.-31. Snakehead of cucumber, probably the result of mechanical injury.
Normal plant on the left.








Bulletin 208, Cucumber Diseases in Florida


has been applied to seedlings showing this condition. This injury
may have taken place at any time between the separation of the
seeds from the pulp and the development of the first true leaf
following the appearance of the cotyledons of the seedling above
ground. This condition results from the partial or complete
severance of the plumule in the seed or the growing tip in the
young seedling. The loss of the growing tip naturally delays the
growth of the plant. Often secondary buds develop when the
injury does not involve the whole growing tip. These buds oc-
casionally develop after a normal fashion but more often they
show only feeble and distorted growth. The seedlings thus af-
fected are darker green in color than unaffected seedlings. The
cotyledons are larger and more leaf-like, whereas if a single leaf
develops, as often occurs, it is dark green, ill-shapen and thicker
than normal leaves. It is more cotyledon-like in its general tex-
ture. Growers have often observed this type of plant and have
referred to them as "giant" plants.
The exact cause of this injury is not definitely known but it
seems safe to suppose that it is the result of mechanical injury
as differentiated from any other cause. The possible mechanical
causes may be blows or pressure applied to the seed or there
may be attacks of fungi or insects in which the young growing
tip of the seedling is killed or eaten. In a small planting of com-
mercial seed on the Experiment Station grounds 3.8 percent of
the seedlings showed snakehead. No method of control for this
trouble is known.


LEAF SPOTS

There are several unimportant leaf spots occurring on the
cucumber plant which have not been found in Florida. They
have been found elsewhere but seldom known to be serious factors
except in isolated localities in northern sections of the country.
They are listed here as information, however. Cercospora citrul-
lina Cke.; Cladosporium cucumerinum E. & A.; Septoria cucur-
bitacearum Sacc.; Phyllosticta cucurbitacearum Sacc.
A description of these individual leaf spots is not important at
this time and as for control methods, they will be taken care of in
the control measures applied for the control of downy mildew.








40 Florida Agricultural Experiment Station

BORDEAUX INJURY
There has been considerable controversy among growers as
to whether home-made Bordeaux mixture does enough harm to
cucumber plants to offset the good derived from controlling
disease. It is true that this fungicide is very active and it is
necessary to use care and
precautions in handling it.
If it is used too strong it will
burn plants to such an ex-
tent as to almost kill them.
Figure 32 shows Bordeaux
burning on cucumber leaves.
Even though the mixture
was too strong, it burned
the leaves only where the
sun struck them. This burn-
ing was evident very soon
after the leaves dried after
spraying. The burned por-
tions of the leaves at first
appeared scalded,later turn-
Fig. 32. Bordeaux injury caused by spray
ing brown and drying hard. and bright sunshine.

Less than 10 percent of the
leaves showed this burning.
The older leaves were most
seriously affected. The
younger leaves and the
growing tips did not show
any signs of the burning.
Another type of burning
was found on cucumber
leaves caused by Bordeaux
mixture, but differed mark-
edly from the type of injury
just described. This second
type, as shown in Fig. 33.
did not develop until two
days after the spray was
applied and there was usual-
ly only one leaf on each run-
Fig. 33. Bordeaux injury resulting from ly only one leaf on each run-
liquid spray. ner affected. This was the







Bulletin 208. Cucinnber Diseases in Florida


youngest leaf at the growing tip of each of the runners at the
time the spraying was done. The next leaf to develop was normal,
showing none of the markings of the burned leaf. The Bordeaux
mixture caused the leaf to become mottled, almost typical of
mosaic. A day or two later the light yellow areas became slightly
brownish and the tissue dried out and fell away, leaving a more


Fig. 34. Copper injury resulting from spray and dust
applications in cool weather.


or less shothole effect. The leaf as a whole, however, was not
killed. These leaves functioned until the whole plant died.
The injury resulting in this mottling was evident on the plants
on about 1/3 of an acre. The whole patch was sprayed with
Bordeaux mixture of the same strength. During the operation a
small shower came up and thoroughly wet the plants. After the
shower the spraying was resumed. It was found later that all
the plants sprayed before the rain showed this Bordeaux injury
while those sprayed after the rain did not show this injury.
Another type of Bordeaux or copper injury is shown in Fig.
34 in which the cucumber leaf shows a light yellow margin some-







Florida Agricultural Experiment Station


times only along one side or at the tip, other times completely
around the margin of the blade. The band is usually quite wide,
seldom less than 1/4 inch and often an inch wide. This injury is
quite common and is usually found early in the year during the
cooler part of the season. None of these particular injuries have
been found to be serious in any way and can readily be over-
looked as causes for reduced yield.
The question does arise, however, whether or not there is injury
to the blossoms by Bordeaux spray. Some injury is probably
caused by too much pressure by which the flowers are actually
blown off the vines. It may be that the spray itself kills the
pollen before fertilization takes place or it may be that the Bor-
deaux mixture acts as a repellant to the insects which act as pollen
carriers and agents in fertilization.

SEED DISINFECTION

Seed disinfection is recommended to all cucumber growers and
it should be practiced with every planting. The process is easy
and takes only a short time. The results are profitable. In treat-
ing the seed all pathogenic organisms adhering to the seed, such
as bacteria and fungi, are killed. The seed themselves are not
harmed and will germinate as quickly and produce as strong
plants as ones which have not been treated.
The disinfection process is as follows: Place the seed in a
cloth bag, tie the top securely, leaving plenty of space in the bag
for the seed, for instance twice as much room as the seed occupy.
Submerge the bag of seed in a solution of corrosive sublimate,
strength 1:1,000, for 10 minutes. During this time it is well to
move the bag around in the solution, using a short stick. This
will insure all seed coming in contact with the disinfectant and
will remove air bubbles. After the 10-minute period is up, remove
the bag of seed from the disinfectant and rinse in several changes
of clear water. After the seed are thoroughly rinsed, spread them
out in the shade to dry. When dry the seed are ready to plant.
The seed might be planted wet except that they are more diffi-
cult to handle.
The vessel used to contain the disinfectant should not be of
metal because some of the mercury in the corrosive sublimate
unites with the metal, thus weakening the solution. Instead use
earthenware crocks or wooden containers such as pails and half
barrels.








Bulletin 208, Cucumber Diseases in Florida


The disinfectant can be purchased from local druggists and
can be obtained in the form of dry crystals or made up in the
form of pills. An ounce of the crystals dissolved in 71/2 gallons
of water makes a solution the designated strength, 1:1,000.
When smaller quantities of the disinfectant are desired it is
advisable to use pills. One pill dissolved in one pint of water gives
a solution of the strength of 1:1,000. If a gallon of the disinfec-
tant is desired, dissolve eight pills in a gallon of water.
Corrosive sublimate is a deadly poison when taken internally.
Consequently, it should be kept away from children. When the
solution is made up it looks like water, being tasteless and odor-
less, yet deadly poisonous. Thus, necessary precautions should be
taken in disposing of the liquid after it has been used so that
nothing will drink it, as it will kill stock, poultry and human
beings.

FUNGICIDES AND THEIR APPLICATION
It has become an established fact among cucumber growers
that plant diseases are their worst enemies. If they could control
the diseases that attack the host plant, they could produce a
good crop of cucumbers almost every season. The use of fungi-
cides for the control of diseases has not been generally practiced
throughout the cucumber growing sections of the state up to the
present time, although more growers are using some sort of
fungicide for the control of diseases than ever before.

BORDEAUX MIXTURE
Home-made Bordeaux mixture, 4-4-50, is the most valuable
spray for the control of diseases. Although not used exclusively
by the growers, it is probably used more than all other fungicides
combined. When weather conditions are normal it gives good
control if properly made and applied.
If a large amount of spraying is to be done, it is most convenient
to make up stock solutions of bluestone and lime in such propor-
tions that one pound of either bluestone or lime is contained 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.








Florida Agricultural Experiment Station


STOCK SOLUTION A, BLUESTONE: Dissolve at the rate of
1 pound of bluestone to 1 gallon of water; put 50 pounds of blue-
stone 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
container 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. Always stir the stock solution be-
fore taking any out. Do not stir the 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 solution to half the
amount of spray to be made. Dilute the required amount of lime
in a separate container to half the amount of spray to be made.
Then pour the contents of the two containers into a third con-
tainer or spray tank simultaneously, stirring the combined mix-
ture 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.

MIXING PLATFORM. If many acres are to be sprayed during
the season, it will be quite necessary to construct a mixing plat-
form where the Bordeaux spray 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. 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 small platform upon which the
stock solutions are made. The smaller platform should be ele-
vated enough so that the stock solutions can flow into the barrels
on the main platform. By following these principles in a general
way the laborious job of making Bordeaux mixture is extremely
simple. Fig. 35 shows a handy mixing platform.
It is essential that this mixture be applied soon after it is made.
It is of little value after standing 12 hours.








Bulletin 208, Cucumber Diseases in Florida


DIFFERENT AMOUNTS OF 4-4-50 BORDEAUX MIX-
TURE: In making 50 gallons of the mixture, use 4 gallons of
stock A, diluted to 25 gal-
lons, and 4 gallons of stock
B, diluted to 25 gallons. Run
both of these into the
sprayer at the same time
with the agitator going.
To make 100 gallons of
spray, use 8 gallons of stock
A, diluted to 50 gallons, and
8 gallons of stock B, diluted
to 50 gallons. Mix as above.
To make 200 gallons of
spray, use 16 gallons of
stock A, diluted to 100 gal-
lons, and 16 gallons of stock
B, diluted to 100 gallons.
Mix as above.
If it is impractical to use
the above method of mixing
the above method of mixing a Fig. 35. Bordeaux mixing plant.
the Bordeaux, the following (,.murtesy U. S. D. A.)
method may be used: Pour
the diluted lime solution into the spray tank, set the agitator
going and add slowly the diluted bluestone solution.

THOROUGHNESS IN SPRAYING NECESSARY
Spraying must be done thoroughly to be a paying proposition.
The tank pressure should not be below 100 pounds. The plants
must be covered completely so that the spores of the fungi will be
killed. The spray should be applied often enough to keep the
growing plants well protected. This usually calls for an appli-
cation every week.
Spraying should begin as soon as the plants are well up and it
should be continued methodically until the crop is gathered. Some
variation in exact time of application usually occurs, depending
upon the development of the plants and also upon the general
absence or occurrence of specific diseases.
POWER SPRAYING MACHINERY: In order to thoroughly
spray cucumbers often enough, where large acreages are grown,
it is necessary to select a power sprayer that is fitted to your








Florida Agricultural Experiment Station


needs. It is important to select a machine that maintains a pres-
sure of 200 pounds when several nozzles are running. A machine
with plenty of pressure produces a mist and covers the plants
with a fine film.
A spray machine equipped with a four- or five-horsepower gas-
oline engine for operating the pump will give good service, al-


Fig. 36. Efficient type of knapsack hand sprayer.


though there are certain objections to the use of an engine, since
it is often difficult to keep it in operating condition. More surface
of the plant will be covered when high pressure is maintained.
Spray machines should be thoroughly cleaned immediately
after use. Do this by running several buckets of water through
the nozzles while the pump is operating. If this precaution is







Bulletin 208, Cucumber Diseases in Florida


taken regularly, considerable time will be saved, as it will not be
necessary to spend a half day cleaning out the nozzles when the
machine is used again. If the spray material is allowed to remain
in the machine, it will dry and form flakes or cakes that will not
pass through the nozzles.
A good traction-driven spray machine will often give good
service, if it is given the proper attention and kept in good con-
dition, oiled frequently and cleaned thoroughly.
HAND SPRAYING: A large number of growers plant only
small acreages of cucumbers and the purchase of power sprayers
is out of the question. In such cases it is necessary to do the
spraying with smaller sprayers the power of which is furnished
by hand labor. An efficient sprayer for small acreages is a type
of knapsack sprayer as shown in Fig. 36. The rod is easily
handled and the leaves can be thoroughly sprayed.

COPPER-LIME DUST
The use of copper-lime dust is looked upon with much favor
by a large number of growers, principally because of the ease of
handling and the larger acreages that can be taken care of by a
single machine. The cost of material is considerably higher when
the same control is obtained as with home-made Bordeaux mix-
ture.
In selecting a power duster give it the same considerations you
would a power sprayer both in operation and after the operations
are finished. There should be plenty of power, preferably fur-
nished by an engine rather than by traction. To obtain the best
results the dusting should always be done when the plants are
wet with dew or rain and when there is little or no wind. Dust
that contains 6 to 7 percent metallic copper should average 30
to 40 pounds per acre when the vines are covering two-thirds of
the ground. Younger plants require less dust per acre and older
plants more. The 80-20 (80 percent lime and 20 percent dehy-
drated copper sulphate) dust has proved most satisfactory. When
using power dusters two nozzles per row are very satisfactory.
They should be arranged so as to direct the dust on each side of
each row. Thus, on average dusters carrying eight nozzles four
rows can be dusted, provided they are not planted too far apart;
HAND DUSTING: In smaller fields where the maintaining
and operating of power dusters is not practicable it is necessary
to use smaller dusters worked by hand. These dusters are very







Florida Agricultoural Experiment Station


efficient and several acres can be cared for by a single duster.
The duster which has given the best results out of almost a dozen
tried is shown in Fig. 37. This duster is easy to operate, throws
out a continuous, powerful stream of dust which penetrates the
densest foliage. The amount of dust applied can be definitely
regulated.


Fig. 37. Type of hand duster giving good results.




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