• TABLE OF CONTENTS
HIDE
 Title Page
 Credits
 Table of Contents
 Introduction
 Downy mildew of cucumbers
 Anthracnose
 Angular leaf spot
 Mosaic
 Root-knot
 Bacterial wilt of cucumbers
 Black rot of cucumbers
 Stem rot of cucumbers
 Powdery mildew of cucumbers
 Southern blight
 Fusarium wilt
 Stemphylium leaf spot
 Macrosporium blight of cucumbe...
 Leaf spots
 Bordeaux injury
 Seed disinfection
 Fungicides and their applicati...














Group Title: Bulletin - University of Florida. Agricultural Experiment Station ; no. 177
Title: Diseases of cucumbers
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00027361/00001
 Material Information
Title: Diseases of cucumbers
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: p. 25-71 : 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: 1925
 Subjects
Subject: Cucumbers -- Diseases and pests -- Florida   ( lcsh )
Cucumbers -- Diseases and pests -- Control -- 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.
Funding: Bulletin (University of Florida. Agricultural Experiment Station) ;
 Record Information
Bibliographic ID: UF00027361
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000923476
oclc - 18171656
notis - AEN4027

Table of Contents
    Title Page
        Page 25
    Credits
        Page 26
    Table of Contents
        Page 27
        Page 28
    Introduction
        Page 29
    Downy mildew of cucumbers
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
    Anthracnose
        Page 37
        Page 38
        Page 39
        Page 40
    Angular leaf spot
        Page 41
        Page 42
        Page 43
        Page 44
        Page 45
    Mosaic
        Page 46
        Page 47
        Page 48
    Root-knot
        Page 49
        Page 50
        Page 51
        Page 52
        Page 53
    Bacterial wilt of cucumbers
        Page 54
    Black rot of cucumbers
        Page 55
    Stem rot of cucumbers
        Page 56
        Page 57
    Powdery mildew of cucumbers
        Page 58
    Southern blight
        Page 59
    Fusarium wilt
        Page 60
    Stemphylium leaf spot
        Page 60
        Page 61
    Macrosporium blight of cucumbers
        Page 62
    Leaf spots
        Page 63
    Bordeaux injury
        Page 63
        Page 64
    Seed disinfection
        Page 65
    Fungicides and their application
        Page 66
        Page 67
        Page 68
        Page 69
        Page 70
        Page 71
Full Text


Bulletin 177


December, 1925


UNIVERSITY OF FLORIDA
Agricultural Experiment Station



DISEASES OF CUCUMBERS

By

G. F. WEBER


Fig. 7.-Infection of cucumbers caused by the angular leaf spot organism.



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






BOARD OF CONTROL


P. K. YONGE, Chairman, Pensacola
E. L. WARTMANN, Citra
E. W. LANE, Jacksonville
A. H. BLENDING, Leesburg
W. B. DAvis, Perry
J. DIAMOND, Secretary, Tallahassee
J. G. KELLUM, Auditor, Tallahassee

STATION STAFF

WILMON NEWELL, D. Sc., Director
JOHN M. SCOTT. B. S., Vice Director and Animal Industrialist
J. R. WATSON, A. M. Entomologist
ARCHIE N. TISSOT, M. S., Assistant Entomologist
H. E. BRATLEY, M. S. A., Asst. in Entomology
R. W. RUPRECHT, Ph. D., Chemist
R. M. BARNETTE, Ph. D., Assistant Chemist
C. E. BELL, M. S. Assistant Chemist
E. W. COWAN, A. M.. Assistant Chemist
J. M. COLEMAN, B. S., Assistant Chemist
O. F. BURGER, D. Se., Plant Pathologist
G. F. WEBER, Ph. D., Associate Plant Pathologist
J. L. SEAL, M. S., Assistant Plant Pathologist
ROBERT E. NOLEN, M. S. A., Lab. Asst. in Plant Pathology
K. W. LOUCKs, A. B., Lab. Asst. in Plant Pathology
ERDMAN WEST, B. S., Lab. Asst. in Plant Pathology
D. G. A. KELBERT, Field Asst. in Plant Pathology
W. E. STOKES, M. S., Grass and Forage Crops Specialist
W. A. LEUKEL, Ph. D., Assistant Grass and Forage Crops Specialist
A. F. CAMP, Ph. D., Plant Physiologist, Cotton Investigations
W. A. CARVER, Ph. D., Assistant Cotton Specialist
EDGAR F. GROSSMAN, M. A., Assistant Entomologist, Cotton Investigations
RAYMOND CROWN, Field Asst., Cotton Investigations
A. L. SHEALY, D. V. M., Veterinarian
D. A. SANDERS, D. V. M., Assistant Veterinarian
OUIDA DAVIS ABBOTT, Ph. D., Head, Home Economics Research
HAROLD MOWRY, Assistant Horticulturist
G. H. BLACKMON, B. S. A., Pecan Culturist
IDA KEELING CRESAP, Librarian
J. FRANCIS COOPER, B. S. A.. Editor
RUBY NEWHALL, Secretary
HENRY ZEIGLER, Farm Foreman
W. B. TISDALE, Ph. D., Plant Pathologist, in charge Tobacco Experiment
Station (Quincy)
J. G. KELLY, B. S. A., Lab. Asst. in Plant Pathology (Quincy)
JESSE REEVES, Foreman Tobacco Experiment Station (Quincy)
L. O. GRATZ, Ph. D., Assistant Plant Pathologist (Hastings)
A. S. RHOADS, Ph. D., Assistant Plant Pathologist (Cocoa)
W. A. KUNTZ, A. M., Assistant Plant Pathologist (Lake Alfred)
J. H. JEFFERIES, Superintendent Citrus Experiment Station (Lake Alfred)
GEO. E. TEDDER, Foreman, Everglades Experiment Station (Belle Glade)


K. H. GRAHAM, Auditor
RACHEL MCQUARRIE, Assistant Auditor







CONTENTS
PAGE
INTRODUCTION ................................ -..--- --- 29
DOWNY MILDEW OF CUCUMBERS.........---..-- .. ----------------------- 29
Description -..-..... ---.-- ---..--... ...-..-...--.--....- 30
Control ...------.--.--- -...------....-.---...... -------- 33
ANTHRACNOSE ....-.....-.....-...-..-------- ------------- ..--------- 37
Description .....-....... .... ----..---------....... .... .... .----- 39
Control ----- --...................--------------........ ------..--.. 41
ANGULAR LEAF SPOT ....----. ..--......--........--- ---...-...-...-.-- 41
Description --..-- ..- ..-- ..-- ..-.....------ -- -----..--- ...-.. .--.....-.. --- 42
Control --...... ...------ .....-....----......... ..... .. ------..... ....--- 45
MOSAIC ...... .......... .. ...-.. ...-------------...... .-- -...........------ 46
Description .... .... .......... ............... ....... .. .. 47
Control .... ...-..-.- ........... ...-....-....... -..- ......----- 49
ROOT-KNOT ....---..- ...-- ..- .- .... ... .-.........--- ........- ..... 49
Description -.......... ...-------- ....---------.........- .. ........... 52
Control .....- ...... ... ..... ..... .....- --------... ..- ..- ..-....------- 5
BCEILWL----- ------------------------------------------........54
BACTERIAL WILT ...... ............-..--- .----..--- ...--.....--...--- 54
Description ... ... ... ..... ...... .. ...... ............. ... 54
Control ...--. ......-- ....... -...--..---....-...- .....-..-- .. 55
BLACK ROT .-...-...-..-...........--..............--..- -----.... 55
Description -...-.--. ... .. -....---... .......--- ........-....---- .... .-.....-- 56
Control .....------------ ........ ... ... .. ..... ...-----..--......- 56
STEM ROT -...-....... --- ..-..-- .....---.....----- --....---- .....-- 56
Description .. ....... -. .............. -----........... 57
Control ....- ....-- ... ..-...... ..-......... ............ 58
POWDERY MILDEW ........... ..------ --.... .................... ---- -... 58
Description .--.... ~. .................... ...... 58
Descriton --- --------------------------------- -------------- ------ ------- 58
Control ....-..--.. .........-.....- .--.-----............-- 58
SOUTHERN BLIGHT ......--..-- ..--..- ......---- ---....... ......... 59
D description --..-.. ----..- .. ....... ......... .. ... .. ..- ..- ... ....-...... ... 59
Control ..--...... ....................-.....-- .......- -----------.... 60
FUSARIUM W ILT ..~....... ................. ...... -. ..--- -- -- 60
Description ..--......... ................ ...... 60
Control .....------ --....---..--------- ...-- ......... 60
STEMPHYLLIUM LEAF SPOT .-..--...... -----...-..--..--------.. 60
MACROSPORIUM BLIGHT ........-.....-.......-. -------..-----. 62
Description -----------2
Description ....................-- .-----.. ---- ---------------------62
Control .-..-....------......-....------- .. -----------62
Cercospora citrullina ...-. -- ---- --...--......-- --------. 63
Cladosporium cucumerinum ................-...----------------------- 63
Septoria cucurbitacearum --..---------....... ....---.---- .------------ -------63
Phyllosticta cucurbitacearm .---....-...-. ---...-..-------- ----------- 63
BORDEAUX INJURY ......----........--... .---.---.-------------- 63
SEED DISINFECTION --...........---.---.....-..------------ 65
FUNGICIDES AND THEIR APPLICATION...........-......-- ----------------- 66
Bordeaux Mixture ....----- -- .. ............--.---- --------- 66
Thoroness in spraying necessary.................. ------- ------. 68
Power spray machinery ..................--- ----------------- .69
Hand spraying .....-..--..........---...--------.-------. 70
Copper-lime dust .........-............- -------- ------. 70
Hand dusting ................ .......------------.... --- ------- 71












DISEASES OF CUCUMBERS
By G. F. WEBER
Cucumbers have been profitably grown in Florida for a quar-
ter of a century. The quantity of production has steadily in-
creased until at present this crop is one of the leading truck
crops of the state, returning to the grower millions of dollars
each year. The plant has been successfully cultivated in nearly
every section of the state and will grow during almost all of the
seasons.
During certain seasons the yields are reduced because of the
prevalence of diseases. There are a large number of these dis-
eases 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. The occurrence and sea-
sonal development of the diseases are discussed. A detailed
description of each disease is given, followed by control methods
in each case.

DOWNY MILDEW OF CUCUMBERS
One of the most destructive diseases of cucumbers in Flor-
ida, commonly called "downy mildew", is caused by the fungus
Pseudoperonospora cubensis (B. & C.) Rostow. The disease
on the host plant 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
Southeastern states than in the Northern states. In Florida
the disease has been found in every county and has been col-
lected 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.
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. It was reported common during the last five
years. The past season, 1925, has been most successful from
the growers' viewpoint. The disease appeared at the usual
time but the lack of rain coupled with continued high tempera-
tures held it in check for two weeks. Consequently, growers in









DISEASES OF CUCUMBERS
By G. F. WEBER
Cucumbers have been profitably grown in Florida for a quar-
ter of a century. The quantity of production has steadily in-
creased until at present this crop is one of the leading truck
crops of the state, returning to the grower millions of dollars
each year. The plant has been successfully cultivated in nearly
every section of the state and will grow during almost all of the
seasons.
During certain seasons the yields are reduced because of the
prevalence of diseases. There are a large number of these dis-
eases 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. The occurrence and sea-
sonal development of the diseases are discussed. A detailed
description of each disease is given, followed by control methods
in each case.

DOWNY MILDEW OF CUCUMBERS
One of the most destructive diseases of cucumbers in Flor-
ida, commonly called "downy mildew", is caused by the fungus
Pseudoperonospora cubensis (B. & C.) Rostow. The disease
on the host plant 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
Southeastern states than in the Northern states. In Florida
the disease has been found in every county and has been col-
lected 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.
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. It was reported common during the last five
years. The past season, 1925, has been most successful from
the growers' viewpoint. The disease appeared at the usual
time but the lack of rain coupled with continued high tempera-
tures held it in check for two weeks. Consequently, growers in






Florida Agricultural Experiment Station


the central part of the state enjoyed a four-week picking sea-
son in which they harvested a bumper crop. Losses attributed
to the disease did not exceed 10 percent.
The fungus is not only found commonly on cucumbers but it
is also found on watermelon, cantaloupe, gourds, pumpkins,
squashes and gherkins. None of these plants suffer from the
disease as much as cucumbers. Given favorable conditions, the
disease will show up on the host plant at any time during the
year.
The fungus attacks only the leaves, rapidly killing them. The
fungus produces spores 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 ger-
S minute in the
moisture su p-
S plied by the dew
and infect the
plant. After
three or four
days the infec-
tion can be de-
tected by the ap-
pearance of yel-
Fig. 8.-Downy mildew on plants in field, early low spots. (Fig.
stage. 8.) The disease
spreads most rapidly during periods of comparatively low tem-
perature, heavy dews and rains and windy days. Dry weather
and high temperature are not favorable for the spread of the
disease, in fact, very little progress was made by the disease for
a period of two weeks during the past season because of con-
tinuous high temperatures.
Description: 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






Bulletin 177, Diseases of Cucumbers


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

r -. I -,


Fig. 9.-Typical downy mildew spotting of a cucumber leaf.
will again become evident with dew or rain. These spots are
more or less angular in outline and are delimited by the veins
of the leaf blade. (Fig. 9.)
The spots may be few or many on a single leaf, depending
on the number of spores causing the different infections. A
single spot seldom develops to more than a centimeter in
diameter. If the spots are numerous enough on a leaf they will






Florida Agricultural Experiment Station


coalesce and in
a day or two kill
the whole leaf,
which will be-
come brown and
d r y, remaining
erect instead of
wilting, and the
edges of the
blade will curl
inward very
characteristically.
(Fi g. 10.) A
few days after
the yellow spots
are visible on the Fig. 10.-Downy mildew killing the leaves of cu-
cumber plants, last stage.
leaves a careful
examination of one of these spots on the lower surface will re-
veal a fine, white,
downy growth,
which is at times
easily seen while
at other times is
seen with difficul-
ty, even with the
aid of a good hand
lens. The spores
of the fungus are
borne on the tips of
this downy growth.
(Fig. 11.) These
spores are usually
dark colored and
give the areas of
the leaf which
they occupy a
Grayish color
which, upon clos-
er examination,
Fig. 11.-Branched conidiophore of downy mildew appears to be cov-
fungus and spores that grow upon its branches. a t e o-
Highly magnified. ered with very
fine earth particles which are sticking to the surface among






Bulletin 177, Diseases of Cucumbers


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 being so small and light are
carried considerable distances by the wind. They may cause
additional infections on otherwise healthy plants in the next
24 hours, should temperature and moisture conditions be favor-
able for their germination.
Control: The control of downy mildew is necessary before
a grower can feel safe in risking the growing of a field of cu-
cumbers.
During the past season 37 varieties of cucumbers were 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 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
killed the plants three to four weeks later. All varieties were
susceptible to the disease and careful observations failed to
reveal any varieties which showed resistance.
The following varieties were grown: Kirby Staygreen, Vick-
ers 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,
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.
Experimental plots were sprayed and dusted during the
past season to determine the advisability of using fungicides,
their benefit, if any, and the cost. (Fig. 12.) The spraying
was done with a hand sprayer of the knapsack type (Fig. 38),
and the dusting was done with a hand dusting machine
(Fig. 39).
Plot Number I was divided into 16 parts, and each part,'con-
sisting of six rows approximately 200 feet long, was sprayed,





Florida Agricultural Experiment Station


dusted or left as check (neither sprayed or dusted).. The data
in Table I are a consolidation of the figures obtained from the
plot in reference to spray, dust and check. The data in Tables
II and III were obtained from two other plots similar to Plot I.

















Fig. 12.-Portion of experimental plot showing dusted plants on right
and undusted (check) plants on left.
The'liquid sprays applied consisted of two commercial cop-
per sprays, copper hydroxide and 4-4-50 Bordeaux mixture.
The Bordeaux mixture was made up with rock or hydrated lime.
The sprays were applied thoroly at intervals of 7 to 10 days.
Burning caused by Bordeaux mixture was noted on one of
the three plots. The spray was applied during the middle of a
hot day. Before the plots were entirely sprayed a thunder
shower stopped the work for half an hour. The spraying was
then resumed. Two days later the plants sprayed before the
rain showed the burning, while those sprayed immediately after
the rain did not show any injury. The cause of this burning
has not been determined but is probably associated with the
increased evaporation caused by the ingredients of the spray
during the exceptionally hot period previous to the rain. Since
burning was detected after oly one of the several applica-
tions of the spray, it was concluded that weather conditions
were more important than the spray in causing the injury.
Consequently a weaker spray formula is not recommended.
The dust used consisted of copper-lime dust (80-20 formula)
and copper-lime-arsenic dust (60-20-20 formula). Very little






Bulletin 177, Diseases of Cucumbers


difference was noted in comparing these plots except that the
pickle worm was controlled where the arsenic dust was used.
The dusts were always applied in the early morning when the
dew was on the plants.

TABLE I.-DATA SHOWING THE NUMBER OF PLANTS, YIELD, COST OF
LABOR AND FUNGICIDES, RETURNS AND NET PROFITS OF SPRAYED, DUSTED
AND CHECK (NEITHER SPRAYED NOR DUSTED) CUCUMBER PLOTS NEAR
GAINESVILLE, FLORIDA, DURING 1925.


Above data computed on an acre basis.

Check ............ 5,952 286.8 $553.60
Spray -........... 5,960 344 $24.24 688.00 $110.16
Dust ....-...... 5,712 336 40.56 672.00 77.84


Fig. 13.-Portion of experimental plot showing sprayed plants on left and
unsprayed (check) plants on right.

The data in Table I show that the application of good fungi-
cides gave a profit of approximately $100 per acre after all
costs were paid, also that the cost of the dust was almost twice
the cost of home-made Bordeaux mixture.







Florida Agricultural Experiment Station


TABLE rI.-RESULTS OF EXPERIMENT NO. 2 FOR CONTROL OF DOWNY
MILDEW.


Check .......
Spray ---------
Dust ................


Check ---
Spray ......
Dust .........--.....


115
170
161.5


0 w
o .0




4.83
5.08


Above data computed
230 ---
340 9.66
323 10.16


p-s


$230.00
340.00
323.00


.2



$105.17
93.00


on an acre basis.
$4'0.00
680.00 $210.34
646.00 175.84


Table II shows practically the same results as are shown in
Table I, namely, that Bordeaux 4-4-50 gave the best control of
the disease determined by yield. Dust was very good and
profitable in comparison with the checks. This table again
shows that the use of fungicides to control downy mildew is
profitable.

TABLE III.-RESULTS OF EXPERIMENT NO. 3 FOR CONTROL OF DOWNY
MILDEW.

-4 -4-, 0 ia

CI -9) a)

lei i4 odD
Check ---............ 74 $148
Spray .-------------- 74 $3.62 148 $ -3.62
Dust .................. 92 9.42 184 26.58
Above data computed on an acre basis.


Check ...-......
Spray -
Dust .--- .....


....... 296 $592
296 $14.48 592
...... 368 37.68 736


$-14.48
106.32


In applying the second application of fungicides the portion
sprayed with 4-4-50 Bordeaux was severely burned. This was
at blossoming time and as a result the development of the
plants was hindered for the next two weeks. The first week's
picking, made when no mildew was present on the plots, gave
a yield of half as much fruit on the sprayed plot as on the
dusted or check plots. The second week's picking was a third
larger on the checks and dusted plots than on the sprayed plot.






Bulletin 177, Diseases of Cucumbers


After this time the sprayed plot had caught up with the others
and during the remainder of the season averaged about the same
as the dust plot and exceeded the checks by 25 percent.
These data are of one season's results, however, and should
not be considered as final. The previous recommendations of
the Experiment Station are not to be changed and 4-4-50 home
made Bordeaux mixture will be recommended as the best con-
trol for the disease.

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 West-
ern 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 musk-
melons, watermelons and some varieties of gourds.
The disease is favored by high temperature and high humid-
ity, 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. Several fields planted in the fall in old water-
melon 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, cu-
cumbers, cantaloupes and gourds and from each of these hosts
to the others.
The fungus lives during the season on the numerous host
plants and when they die it remains in the old vines and fruits
left in the fields. The climate is such that the fungus readily
lives the year around. When a new crop is planted the fungus
being present invariably infects the first leaves.
Ten days to two weeks are required for the fungus to pro-
duce dead areas in the leaves, altho some yellowing is often
visible after one week. (Fig. 14.) Because of this early in-







Florida Agricultural Experiment Station


fection observers note the first signs of the disease on the leaves
in the immediate vicinity of the hill. General infections take
place following the appearance of the disease in the hill. It is
at this time that the grower begins to find that the disease is
giving him trouble.
This disease causes considerable loss in transit. Early in-


Fig. 14.-Cucumber leaf showing anthracnose spots.
fections on fruits being packed for market are often overlooked
or even not possible to detect. Should these shipments be de-
layed in transit the disease develops and results in unmarket-
able 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 their







Bulletin 177, Diseases of Cucumbers


relative importance. The spores are washed from diseased
plants and spattered upon healthy plants. Heavy dews so com-
mon in Florida offer the proper conditions for infection.
Description: All parts of the host plant above ground are
subject to attack by anthracnose. The disease has not been ob-
served 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; where-

















Fig. 15.-The general effect of anthracnose on a cucumber plant.

as in other instances when the leaves are almost killed the fruit
still remains free from the disease. (Fig. 15.)
The first symptoms of the disease are slightly yellowish
areas on the leaf blades. This yellow color rapidly spreads in
the central 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 (unite)
and cause the premature death of the leaf.
These spots can be distinguished from other important leaf
spots on this host in that they are not delimited by the veins
and thus tend to be circular rather than angular in outline.
(See Fig. 14.)
The spores develop on these spots and are readily scattered
to other plants by the many disseminating agents. On the peti-
oles and stems the lesions (spots) are usually sunken and linear






Florida Agricultural Experiment Station


in. outline. (See Fig. 16 B.) The tissue is killed and in many
instances the stem is completely girdled and the portion beyond
the spot dies. The spores form on these lesions in a very short
time,and can
be- seen in
Sthe form of
small groups
i of pinkish
head-like
masses in the
central por-
A, tion of the le-
sions.
On the
fruits the in-
fections first
B appear as
more or less
circular owater
o oval water-
.. soaked spots.
As the lesion
Fig. 16.-Anthracnose lesions (spots) on the fruit and enlarges the
stems of cucumbers., (Courtesy U. S. D. A.) central por-
tion becomes sunken and the sunken area becomes covered
with the pinkish spore masses as described on the stems. (Fig.
16'A.) These spore masses can be found readily on the lesion
in the morning before the dew has disappeared.


Fig. 17.-Portion of large field completely killed by anthracnose.






Bulletin 177, Diseases of Cucumbers


Control: Experimental data are not conclusive as to the
control of anthracnose in the field by the use of fungicides.
At the present time it may be said that fungicides properly
applied will check the disease and give a commercial control but
will not without burdensome expense absolutely control the
disease. (Fig. 17.) Four-four-fifty (4-4-50) Bordeaux mix-
ture 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 con-
siderably 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 from 30 to 50 pounds per acre per application.

ANGULAR LEAF SPOT

The disease of cucumbers known as angular leaf spot is
caused by a bacterial organism, Bacterium lachrymans E. F. S.
& Bryan. It has been found on the host plant every season and,
altho not always of serious economic importance, causes con-
siderable damage. The disease has been known to the Florida
trucker for the past 15 years and is quite generally distributed
over the state. It has also been reported from most of the
states north of the Ohio River but probably is not as severe in
these states as in Florida.
In Florida the most 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 cer-
tain fields in 1924 which were unmarketable, resulting in total
losses. (Fig. 18.) This loss however, does not include the re-
duction in stand in the field due to seedling infection, neither
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, previous
to shipment, infections may be overlooked and as a result soft
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 the best.





Florida Agricultural Experiment Station


The organism causing this disease has been found on a large
number of the commercial varieties of cucumbers, and several
species of gourd which are closely related to the cucumber.
From observations made in Florida the disease is favored in












Fig. 18.-Pile of cull cucumbers discarded because of infections of the
angular leaf spot organism.

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 thru the stomata
(pores) and results in the formation of the spot that is known
to cucumber growers. Wind, insects and pickers are also car-
riers 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 considerable lengths 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 impossible to look at cucumber seed and
tell whether or not it is infected with angular leaf spot. When
the young plants emerge the first indications of the disease may
be found by the appearance of spots on the cotyledons. It may
be so severe as to kill the seedling or may not be serious at all
except that it is a source of infection from which other healthy
plants can become diseased. The lesions appear anywhere on






Bulletin 177, Diseases of Cucumbers


the cotyledons and are usually
they are located at the base
of the cotyledon. From here
it readily attacks the bud,
killing the seedling.
The lesions on the coty-
ledons are small, sunken, cir-
cular 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 sub-
ject to infection and the
spots appear upon them
when about a week old. At
first there appears only a
small water-soaked, circu-
lar area. The spot enlarges
and becomes limited in ex-
tent by the veins of the leaf.
(Fig. 19.) It varies in size
from 1/16 to 1/ inch in di-
ameter. It is very seldom
circular or oval but rather
angular in outline, being
three-, four-, or five-sided















Fig. 20.-General effect of angul
spot disease on the foliage of cucl


y not fatal to the plant unless


A&^


Fig. 19.-Typical angular leaf spot le-
sions on cucumber leaves.

depending on the sur-
rounding veins.
The spots are most
easily detected in the
morning when the dew
is still on the plants.
They are water-soaked
anu of a darker green
color than the remain-
der of the leaf and are
practically the same on
each side of the leaf. If
one examines these
spots at this time there
ar leaf b f
umbers. can be found milky






Florida Agricultural Experiment Station


white ooze in the form of small drops around the spots. This
ooze known as exudate is liquid from the leaf containing mil-
lions of bacteria and appears whitish because of their pres-
ence. 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, leaving holes in the leaves. (Fig. 20.) For


Fig. 21.-Internal effect of the angular leaf spot disease.
this reason the common name shotholee disease" is often heard
when referring to this disease.
On the fruit the first indication of infection is the appear-
ance of small circular water-soaked spots, 1/16 of an inch or
smaller in diameter. (Fig. 7.) 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 appears on its surface. There is very little outward
development from this stage; instead the fruit begins to decay
on the inside. From the lesion on the surface a brownish path






Bulletin 177, Diseases of Cucumbers


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 placentae and caus-
ing the tissue to break down and result in a soft mushy mass.
(Fig. 21.) 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 conse-
quently the possibility of securing resistant plants of the right
marketable 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) are 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 con-
trolled by the same application of spray or dust used to con-
trol the mildew. (See page 33.)
The most effective method, however, of combating the disease
is by the treatment, or disinfection of the seed. Tie the seed
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 65, 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
plantings to obtain a stand. Seed treatment was advocated
and generally practiced by a large number of the growers.
Practically 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 re-
sult the third and fourth plantings were only 12 percent treated,
while in the first plantings, 90 percent of the seed were treated.
Many growers blamed the treatment for the rotting of the seed
but check plots, which were untreated, failed to germinate the
same as the treated seed.
After the plants had developed several true leaves a sur-
vey was made of 26 cucumber fields and the occurrence, or ab-







Florida Agricultural Experiment Station


sence of angular leaf spot was recorded. In 18 of these fields
the disease was found. A closer check and interview with the
growers revealed 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 dis-
ease, and this method of control is efficient, cheap, simple and
quickly done.
MOSAIC

The cause of mosaic is at present not known. Extensive ex-
perimental work has been conducted in the United States and
foreign countries in an endeavor to determine the cause of the
disease and also to find out the ways of dissemination, over-
wintering and means of control. In the United States the dis-
ease is widespread and may be said to occur wherever cucum-
bers are grown. Altho being generally distributed over the
cucumber area of the United States, it has been severe in rela-
tively few states and these instances have been in the North.
The disease in Florida may be classed as relatively unimpor-
tant, its occurrence is rare and during the past several seasons
it has been of no economic importance. During the past sea-
son, however, more reports of its occurrence and a greater dis-
tribution have been noted than during all the previous years.
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 ex-
change 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 inocu-
lated 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







Bulletin 177, Diseases of Cucumbers


the field by first stepping on or brushing diseased plants and
then healthy plants.
It has been found that a large number of plants closely re-
lated to the cucumber are susceptible to the disease. There are
also a 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 pro-
duce the disease. Recent experiments1 have shown that mo-
saic can be transmitted from cucumber to muskmelon, pepper,
ground cherry, tomato, potato, tobacco, martynia, horseweed,
catnip, pokeweed, 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 year so that the possible source of inoculum is always
present and all that is necessary for its spread is carrying
agents.




















Fig. 22.-Deeply notched, pointed, mottled cucumber leaves, symptoms of
mosaic. (Courtesy U. S. D. A.)

Description: In general it may be said that the two charac-
teristic symptoms of mosaic are a definite green mottling and a
marked stunting of the vines. These symptoms vary somewhat

"'Further Studies on the Overwintering and Dissemination of Cur-
cubit Mosaic." S. P. Doolittle and M. N. Walker. Jour. Agr. Res. 31: 1925.







Florida Agricultural Experiment Station


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 mani-



















Fig. 23.-Last stage of the mosaic disease. (Courtesy U. S. D. A.)

























L ..


Fig. 24.-The warty, mottled effect of mosaic on the fruits.







Bulletin 177, Diseases of Cucumbers


fested itself about the time the first fruits set. At this time the
plants have developed runners 12 to 18 inches long. (Fig. 22.)
The younger leaves show a distinct mottling of dark and light
green color, a sort of patchwork over the leaf. In other re-
spects the leaf appears quite normal.
As the plant grows older the new growth at the ends of the
runners does not develop normally but rather appears rossetted
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. 23.) The
disease shows up early on the fruit of mosaic plants. The mot-
tling is quite similar to that described on the leaves and in se-
vere instances the fruits become distorted, rough and warty.
These fruits are not marketable because of their appearance.
(Fig. 24.)
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 suscep-
tible to mosaic.
Field sanitation has been successfully practiced in certain
districts by cutting all weeds showing the symptoms of mosaic,
thus removing the source of infection so that the disease can-
not be spread. This practice has given good results and will
probably prove to be the only way to control the disease in Flor-
ida should it become severe.
Whenever the plants are found they should be pulled up
carefully and removed from the field and the hands washed
thoroly 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.

ROOT-KNOT

The small worms commonly known as nematodes (Hetero-
dera radicicola), readily attack cucumber plants and cause
serious trouble. They invade the roots, causing swelling, galls






Florida Agricultural Experiment Station


or knots, hence the common name, root-knot. (Fig. 25.) The
adults are barely visible to the naked eye and will be over-
looked unless one knows for what to look. The disease itself,
however, cannot be mistaken because it is the only disease of
the host plant in which these knots appear on the roots.


Fig. 25.-Roots infested with nematodes, advanced stage.

The young nematodes work their way thru the soil until they
come in contact with the root of a plant they prefer. They
then bore into the roots and feed upon the juices. At the
same time they irritate the plant causing it to form knot-like
galls. In this way the feeding roots of the plant are rendered
worthless or practically so as a means of support and growth
for the host plant.







Bulletin 177, Diseases of Cucumbers


coon ai e









(i a











Fig. 26.-Life history of the nematode, Heterodera radicicola (Greef)
Mull, (sizes not comparable). Top, four stages of development of the
egg. Nos. 1, 1, 2, stages of growth of young worms. Nos. 3, 4, 6,
development of the female. Others, four stages in development of
male. (After Stone, G. E., and Smith, R. E., Mass. Agrl. Exp. Bul.
55, 1898.






Florida Agricultural Experiment Station


The worms are widely distributed thru most sections of Flor-
ida, especially in well drained sandy fields that have been
cleared for several years. They are much worse on sandy soils
than on clay and also on well drained soils than wet lands.
These worms are more or less dormant during a certain
period in the winter. At Gainesville they remain dormant
from November to the last of March, farther south the dormant
period is much
shorter and in
the extreme
south they may
be found active
all the year.
(Fig. 26.)
The eggs are
laid in the knots
on the roots, the
young hatch in
three or four
days if condi-
tions are favor-
able, otherwise
the eggs may lay
down a thick
wall around
themselves and lie
dormant in this
encysted s t a g e
for indefinite pe-
riods, even years,
until conditions
become right for
them to hatch.
Moisture, te m-
Fig. 27.-Root knot on seedling cucumber plant
caused by attack of nematodes. perature and air
in certain combinations are necessary for their development.
Description: Since the roots of the plants are the only parts
attacked it is impossible to tell when infection takes place on
the plants. After the worms have entered the roots and their






Bulletin 177, Diseases of Cucumbers


presence has cut down the food supply to the plant it will be
noted that these plants fail to grow as rapidly as the healthy
ones. They appear stunted and finally actually fail to grow.
Often they remain in this condition for weeks, not putting on
new growth, nor dying outright. Generally, however, if the
attack is during the seedling stage the plants will be killed be-
fore they have developed many leaves.
If the plants become infected late they may grow during the
whole season and produce fruit. These plants can be readily
distinguished from the healthy plants in the field by the yel-
lower leaves and slower growth. In pulling an infected plant
and examining the roots one will find the various sizes and
shapes of knots as shown in Fig. 27. The worms will be found
by opening these knots and examining with a lens. On older
roots the knots often become brown and in various stages of
disintegration. By this process the worms and eggs are dis-
tributed in the soil.
Control: Fumigation by sodium cyanide may be used to
free a field of nematodes but it is too expensive an operation
for the cucumber grower. A better method is to starve them
out by growing on the land for two or three years crops on
which the nematodes will not feed, such as corn, oats, velvet
beans, etc. See Bulletin 159 of this Station.
The summer fallow method is probably the most efficient
method to rid soil of nematodes in a single season. The land
is plowed immediately after the crop is off and kept bare of
vegetation all summer; it must be harrowed at least once a
week and after heavy rains. It is essential that a crust does
not form over the soil because it excludes air and prevents the
eggs of the nematodes from hatching. Thus the eggs are
hatched and the young worms, finding no food plants, starve
to death. This method of control is very severe on the soil,
materially reducing the fertility.
A slight modification of this method is the planting of bush
velvet beans instead of leaving the soil bare, thus retaining
present fertility and also gaining the benefit of a cover crop.
The beans must be well and frequently cultivated. In fact all
weeds must be removed from the field to insure starving the
nematodes.






Florida Agricultural Experiment Station


BACTERIAL WILT OF CUCUMBERS

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 there have been ob-
served only isolated cases, in which instances the economic im-
portance of the disease was negligible. It has been known in
Florida for probably 10 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














Fig. 28.-Cucumbers affected with bacterial wilt.

is not carried on the seed. The conditions in Florida are such
that the organism can survive the period when cucumbers are
not grown, on wild host plants, as the fence corners and ditches
are full of weeds during the whole year. This has not been
thoroly investigated, nevertheless there may be possibilities of
the survival of the organism in this way.
Description: The first symptom of bacterial wilt is a grad-
ual progressive wilting of the plant, the earliest evidences of
which are at the extreme tips of the runners. If the plant is

"Rand, F. V. & Enlows, E. M. A. Bacterial Wilt of Curcubits. U. S.
D. A. Bul. 828: 21, 1920.






Bulletin 177, Diseases of Cucumbers


infected upon the main stem all the tips wilt, but if the infec-
tion is on a single runner some distance from the main stern,
the wilting gradually works back toward the base of the plant
and then all. runners are affected and show the wilt disease
which becomes more severe each day until the plant is unable
to recover and soon dies. (Fig. 28.)
Control: It is necessary to control the insects in the field,
especially 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 and removed from the field.
The disease is transmitted primarily by the injury and inocu-


Fig. 29.-Cotyledons attacked
lation of plants by biting insects that
wilt-diseased plants.


by black rot.
have fed previously on


BLACK ROT OF CUCUMBERS
This disease, caused by the fungus Mycosphaerella citrullina
(Sm.) Gross, is found on the fruits, and causes a wilt of






Florida Agricultural Experiment Station


the young seedlings. It also causes a leaf spot, especially
on the cotyledons of seedlings and occasionally kills the young
plants soon after they are out of the ground. (Fig. 29.)
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 brown-
ish black color, circular, and often are 14 of an inch in diam-
eter. The tissue rapidly dries out and becomes wrinkled or
cracks and falls away. When an infection is located near the
petiole of a cotyledon the whole cotyledon is killed. In a par-
ticular field 18 percent 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 oval to circular, at first, a greasy
green in color later becoming dark brown. The rot develops
within the fruit and the whole fruit becomes darker colored
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 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
controlling 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






Bulletin 177, Diseases. of Cucumbers


in transit when diseased fruits are packed for shipment. The fun-
gus develops rapidly in transit, resulting in a watery soft rot.
This is the same fungus which causes a common disease of
lettuce known as drop, and the destructive disease of celery
known 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 condi-
tions are again favorable
for its growth they germi-
nate, produce spores and
spread the fungus over
large areas. 9
Description: The plants
are attacked near or at the
soil line. At first there is
very little effect shown on
the plant even tho the white
growth of the fungus is con-
spicuously evident. Gradu-
ally the stem begins to turn
yellow and shrivel. The de--
cay is comparatively dry.
The softer tissue is rapid-
ly disintegrated, leaving
only the vascular tissue
(v e i n s ) connecting the
roots and top. (Fig. 30.)
The plant soon dies after
this stage is reached. When .
the parasite attacks the
S. Fig. 30.-Stem rot of cucumbers on
fruit a soft watery rot is mature plants.
produced that involves the whole fruit in a very short time.
This condition of the product in transit is readily detected be-
cause of the leaking container.






Florida Agricultural Experiment Station


Control: There is no inexpensive way to control 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 sterilize the
soil with formaldehyde 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.

POWDERY MILDEW OF CUCUMBERS
Powdery mildew, caused by Erysiphe cichoracearum DC.,
appears upon the leaves of the host plant in all sections of the
state, its severity depending upon the time of year when 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,
altho in Florida it is of very little importance, since the cucum-
ber crop is produced before June 1. Some trouble has been
noted in the greenhouses in the state.
The fungus is found on all members of the cucumber fam-
ily, especially squashes on which it is severe. The spores are
produced in abundance on the leaves, mostly on the upper sur-
face 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 road-
sides during the period cucumbers are not growing.
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 and above the epidermis. The developing spores give
it the powdery appearance. The fungus penetrates the epi-
dermis 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 fungous
growth. These spots enlarge and when very many of these
spots occupy a single leaf it is rapidly killed.
Control: In greenhouses flowers of sulphur dusted on the
plants is recommended. For the field the spraying with Bor-
deaux mixture or dusting with copper-lime dust for the control
of other diseases is sufficient to take care of the powdery
mildew.






Bulletin 177, Diseases of Cucumbers


SOUTHERN BLIGHT

Southern blight is caused by the fungus Sclerotium rolfsii
Sacc. Altho the fungus is very common in Florida and has
been found to be a serious factor on a large number of the cul-
tivated and wild plants in the state, it
has not been important on cucumbers.
Its occurrence and destructiveness are
variable and sporadic, depending prin-
cipally on weather conditions, always
worse in the summer months during
the rainy season. A plant once at-
tacked by the fungus is always killed,
as it is usually girdled at the surface
of the soil.
Numerous brown sclerotia are devel-
oped which are white when young,
gradually turning light brown, later
becoming darker. They vary some-
what in size, averaging about the size
of mustard seed. (Fig. 31.) These
sclerotia are easily scattered in tilling
the soil, also by rain and running
water. They germinate quickly in a
moist atmosphere and infect other
plants. Once the fungus is established
only a few days are required to kill the
plants.
Description: Southern blight is usu-
ally 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 recover Fi. 3.-Southern bight
and is then quickly killed. When such ing white mycelia and
a plant is found wilted in the field it is small brown sclerotia.
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, mus-
tard seed-like, brown sclerotia clustered on the stem at the
soil line.






Florida Agricultural Experiment Station


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 green-
houses, however, it has at times become a serious factor and
has caused considerable loss. The organism causing this dis-
ease 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 dis-
eased. 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
wilting of the growing tips, followed by the wilting of the
whole plant. After the 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 steril-
ize it. Soil used in greenhouses should always be sterilized be-
fore seed are planted. Sterilize it with either live steam or
formaldehyde.

STEMPHYLIUM LEAF SPOT

This spotting of cucumber leaves is caused by Stemphylium
cucurbitacearum Osner, a fungus recently isolated from dis-
eased leaves." Altho this disease has not been observed in
Florida, a short description is given here so that growers may
be able to recognize the disease should it appear.
The disease was first found in Indiana and Ohio where it

'Osner, Geo. A. Stemphylium Leafspot of Cucumbers. Jour. of Agr.
Res. 13: 295-306. 1918.






Florida Agricultural Experiment Station


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 green-
houses, however, it has at times become a serious factor and
has caused considerable loss. The organism causing this dis-
ease 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 dis-
eased. 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
wilting of the growing tips, followed by the wilting of the
whole plant. After the 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 steril-
ize it. Soil used in greenhouses should always be sterilized be-
fore seed are planted. Sterilize it with either live steam or
formaldehyde.

STEMPHYLIUM LEAF SPOT

This spotting of cucumber leaves is caused by Stemphylium
cucurbitacearum Osner, a fungus recently isolated from dis-
eased leaves." Altho this disease has not been observed in
Florida, a short description is given here so that growers may
be able to recognize the disease should it appear.
The disease was first found in Indiana and Ohio where it

'Osner, Geo. A. Stemphylium Leafspot of Cucumbers. Jour. of Agr.
Res. 13: 295-306. 1918.






Bulletin 177, Diseases of Cucumbers


caused some damage. (Fig. 32.) The disease was found on
the leaves of the host plant in the form of spots varying in
size from 1/32 to almost 1/ of an inch in diameter, being either
circular or angular in outline. Coalescing spots may kill large
areas of the leaf. The spots are yellowish and become whitish
with age and are surrounded by a brownish border.
The fungus is favored in its growth by cool and moist-con-
ditions which describe the Florida weather at the time the
early spring crop is grown. The spores are disseminated by


Fig. 32.-Spotting of cucumber leaves by stemphylium. (Courtesy U. S.
D. A.)
wind and rain and produce the disease in from seven to 10 days.
Bordeaux mixture is recommended as a possible control. Sani-
tation should also be practiced in the fields at all times, especi-
ally after the picking season. .






Florida Agricultural Experiment Station


MACROSPORIUM BLIGHT OF CUCUMBERS

This leaf blight is caused by the fungus Macrosporium cu-
cumerinum E. & C. It is not found commonly on cucumbers in
Florida, altho it may be considered common on cantaloupe and
watermelon. The disease has not
been of economic importance
up to the present time in Flor-
ida 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 des-
troyed. The spores are scat-
tered by the wind and rain and
germinate quickly in water
from rain or heavy dew.
0 Description: The first no-
ticeable evidence of macrospo-
rium blight on the host is a
small brownish spot. These
spots enlarge and become dark
brown, showing concentric zon-
ing as they develop, often en-
larging to almost a centimeter
in diameter. At this time the
brown, dried central portions
often crack and fall away, leav-
ing 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
Fig. 33.-Macrosporium spotting on the stems but has caused
of sunburned fruit.
some infections on the fruits.
(Fig. 33.) It has not been important, however, on the fruits.

Control:' This blight can be controlled by the application of
Bordeaux mixture or copper-lime dust.






Bulletin 177, Diseases of Cucumbers


LEAF SPOTS

There are several unimportant leaf spots occurring on the
host 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 cit-
rullina Cke.; Cladosporium cucumerinum E. & A.; Septoria
cucurbitacearum 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.

BORDEAUX INJURY
There has been considerable controversy among growers as
to whether or not home-made Bordeaux mixture does enough
harm to cucumber plants to offset the good derived from con-
trolling 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 extent as
to almost kill them.
Figure 34 shows Bor-
deaux burning on cucumber
leaves. Even tho the mix-
ture was too strong, it
burned the leaves only
where the sun struck them.
This burning was evident
Fig. 34.-Bordeaux injury caused by very soon after the leaves
spray and bright sunshine. dried after spraying. The
burned portions of the leaves at first appeared scalded, later
turning brown and drying hard. Less than 10 percent of the
leaves showed this burning. The older leaves were most seri-
ously affected. The younger leaves and the growing tips did
not show any effect of the burning.
Another type of burning was found on cucumber leaves






Bulletin 177, Diseases of Cucumbers


LEAF SPOTS

There are several unimportant leaf spots occurring on the
host 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 cit-
rullina Cke.; Cladosporium cucumerinum E. & A.; Septoria
cucurbitacearum 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.

BORDEAUX INJURY
There has been considerable controversy among growers as
to whether or not home-made Bordeaux mixture does enough
harm to cucumber plants to offset the good derived from con-
trolling 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 extent as
to almost kill them.
Figure 34 shows Bor-
deaux burning on cucumber
leaves. Even tho the mix-
ture was too strong, it
burned the leaves only
where the sun struck them.
This burning was evident
Fig. 34.-Bordeaux injury caused by very soon after the leaves
spray and bright sunshine. dried after spraying. The
burned portions of the leaves at first appeared scalded, later
turning brown and drying hard. Less than 10 percent of the
leaves showed this burning. The older leaves were most seri-
ously affected. The younger leaves and the growing tips did
not show any effect of the burning.
Another type of burning was found on cucumber leaves






Florida Agricultural Experiment Station


caused by Bordeaux Mixture, but differed markedly from
the type of injury just described. This second type as
shown in Fig. 35 did not develop until two days after the spray
was applied and there was usually only one leaf on each runner
affected. This was the
youngest leaf at the grow-
ing tip of each of the run-
ners at the time the spray-
ing was done. The next
leaf to develop was nor-
mal, showing none of the
markings of the burned
leaf. The Bordeaux mix-
ture caused the leaf to be-
come mottled, almost typi-
cal 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
or less shothole effect. The
Fig. 35.-Bordeaux injury resulting leaf as a whole, however,
from liquid spray. 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 oper-
ation a small shower came up and thorol3y wet the plants. After
the shower the spraying was resumed. It was found later
that all the plants sprayed before the rain showed this Bor-
deaux injury while those sprayed after the rain did not show
this injury.
Another type of Bordeaux injury is shown in Fig. 36 in
which the cucumber leaf shows a light yellow margin sometimes
only along one side or at the tip, other times completely around
the margin of the blade. The band is usually quite wide, sel-
dom 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 ini any way and can readily be
overlooked as causes for reduced yield.






Bulletin 177, Diseases of Cucwmb


The question does arise, however, whether
injury to the blossoms by Bordeaux spray.
probably caused
by too much
pressure by
which the flow-
ers are actually
blown off the
vines. It may be
that the spray it-
self kills the pol-
len before fertil-
ization takes
place or it may
be that the Bor-


deaux mixture
acts as a repel-
lant to the insects
which act as pol-
len carriers and
agents in fertili-
zation.


ers 65

or not there is
Some injury is


Fig. 36.-Copper injury resulting from spray and
dust applications in cool weather.


SEED DISINFECTION

Seed disinfection is recommended to all cucumber growers,
in fact, it should be practiced with every planting. The pro-
cess is easy and takes only a short time and the results are
profitable. In treating the seed all pathogenic organisms ad-
hering 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






Florida Agricultural Experiment Station


stick. This will insure all seed coming in contact with the dis-
infectant 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
thoroly 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 difficult 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 wooden containers such as pails, half barrels or earthen-
ware crocks.
The disinfectant can be purchased from your local druggist
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 de-
sired it is advisable to use pills. One pill dissolved in one pint
of water gives a solution to the strength of 1:1,000. If a gal-
lon of the disinfectant 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
odorless, 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 humans.

FUNGICIDES AND THEIR APPLICATION
It has become an established fact among old cucumber grow-
ers that plant diseases are their worst enemies. If they could
control the diseases that attack the host plant they could pro-
duce a good crop of cucumbers almost every season. The use
of fungicides for the control of diseases has not been generally
practiced thruout the cucumber growing sections of the state
up to the present time, altho 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. Altho not used exclusively






Bulletin 177, Diseases of Cucumbers


by the growers, it is probably used more than all other fungi-
cides 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 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 providing 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 thoroly stirred before any of the
materials are used. Keep stock solutions covered.
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. Always stir the stock solution
before taking any out. Do not stir the stock solutions with
the same stick.
Hydrated lime may be used in place of rock lime. If hy-
drated lime is used it is necessary to use 1/2 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 direc-
tions: 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 at the same time pour the contents
of the two containers into a third container or spray tank, stir-
ring the combined mixture as the two are poured together. Be
sure to place a fine strainer either over the faucets on the bar-
rels 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
platform where the Bordeaux spray can be conveniently made.
The first thing to consider is the water supply. Build the plat-






Florida Agricultural. Experiment Station


form 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 plat-
form upon which the stock solutions are made. The smaller
platform should be elevated 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. Figure 37 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.
Different Amounts of 4-4-50 Bordeaux Mixture: In making
50 gallons of the mixture,
use 4 gallons of stock A, di-
luted to 25 gallons, and 4
I gallons of stock B, diluted
to 25 gallons. Run both of
these into the sprayer at
the same time with the agi-
tator going.
To make 100 gallons of
spray, use 8 gallons of
stock A, diluted to 50 gal-
lons, 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 gal-
Fig. 37.-Bordeaux mixing plant.
(Courtesy U. S. D. A.) lons. Mix as above.
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.
THORONESS IN SPRAYING NECESSARY
Spraying must be done thoroly to be a paying proposition.
The tank pressure should not be below 100 pounds. The plants






Bulletin 177, Diseases of Cucumbers


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 application every week or 10 days.
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 usu-
ally occurs, de-
pending u p o n
the development
of the plants and
also upon the
general absence
or occurrence of
specific diseases.
Power Spray-
ing Machinery:
In order to
thoroly spray cu-
cumbers often
enough, where
large acreages -J
are grown it is
necessary to se- -
lect a power
sprayer that is
fitted to your .
needs. It is im-
portant to select
a machine that ,
maintLins a pres- .
sure of 200
pounds when Fig. 38.-Efficient type of knapsack hand sprayer.
several nozzles are running. A machine with plenty of pres-
sure produces a mist and covers the plants with a fine film.
A spray machine equipped with a four- or five-horsepower
gasoline engine as motive power for operating the pump will
give good service, altho there are certain objections to the use
of an engine, since it is often difficult to keep it in operating






Florida Agricultural Experiment Station


condition. More surface of the plant will be covered when high
pressure is maintained.
Spray machines should be thoroly cleaned immediately after
use. Do this by running several buckets of water thru the
nozzles operating the pump. If this precaution is taken regular-
ly, 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
thru the nozzles.
A good traction-driven spray machine will often give good
service, if it is given the proper attention and kept in good
condition, oiled frequently and cleaned thoroly.
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 fur-
nished by hand labor. An efficient sprayer for small acreages
is a type of knapsack sprayer as shown in Fig. 38. The rod is
easily handled and the leaves can be thoroly 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 mixture.
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 furnished by an engine rather than by traction.
The dusting should always be done when the plants are wet
with dew or rain and when there is little or no wind in order
to obtain the best results. Dust that contains 6-7 percent
metallic copper should average 30-40 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 hydrated copper sulphate)
dust has proven most satisfactory. When using power dusters






Bulletin 177, Diseases of Cucumbers


two nozzles per row are very satisfactory. They should be ar-
ranged so as to direct the dust on each side of each row. Thus
on average dusters carrying eight nozzles four rows can be
dusted providing
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 dust-
ers worked by
hand. These
dusters are very
S" efficient and sev-
-.. eral acres can be
cared for by a
single duster.
The duster
which has given
- .. the best results
out of almost a
i: dozen tried is
.- shown in Fig.
39. This duster
is easy to oper-
ate, throws out a
continuous, pow-
Fig. 39.-Type of hand duster giving good results. erful stream of
dust which pene-
trates the densest foliage. The amount of dust applied can be
definitely regulated.




University of Florida Home Page
© 2004 - 2010 University of Florida George A. Smathers Libraries.
All rights reserved.

Acceptable Use, Copyright, and Disclaimer Statement
Last updated October 10, 2010 - - mvs