Group Title: Bulletin - University of Florida. Agricultural Experiment Station ; 457
Title: The sclerotiniose disease of vegetable crops in Florida
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00026424/00001
 Material Information
Title: The sclerotiniose disease of vegetable crops in Florida
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 20 p. : ill. ; 23 cm.
Language: English
Creator: Moore, W. D ( William Dewey ), 1897-
Conover, Robert A
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1949
 Subjects
Subject: Vegetables -- Diseases and pests -- Florida   ( lcsh )
Fungal diseases of plants -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Bibliography: p. 20.
Statement of Responsibility: W.D. Moore, Robert A. Conover and David L. Stoddard.
General Note: Cover title.
General Note: "In cooperation with U.S. Department of Agriculture"--T.p.
 Record Information
Bibliographic ID: UF00026424
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000925538
oclc - 18254212
notis - AEN6191

Full Text





HISTORIC NOTE


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
(EDIS)

site maintained by the Florida
Cooperative Extension Service.






Copyright 2005, Board of Trustees, University
of Florida






Bulletin 57 March, 1949

UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATIONS
HAROLD MOWRY, Director
GAINESVILLE, FLORIDA
(In Cooperation with U. S. Department of Agriculture)




The Sclerotiniose Disease of Vegetable

Crops in Florida

W. D. MOORE, ROBERT A. CONOVER and DAVID L. STODDARD


Fig. 1.-Sclerotiniose disease on bean pods.


Single copies free to Florida residents upon request to
AGRICULTURAL EXPERIMENT STATION
GAINESVILLE, FLORIDA







BOARD OF CONTROL

J. Thos. Gurney. Chairman, Orlando
N. B. Jordan, Quincy
Thos. W. Bryant, Lakeland
J. Henson Markham, Jacksonville
Hollis Rinehart, Miami
W. F. Powers, Secretary, Tallahassee


EXECUTIVE STAFF
J. Hillis Miller, Ph.D., President of the
University3
H. Harold Hume, D.Sc., Provost for Agr.s
Harold Mowry, M.S.A., Director
L. O. Gratz, Ph.D., Asst. Dir., Research
W. M. Fifield, M.S., Asst. Dir., Admin.
J. Francis Cooper, M.S.A., Editur8
Clyde Beale, A.B.J., Associate Editors
Ida Keeling Cresap, Librarian
Ruby Newhall, Administrative Managers
Geo. F. Baughman, M.A., Business Managers
Claranelle Alderman, Accountant3


MAIN STATION, GAINESVILLE

AGRICULTURAL ENGINEERING
Frazier Rogers, M.S.A., Agr. Engineers
J. M. Johnson, B.S.A.E., Asso. Agr. Engineers
J. M. Myers, B.S., Asso. Agr. Engineer
R. E. Choate, B.S.A.E., Asst. Agr. Engineers
A. M. Pettis, B.S.A.E., Asst. Agr. Engineers

AGRONOMY
Fred H. Hull, Ph.D., Agronomist1
G. E. Ritchey, M.S., Agronomist2
G. B. Killinger, Ph.D., Agronomist"
H. C. Harris, Ph.D., Agronomist3
R. W. Bledsoe, Ph.D., Agronomist
S. C. Litzenberger, Ph.D., Associate
W. A. Carver, Ph.D., Associate
Fred A. Clark, B.S., Assistant
M. N. Gist, Collaborator2

ANIMAL INDUSTRY
A. L. Shealy, D.V.M., An. Industrialist' S
R. B. Becker, Ph.D., Dairy Husbandman3
E. L. Fouts, Ph.D., Dairy Technologists
D. A. Sanders, D.V.M., Veterinarian
M. W. Emmel, D.V.M. Veterinarians
L. E. Swanson, D.V.M., Parasitologist
N. R. Mehrhof, M.Agr., Poultry Husb.3
G. K. Davis, Ph.D., Animal Nutritionist3
R. S. Glasscock, Ph.D., An. Husbandmans
P. T. Dix Arnold, M.S.A., Asst. Dairy Husb.S
L. E. Mull, M.S., Asst. in Dairy Tech.
Katherine Boney, B.S., Asst. Chem.
J. C. Driggers, B.S.A., Asst. Poultry Husb.8
Glenn Van Ness, D.V.M., Asso. Poultry
Pathologist
S. John Folks, B.S.A., Asst. An. Husb.3
W. A. Krienke, M.S., Asso. in Dairy Mfs.8
S. P. Marshall, Ph.D., Asso. Dairy Husb.3
C. F. Simpson, D.V.M., Asso. Veterinarian
C. F. Winchester, Ph.D., Asso. Biochemists


ECONOMICS, AGRICULTURAL
C. V. Noble, Ph.D., Agri. Economist s
Zach Savage, M.S.A., Associate
A. H. Spurlock, M.S.A., Associate
D. E. Alleger, M.S., Associate
D. L. Brooke, M.S.A., Associate
R. E. L. Greene, Ph.D., Agri. Economist
H. W. Little, M.S., Assistant
Tallmadge Bergen, B.S., Asst.
Orlando, Florida (Cooperative USDA)
G. Norman Rose, B.S., Asso. Agr. Economist
J. C. Townsend, Jr., B.S.A., Agr. Statisticians
J. B. Owens, B.S.A., Agr. Statisticians
J. F. Steffens, Jr., B.S.A., Agr. Statistician2

ECONOMICS, HOME
Ouida D. Abbott, Ph.D., Home Econ.'
R. B. French, Ph.D., Biochemist

ENTOMOLOGY
A. N. Tissot, Ph.D., Entomologist'
L. C. Kuitert, Ph.D., Assistant
H. E. Bratley, M.S.A., Assistant

HORTICULTURE
G. H. Blackmon, M.S.A., Horticulturist'
F. S. Jamison, Ph.D., Horticulturists
H. M. Reed, B.S., Chem., Veg. Processing
Byron E. Janes, Ph.D., Asso. Hort.
R. A. D'ennison, Ph.D., Asso. Hort.
R. K. Showalter, M.S., Asso. Hort.
Albert P. Lorz, Ph.D., Asso. Hort.
R. H. Sharpe, M.S., Asso. Hort.
R. J. Wilmot, M.S.A., Asst. Hort.
R. D. Dickey, M.S.A., Asst. Hort.
Victor F. Nettles, M.S.A., Aast. Hort.'
F. S. Lagasse, Ph.D., Asso. Hort.2
L. H. Halsey, B.S.A., Asst. Hort.
Forrest E. Myers, B.S.A., Asst. Hort.

PLANT PATHOLOGY
W. B. Tisdale, Ph.D., Plant Pathologist'
Phares Decker, Ph.D., Asso. Plant Path.
Erdman West, M.S., Mycologist and Botanist
Howard N. Miller, Ph.D., Asso. Plant Path.
Lillian E. Arnold, M.S.. Asst. Botanist

SOILS
F. B. Smith, Ph.D., Microbiologist'
Gaylord M. Volk, Ph.D., Chemist
J. R. Henderson, M.S.A., Soil Technologists
J. R. Neller, Ph.D., Soils Chemist
Nathan Gammon, Jr., Ph.D., Soils Chemist
C. E. Bell, Ph.D., Associate Chemist
R. A. Carrigan, Ph.D., Asso. Biochemists
H. W. Winsor, B.S.A., Assistant Chemist
Geo. D. Thornton, Ph.D., Asso. Microbiologists
R. E. Caldwell, M.S.A., Asst. Chemists
J. B. Cromartie, B.S.A., Soil Surveyor
Ralph G L-i-.hi,. E.S., Asso. Soil Surveyor
V. W. C I.. :'i, U -. Asst. Soil Surveyor
R. B. Forbes, M.S., Asst. -..i. il:,ir.'iL
W. L. Pritchett, M.S., Assr Cr.,-ril
Jean Beem, B.S.A., Asst. Soil Surveyor

1Head of Department.
2In cooperation with U. S.
n Cooperative, other divisions, U. of F.
SOn leave.







BRANCH STATIONS

NORTH FLORIDA STATION, QUINCY
J. D. Warner, M.S., Vice-Director in Charge
R. R. Kincaid, Ph.D., Plant Pathologist
W. H. Chapman, M.S., Asso. Agron.
L. G. Thompson, Ph.D., Soils Chemist
Frank S. Baker, Jr., B.S., Asst. An. Husb.4

Mobile Unit, Monticello
R. W. Wallace, B.S., Associate Agronomist

Mobile Unit, Marianna
R. W. Lipscomb, M.S., Associate Agronomist

Mobile Unit, Wewahitchka
J. B. White, B.S.A., Associate Agronomist

Mobile Unit, DeFuniak Springs
R. L. Smith, M.S., Associate Agronomist

CITRUS STATION, LAKE ALFRED
A. F. Camp, Ph.D., Vice-Director in Charge
W. L. Thompson, B.S., Entomologist
J. T. Griffiths, Ph.D., Asso. Entomologist
R. F. Suit, Ph.D., Plant Pathologist
E. P. Ducharme, M.S., Plant Pathologist4
R. K. Voorhees, Ph.D., Asso. Horticulturist
C. R. Stearns, Jr., B.S.A., Asso. Chemist
T. W. Young, Ph.D., Asso. Horticulturist
J. W. Sites, M.S.A., Horticulturist
H. O. Sterling, B.S., Asst. Horticulturist
J. A. Granger, B.S.A., Asst. Horticulturist
H. J. Reitz, M.S., Asso. Horticulturist
Francine Fisher, M.S., Asst. Plant Path.
I. W. Wander, Ph.D., Soils Chemist
A. E. Willson, B.S.A., Asso. Biochemist
J. W. Kesterson, M.S., Asso. Chemist
R. N. Hendrickson, B.S., Asst. Chemist
Joe P. Barnett, B.S.A., Asst. Horticulturist
J. C. Bowers, B.S., Asst. Chemist
D. S. Prosser, Jr., B.S., Asst. Horticulturist
R. W. Olsen, B.S., Biochemist
F. W. Wenzel, Jr., Ph.D., Supervisory Chem.
Alvin H. Rouse, M.S., Asso. Chemist
L. W. Fayville, Ph.D., Asst. Chemist

EVERGLADES STATION, BELLE GLADE
R. V. Allison, Ph.D., Vice-Director in Charge
F. D. Stevens, B.S., Sugarcane Agronomist
Thomas Bregger, Ph.D., Sugarcane
Physiologist
J. W. Randolph, M.S., Agricultural Engineer
W. T. Forsee, Jr., Ph.D., Chemist
R. W. Kidder, M.S., Asso. Animal Husb.
T. C. Erwin, Assistant Chemist
Roy A. Bair, Ph.D., Agronomist
C. C. Scale, Asso. Agronomist
N. C. Hayslip, B.S.A., Asso. Entomologist
E. H. Wolf, Ph.D., Asst. Horticulturist
W. H. Thames, M.S., Asst. Entomologist
J. C. Hoffman, M.S.. Asso. Horticulturist
C. B. Savage, M.S.A., Asst. Horticulturist
D. L. Stoddard, Ph.D., Asso. Plant Path.


SUB-TROPICAL STATION, HOMESTEAD

Geo. D. Ruehle, Ph.D., Vice-Dir. in Charge
D. 0. Wolfenbarger, Ph.D., Entomologist
Francis B. Lincoln, Ph.D., Horticulturist
Robt. A. Conover, Ph.D., Asso. Plant Path.
R. W. Harkness, Ph.D., Asst. Chemist
Milton Cobin, B.S., Asso. Horticulturist


W. CENT. FLA. STATION, BROOKSVILLE
William Jackson, B.S.A., Animal Husband-
man in Charge2


RANGE CATTLE STATION, ONA
W. G. Kirk, Ph.D., Vice-Director in Charge
E. M. Hodges, Ph.D., Associate Agronomist
D. W. Jones, B.S., Asst. Soil Technologist
H. J. Fulford, B.S.A. Asst. Animal Hush.


CENTRAL FLORIDA STATION, SANFORD
R. W. Ruprecht, Ph.D., Vice-Dir. in Charge
J. W. Wilson, Sc.D., Entomologist
Ben F. Whitner, Jr., B.S.A., Asst. Hort.


WEST FLORIDA STATION, MILTON
H. W. Lundy, B.S.A., Associate Agronomist



FIELD STATIONS

Leesburg
G. K. Parris, Ph.D., Plant Path. in Charge

Plant City
A. N. Brooks, Ph.D., Plant Pathologist

Hastings
A. H. Eddins, Ph.D., Plant Path. in Charge
E. N. McCubbin, Ph.D., Horticulturist

Monticello
A. M. Phillips, B.S., Asso. Entomologist2
John R. Large, M.S., Asso. Plant Path.

Bradenton
J. R. Beckenbach, Ph.D., Hort. in Charge
E. G. Kelsheimer, Ph.D., Entomologist
David G. Kelbert, Asso. Horticulturist
E. L. Spencer, Ph.D., Soils Chemist
Robert 0. Magie, Ph.D., Gladioli Hort.
J. M. Walter, Ph.D., Plant Pathologist
Donald S. Burgis, M.S.A., Asst. Hort.

Lakeland
Warren O. Johnson, B.S., Meteorologist2

1 Head of Department.
2 In cooperation with U. S.
3 Cooperative, other divisions, U. of F.
4 On leave.











Contents
Page

INTRODUCTION ............--.................-------- 5

HISTORY OF DISEASE IN FLORIDA ....--...-------.------- .......-------- 5

THE SCLEROTINIOSE ORGANISM ....-.....-....-- ....--- .---.--- -------- 6

WEATHER RELATIONSHIPS .......................- ------ ------------- 7

CROPS AFFECTED .....-..........------- .-----------.--- ---.- ------ 7

Snap Beans .........-----...... ...----------------.-. 7

Tomatoes ...----------------..............------------- 9

Potatoes .......................----------------............. 10

Celery ........-....... .. ..... ... ............. ---- --------- -- 12

Lettuce .---. ----..... .... -..- ......-..--------------. 12

*Cabbage ----............. .......................--- 14

Miscellaneous Crops ...------------...---.... --------.. -------- 16

WILD HOSTS .-..---..----..... ----.----.-------- ...........--- --- 16

CONTROL ....... -- --........... ----.. --. -----...........- ---- ;17

Soil Treatments .......------... ---.-------..------ ---- 17

Flooding .............................. ---- ---------- 18

Control of Wild Hosts .................. --- ........... ---- ------ 18

Removal of Infected Plants --.............-.... -------- -..-- 18

Sprays and Dusts .........-...- ----------... .------..... 19

Row and Drill Spacing .--..-----...-............. ----. ---- 19

Crop Rotation .........................--- ------- ----. 19

Pre-Cooling Before Shipping ..............---... -------------- --- 19

LITERATURE CITED -------- ---------------------- 20








The Sclerotiniose Disease of Vegetable
Crops in Florida

W. D. MOORE,1 ROBERT A. CONOVER2 and DAVID L. STODDARD3

Introduction
Vegetable growing has for many years been one of the most
important phases of agriculture in Florida, more than 200,000
acres (6) being planted annually to such crops as snap beans,
lima beans, cabbage, carrots, celery, eggplant, lettuce, peppers,
potatoes and tomatoes. This acreage is distributed over a wide
area extending from Jacksonville to the Keys and encompasses
a diversity of soil types and weather conditions not duplicated
in any other part of the country. Plantings are started in some
areas in August and continued in others throughout the fall
and winter months until late spring. Under this system of
culture, conditions are afforded during practically all seasons
of the year for the outbreak of diseases of many kinds. One
of the most serious of these, which usually occurs during the
winter months, is sclerotiniose (Sclerotinia sclerotiorum (Lib.
D.By.), a fungous disease which can affect practically all vege-
table crops and one that has in recent years become serious on
beans, potatoes, tomatoes, celery and lettuce (1). This disease
is known by such common names as pink rot on celery, drop on
lettuce, sclerotiniose, white mold, and watery soft rot on beans
and tomatoes; however, throughout this bulletin, it will be
referred to on all crops by the general name of sclerotiniose.

History of the Disease in Florida
SSclerotiniose has been known in Florida for many years,
having been reported on celery as early as 1909 (7). Just why
it did not spread to other crops or cause more than incidental
losses in the beginning is not clearly known, although the kinds
of crops planted and weather conditions during the growing
seasons probably influenced its development to some degree.
Other than intermittent appearances on celery, no serious out-
breaks occurred until 1933, when it appeared on potatoes at
1 Senior Pathologist, Bureau of Plant Industry, Soils and Agricultural
Engineering, U. S. Department of Agriculture.
2 Associate Plant Pathologist, Sub-Tropical Experiment Station, Home-
stead, Florida.
SAssociate Plant Pathologist, Everglades Experiment Station, Belle
Glade, Florida.





Florida Agricultural Experiment Station


Hastings (5), causing considerable losses in small acreages.
The disease has appeared in that area 'in appreciable degrees
during several of the succeeding years on both potatoes and
cabbage and has also come to be of importance to the celery
industry around Sarasota. Between the years 1935 and 1940
its occurrence increased from one field near Homestead to
practically all of the vegetable growing area south of Miami,
infecting such major crops as beans, potatoes, and tomatoes.
Since 1940 it has assumed considerable importance also on
beans, peppers and other vegetable crops in the coastal area
between Miami and West Palm Beach. In 1945 sclerotiniose
was found to be causing considerable damage to lupine near
Quincy (4) and it later occurred in other farming areas in
northern Florida. During the same season the disease was
found in one celery field near Belle Glade but was not found
elsewhere in the district. At first it caused no appreciable
damage; however, during the next three seasons it was found
to have moved into practically every farm examined in the
Lake Okeechobee area, causing in some fields very heavy losses
to both celery and lettuce. From these citations it is apparent
that sclerotiniose has increased in severity in a number of
areas in the state during the past 15 years and that it is at
present a disease of considerable importance to much of the
vegetable growing industry.

The Sclerotiniose Organism
Sclerotiniose is caused by a fungus which lives from one
year to the next in the form of hard, black, irregularly shaped
bodies called sclerotia. These bodies vary from the size of a
grain of wheat to an inch or more in diameter, depending upon
the species of plant on which they are formed and upon weather
and field conditions during the period of fungus growth.
Under cool, moist conditions white fungous threads may grow
out through the soil from these bodies and infect directly plant
parts in contact with the soil. More often, however, the
sclerotia produce very small mushroom-like bodies called
apothecia in which develop large numbers of spores. These
spores are forcibly ejected into the air and are blown over
wide areas. Under conditions of frequent rains, fogs, heavy
dews and fairly cool temperatures, they germinate rapidly,
usually causing initial infections within a period of one to
two days.






Sclerotiniose Disease of Vegetable Crops in Florida


Weather Relationships
The development and spread of sclerotiniose is affected to
an important extent by weather conditions. When mean daily
temperatures fall to near 700 F. or below and when there is
sufficient rain or irrigation to hold soil moisture near the
saturation point, apothecia grow out from the black sclerotia
within three to four weeks. From these, spores in large num-
bers are released over a period of several days, producing a
heavy inoculum capable of immediate plant infection. If there
are frequent rains, fogs or heavy dews, infection may take place
at once, otherwise the spores lie in an inactive state until the
necessary moisture conditions develop. Tests have indicated
that spores germinate after periods of five to six weeks, which
emphasizes the danger of weather conditions that change from
dry to wet.
Crops Affected
The appearance of sclerotiniose varies somewhat from one
crop to another, due primarily to the manner in which initial
infections begin. However, once the general characteristics
are known, it is easily recognized on any species of plant. The
soft watery lesions with the accompanying white moldy growth
and black sclerotial bodies are quite distinct and are seldom
confused with other types of fungous infection that are likely
to occur under the conditions described. Based on Florida
conditions, a brief general description of the disease, together
with some special characteristics, is given below for several
of the major vegetable crops concerned.
Snap Beans.-Infections by Sclerotinia sp. may occur at any
time after bean plants emerge in the field. Young plants,
from one to six inches high, may be attacked directly by the
white thread-like growth which originates from sclerotia in
the soil, resulting in a damping-off similar to that caused by
Pythium and Rhizoctonia. In general, however, infections are
more abundant when the plants are older, usually about bloom-
ing time or later, when there is sufficient foliage to hold high
moisture around the stems and branches of the plants. Most
infections occurring at this time are due to spores which are
liberated by the apothecia in the soil and are subsequently
carried to the plants by air currents. Under conditions of high
moisture, the spores germinate .and the fungus invades the
plant tissues directly or through abrasions, broken stems, or






Florida Agricultural Experiment Station


old blossom parts. Infections appear first as irregular, soft,
watery spots which enlarge very rapidly. Within a day or two
heavy masses of white mold grow out from the diseased areas
and in these are formed numerous black sclerotia. Quite often,
infected stems, leaves, and pods fall or are blown against healthy
plants, causing additional spread of the disease by direct con-
tact.
Field infections of sclerotiniose on beans range from occa-
sional single plants to 100% of the stand, depending upon
amount of inoculum present, conditions of culture, and type
of prevailing weather. Heaviest infections occur when tempera-
tures are between 40 and 70' F. and when rains, fogs and heavy
dews are frequent. Sudden changes to warm dry weather check
the progress of the disease rather promptly and then cause it
to decrease gradually. In general, infections are scattered ir-
regularly over the fields, failing in many instances to reveal at

Fig. 2.-Bean pods in shipping crate affected with Sclerotiniose.
Pu U ~I






Sclerotiniose Disease of Vegetable Crops in Florida


casual inspection the potential economic loss. This arises from
the fact that infected pods from scattered plants are easily over-
looked and often get into shipping containers. One or two
infected pods in a container may cause the entire contents of
a basket to become infected within two or three days (Fig. 2).
It is not unusual for entire shipments to start to market in
apparently good condition, only to arrive so badly affected as
to be worthless. This type of latent development constitutes
one of the most serious problems of sclerotiniose on beans.
Tomatoes.-Unlike beans, tomato plants generally are not
attacked by sclerotiniose when they are small, probably due
in part to wide spacing in the fields which allows ample air
circulation and prevents the retaining of excessive moisture
around the branches and stems. When the plants reach a
height of 2 to 21/2 feet and the foliage becomes dense, conditions
of excessive moisture are created under the heavy growth and

Fig. 3.-Tomato stems (left) affected with Sclerotiniose. Tomato fruits
(right) showing sclerotia on surface.





Florida Agricultural Experiment Station


infections occur on or near the main stems. These may arise
either from mycelium in the soil or from air-borne spores, and
appear first as small irregular watery spots which enlarge very
rapidly in all directions. Any part of the plant above ground
may become infected-fruits, leaves, stems, and branches-but
all invariably show the typical mats of white mold, which grow
out from the diseased lesions (Fig. 3). If moisture under the
plant foliage remains high, the white moldy growth spreads
rapidly, attacking stems, leaves and branches, often killing the
plants. If tomato fruits are set when infection begins they
may become involved also. The fungus usually penetrates the
entire fruit, causing it to become soft and watery. Within a
few days black sclerotia begin to form in the fungus mass, some
becoming large enough to cover half of the fruit. These sclerotia
ultimately dry out and fall to the ground where they remain as
potential disease inoculum the following season.
In contrast to the heavy losses sustained by beans during
shipment to market, tomatoes in transit suffer only minor
damage from sclerotiniose. This is due largely to the fact
that infected tomato fruits are easily detected in the field and
on the grading belts and are usually discarded before reaching
the shipping crates. Furthermore, each fruit is wrapped sep-
arately for shipping and is thus protected from spread of the
disease in the few instances where infected fruits are packed.
Potatoes.-As in the case of tomatoes, sclerotiniose does not
ordinarily attack potato plants in their early stages of growth.
This is due not to disease resistance but to the fact that foliage
is sparse and moisture does not accumulate to an excessive
degree around the young plants. However, when growth is
sufficiently advanced for the branches to lap from one row to
another, moisture accumulates and is held under the foliage,
usually making it possible for the disease to develop at any
time thereafter if temperatures are not too high. Although
a limited amount of infection comes directly from the soil, the
source of the major portion appears to be from air-borne spores.
Under proper weather conditions these spores germinate quickly
and produce small watery spots on leaves, petioles and stems,
which may be easily confused at first with potato late blight.
Initial infections may often start in old leaf spots that were
caused by early blight, late blight or spray burn. Within a day
or two after invasion, heavy growths of white mycelium (Fig.
4) appear on the infected areas and in these are formed numer-






Sclerotiniose Disease of Vegetable Crops in Florida


Fig. 4.-Sclerotiniose on potato plant, showing fungus growth along the
petiole and the midrib of the leaflet.

ous small black sclerotia. The disease in potatoes is usually
sporadic, appearing on individual plants or small groups of
plants, seldom causing an over-all "blighting" of foliage such
as that caused by the early and late blights.
The most serious damage by the sclerotiniose disease on pota-
toes follows the attacks on the main stems. From infected
leaves and branches and from organic matter on the surface
of the soil, the fungus invades the pithy part of the plant stems,
causing them to turn yellow and die prematurely. Following
death of the plants the main stems remain in an upright posi-
tion and turn chalky white, and this distinguishes them from
the healthy plants. When these white stems are broken open





Florida Agricultural Experiment Station


numerous black sclerotia are found in the pith region. Potato
tubers are not infected by the fungus but yields and grades
are often reduced materially by premature death of the plants.
Celery.-Due to the fact that celery requires moderately high
soil moisture for best growth and that plants are set close
together in fairly narrow rows, cultural conditions are usually
more conducive to sclerotiniose infection on this crop than any
other grown in Florida. For several weeks prior to harvest
overlapping plant growth creates and holds a moisture condi-
tion around the lower stems that is optimum for disease develop-
ment. If the sclerotiniose organism is present in the fields and
temperatures are moderately low, plant infection may occur at
any time.
During the growing season celery plants are subjected to
numerous small injuries by plows, spray machinery and blight
diseases which afford points of entrance for the sclerotiniose
organism. Infections may arise from the soil or from air-borne
spores and may develop at any point on the plant (Fig. 5), but
they are usually most conspicuous on the stalks near the ground
line.' Soft watery spots appear first and spread rapidly in all
directions. In these spots are found masses of white mold
which later produce numerous black sclerotia. The plant tissues
in and around the infected areas turn to a pale pink color, giving
rise to the common name of pink rot on celery. Sclerotiniose
frequently develops in celery seedbeds during the winter. Be-
cause it is impossible to detect and throw out all infected seed-
lings during the transplanting operation, growers should not
use plants from a diseased bed. Such a practice will introduce
the disease into the field and may result in serious losses.
Much as in the case.of beans, the early stage of sclerotiniose
infection on celery is very difficult to detect and grade out
during the process of harvesting and packing. Small infected
spots often go unnoticed and, if packed in shipping crates, may
cause heavy losses during transit. Even if diseased stalks reach
the market they are seldom salable, due to the slimy fungous
growth on them and a slightly bitter taste to the edible parts.
Lettuce.-Sclerotiniose is a very destructive disease on let-
tuce, causing losses that range from a trace in some fields to
100% of the plants in others. As with other vegetable crops,
cool temperature and excessive moisture favor its development.
Due to the low, spreading nature of the lettuce plant, however,
high moisture is maintained beneath the foliage for long periods






Sclerotiniose Disease of Vegetable Crops in Florida 13



















4 1


Fig. 5.-Sclerotiniose on celery. Note decay on stems extending from
base of plant to foliage.






Florida Agricultural Experiment Station


of time and results in heavy infections during some seasons
when it would be light or absent on taller growing plants such
as beans and potatoes.
Infection of lettuce may arise from mycelium in the soil or
from air-borne spores. Initial infections appear as small watery
lesions on the main stems and leaf bases near the ground which
spread downward, causing a damping-off and, more often, up-
ward, involving the bases of all leaves. As the leaf petioles are
invaded, the leaves wilt and drop. This process of fungus in-
vasion continues rapidly, leaf by leaf, until the entire plant is
involved, causing it to appear collapsed, with all leaves wilted
and dropped towards the ground (Fig. 6). When such plants



















Fig. 6.-Lettuce plant killed by Sclerotiniose fungus.
are removed from the soil heavy masses of white fungus growth
are usually found around the lower leaves and main stems. As
these diseased parts dry out many small black sclerotia are
found in the fungus mat, and these eventually fall to the ground,
where they remain until the following season and act as potential
inoculum for succeeding crops.
Cabbage.-Sclerotiniose attacks cabbage in much the same
way as it does lettuce. Infection usually starts near the ground
line on the lower leaves and main stems and progresses upward
and downward from that point. The disease may originate
from the soil or from air-borne spores, and is recognized in its





Sclerotiniose Disease of Vegetable Crops in Florida 15

early stages by the typical irregular soft watery spots. Some
plants may be killed outright while others are stunted, yellowed
and partially defoliated. Infections usually occur after the
heads begin to form and may continue until after harvest. In
many cases the fungus spreads over the top of the cabbage


'42


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/i M

' ,~n.^


Fig. 7.-Sclerotiniose on cabbage plant. Note white fungus growth on
head and along main stem.


s~:ci~3:
"
"`~fr~;53





Florida Agricultural Experiment Station


heads, causing the outer leaves to become slimy and partially
decayed (Fig. 7). The typical white moldy growth develops
on all of the diseased tissues, and as soon as it begins to dry
out numerous black sclerotia appear. As in beans, celery and
lettuce, newly infected plant parts may be overlooked during
harvesting and packing and when this happens considerable
losses are sustained in transit due to a rapid soft rot.
Miscellaneous Crops.-In addition to the above major crops,
sclerotiniose may attack practically any of the other vegetable
crops grown in the state, but on these seldom causes more than
minor damage. Peppers and eggplants along the Lower East
Coast are affected to a limited extent in some seasons but in-
jury is confined largely to plant stems and branches. An occa-
sional plant is killed by a girdling of the main stem but most
of the injury is to individual branches. The fruits of these
two crops are seldom attacked by this disease.
Squash and cucumbers are two other crops that become in-
fected at times but damage in Florida is usually light. Both
stems and fruits are attacked by the fungus but usually the
disease is confined to scattered plants. In the Pacific North-
west damage to winter squash is sometimes very heavy.
Turnips and carrots are heavily attacked by sclerotiniose at
times but losses have not been generally serious. Infections
usually occur just before harvest time and are always on the
leaf petioles and crowns near the ground line. Large, watery
lesions appear first, followed later by masses of white mold.
Many of the leaf petioles are girdled, after which they wilt
and fall over. When infected plant parts are packed during
shipping, considerable damage may occur as soft rots while
in transit.

Wild Hosts
The fungus causing sclerotiniose is known to attack more
than 100 species of cultivated and non-cultivated plants (8).
A complete record of its host range in Florida has not been
attempted, but it has been observed on numerous wild hosts as
well as on the cultivated crops mentioned above. Of these rag-
weed is probably the most notable. This weed grows in pro-
fusion throughout the state and is particularly susceptible to
the sclerotiniose organism. In many instances it has been found
to harbor and increase the disease in and around cultivated fields
many weeks after harvest had been completed. It is also prob-





Sclerotiniose Disease of Vegetable Crops in Florida 17

able that the ragweed plant perpetuates the sclerotiniose or-
ganism in inaccessible areas, thus making any sort of control
much more difficult. In addition to ragweed, milkweed, pig-
weed, sow thistle, fireweed, and water cress are known to be
susceptible to the disease in this state. With this group of
host plants widely scattered over the farming areas, it is possible
for sclerotiniose to develop and persist to some extent in many
areas, whether they are under cultivation or not.

Control
Since crop, soil and weather conditions in Florida vary widely
from one section to another and since the causal fungus lives
on many kinds of plants and persists for long periods in the
soil, the problem of control of sclerotiniose is very difficult
and complex. Measures helpful in one section may be useless
in another or may not be feasible on account of local factors.
No thoroughly effective control is yet known. No over-all
recommendation can be made at present, but a number of steps
can be suggested that may be used as a whole or in part, as
conditions justify, to help hold the disease in check.
Soil Treatments.--Treating soils with cyanamid has shown
some promise under certain conditions. Brooks (2, 3) has shown
that applications of cyanamid at rates of 800 to 2,000 pounds
per acre gave good control of sclerotiniose on celery in the muck
soils of the West Coast of Florida. Preliminary tests indicate
that such applications do not give good control on beans in the
sandy soils along the Lower East Coast. On the other hand,
rates of cyanamid as low as 500 to 750 pounds per acre have
materially reduced infection on potatoes in the marl soils around
Homestead.
In using cyanamid it should be remembered that it is not
a fungicide and that its action is either to aid in rotting the
sclerotia or to prevent the formation of apothecia. Sinde this
is brought about by toxic action on the sclerotia in the soil,
complete coverage and uniformity of application are very im-
portant. This can be done best by using a distributor equipped
with a scatterboard which aids in spreading the chemical evenly
over the soil. The soil should be plowed and harrowed smoothly,
the cyanamid applied on the surface, then harrowed in to a
depth of two to three inches. On sandy soils applications
should be made from four to six weeks before planting in order
to avoid injury to germination from the toxic action of the





Florida Agricultural Experiment Station


cyanamid. There is apparently no toxic action from this mate-
rial on marl soils and plantings may be made immediately follow-
ing cyanamid applications. Under no conditions, however,
should cyanamid be applied to any soil after cultivated crops
are planted. To do so may result in serious injury to the
growing plants.
Flooding.-Keeping cultivated fields flooded during the sum-
mer for periods of four to five weeks where feasible has proven
to be an economical and efficient method of killing sclerotia.
This practice has bedn followed in the Sarasota area for a
number of years. It is important that fields be harrowed or
cut over prior to flooding in order that all weeds and high
masses of soil be covered with water. Laboratory tests have
indicated that interval flooding of three days on and three days
off gave approximately as good results as continuous flooding
but the over-all time of four to five weeks was necessary in all
cases, indicating that elapsed time is the important factor.
This flooding treatment causes the sclerotia to soften and rot,
thus ridding the fields of the disease organism.
Control of Wild Hosts.-Although the above treatments will
reduce the parasite in cultivated fields to a marked degree,
they give no protection against spores produced by apothecia
growing on ditch and canal banks, roadsides and levees. Since
numerous wild hosts may harbor the organism, thorough killing
of all susceptible weeds and shrubs adjacent to cultivated fields
is necessary. This can be accomplished best by the use of chemi-
cal weed killers applied as sprays. Applications should be made
immediately before crops are planted to keep down active growth
during the farming season and, if necessary, again after harvest
in order to kill all weeds that escaped the first application. With-
out adequate weed control, soil treatments and flooding will
likely be only partially successful. And for weed control to be
fully successful it should be conducted on a community-wide
basis.
Removal of Infected Plants.-The removal of infected plant
material from cultivated fields will help in preventing an ac-
cumulation of inoculum that may result in added infections
during subsequent seasons. Such plant material should be re-
moved and destroyed before it dries out, otherwise the sclerotia
will shatter and fall to the ground. While this type of sanitary
work will prevent an appreciable increase in the amount of
disease in a field, it should not be depended upon as a means of






Sclerotiniose Disease of Vegetable Crops in Florida


adequate control, since there is usually sufficient inoculum left
in all infected areas to cause an outbreak on crops planted the
following season.
Sprays and Dusts.-No chemical sprays or dusts have been
found thus far that are of material benefit in the control of
sclerotiniose under Florida conditions. During the past several
years many of the chemicals commonly used in vegetable dis-
ease control have been tested and all proved to be inadequate.
In view of this situation, no recommendations can be made at
this time for the use of either sprays or dusts in the control of
this disease.
Row and Drill Spacing.-In some instances such crops as
beans, potatoes and celery are planted rather thickly in the
drill and in very narrow rows, causing an overlapping of the
foliage and an accumulation of excess moisture around the
plants. While wider spacing of both plants and rows will not
necessarily control sclerotiniose, it will allow greater circula-
tion of air around the plants, bring about a reduction in the
amount of humidity, and quite often result in considerably
less disease. Any measure of this sort that will lower the
amount of moisture at the surface of the soil and around grow-
ing plants may help to reduce the amount and severity of
sclerotiniose.
Crop Rotation.-Where possible, crop rotation should be prac-
ticed as a means of reducing the amount of disease inoculum in
cultivated fields. The length of time that the sclerotiniose
organism can survive in Florida soils under average weather
conditions is not known but the planting of a highly resistant
crop such as corn for one or two seasons will aid materially in
preventing an accumulation of sclerotia in the fields. Highly
susceptible crops, such as beans, celery, tomatoes, lettuce and
potatoes, should not be planted on soils known to- be infested
unless first treated either with cyanamid or by flooding or after
having been planted to non-susceptible crops for two or more
years.
Pre-cooling Before Shipping.-While pre-cooling can in no
way be considered as a step in sclerotiniose control, it is a
practice that may be used to advantage in shipping lettuce,
celery, cabbage, beans and other susceptible crops that will stand
low temperatures. By the use of pre-cooling fans in refrigerator
cars, commodity temperatures may be lowered to 40 450 F.
within,six to eight hours. If this is done before the cars are






Florida Agricultural Experiment Station


moved from the loading yards, further development and spread
of sclerotiniose can be held in check for several days-usually
until the cars reach their destination. This reduces transit
losses to a minimum and, quite often, insures the sale of ship-
ments that might otherwise be lost. It should be borne in mind,
however, that low temperatures do not kill the sclerotiniose
organism and that it will become active again as soon as the
infected commodity is brought into temperatures above 50 F.
For this reason all commodities showing even a trace of infec-
tion should be carried through trade channels as rapidly as
possible in order that disease spread may be held to a minimum.

Literature Cited
1. ANDERSON, P. J., and others. Check list of diseases of economic plants
in the United States. U.S.D.A. Bul. 1366. 1926.
2. BROOKS, A. N. Control of celery Pink Rot. Fla. Agr. Exp. Sta. Press
Bul. 567. 1942.
3. BROOKS, A. N., W. D. MOORE and H. I. BORDERS. Sclerotiniose of vege-
tables and tentative suggestions for its control. Fla. Agr. Exp.
Sta. Press Bul. 613. 1945.
4. DECKER, PHARES. A Sclerotinia Disease of Lupine in Florida. Plant
Dis. Reporter. 30: 8. 1946.
5. EDDINS, A. H. Sclerotinia Rot of Irish Potatoes. Phytopath 27: 1:
100-103. 1937.
6. Fla. Crop and Livestock Reporting Service. Vol. 3. 1947.
7. WINTERS, R. Y. Report of Assistant in Botany. Fla. Agr. Exp. Sta.
Ann. Rpt. 1909.
8. YOUNG, PAUL A. Sclerotinia rot of squash and pumpkin. jPhytopath
26: 2: 184-90. 1936.




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