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Group Title: Bulletin University of Florida. Agricultural Experiment Station
Title: Control of downy mildew of cabbage with fungicides
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 Material Information
Title: Control of downy mildew of cabbage with fungicides
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 23 p. : ill. ; 23 cm.
Language: English
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1954
Copyright Date: 1954
 Subjects
Subject: Downy mildew diseases   ( lcsh )
Cabbage -- Diseases and pests -- Biological control   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references (p. 23).
Statement of Responsibility: A.H. Eddins.
General Note: Cover title.
General Note: "Contribution from the Potato Investigations Laboratory."
 Record Information
Bibliographic ID: UF00026937
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: ltuf - AEN7059
oclc - 18272471
alephbibnum - 000926388

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Full Text
OCT 27: :

Bulletin 543 July 1954

UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATIONS
WILLARD M. FIFIELD, Director
GAINESVILLE, FLORIDA
(Contribution from the Potato Investigations Laboratory)



Control of Downy Mildew of Cabbage

with Fungicides

A. H. EDDINS









i r
















Fig. 1.-Sections of cabbage plant beds. A, Plants treated with chloranil





GAINESVILLE, FLORIDA
GAINESVILLE, FLORIDA











BOARD OF CONTROL EDITORIAL
Hollis Rinehart, Chairman, Miami J. Francis Cooper, M.S.A., Editor 1 :
J. Lee Ballard, St. Petersburg Clyde Beale, A.B.J., Editor 3
Fred H. Kent, Jacksonville William G. Mitchell, A.B.J., Assistant Editor
Wm. H. Dial, Orlando Samuel L. Burgess. A.R.J., Assistant Editor
Mrs. Alfred 1. duPont, Jacksonville H. L. Moreland, Jr., B.S.A., Assistant Editor
George W. English, Jr., Ft. Lauderdale
W. Glenn Miller, Monticello ENTOMOLOGY
J. B. Culpepper, Secretary, Tallahassee A. N. Tissot, Ph.D., Entomologist
EXECUTIVE STAFF L. C. Kuitert, Ph.D., Associate
H. E. Bratley, M.S.A., Assistant
John S. Allen, Acting President F. A. Robinson, M.S., Asst. Apiculturist
J. Wayne Reitz, Ph.D., Provost for Agr.' R. E. Waites, Ph.D., Asst. Entomologist
Willard M. Fifield, M.S., Director S. H. Kerr, Ph.D., Asst. Entomologist
J. R. Beckenbach, Ph.D., Asso. Director J. R. Christie, Ph.D., Nematologist
R. W. Bledsoe, Ph.D., Assistant Director
Rogers L. Bartley, B.S., Admin. Mgr.3 HOME ECONOMICS
Geo. R. Freeman, B.S., Farm Superintendent Ouda D. Abbott, Ph.D., Home Econ.i

MAIN STATION, GAINESVILLE R. B. French, Ph.D., Biochemist
AGRICULTURAL ECONOMICS HORTICULTURE
H. Hamiln, P ., Ar. s G. H. Blackmon, M.S.A., 'Horticulturist'
It. G. Hamlto Greene, Ph.., Agr. Economists R. A. Dennison, Ph.D., Hort. & Interim Head
. Greeneooker, Ph.D., Agr. Economist F. S. Jamison, Ph.D., Horticulturist
M. A. Brooke, PhD., Asr. Economist Albert P. Lorz, Ph.D., Horticulturist
Zach Savage, M.S.A., Associate R. K. Showalter, M.S., Asso. Hort.
A. H. Spurlock, M.S.A., Agr. Economist H. Sharpe, M.S., Asso. Horticulturist
"D. E. Alleer, M.S., Associate V. F. Nettles, Ph.D., Asso. Horticulturist
D. L. Brooke, Ph.D., Associate F. S. Lagasse, Ph.D., Horticulturist2
M. R. Godwin, Ph.D., Associate R. D. Dickey, M.S.A., Asso. Hort.
W. K. McPherson, M.S., Agr. Economist L. H. Halsey, M.S.A., Asst. Hort.
Eric Thor, M.S., Asso. Agr. Economists C. B. Hall, Ph.D., Asst. Horticulturist
Cecil N. Smith, M.A., Asso. Agr. Economist Austin Griffiths, Jr., B.S., Asst. Hort.
Levi A. Powell, Sr., M.S.A., Assistant S. E. McFadden, Jr., Ph.D., Asst. Hort.
E. D. Smith, Ph.D., Asst. Agr. Economist C. H. VanMiddelem, Ph.D., Asst. Biochemist
N. K. Roberts, M.A., Asst. Agr. Economist B. D. Thompson, M.S.A., Interim Asst. Hort.
Orlando, Florida (Cooperative USDA) M. W. Hoover, M.S.A., Asst. Hort.
G. Norman Rose, B.S., Asso. Agri. Economist
J. C. Townsend, Jr., B.S.A., Agr. Statistician2 LIBRARY
J. B. Owens, B.S.A., Agr. Statistician 2 Ida Keeling Cresap, Librarian
F. T. Calloway, M.S., Agr. Statistician
C. L. Crenshaw, M.S., Asst. Agr. Economist PLANT PATHOLOGY
B. W. Kelly, M.S., Asst. Agr. Economist W. B. Tisdale, Ph.D., Plant Pathologist 1
AGRICULTURAL ENGINEERING Phares Decker, Ph.D., Plant Pathologist
Erdman West, M.S., Botanist & Mycologist'
Frazier Rogers, M.S.A., Agr. Engineer Robert W. Earhart, Ph.I., Plant Path.2
J. M. Myers, M.S.A., Asso. Agr. Engineer Howard N. Miller, Ph.D., Asso. Plant Path.
J. S. Norton, M.S., Asst. Agr. Engineer Lillian E. Arnold, M.S., Asso. Botanist
AGRONOMY C. W. Anderson, Ph.D., Asst. Plant Path.
Fred H. Hull, Ph.D., Agronomist POULTRY HUSBANDRY
G. B. Killinger, Ph.D., Agronomist N. R. Mehrhof, M.Agr., Poultry Husb.1 a
H. C. Harris, Ph.D., Agronomist J. C. Driggers. Ph.D., Asso. Poultry Husb.
W. A. Carver, Ph.D., Agronomist
Fred A. Clark, M.S., Associate2 SOILS
E. S. Horner, Ph.D., Assistant mi h ic biologist
A. T. Wallace, Pi.D., Assistant F. B Smith, Ph.D., Microbiologist'
D. E. McCloud, Ph.D., Assistant Gaylord M. Volk, h.D, Soils Chemist
G. C. Nutter, Ph.D., Asst. Agronomist J. R. Neller, Ph.D., Soils Chemist
I. M. Wofford, Ph.D., Asst. Agronomist Nathan Gammon, Jr., Ph.D., Soils Chemist
E. 0. Burt, Ph.D., Asst. Agronomist Ralph G. Leighty, B.S., Asst. Soil Surveyor
J. R. Edwardson, Ph.D., Asst. Agronomist G. D. Thornton, Ph.D, Microbiologist
C. F. Eno, Ph.D., Asst. Soils Microbiologist
ANIMAL HUSBANDRY AND NUTRITION H. W. Winsor, B.S.A., Assistant Chemist
R. E. Caldwell, Ph.D., Asst. Chemist a
T. J. Cunha, Ph.D., Animal Husbandman V. W. Carlisle, B.S., Asst. Soil Surveyor
G. K. Davis, Ph.D., Animal Nutritionist J. H. Walker, M.S.A., Asst. Soil Surveyor
It. L. Shirley, Ph.D., Biochemist William K. Robertson, Ph.D., Asst. Chemist
A. M. Pearlson, Ph.D., Asso. An. Hush.3 0. E. Cruz, B.S.A., Asst. Soil Surveyor
John P. Feaster, Ph.D., Asst. An. Nutri. W. G. Blue, Ph.D., Asst. Biochemist
H. D. Wallace, Ph.D., Asso. An. Hush.3 J. G. A. Fiskel, Ph.D., Asst. Biochemist a
M. Koger, Ph.D., An. I-usbandman 3 L. C. Hammond, Ph.D., Asst. Soil Physicist s
J. F. Hentges, Jr., Ph.D., Asst. An. Husb. H L. Breland, Ph.D., Asst. Soils Chem.
L. R. Arrington, Ph.D., Asst. An. Husb. W. L. Pritchett, Ph.D., Soil Technologist
A. C. Warnick, Ph.D., Asst. Physiologist
VETERINARY SCIENCE
DAIRY SCIENCE D. A. Sanders, D.V.M., Veterinarian 1
E. L. Fouts, Ph.D., Dairy Technologist 1 M. W. Emmel, D.V.M., Veterinarian
R. B. Becker, Ph.D., Dairy Husbandman C. F. Simpson, D.V.M., Asso. Veterinarian
S. P. Marshall, Ph.D., Asso. Dairy Husb.3 L. E. Swanson, D.V.M., Parasitologist
W. A. Krienke, M.S., Asso. Dairy Tech.3 W. R. Dennis, D.V.M., Asst. Parasitologist
P. T. Dix Arnold, M.S.A., Asso. Dairy iHusb. E. W. Swarthout, D.V.M., Asso. Poultry
Leon Mull, Ph.D., Asso. Dairy Tech.3 Pathologist (Dade City)
H. H. Wilkowske, Ph.D., Asst. Dairy Tech.3 M. Ristic, D.V.M., Associate Pathologist
James M. Wing. Ph.D., Asst. Dairy Hush. J. G. Wadsworth. D.V.M., Asst. Poul. Path.











BRANCH STATIONS D. W. Beardsley, M.S., Asst. Animal Hush.
R. S. Cox, Ph.D., Asso. Plant Pathologist
Donald M. Coe, Ph.D., Asst. Plant Pathologist
NORTH FLORIDA STATION, QUINCY
SUB-TROPICAL STATION, HOMESTEAD
W. C. Rhoades, M.S., Entomologist in Charge
R. R. Kincaid, Ph.D., Plant Pathologist Geo. D. Ruehle, Ph.D., Vice-Dir. in Charge
L. G. Thompson, Jr., Ph.D., Soils Chemist D. O. Wolfenbarger, Ph.D., Entomologist
W. H. Chapman, M.S., Agronomist Francis B. Lincoln, Ph.D., Horticulturist
Frank S. Baker, Jr., B.S., Asst. An. Husb. Robert A. Conover, Ph.D., Plant Path.
Frank E. Guthrie, Ph.D., Asst. Entomologist John L. Malcolm, Ph.D., Asso. Soils Chemist
R. W. Harkness, Ph.D., Asst. Chemist
Mobile Unit, Monticello R. Bruce Ledin, Ph.D., Asst. Hort.
R. W. Wallace, B.S., Associate Agronomist J. C. Noonan, M.S., Asst. Hort.
M. H. Gallatin, B.S., Soil Conservationist'
Mobile Unit, Marianna T. W. Young, Ph.D., Asso. Horticulturist
R. W. Lipscomb, M.S., Associate Agronomist WEST CENTRAL FLORIDA STATION
Mobile Unit, Pensacola BROOKSVILLE
R. L. Smith, M.S., Associate Agronomist arian W. Hazen M.S., Animal Husband-
Marian W. Hazen, M.S., Animal Husband-
Mobile Unit, Chipley man in Charge2
J. B. White, B.S.A., Associate Agronomist RANGE CATTLE STATION, ONA

W. G. Kirk, Ph.D., Vice-Director in Charge
CITRUS STATION, LAKE ALFRED E. M. Hodges, Ph.D., Agronomist
D. W. Jones, M.S., Asst. Soil Technologist
A. F. Camp, Ph.D., Vice-Director in Charge
W. L. Thompson, B.S., Entomologist CENTRAL FLORIDA STATION, SANFORD
R. F. Suit, Ph.D., Plant Pathologist
E. P. Ducharme, Ph.D., Asso. Plant Path. R. W. Ruprecht, Ph.D., Vice-Dir. in Charge
J. W. Sites, Ph.D., Horticulturist J. W. Wilson, ScD., Entomologist
H. O. Sterling, B.S., Asst. Horticulturist P. J. Westgate, Ph.D., Asso. Hort.
H. J. Reitz, Ph.D., Horticulturist Ben F. Whitner, Jr., B.S.A., Asst. Hort.
Francine Fisher, M.S., Asst. Plant Path. J. F. Darby, Ph.D., Asst. Plant Path.
I. W. Wander, Ph.D., Soils Chemist
J. W. Kesterson, M.S., Asso. Chemist WEST FLORIDA STATION, JAY
R. Hendrickson, B.S., Asst. Chemist C. E. Hutton, Ph.D., Vice-Director in Charge
Ivan Stewart, Ph.D., Asst. Biochemist H. W. Lundy, B.S.A., Associate Agronomist
D. S. Prosser, Jr., B.S., Asst. Engineer R. L. Jeffers. Ph.D., Asso. Agronomist
R. W. Olsen, B.S., Biochemist
F. W .Wenzel, Jr., Ph.D., Chemist SUWANNEE VALLEY STATION,
Alvin H. Rouse, M.S., Asso. Chemist LIVE OAK
H. W. Ford, Ph.D., Asst. Horticulturist
L. C. Knorr, Ph.D., Asso. Histologist G. E. Ritchey, M.S., Agronomist in Charge
R. M. Pratt, Ph.D., Asso. Ent.-Pathologist
W. A. Simanton, Ph.D., Entomologist GULF COAST STATION, BRADENTON
E. J. Deszyck, Ph.D., Asso. Horticulturist E. L. Spencer, Ph.D., Soils Chemist in Charge
C. D. Leonard, Ph.D., Asso. Horticulturist E. G. Kelsheimer, Ph.D., Entomologist
W. T. Long, M.S., Asst. Horticulturist David G. A. Kelbert, Asso. Horticulturist
M. H. Muma, Ph.D., Asso. Entomologist Robert O. Magie, Ph.D., Plant Pathologist
F. J. Reynolds, Ph.D., Asso. Hort. J. M. Walter, Ph.D., Plant Pathologist
R. B. Johnson, Ph.D., Asst. Entomologist S. S. Woltz, Ph.D., Asst. Horticulturist
W. F. Newhall, Ph.D., Asst. Biochemist Donald S. Burgis, M.S.A., Asst. Hort.
W. F. Grierson-Jackson, Ph.D., Asst. Chem. C. M. Geraldson, Ph.D., Asst. Horticulturist
Roger Patrick, Ph.D., Bacteriologist G. Sowell, Jr., Ph.D., Asst. Plant Pathologist
M. F. Oberbacher, Ph.D., Asst. Plant Physiol
R. C. J. Koo, Ph.D., Asst. Biochemist
J. R. Kuykendall, Ph.D., Asst. Horticulturist FIELD LABORATORIES
W. C. Price, Ph.D., Virologist
J. J. McBride, Jr., Ph.D., Assistant Chemist Watermelon, Grape, Pasture-Leesburg
J. M. Crall, Ph.D., Asso. Plant Path. in Chg.
C. C. Helms, Jr., B.S., Asst. Agronomist
EVERGLADES STATION, BELLE GLADE L. H. Stover, Assistant in Horticulture
W. T. Forsee, Jr., Ph.D., Chemist in Charge Strawberry-Plant City
R. V. Allison, Ph.D., Fiber Technologist
Thomas Bregger, Ph.D., Physiologist A. N. Brooks, Ph.D., Plant Pathologist
J. W. Randolph, M.S., Agricultural Engr. Vegetables-Hastings
R. W. Kidder, M.S.. Asso. Animal Husb.
C. C. Seale, Associate Agronomist A. H. Eddins, Ph.D., Plant Path. in Charge
N. C. Hayslip, B.S.A. Asso. Entomologist E. N. McCubbin, Ph.D., Horticulturist
E. A. Wolf, M.S., Asst. Horticulturist T. M. Dobrovsky, Ph.D., Asst. Entomologist
W. H. Thames, M.S., Asst. Entomologist D. L. Myhre, Ph.D.. Asst. Soils Chemist
W. G. Genung, M.S., Asst. Entomologist Pecans-Monticello
Robert J. Allen, Ph.D., Asst. Agronomist
V. E. Green, Ph.D., Asst. Agronomist A. M. Phillips, B.S., Asso. Entomologist'
V. L. Guzman, Ph.D., Asst. Hort. John R. Large, M.S., Asso. Plant Path.
J. C. Stephens, B.S., Drainage Engineer 2 Frost Forecasting-Lakeland
A. E. Kretschmer, Jr., Ph.D., Asst. Soils
Chem. Warren O. Johnson, B.S., Meteorologist in
Charles T. Ozaki, Ph.D., Asst. Chemist Charge 2
Thomas L. Meade, Ph.D., Asst. An. Nutri.
I. S. Harrison M.S.. Asst. Agri. Engr. 1 Head of Department
F. T. Boyd. Ph.D., Asso. Agronomist In cooperation with U. S.
M. G. Hamilton, Ph.D., Asst. Horticulturist 3 Cooperative, other divisions, U. of F.
J. N. Simons, Ph.D., Asst. Virologist 4 On leave





















CONTENTS

PAGE

INTRODUCTION ............ ........... .... ..... 5


FUNGICIDES USED IN PLANT BEDS ......-...----------- --. -..... .....--....... 6


1940-1943 Tests ...------------........------........... .... 6


1944-1946 Tests ...------- --- -----......-........--------............ 10


1948-1952 Tests ..-........ ....----- ........- --------------------- ..-. .....- 12


FUNGICIDES USED ON HEADING CABBAGE ......................--.. ---.........-- --. 14


CONCLUSIONS ....-.....- .... ...... ....- ... ... ............. 19


SUMMARY ....------....---. ----.... --- ----... ---...-.-- .---.. ---...--------.............. 20


RECOMMENDATIONS ....-- ....----------------- --..- -........ ..-..-.. --------.... ... .. 22


LITERATURE CITED ...- ...-.----.--..-...-...-. ...- ..............-....--............-- 23










Control of Downy Mildew of Cabbage

with Fungicides

A. H. EDDINS1

INTRODUCTION
Downy mildew of cabbage, cauliflower, collards, Chinese cab-
bage, Brussels sprouts, broccoli, kale and kohlrabi is caused by
the fungus Peronospora parasitica (Pers.) ex Fr. It is the most
destructive seedling disease of cabbage, cauliflower and broccoli
in Florida. The disease makes it impossible to grow enough
plants at Hastings to set the acreage unless they are protected
with fungicides. Losses cannot be prevented by using plants
grown in other parts of the country for transplanting stock, as
they usually are affected with downy mildew and may carry
other troublesome diseases. Furthermore, imported plants are
not always true as to variety or strain and may be infested
with aphids and other insects.
Downy mildew usually is present on cabbage plants in the
field and may cause yellowing and shedding of the oldest leaves
and retard the growth of plants. Downy mildew spots on head
leaves of cabbage impair the appearance and market value of
the heads. Furthermore, secondary organisms which enter
openings made by the downy mildew fungus in head leaves may
hasten decay of the heads in the field or while the cabbage is in
transit to market.
Downy mildew may be initiated by resting spores of the fungus
which live over the summer in the soil (8).2 Outbreaks of the
disease occur also in new plantings when spores are blown into
them from downy mildew-affected plants in nearby plant beds
and fields. The disease may be present on susceptible host plants
in Florida from September to the following May. The fungus
grows best and the disease develops rapidly when night tem-
peratures range between 50 and 600 F. for four or more suc-
cessive nights and the plants remain wet until midmorning or
later (1, 5). Little growth of the fungus occurs when the tem-
perature is below 400 F. or above 820 F. (1, 5). Young seedlings
"The author is indebted to S. M. Burrell, formerly laboratory assistant,
Potato Investigations Laboratory, who helped conduct the fungicide tests
from 1948 to 1953 and to various chemical companies who furnished in part
fungicides used in the tests.
2 Italic figures in parentheses refer to Literature Cited.








6 Florida Agricultural Experiment Stations

may perish from the disease during periods when there are heavy
dews even though the days are dry and sunny (5).
Fungicides were tested for control of downy mildew on cab-
bage seedlings in plant beds and on heads of maturing cabbage
plants at Hastings from 1940 to 1953. None of the fungicides
except those containing copper had been tested for control of
the disease prior to 1940. All materials except paradichloro-
benzene were applied as sprays and dusts with hand-operated,
traction and tractor-operated sprayers and dusters. Treatments
were started in plant beds before or immediately after downy
mildew was first observed on the seedlings and in cabbage fields
one to three weeks before harvest. Plant bed tests were con-
ducted in October, November, December and January and field
tests were made in February, March and April. At the begin-
ning of the tests insects were controlled with insecticides con-
taining nicotine and arsenic and in later years with DDT, chlor-
dane, TEPP and parathion as they became available.
Notes were taken on the amount of plant injury caused by
downy mildew and the fungicides. Records were made of the
number and weight of plants in samples drawn from similar-size
areas in treated and non-treated plant beds. The number of
cabbage heads with different degrees of injury caused by downy
mildew and the number free of the disease in field test plots were
recorded. Results of the tests not heretofore published (1, 2,
3, 4) are reported in this bulletin.

FUNGICIDES USED IN PLANT BEDS
1940-1943 TESTS
Paradichlorobenzene and one or more formulations of Ceresan,
bismuth subsalicylate, ferbam, chloranil, U. S. Rubber Co. Fungi-
cide 366, and sulfur- and copper-containing fungicides were
tested for control of downy mildew from 1940 to 1943.
Paradichlorobenzene (PDB).-This chemical was tested in
1940 and 1941. It was applied under frames in about the same
manner as described by Tisdale and Kincaid, who used it for
control of down mildew of tobacco (Peronospora tabacina Adam)
in plant beds (11). The frames were made of 1 x 10-inch and
1 x 12-inch cypress boards and measured 2 to 6 feet in width
and 7 to 16 feet in length. Unbleached sheeting woven with
about 60 threads to the inch was used as covers which could be
fastened to the tops of the frames with grommets. Frames of
appropriate sizes were used on plants grown in broadcasted and








Control of Downy Mildew of Cabbage with Fungicides 7

in two- to eight-drill-row seedbeds. The PDB crystals were
vaporized on rough boards about 6 inches wide and also on
strips of cheesecloth mounted in the frames lengthwise and 3
to 4 inches above tops of the plants. Soil was ridged and pressed
around the bottom edges of each frame after it was placed over
the plants to prevent excessive leakage of the PDB vapor. Two
to 5 pounds of PDB crystals per 100 square yards of seedbed
were spread evenly over the boards on cheesecloth between 4
and 5 o'clock in the afternoon and the covers were wetted and
placed on the frames. Treatments were started when downy
mildew was first observed in the seedbeds. Some of the covered
frames were left over the plants during the day and others were
removed between 8 and 9 o'clock the next morning. Some plants
were treated two and others three successive nights at weekly
and fortnightly intervals.
Three pounds of PDB crystals per 100 square yards of seedbed
applied in the afternoon of three successive days at weekly
intervals gave good control of downy mildew. Two pounds of
the crystals applied in a similar manner gave poor control, as
there was not enough PDB vapor produced to kill the fungus.
The 2- and 3-pound treatments did not injure the plants when
the frames or covers were removed from the seedbeds at 8 or 9
o'clock in the mornings and the plants were left uncovered until
PDB was applied again in the afternoons.
The 4- and 5-pound treatments made on three successive days
at weekly intervals controlled downy mildew but burned the
leaves and stunted the plants. Plant injury was worst when
minimum noturnal temperatures were 70 F. and higher during
the treating period. Apparently, concentrations of PDB vapor
injurious to the plants were produced when more than 3 pounds
of crystals were used on each 100 square yards of seedbed and
when high temperatures caused rapid vaporization of the crystals.
None of the treatments controlled the disease when applied
during periods when nocturnal temperatures dropped to 400 F.
or lower, as the fungus was not very active and most of the
PDB crystals failed to vaporize at those temperatures. Treat-
ments made at fortnightly intervals also were ineffective, as the
disease developed during the two weeks between treatments.
When PDB crystals were spilled on the seedbed during appli-
cation, plants in these areas were injured or killed. Plants also
were injured or killed when treated with 4 to 5 pounds of the
crystals per 100 square yards of seedbed and exposed continu-
ously to PDB vapor 24 to 48 hours. The worst damage occurred








8 Florida Agricultural Experiment Stations

when 5 pounds of the crystals were applied and the covered
frames were left on the seedbeds 48 hours and not removed
except to repeat the treatment the second afternoon.
Other Fungicides.-Other fungicides were applied as sprays
or dusts with knapsack, barrel and traction sprayers and hand-
operated dusters. Quantities of spray and dust used varied
according to the size of the plants, as listed in Table 1.

TABLE 1.-QUANTITIES OF SPRAY AND DUST USED AT EACH APPLICATION IN
PLANT BEDS FROM 1940 TO 1943.

Narrow Two-Drill-Row Plant Beds
Plant Height _40 Inches Apart
Spray Dust
Gals. per Acre Lbs. per Acre
Less than 2 inches ............... 40 to 60 8 to 10
2 to 4 inches ............................ 60 to 100 10 to 15
4 to 8 inches --------...........-..- 100 to 150 15 to 25


Most plants are grown in narrow, raised seedbeds in low-lying
flatwoods soils at Hastings and in other areas of the state where
natural drainage is poor. The beds are 12 to 18 inches wide
on top, 8 to 10 inches high and 40 inches apart from middle to
middle. The seed is planted about 1/4 inch deep in tops of the
beds in one to three drills, usually two, which are spaced 4 to 6
inches apart.
The fungicides were applied to plants grown in 10- to 50-foot
sections in narrow, two-drill-row plant beds. The tests ran
from two to seven weeks, depending upon the stage of growth
of the plants when treatments were started and time required
for them to grow large enough for transplanting. Different
formulations of the various fungicides were tested one to eight
times. Tests made in 1941 showed that three applications per
week of chloranil with a one- to two-day interval between treat-
ments gave best control of downy mildew. Thereafter that
schedule was used with all fungicides (2). Degree of downy
mildew control obtained from each fungicide and the degree of
plant injury it caused are summarized in Table 2.
Full strength bordeaux mixture, Flordo and Flordo K sprays
(7, 9) gave good control of downy mildew but injured the plants.
They did not give satisfactory control when used at half- and
quarter-strength.








Control of Downy Mildew of Cabbage with Fungicides 9

TABLE 2.-RESULTS OF TREATING CABBAGE PLANTS WITH DIFFERENT FUNGI-
CIDES FOR CONTROL OF DOWNY MILDEW IN PLANT BEDS FROM 1940 TO 1943.

Pounds
of Each Num- ] Injury
Ingredi- ber of I Mildew from
Fungicides ent in Times I Control* Fungi-
100 Gals. Tested cides**
__Water __

Sprays
Bordeaux mixture (bluestone-
hydrated lime)
Full strength ....................... 8-12 4 Good Moderate
Half strength-SS3 spreader-
sticker .................................. 4-6-1/% 5 Poor Moderate

Flordo (bluestone-soap-
ammonia)
Full strength ....... ..........- 2 2-10-2 2 Good Mild
Half strength ........ ......1... -5-1 7 Poor None
Quarter strength --............ %-2% -% 2 iVery Poor INone

Flordo K (bluestone-soap)
Full strength .........................- 3-14 2 Good I Mild
Half strength ..................... 1%-7 i 6 [Poor None
Quarter strength ...---............... %-3%Y 2 Poor None

Flordo Cl (bluestone-soap- I
sodium silicate) .................... 5-8-24 2 Poor Mild
Cuprocide ..............................-.... 1 4 I Good M ild
Cuprocide-emulsified cotton-
seed oil .................................... 1-8 2 Good Severe
Ceresan-SS3 spreader-sticker %-% 1 Poor Moderate
U. S. Rubber Company No. 366 4 2 I Very Poor None
Sulfur (33% wettable) ............ 6 2 IPoor Moderate
Bismuth subsalicylate-vatsol .. 1-1 3 I Very Poor Mild
Ferbam (70%)-SS3 spreader-
sticker ...................................... 12-1/ 3 Good Moderate
Chloranil (48% wettable) ...... 4 8 Good I None
Chloranil (40% paste) .............. 4 5 Good I None

Dusts
Copper lime (20% 80%) ...... 8 Poor Mild
15% Copper Compound A .-... 3 Poor Mild
83% Sulfur ..................... ... 2 IPoor Mild
10% Ferbam ....................... 5 Poor Moderate
20% Ferbam ..................... 1 IPoor Moderate
12% Chloranil ....................... 6 Good None


Check ..... ........................ I 8 N one ..

* Control rating:
Good = Few spots on leaves of scattered plants.
Poor = Spots on seed-leaves and true leaves of most plants, some seed-leaves shed and
some plants stunted and 1 to 5 percent killed.
Very Poor = Spots on most leaves, seed-leaves mostly killed and shed, most plants
stunted and 6 to 25 percent killed.
None = Spots on all leaves, plants severely stunted and over 25 percent killed.
** Injury rating:
None = No injury.
Mild = A few necrotic spots on leaves and most plants slightly stunted.
Moderate = Many necrotic spots on leaves and plants stunted.
Severe = Leaves burned severely and malformed, plants stunted severely and 25 per-
cent or more killed







10 Florida Agricultural Experiment Stations

Poor to very poor control of the disease was obtained when
plants were sprayed with Flordo Cl, Ceresan plus SS3 spreader-
sticker, U. S. Rubber Co. No. 366, sulfur wettable and bismuth
subsalicylate plus vatsol. Copper-lime, copper compound A,
sulfur and ferbam dusts also gave poor control.
Cuprocide spray controlled downy mildew but burned and
stunted the plants. Addition of 8 pounds of emulsified cotton-
seed oil to 100 gallons Cuprocide spray increased plant injury.
Ferbam spray containing SS3 spreader-sticker controlled the
disease but injured the plants.
Chloranil sprays and dusts 3 proved superior to the other
fungicides, as they gave good control of downy mildew without
injuring the plants (6).

1944-1946 TESTS
Chloranil, nabam, zineb and manzate sprays; and zineb, chlora-
nil, chloranil plus ferbam, ziram and copper compound A dusts
were tested for control of downy mildew during the 1944-1946
period. Treatments were made with a traction sprayer and a
traction duster in two-drill-row plant beds 25 to 50 feet in length.
The schedule developed in 1941 was used in applying the fungi-
cides. Treatments were not made on schedule when temper-
atures dropped to 400 F. or lower and when heavy rains flooded
the field, making it impossible to operate sprayers and dusters
without miring. The quantity of spray and dust used at each
application is given in Table 1.
Number and weight of plants drawn from 5 feet of plant bed
in each plot were used in evaluating the fungicides. Plant bed
areas selected for sampling were chosen so that plants in each
sample would be as representative as possible of other plants
in the plot. Differences in the average number of plants per
treatment were a good indication of the effectiveness of the
fungicides for downy mildew control only when the disease ap-
peared early and killed seedlings before they grew large enough
to withstand it. Average weight of plants from different treat-
ments was a better criterion for evaluating the fungicides, as

3 Chloranil sprays used in tests reported in this bulletin were made of
chloranil paste and chloranil wettable containing 40 to 50 percent tetra-
chloro-para-benzoquinone and also a wetting agent which aided in mixing
the fungicide with water and wetting plants with the spray. Chloranil
dusts used contained 5 and 12 percent tetrachloro-para-benzoquinone.
Chloranil wettable containing 50 percent of the active ingredient and the
5 percent dust were special mixtures labeled stabilized by the manufacturer.
The other forms of chloranil tested were regular commercial mixtures.








Control of Downy Mildew of Cabbage with Fungicides 11

plant weight varied according to the amount of downy mildew
present and the degree it retarded growth of the plants.
Significant control of downy mildew was obtained with all
fungicides used in the 1944-1946 tests, except 4 percent zineb,
12.5 percent ziram and 15 percent copper compound A dusts
applied in 1944 (see Table 3).

TABLE 3.-RESULTS OF TREATING CABBAGE PLANTS WITH DIFFERENT FUNGI-
CIDES FOR CONTROL OF DOWNY MILDEW IN PLANT BEDS FROM 1944 TO 1946.

1944 1945 1946
Plants Plants Plants
Fungicides* per Plot** per Plot** per Plot**
Aver- Aver- Aver- Aver- Aver- Aver-
age age age age age age
Num- Wt. Num- Wt. Num- Wt.
ber Grams her Grams ber Grams

Sprayst
Chloranil (48%)
4 lbs .......... ..... .. 471 1,246 285 1,022 545 1,883
4 h---- ----------- --47 ,4 8 ,
Nabam (27%)-ZnSO,
-hydrated lime
1Y lbs.- 1 lb.- y2 lb. .... ...... ..... ...... 467 1,187
Zineb (65%)
11/2lbs. ........... ..---452 1,120 252 737 531 1,295
Manzate (70%)
11% lbs ........ ........ ...... ..... ...... 404 739
Dusts
4% Zineb ................... 346 624 ...... 409 738
12% Chloranil ........ 453 1,439 312 1,266 550 1,557
12% Chloranil plus
10% Ferbam.....--- ..------ - ...... ..... 409 671
12.5% Ziram ..---............ 441 752 .
15% Copper Com-
pound A .......... ..--- 338 709 .


Check .......... ... .... ... 370 610 182 378 295 425


Least Significant
Difference .05 Level 75 193 33 159 102 233


Applied 11 times in 1944, 5 times in 1945 and 11 times in 1946. Each treatment
replicated 3 to 5 times.
** Consisted of samples drawn from 5 feet of plant bed in each plot.
f Pounds and quarts listed under the different fungicides were the amounts used per
100 gallons water.

Chloranil spray and dust gave best control of downy mildew.
Chloranil dust was statistically better than chloranil spray in
1944 and 1945, but in 1946 the spray excelled the dust. Downy







12 Florida Agricultural Experiment Stations

mildew control obtained by treating plants with chloranil dust
is shown in Figure 1.
Zineb spray, which was tested three years, and nabam spray,
one year, gave good control of downy mildew. Zineb spray was
as effective as chloranil spray in 1944. In 1946 nabam and zineb
sprays gave better control than manzate spray, and 4 percent
zineb and 12 percent chloranil plus 10 percent ferbam dusts.

1948-1952 TESTS
Chloranil, nabam, phygon XL-N and manzate sprays; and 12
percent chloranil, 5 percent chloranil and 6.5 percent zineb dusts
were tested for control of downy mildew in the 1948-1952 period.
Plants were grown in the same area during the five years.
Each plot consisted of three two-drill-row plant beds 40 feet in
length. Treatments were made with a tractor-operated sprayer
and duster equipped with enough nozzles to cover the plants
with fungicides. A 30-foot turnrow between the ends and a
10-foot unplanted space between the sides of plots minimized
drift of the fungicides from one treatment to the next. The
materials were applied on the same schedule as that used in the
1944-1946 tests, but minimum quantities of spray and dust used
at the first application were larger, as shown in Table 4. It was
impossible to adjust the sprayer and duster to apply less than
the amounts shown. As the plants grew larger, more spray
and dust were used in the 1948-1952 tests than were used on
similar size plants in previous tests. Maximum quantities used
per acre on the largest plants were 150 gallons spray and 35
pounds dust. Percentages of the foliage killed by downy mildew
in each plot and the number and weight of plants in samples
drawn from the plots were used in determining effectiveness of
the different fungicides (see Table 5).

TABLE 4.-QUANTITIES OF SPRAY AND DUST USED AT EACH APPLICATION
IN PLANT BEDS FROM 1948 TO 1952.

Narrow Two-Drill-Row Plant Beds 40 Inches Apart
Plant Height Spray Dust
Gals. per Acre Lbs. per Acre
Less than 2 inches.. 80 to 100 15 to 20
2 to 4 inches .......... 100 to 120 20 to 25
4 to 8 inches .... 120 to 150 25 to 35







TABLE 5.-RESULTS OF TREATING CABBAGE PLANTS WITH DIFFERENT FUNGICIDES FOR CONTROL OF DOWNY MILDEW IN PLANT BEDS
FROM 1948 TO 1952.

S1948 1949 1 1950 1951 1952
Foliage Plan:s/Plot** Foliage I Plants/Plot**I Foliage IPlants/Plot**l Foliage IPlants/Plot**i Foliage Plants/Plot**
Fungicides* Killed by Avg. Killed by Avg. Killed by 1 1 Avg. Killed by Avg. Killed by Avg.
Downy Avg. Wt. Downy Avg. Wt. Downy Avg. Wt. Downy Avg. Wt. Downy Avg. Wt.
Mildew No. Grams Mildew No. Grams Mildew I No. Grams Mildew No. Grams Mildew No. Grams
SAn- An- | An- ( I An- A-
Avg. gles Avg. gles Av gles I I Avg. gles Avg. fles
Pet. Deg.$ I Pct. Deg.t P'ct. Deg.$ I Pet. I Deg. P'ct. Deg.t
Sprayst
Chloranil (48%) 5
4 lbs............. 1 6 21 2,814 7 1i 276 1,617 1S 25 | 374 | 96 9 17 109 88 4 | 11 1'42 1,61
2 lbs. 7 14 5 51 1,265
Chloranil (50%)
2 lbs ... .......... 11 19 421 .770 13 | 462 1,0 5
Nabam(27%)-ZnSO4
2 qts.-1 lb .......... 7 15 487 1,607 17 24 300 1,487 12 20 293 1,074 13 19 377 634 15 22 514 1,269
4 qts.-- 2 lbs. ......... ..... 7 15 288 1,559 ... .
Phygon XL-N (50%)
1 lb. .. .......... .... ..... 20 26 398 647 18 i 599 1,115
Manzate (70%)
11/ lbs ........ .. .. 19 25 408 616 17 21 488 1,032

Dusts I I I
12% Chloranil .... 13 463 2,278 15 22 283 1,626 12 20 297 1,028 0.1 2 584 1,62.
5% Chloranil ... .... ...... . 1 6 517 1,575
6.5% Zineb ........ 30 33 486 1,333 27 31 284 1,194 35 3 262 528 ......
I
Check .......... 63 51 429 726 50 46 249 826 41 29 268 376 23 26 334 342 50 45 436 684

Leass Significant I
Difference .05 Level.... 5 84 433 ... 8 32 207 11 87 347 N.S. 8 17 .... 10 120 242

"*Applied 11 to 15 times. Each treatment replicated 3 to 5 times.
** Consisted of samples drawn from 5 feet of plant bed in each plot.
t Pounds and quarts listed under the different fungicides were the amounts u d in 100 gallons water.
$ The angles corresponding to the percentages were obtained according to t1:e nrc sin transformation method as described by Snedecor (10) pp. 445-452.







14 Florida Agricultural Experiment Stations

Average percentages of foliage killed by downy mildew in
the check plots during the 1948-1952 period ranged from 20
percent in 1951 to 60 percent in 1948. Differences in effective-
ness of the fungicides for control of the disease were wider in
those years when the disease killed 40 to 60 percent of the foliage
in the check plots.
Significant control of downy mildew was obtained with all
fungicides used in plant beds from 1948 to 1952, with the ex-
ception of 6.5 percent zineb dust in 1950.
Forty-eight percent chloranil (4 lbs. -100 gals. water) gave
significantly better control of the disease in 1952 as measured
by average weight of plants per plot, than sprays containing
2 pounds 48 percent chloranil and 2 pounds of 50 percent chlora-
nil per 100 gallons water. However, in 1951 when the disease
was less severe than in 1952, a spray containing 2 pounds 50
percent chloranil was as effective as one containing 4 pounds
of 48 percent chloranil per 100 gallons water.
Five percent chloranil dust gave as good control of downy
mildew as 12 percent chloranil dust in 1952, as there were no
significant differences in average percentages of foliage killed
and average numbers and weights of plants in plots treated
with these materials. The chloranil dusts were as effective
against the disease as the best chloranil spray, except in 1948.
In 1949 and 1950 there were no significant differences between
average number and weight of plants treated with nabam (2
qts. 1 lb. ZnSO 100 gals. water or 4 qts. 2 lbs. ZnS4 100
gals. water) and average number and weight of those treated
with 48 percent chloranil (4 lbs. 100 gals. water). But in 1948,
1951 and 1952 weights of plants treated with 48 percent chloranil
(4 lbs. 100 gals. water) significantly exceeded weights of those
treated with nabam spray.
In 1951 and 1952 phygon XL-N and manzate sprays were as
effective against downy mildew as other sprays tested in those
years, with the exception of 48 percent chloranil (4 lbs. -100
gals. water).

FUNGICIDES USED ON HEADING CABBAGE
Sprays, including two formulations of chloranil and one formu-
lation each of six other chemicals, and five fungicidal dusts were
tested for control of downy mildew on heading cabbage from
1949 to 1953. Four to 6 ounces of SS3 spreader-sticker or Triton
B 1956 were used with each 100 gallons of spray. The fungicides







Control of Downy Mildew of Cabbage with Fungicides 15

were applied with a tractor-operated sprayer or duster to cab-
bage grown in three-row plots 28 to 50 feet in length. A turn-
row between ends of the plots and a 10-foot unplanted space
between sides of the plots minimized drift of the fungicides
from one treatment to the next. Treatments were started one
to three weeks before the earliest heads were large enough for
cutting and were completed a few days before the last cutting.
Treatments were made three to eight times and at three- to
seven-day intervals during the different years, except when the
schedules were interrupted by rains.






























Fig. 2.-Cabbage head severely damaged by downy mildew.

As the heads were cut they were grouped into two classes
according to the degree of injury caused by downy mildew on
the head leaves. The first class consisted of heads free of the
disease and others slightly to moderately damaged but with
)I!




S.. .. t .









disease and others slightly to moderately damaged but with







16 Florida Agricultural Experiment Stations

less than 20 mildew spots 1/32" or less in diameter. The second
class consisted of severely damaged heads where appearance
was badly marred by spots 1/32" or larger in diameter and
others with parts of the head leaves badly discolored and decayed
by the disease, as shown in Figure 2. The first class was con-
sidered salable and the second unsalable. The average percent-
age of severely damaged heads per plot was used to measure
effectiveness of the different fungicides for downy mildew control.
Damage caused by downy mildew on heading cabbage varies,
depending upon whether conditions favor development of the
disease during the last few weeks of the growing period. Heads
severely damaged by the disease in the check plots ranged from
0.1 to 21.3 percent during the five-year period, as recorded in
Table 6.
In 1949, when downy mildew ruined the salability of 11.2 per-
cent of the heads in the check plots, all fungicides controlled
the disease. Forty-eight percent chloranil (4 lbs. -100 gals.
water) gave significantly better control than the other fungi-
cides, except 12 percent chloranil dust.
Nabam spray was significantly more effective against downy
mildew than zineb dust in 1950, when 21.3 percent of the heads
of non-treated plants were severely damaged by the disease.
Mildew was very mild in 1951 and 1952 and not enough heads
were damaged by the disease to measure effectiveness of the
different treatments.
In 1953, when 5.3 percent of the heads of non-treated plants
were damaged severely by downy mildew, significant control of
the disease was obtained with 48 percent chloranil (4 lbs. 100
gals. water), 50 percent chloranil (2 lbs. 100 gals. water) and
nabam spray.
Single and double strength nabam spray and zineb dust were
applied to heading cabbage on a three- to four-day and a six-
to seven-day schedule in 1950 and results are given in Table 7.
Only 5 percent of the non-treated heads were damaged severely
by downy mildew. There were no significant differences between
percentages of severely damaged heads of non-treated and treated
plants.
None of the fungicides injured cabbage plants, except in 1951
when phygon XL-N produced numerous small brown to black
spots on the head leaves which marred the appearance of the
heads but did not make them unsalable. Yields were not affected
by any of the fungicides used on heading cabbage.








TABLE 6.-RESULTS OF TREATING HEADING CABBAGE WITH DIFFERENT FUNGICIDES FOR CONTROL OF DOWNY MILDEW
FROM 1949 TO 1953.

Heads per Plot
1949 | 1950 1 1951 | 1952 I 1953
Fungicides* Average Average i Average I Average Average
Severely Severely Average Severely Severely Severely
Average Damaged by Average Damaged by Number Damaged byama Average Damagedby average Damaged by
Number Downy Mildew Number Downy Mildew | Downy Mildew INumber Downy Mildew Number Downy Mildew
SAngles | Angles et. Angles | I Angles I IAngles
Sprays** Pet. IDeg.ft Pet. Deg.Pt D'geg.t Pet. De,.t I Pet. Deg.f
Chloranil (48%)
4 lbs ............... 2 0.6 3 :ii 0.1 1 110 0.4 2 114 0.2 1
Chloranil (50%)
2 lbs. .................. 110 0.5 2 110 0.2 1
Nabam (27%)-ZnSO, I I I I
2 qts.- l b........... 8'i 2.7 9 117 0.3 2 36 0.1 1 109 1 0.4 3 117 0.9 3
Manzate (70%)
1% lbs .................. .... | 0.0 0 109 0.5 3
Tribasic Copper (53%)
7 lbs. ..................... 81 2.8 10
Ziram (76%)
2 lbs. ............ 81 5.0 12 .
Phygon XL-N (50%) II
1 lb. ...................... .. I . | .... .... .. ... : 0.1 1 112 0.2 1 ...
Captan (50%)
4 lbs ........ .... ..... 36 0.0 0 ... ..
Dusts
12% Chloranil 82 1.8 7 112 2.3 6
5% Chloranil .. 114 1.8 7
7% Tribasic Copper 82 3.4 10
6.5% Zineb............ 82 3.7 11 113 8.7 17 .
4% Ziram ......... 79 I .8 11 .. .... ..

Check .... 80 11.2 19 118 | 21.3 27 37 0.1 1 112 1.3 6 113 5.3 13

Least Significant
Difference .05 Level 9 N.S. N.S. 8

Applied 7 times in 1949, 4 times in 1950 and 1953, 3 times in 1951 and 5 times in 1952. Three- to four-day and five- to seven-day schedules were used
and the treatments were replicated 3 to 4 times in the different years. Sprays were applied at 125 to 150 gallons and dusts at 30 to 35 pounds per acre at
each application.
"** Pounds and quarts listed under the different fungicides were the amounts used in 100 gallons water.
t The angles corresponding to the percentages were obtained according to the arc sin transformation method as described by Snedecor (10) pp. 445-452.









18 Florida Agricultural Experiment Stations

TABLE 7.-RESULTS OF TREATING HEADING CABBAGE WITH SINGLE AND
DOUBLE STRENGTH NABAM SPRAY AND ZINEB DUST AT THREE- TO FOUR-
DAY AND SIX- TO SEVEN-DAY INTERVALS FOR CONTROL OF DOWNY MILDEW
IN 1950.

Days Heads per Plot
Between Average
Fungicides* Applica- Average Severely
tions Number Damaged by
SDowny Mildew
Angles
Pet. Deg.**
Nabam (27%)

"2 qts.- 1 lb. ZnSO0 100 3-4 148 2.5 9
gals. water .............------.............. 6-7 147 1.8 9

4 qts. 2 lbs. ZnSO 100 3 3-4 150 2.4 9
gals. water ................................. 6-7 147 1.6 6


5 3-4 146 2.0 8
6.5% Zineb Dust ........................ 6 7 148 1.8 8

Check ---.....---.....--..... --.........- -.... 141 5.0 13


Least Significant Difference
.05 L evel ....................... ... ...... .... N .S.

Applied 4 times on a six- to seven-day schedule and 8 times on a three- to four-day
schedule. Treatments were replicated 3 times. Sprays were used at 150 gallons and dust
at 35 pounds per acre at each application.
** The angles corresponding to the percentages were obtained according to the arc sin
transformation method as described by Snedecor (10) pp. 445-452.

TABLE 8.-NUMBER OF DAYS WHEN MINIMUM TEMPERATURES WERE OPTI-
MUM FOR DEVELOPMENT OF DOWNY MILDEW IN THE HASTINGS SECTION
DURING A THIRTEEN-YEAR PERIOD, 1940 TO 1952.

S Number of Nights Minimum Temperatures
Month __Were 500 to 60 F.*

Least Greatest Average

January ........ 4 30 11.8
February ...... 6 19 11.0
March ......... 8 17 12.6
April ............. 5 18 12.5
May .............. 0 18 7.1
June .........0. 0 3 0.2
July ................ 0 0 0.0
August .......... 0 0 0.0
September .... 0 4 0.3
October .......... 0 22 7.8
November ...... 4 21 13.1
December ...... 6 21 12.5

As recorded by the U. S. Weather Bureau at Federal Point. St. Augustine and Palatka
records were used when those at Federal Point were missing,








Control of Downy Mildew of Cabbage with Fungicides 19

CONCLUSIONS
Outbreaks of downy mildew occur at Hastings when heavy
dews or rains keep plants wet for long periods and nocturnal
temperatures range between 50 and 600 F. for several nights in
succession. Warm or cold dry periods retard development of
the disease. Usually temperatures are most favorable for de-
velopment of downy mildew at Hastings in November and Decem-
ber, when most of the plants are being produced for setting in
the field, and also in March and April, when most of the crop is
maturing, as shown in Table 8.
Downy mildew may kill most plants in the seed-leaf stage and
severely damage the remainder in unprotected plant beds if the
seedlings emerge from the soil when conditions are favorable
for development of the disease. Larger plants with true leaves
usually survive the disease but their growth is retarded. Thus,
downy mildew is a constant threat to successful production of
cabbage, cauliflower and broccoli plants in Florida from the date
of its first appearance in the fall until the end of the plant-
growing season the following February.
Data presented in this bulletin and in other publications (1,
2, 3, 4, 6) prove that serious damage from downy mildew in
plant beds can be prevented by regular applications of several
different fungicides. Of those tested at Hastings from 1940 to
1953, chloranil sprays and dusts and nabam and zineb sprays
gave best control of downy mildew in plant beds.
Results of tests reported in Table 5 showed that 48 percent
chloranil (4 lbs. 100 gals. water) was more effective against
downy mildew in plant beds when the disease was severe than
sprays containing 2 pounds 48 or 50 percent chloranil per 100
gallons of water. Since results showed that 5 percent chloranil
dust was as effective against the disease as 12 percent chloranil
dust, cost of control may be reduced by using the former, as it
contains about one-half as much of the active ingredient as the
latter and should cost proportionately less.
When downy mildew damaged enough heads in test plots at
Hastings to measure effectiveness of different fungicides for
controlling the disease on heading cabbage, results showed that
it could be controlled by applying chloranil, nabam and other
fungicides every three to seven days during the last three to
five weeks of the growing season.
It would be impractical to control downy mildew with para-
dichlorobenzene in low-lying, poorly-drained flatwoods soils at







20 Florida Agricultural Experiment Stations

Hastings and similar areas of the state because of the excessive
cost of frames and labor required to treat plants grown in nar-
row seedbeds. Furthermore, chloranil and nabam are as effec-
tive against the disease as PDB and can be applied at less expense.
As the earliest date the disease has appeared on seedling plants
in the Hastings area during the last 13 years is September 19,
it is safe to delay treatment of cabbage plant beds with fungi-
cides for control of downy mildew until September 15 in that
area. In other areas of the state where the disease is known
to have occurred earlier in the fall, treatment for downy mildew
control should be started sooner.

SUMMARY

Data are presented showing results of tests conducted at Hast-
ings from 1940 to 1953 for evaluating fungicides for control of
downy mildew of cabbage.
Fungicides Used in Plant Beds.-Paradichlorobenzene gave
good control of downy mildew in 1940 and 1941, when 3 pounds
PDB crystals per 100 square yards of seedbed were applied be-
tween 4 and 5 P.M. on each of three successive days at weekly
intervals. Treatment with 2 pounds of PDB crystals per 100
square yards of seedbed gave poor control and the 4- and 5-pound
treatments injured the plants. Injury was highest when noc-
turnal temperatures (70 F. and higher) caused rapid vaporiza-
tion of the PDB crystals. Treatments were not effective when
made during periods when nocturnal temperatures were 400 F.
or lower.
In tests from 1940 to 1943 bordeaux mixture, Flordo and
Flordo K sprays gave good control of downy mildew when used
at full strength but injured the plants. They gave poor control
when used at half- and quarter-strength.
Downy mildew was not controlled satisfactorily when the
plants were sprayed with Flordo Cl, Ceresan plus SS3 spreader-
sticker, U. S. Rubber Co. No. 366, sulfur wettable and bismuth
subsalicylate plus vatsol; or when the plants were dusted with
copper-lime, copper compound A, sulfur and ferbam dust. Cupro-
cide spray used with or without emulsified cottonseed oil con-
trolled the disease but injured the plants; oil increased the injury.
Ferbam spray containing SS3 spreader-sticker also controlled
downy mildew but was injurious to the plants.







Control of Downy Mildew of Cabbage with Fungicides 21

Chloranil sprays and chloranil dust proved superior to other
fungicides tested for control of downy mildew during the 1940-
1943 period.
Chloranil, nabam and zineb sprays and chloranil dust were
more effective against downy mildew than other fungicides used
in plant beds from 1944 to 1946. Manzate spray, and 4 percent
zineb, 12 percent chloranil plus 10 percent ferbam, 12.5 percent
ziram and 15 percent copper compound A dusts were less effective
against the disease. None of the fungicides injured the plants.
Forty-eight percent chloranil (4 lbs. 100 gals. water) and 12
percent chloranil dust gave significantly better control of downy
mildew than other fungicides tested from 1948 to 1952, with the
exception of nabam spray in 1949 and 1950, 50 percent chloranil
(2 lbs. 100 gals. water) in 1951 and 5 percent chloranil dust
in 1952.
Phygon XL-N and manzate sprays were as effective against
downy mildew as other sprays tested in 1951 and 1952, with the
exception of 48 percent chloranil (4 lbs. 100 gals. water).
The 6.5 percent zineb dust was not as effective against downy
mildew as chloranil spray and dust in the three years these
fungicides were compared. Zineb dust was statistically equal
to nabam spray in 1948 but not in 1949 and 1950, as measured
by weights of plants.
Fungicides Used on Heading Cabbage.-In 1949, 48 percent
chloranil (4 lbs. 100 gals. water) significantly excelled other
fungicides tested for downy mildew control, except 12 percent
chloranil dust.
Nabam spray and zineb dust gave good control of downy mil-
dew in 1950. Nabam spray was significantly more effective
than zineb dust.
Mildew was very mild in 1951 and 1952 and not enough heads
were damaged by the disease to measure effectiveness of differ-
ent treatments.
In 1953 significant control of downy mildew was obtained with
48 percent chloranil (4 lbs. 100 gals. water), 50 percent chlora-
nil (2 lbs. 100 gals. water) and nabam spray.
Owing to mildness of downy mildew in 1950, no information
was obtained on the relative effectiveness of single and double
strength nabam spray and zineb dust in controlling the disease
on heading cabbage when they were applied on a three- to four-
day and a six- to seven-day schedule.
None of the fungicides used on heading cabbage affected yield
or salability of the heads.







22 Florida Agricultural Experiment Stations

RECOMMENDATIONS
Chloranil has been used by cabbage growers at Hastings to
control downy mildew in cabbage plant beds since 1943. Nabam
has been used since 1947, mostly to control the disease on head-
ing cabbage.
Plant Beds and Seeded Fields.-Forty-eight or 50 percent
chloranil (4 lbs. 100 gals. water) and 5 percent chloranil dust
are recommended for control of downy mildew in plant beds.
If chloranil cannot be applied at the rates recommended, spray
the plants with nabam (2 qts. 1 Ib. ZnS04 -100 gals. water)
or zineb (11/ lbs. 100 gals. water), as there is less danger of
injuring small plants by overtreatment with these fungicides
than with chloranil. Nabam has been used at double strength
in plant beds without injury (see Table 5).
Begin treating the plants with a fungicide a week to 10 days
after the seed is planted or before then if the disease is present.
Continue the treatment three times each week with a one- to
two-day interval between applications, except when nocturnal
temperatures drop to 400 F. or lower or heavy rains interrupt
the schedule. Use 80 to 150 gallons of the spray or 15 to 35
pounds of the dust per acre at each application, depending upon
size of the plants. Quantities used successfully in narrow plant
beds are listed in Table 4. Treat plant beds until all usuable
plants are drawn. Where the crop is started from seed sown
in the field, continue treating until the plants are thinned to a
stand.
Sprayer and auxiliary tanks should be calibrated and the cor-
rect amount of fungicide and water used to make the required
quantity and strength of spray recommended. Young cabbage
plants less than 8 inches in height may be injured or killed if
treated with chloranil spray which is stronger than recommended
and if the amounts of chloranil spray or dust used on small
plants at each application exceed those listed in Table 4. Plants
less than 4 inches in height are more susceptible to injury from
overtreatment with chloranil than larger ones. The stem of a
severely-damaged seedling appears water-soaked at first and
later turns white; the seedling falls over and dies as if affected
with damping-off. Overtreatment with chloranil also causes
malformation of the plant; the petioles may be elongated, the
midribs enlarged and the blades undersize and rolled slightly
upward and inward. Leaves of affected plants often are shaped
like rabbit ears. A chloranil-injured, malformed plant will re-








Control of Downy Mildew of Cabbage with Fungicides 23

cover and grow normally after the treatment is discontinued
if it has not been severely stunted and burned; after "rabbit
eared" plants are set in the field, new leaves formed are normal
in size and shape.
Heading Cabbage.-Nabam (2 qts. 1 lb. ZnSO4 100 gals.
water), 50 percent chloranil (2 lbs. 100 gals. water), 5 percent
chloranil dust and 6.5 percent zineb dust are recommended for
control of downy mildew on heading cabbage. Treatment of
plants should begin one to three weeks before harvest, depend-
ing upon severity of the disease. Continue the treatment at
intervals of six to seven days until all marketable heads are cut.
Use 100 to 150 gallons of spray or 30 to 35 pounds of dust per
acre at each application, depending upon size of the plants. Use
a good commercial spreader-sticker with the spray as recom-
mended on the manufacture's label.
Compatibility with Insecticides.-Chloranil, nabam and zineb
are compatible with chlordane, DDT, parathion, TEPP and toxa-
phene which may be used in cabbage plant beds and fields to
control various insects.

LITERATURE CITED
1. EDDINS, A. H. Control downy mildew of cabbage with spergon and
fermate. Fla. Agr. Exp. Sta. Press Bul. 589. 1943.
2. Protecting cabbage plant beds from downy mildew with
spergon. Proc. Fla. State Hort. Soc. 57: 195-199. 1944.
3. Control downy mildew of cabbage with spergon. Fla.
Agr. Exp. Sta. Press Bul. 633. 1947.
4. Diseases, deficiencies and injuries of cabbage and other
crucifers in Florida. Fla. Agr. Exp. Sta. Bul. 492. 1952.
5. FELTON, MATHIAS W., and J. C. WALKER. Environal factors affecting
downy mildew of cabbage. Jour. Agr. Res. 72: 69-81. 1946.
6. FOSTER, H. H. The control of cabbage downy mildew through use of
sprays. Phytopath. 37: 712-720. 1947.
7. KINCAID, RANDALL R. A copper-soap spray for control of tobacco
downy mildew. Phytopath. 31: 286-288. 1941.
8. LEBEAU, F. J. Systemic invasion of cabbage seedlings by the downy
mildew fungus. Jour. Agr. Res. 71: 453-463. 1945.
9. SHIPPY, WILLIAM B. Flordo spray. Fla. Agr. Exp. Sta. Press Bul.
547. 1940.
10. SNEDECOR, GEORGE W. Statistical methods. 485 pp. Ed. 4. Iowa
State College Press. 1953.
11. TISDALE, W. B., and RANDALL R. KINCAID. Controlling tobacco downy
mildew (blue mold) with paradichlorobenzene. Fla. Agr. Exp. Sta.
Bul. 342. 1939.





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