Title: Control of downy mildew of cabbage
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 Material Information
Title: Control of downy mildew of cabbage
Physical Description: Book
Creator: Eddins A. H.
Publisher: Potato Investigations Laboratory,
Copyright Date: 1955
 Record Information
Bibliographic ID: UF00076278
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: 135002314 - OCLC

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POTATO INVESTIGATIONS LABORATORY


Mimeo Report 56-4* September 27, 1955

CONTROL OF DOXaY MILDEI OF CABBAGE

A. H. Eddins

Downy mildew of cabbage, cauliflower, broccoli and closely related crucifers
is caused by the fungus Peronospora parasitica, The fungus appears on the leaves
as a white maid iwich can be seen easily when the plants are wet. Downy mildew
is a leaf spotting disease. It stunts or kills young seedlings, and may retard
the growth of older plants. Spots on the head leaves of cabbage mar the appear-
ance of the heads and may make them unsalable.

Downy mildew begins to appear on cabbage at Hastings, Florida, in September
or October and is present from that time until the end of the growing season the
following spring. Outbreaks of the disease occur when heavy dews or rains keep
plants wet for long periods and nocturnal temperatures range between 500 and 600
F, for several nights in succession, Little of the disease develops at tempera-
tures below 400 F. or above 82 F,

Downy mildew can be contrroQed satisfactorily with several different fungi-
cides* Ones recommended fbr its o t~, at Hastings are chloranil, nabam and
sineb.

Plant Beds and Seeded Field4-t. Forty-eight or 50 percent chloranil
(4 lbs. 100 gals. water. andi percent stabilized chloranil dust art recom-
mended for control of downy mldew in plant beds. Chloranil usually has given
better control of the disease than other fungicides. However, if chloranil can-
not be applied aj the iates recommended, spray the plants with nabam (2 qts. -
1 lb, ZnSO4 100 gals. water) or zineb (1 lbs. 100 gals, water), as there is
less danger of'injuring small plants by overtreatment with these fungicides than
with chloranil.

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 3
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 plAntsj quantities used
successfully in narrow plant'beds are listed in Table 1. 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.



* Reprint of Mimeo Report 55-1

*'









Table 1.- Quanitties of Spray and Dust to Use at Each Application for Control of
Downy Mildew on Small Plants.

Narrow 2- to 3-Drill Row
Beds 40 inches Apart Beds One Yard Wide
Plant Height Spray Dust Spray Dust
Gale, per Acre Lbs. per Acre Gals. per Lbs. per
10 Y 100 Sq. Yds. 100 So, Yds
Less than 2 inches 80 to 100 15 to 20 4 to 5 3/4 to 1

2 to 4 inches 100 to 120 20 to 25 5 to 6 1 to 1,

4 to 8 inches 120 to 150 25 to 35 6 to 7 1* to 2
-- a - Tr r -i -i - ; w r TT f r v l i- inn i T ii i i ; r - ^ .


Sprayer and auxiliary tanks should be calibrated and the correct amount of
fungicide and water used to make the required quantity of spray at the strength
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 1. 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. Over-
treatment 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 recover 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 Ib. ZnSO4 100 gals, water), 48 or
50 percent chloranil (2 Ibs. 100 gals. water), 5 percent stabilized chloranil
dust and 6.5 percent zineb dust are recommended for control of downy mildew on"
heading cabbage. Treatment of plants should begin 1 to 3 weeks before harvest,
depending upon severity of the disease. Continue the treatment at intervals of
6 to 7 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 conmhercial spreader-sticker with the spray as recommended
on the manufacturer's label.

Compatibility with Insecticides.-- Chloranil, nabam and zineb are compatible
with chlordane, DDT, parathion, TEPP and toxaphene which may be used in cabbage
plant beds and fields to control various insects,




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