Title: Control of downy mildew of cabbage
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00076319/00001
 Material Information
Title: Control of downy mildew of cabbage
Physical Description: Book
Creator: Eddins A. H.
Publisher: Potato Investigations Laboratory,
Copyright Date: 1954
 Record Information
Bibliographic ID: UF00076319
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: 138392210 - OCLC

Full Text


Control of Downy Mildew 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 mold which 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 appearance 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 fol-

lowing 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 temperatures below

400 F. or above 82 F.

Downy mildew can be controlled satisfactorily with several different fungicides.

Ones recommended for its control at Hastings are chloranil, nabam and zineb.

Plant Beds and Seeded Fields.- Forty-eight or 50 percent chloranil (4 lbs. -

100 gals. water) and 5 percent stabilized chloranil dust are recommended for control

of downy mildew in plant beds. Chloranil usually has given better control of the

disease than other fungicides. However, if chloranil cannot be applied at the rates

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 noc-

turnal temperatures drop to 00 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 1. Treat plant beds until all usuable plants

are drawn, Where the crop is started from seed sown in the field, continue treat-

ing until the plants are thinned to a stand.

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 ex-

ceed those listed in Table 1. Plants less than 4 inches in height are more suscep-

tible 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 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 lb. ZnSO4 100 gals, water), 48 or 50 per-

cent 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 commercial spreader-sticker with the spray as recommended on the manu-

facturer'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.

Table 1.- Quantities of Spray and Dust to Use at Each
Downy Nildew on Small Plants.

Application for Control of

Narrow 2- to 3-Drill Row Beds One Yard Wide
Beds 40 inches Apart ______ _
Plant Height Spray Dust Spray Dust
Gals. per Acre Lbs. per Acre Gals, per Lbs, per
S. 100 Sq. Yds. 100 Sq. Yds.

Less than 2 inches 80 to 100 15 to 20 to 5 3/4 to 1

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

4 to 8 inches 120 to 150 25 to 35 6 to 7 1I to 2

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