POTATO INVESTIGATIONS LABORATORY
Mimeo Report 58-2* October 1, 1957
CONTROL OF LATE BLIGHT OF POTATOES
A. H. Eddins
A spray containing 2 quarts nabam (Dithane D14 or Parsate Liquid) and 3/4 to
1 pound spray grade zinc sulfate in 100 gallons of water is recommended for con-
trolling late blight. Zineb 65% (2 lbs./10O gals.) and Manzate 70% (1I lbs./
100 gals.) also are recommended.
The member and frequency of applications of spray required to control late
blight in the Hastings area vary according to the date of appearance and severity
of the disease, which is more prevalent and destructive in a wet growing season than
in a dry one. Make the first application of spray when the plants are six to eight
inches tall or before then if the disease appears earlier. During dry seasons spray
the plants at least five times at five to 10-day intervals to prevent damage from
late blight and to combat early blight. During wet seasons when plants are attacked
by late blight soon after they emerge from the soil and weather conditions favor its
development until harvest, it may be necessary to spray the plants ten-times or more
at four- to seven-day intervals to obtain satisfactory control.
Apply the spray as uniformly as possible with a tractor-operated sprayer
equipped with a six- to twelve-row boom and enough nozzles per row to cover the
plants with the spray. Good control can be obtained by using 100 to 125 gallons
spray per acre on small plants at the first application. Increase this quantity as
the plants grow larger and apply 165 to 175 gallons per acre to cover full-grown
Nabam-zinc sulfate, zineb and maneb are compatible with the insecticides, DDT,
parathion, toxaphene and chlordane which may be used for control of insect pests of
*Revision of Mimeo Report 57-1. 9 C
Directions for Making Nabam-zinc sulfate Spray
1. Start running water in tank with agitator going.
2. Keep agitator going while spray is being mixed.
3. Pour in 2 quarts nabam (Dithane Dih or Parzate Liquid) for each 100 gallons
water after agitator is covered with water. Allow at least one minute for the
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nabam to mix with the water.
4. Slowly pour in 3/4 to one pound of finely granulated or completely dissolved
zinc sulfate (36 percent metallic zinc equivalent) for each 100 gallons.
Allow at least two minutes for the zinc sulfate to react with the nabam.
5. Add 1 quart 25% DDT emulsion for each 100 gallons of spray for aphid control on
potatoes. If DDT emulsion is not giving satisfactory control of aphids, use
parathion, 1 pint 25 percent emulsion or equivalent per 100 gallons spray. No
spreader-sticker is needed when the spray is used on potatoes.
6. Keep agitator going in sprayer and auxiliary tanks until the spray is applied.
Materials Required to Make Different Quantities of Spray
For Late Blight Control For Aphid Control
Water Nabam Zinc Sulfate 25% DDT Emulsion OR 25% Parathion
Gallons Quarts Pounds Quarts Emulsion, Pints*
100 2 3/4 to 1 1 1
200 4 l1 to 2 2 2
300 6 2g to 3 3 3
o00 8 3 to 4 4 4
500 10 3-3/4 to 5 5 5
*Note that quantities of parathion required are measured in pints not quarts.
Eddins, A. H. Control of late blight of potatoes with fungicides at Hastings,
Florida. Amer. Potato Jour. 34: 42-48. 1957.