POTATO INVESTIGATIONS LABORATORY
Mimeo Report 57-1 October 1, 1956
RECOMMENDATIONS FOR CONTROL OF LATE BLIGHT OF POTATOES
A. H. Eddins
A spray containing 2 quarts nabam (Dithane D14 or Parzate 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./lO0 gals.) and Manzate 75% (1) lbs./100
gals.) also are recommended.
The number and frequency of applications of spray required to control late
blight in the Hastings area vary according to the 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
Directions for Making Nabam-4inc 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 Blkor Parzate Liquid) for each 100 gallons
water after agitator is covered with water. Allow at least one minute for the
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 1 to 2 2 2
300 6 2 to 3 3 3
4oo 8 3 to 4 4 4
500 10 3 3/4 to $ 5 5
*Note that quantities of parathion required are measured in pints not quarts.