POTATO IfVESTIGATIONS LABORATORY u
Hastings, Florida/ "O
Mimeo Report 59-2* ( ,October 1, 1958
CONTROL OF LATE BLIGHT OF POTATOES
A. H. Eddins
A spray containing 2 quarts nabam (Dithane D1 or Parzate Liqui)id'Ynd 3/4 to
1 pound spray grade zinc sulfate in 100 gallons of water is recommended for control-
ling late blight. Zineb 65% (2 lbs./lOO gals.) and Manb 70% (1i lbs./lOO gals.)
also are recommended. These fungicides also will control early blight which may
occur at Hastings during the latter part of the growing season.
The number and frequency of applications of spray required to control late
blight in the Hastings area vary according to the date of appearance of the disease
and the weather. Weather conditions favorable for its development consist of 8 con-
secutive days when the 7-day average daily temperature ranges from 500 to 770 F. and
the 10-day total rainfall is 1 inch or more. When these weather conditions are met
and the disease is known to be present in the area, it is advisable to start spray-
ing potato plants immediately. During the past 28 potato-growing seasons the number
of times late blight was first reported in the Hastings area by months was as
follows: January, 2; February, 3; March, 10; April, 9; May, 2; and none 2 times.
A maximum of five applications of spray made at 5- to 10-day intervals should afford
sufficient protection against the disease during dry growing seasons when weather
conditions favorable for the disease do not occur frequently and are of short dura-
tion. In wet seasons when favorable periods occur frequently and are of long dura-
tion it may be necessary to spray the plants 10 times or more at 4- to 7-day inter-
vals to obtain satisfactory control of late blight. Information on weather con-
ditions and late blight forecasts can be obtained when needed from the Hastings
Experiment Station (Potato Laboratory); telephone, Myrtle 2-5921.
Nabam-zinc sulfate, zineb and maneb are compatible with the insecticides, DDT,
parathion, thiodan, toxaphene and chlordane which may be used for control of insect
pests of potatoes.
*Revision of Mimeo Report 58-2.
Directions for Making Nabamzinc 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 D14 or 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.
U. 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, or
1 quart 25 percent thiodan emulsion in 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.
Meaterial.s Required to Make Different Quantities of Spray
For Late Blight Control For Aphid Control
Water heabam Zinc 25% DDT OR 25% Thiodan OR 25% Parathion
Gallons Quarts Sul2ate Emulsion Emulsion Emulsion
Pouds Quarts Quarts Pints
100 2 3/4 to 1 1 1 1
200 4 1* to 2 2 2 2
300 6 21 to 3 3 3 3
o00 8 3 to 4 4 4 4
500 10 3-3/4 to 5 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.