F 3 f36l POTATO INVESTIGATIONS LABORATORY
Mimeo Report 62-2* October 6, 1961
DIRECTIONS FOR CONTROLLING LATE BLIGHT AND EARLY BLIGHT OF POTATOES WITH FUNGICIDES
A. H. Eddins
The two most important foliage diseases of potatoes in the Hastings area are
late blight caused by Phytophthora infestans (Mont.) D By. and early blight caused
by Alternaria solani (Ell. & G. Martin) Sor. Late blight usually appears earlier in
the season and is much more prevalent and destructive than early blight. Conse-
quently fungicides are used primarily for control of late blight in the Hastings
area. Fortunately fungicides which are effective against late blight will also con-
trol early blight. Ones recommended for control of both diseases are listed below.
Amounts of Each Ingredient in Water
Fungicide to make following Quantities of Spray
100 gals. 200 gals. 300 gals. 400 gals. 500 gals.
Nabam 19% 2 qts. 4 qts. 6 qts. 8 qts. 10 qts.
ZnSO4 36% 3/4 lb. 1l lbs. 21 lbs. 3 lbs. 3-3/4 lbs.
Zineb 65% 2 Ibs. 4 lbs. 6 lbs. 8 lbs. 10 lbs.
Maneb 80% l1 lbs. 3 lbs. 4 lbs. 6 Ibs. 7T Ibs.
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
or the disease is known to be present in the area, it is advisable to start spraying
potato plants immediately. During the past 31 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, 11; April, 11; May, 2; and none 2 times. Four to
five applications of spray made at 5- to 10-day intervals may be sufficient to con-
trol the disease during dry growing seasons when weather conditions favorable for
its development do not occur frequently and are of short duration. In wet seasons
when favorable periods are numerous and of long duration it may be necessary to
spray the plants 10 times or more at 4- to 7-day intervals for control. The number
of spray applications required to control late blight in the Hastings area can be
held to a minimum and money thereby saved if the grower will keep fully informed on
the weather and occurrence and development of the disease. Information on the
weather and late blight development in the Hastings area can be obtained from the
Potato Investigations Laboratory, telephone 692-1792.
Nabam-zinc sulfate, zineb and maneb are compatible with the insecticides
commonly used for control of insect pests of potatoes.
Directions for Making Nabam-zinc Sulfate Spray
1. Start running water in tank and operate agitator while mixing spray.
2. 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. .-
3. Slowly pour in 3/4 pound of finely granulated or completely dissol)4i?
sulfate (36 percent metallic zinc equivalent) for each 100 g Allo
least two minutes for the zinc sulfate to react with the nab ,
4. Ad insecticides if needed and keep agitator going until spray 141 ed. 1
5. When zineb and maneb are used follow directions given in 1 and above r7m:
*Revision of Mimeo Report 59-2.