EXPERIMENT STATION BULLETINS. 



355 



Fig. 17. The elevated mixing platform lessens the labor of filling the spray tank. 



Spray Materials to Use 



In addition to arsenical poisons for the control of leaf chewing insects, 

 every spray application should contain bordeaux mixture (4-4-50) for the 

 cdlitrol of hopperburn, early blight, and late blight. 



Hopperburn, also called tipburn, is caused by leafhoppers. They are pale 

 green insects that live mostly on the under sides of the leaves where they feed 

 by sucking the plant juice, causing the leaves to curl upward and turn black 

 at the tips and margins. Leafhoppers appear in potato fields about the 

 middle of June and breed in them throughout the season. Bordeaux mix- 

 ture aids in warding off serious attacks of the leafhoppers and helps to keep 

 the plants green. Leafhopper injury is most pronounced late in the season. 

 It is very important that the bordeaux applications be continued until the 

 end of the growing season. The small amount of injury to the vines caused 

 by the wheels of the spray machine is of little consequence. Do not cease 

 spraying because the vines are rank. 



The leafhopper is one of the most serious pests that attacks the potato. 

 It is largely responsible for the average low yields that are secured in this, 

 state. In 1921 many potato fields were dying from leafhopper injury or 

 hopperburn during August and September, right at the time when they should 

 have been in a healthy, green condition. 



Hopperburn is usually most severe in hot, dry weather. Bordeaux mix- 

 ture does not kill the leafhopper but it does act as a repellant. It has been 

 found that in hot, dry weather the bordeaux mixture acts as a stimulant to 

 the potato plants, and in a small degree counteracts the effects of adverse 

 weather conditions. 



Early blight is a fungous disease that is most serious during periods of 

 hot, dry weather. It produces target-like markings on the leaves and reduces 

 the yield of tubers. 



