666 



STATE BOARD OF AGRICULTURE. 



vines before the dusts were applied. The insects which dropped onto 

 tlie paper were not collected until 30 minutes after the dusts were ap- 

 plied in order to allow any insects which were not killed to escape. 

 The effectiveness of the dusts is shown in the accompanying counts of 

 leafhoppers. 



Table VI. Eff3ct of Nicoliae Dusts on Laafhopper Control, 1921 



In addition to the leafhoppers, the impregnated dusts killed great 

 numbers of plant lice (aphids). The trials were made too late in the 

 season to determine the effect on hopperburn or to determine whether 

 the dust had an injurious effect upon the foliage. Although these pre- 

 liminary dusting trials show encouraging results, the practice in addi- 

 tion to the greater cost has not yet passed the experimental stage and 

 cannot be recommended to replace spraying with bordeaux mixture. 



SUMMARY 



Three years' study of the burning injury of potato foliage in Michi- 

 gan has shown — 



1. Hopperburn is one of the greatest factors reducing Michigan 

 potato yields during dry seasons, 



2. The injury is caused by the potato leafhopper, Empoasca nuili. 



3. The insect passes the winter in Michigan as an adult, emerges 

 during May, flies to potato fields about the middle of June, and lays 

 eggs on the vines. 



4. There are two complete generations each season in Michigan 

 approximately one month elajtsing from the time the eggs are laid 

 until the nymphs hatcli and develop into adults. 



5. Time of planting has a marked effect on amount of hopperburn 

 in a field. Fields planted after June 15, in the Upper Peninsula showed 

 very little injury, 



0. Early varieties are more susceptible to hopi)erburu than late 

 varieties. The rural t3q)es, seem most resistant. 



7. The insect is repelled and hopperburn is controlled by spraying 

 tlie vines with 4-4-50 bordeaux mixture. 



8. Dehydrated copper sulphate and lime dust and dusts impregnated 

 with nicotine give some promise for control of hopperburn and the leaf- 

 liopper, but cannot yet be recommended to replace spraying with bor- 

 deaux mixture. 



