﻿42 BULLETIN 19, U. S. DEPARTMENT OF AGRICULTURE. 



The most effective time to make the tobacco spray application 

 against the nymphs is just before those that hatched earliest in the 

 season have reached the fourth molt. This can be determined by 

 the length of the wing pads (PI. I) which, in the fourth stage, extend 

 about one-third the length of the abdomen. At this time a larger 

 number of nymphs are likely to be present on the vines than at any 

 other time during the. season. In the vineyards of the Lake Erie 

 Valley this condition occurs toward the end of the first week in July, 

 and the most effective work with the tobacco-spray liquid may be 

 done during the two weeks following this date. After this period, 

 or toward the end of July, a large percentage of the nymphs of the 

 first brood will have transformed to winged adults, and these latter 

 can not be successfully treated with the diluted tobacco spray. 



In vineyards where black-rot, mildew, the grape rootworm, and 

 the grape-berry moth occur, it is suggested that arsenate of lead 

 and Bordeaux mixture be used with the tobacco extract to take the 

 place of the second spray application in the schedule of treatment 

 recommended against these diseases and insect pests. 



When it is deemed expedient to use sticky shields to capture the 

 winged adults before oviposition takes place, the best sticky sub- 

 stance for this purpose, according to Slingerland, is a mixture of 

 melted resin, 1 quart, in 1 pint of castor oil, smeared liberally over the 

 face of the shield. 



CONCLUSIONS. 



Typhlocyba comes, the species of grape leafhopper discussed in 

 this paper, is at the present time a very destructive enemy of the 

 grapevine throughout the vineyards of the Lake Erie Valley. For 

 several seasons it has caused great losses to the vineyardists of this 

 region by reducing the yield and quality of the grape crop and by 

 curtailing the growth and lowering the vigor of the vines. The 

 vineyardist who desires to maintain his vines in full vigor and produce 

 high-quality fruit can not afford to allow this pest to develop in 

 destructive numbers in his vineyards, for if not controlled sooner or 

 later it is almost sure to occasion serious loss. Field experiments 

 prove conclusively that this pest can be controlled by spraying 

 against the nymphs with a tobacco-extract solution. 



The life-history studies recorded in the preceding pages show that 

 there is only one full brood of nymphs a year in the region of the 

 Great Lakes. 



The spraying experiments recorded in Part I of Bulletin 97 and 

 Part I of Bulletin 116 of the Bureau of Entomology indicate that a 

 single thorough spray application, made when the greater percentage 

 of the nymphs of this brood is present on the underside of the grape 

 leaves, will so reduce their numbers that injury to the crop and the 



