SPRAYING AGAINST THE GRAPE LEAFHOPPER. 



9 



a few vines with different dilutions. Accordingly several vines were 

 sprayed with the following dilutions: 



Table 1. — Dilutions of blackleaf tobacco extract as used in experiments against 



the grape leafhopper. 



Plat 

 No. 



Num- 

 ber of 

 vines. 



Strength of dilution. 



Results. 



1 



4 

 4 

 4 

 4 

 4 

 4 



1 gallon to 75 gallons water 



All nymphs hit by spray were killed. 



2 



1 gallon to 100 gallons water 



Do. 



3 



4 



1 gallon to 125 gallons water 



1 gallon to 150 gallons water 



Do. 

 Do. 



5 



1 gallon to 200 gallons water 



Do. 



6 



Clear water 



No nymphs killed. 









Blackleaf " 40," 1 another form of highly concentrated tobacco ex- 

 tract, was also used at a much greater dilution, as shown in Table II. 



Table II. — Dilutions of blackleaf " //0 " as used in experiments against the grape 



leafhopper. 



Plat 

 No. 



Num- 

 ber of 

 vines. 



Strength of dilution. 



Results. 



1 



4 

 4 

 4 



4 



4 



1 gallon to 1 ,000 gallons water 



All nymphs hit by spray were killed. 

 Do. 



2 



1 gallon to 1 ,500 gallons water 



3 



1 gallon to 1 ,750 gallons water 



Do. 



4 



1 gallon to 2,000 gallons water 



All but fully developed nymphs were 



killed. 

 No nymphs were killed. 



5 



Clear water 







All of the spray applications indicated above were made with a 

 hand pump carrying a pressure of about 80 pounds. A short rod 

 with a nozzle set at right angles attached to a 40-foot hose was used 

 to apply the spray to the nymphs upon the underside of the leaves. 

 Great care was taken to wet the underside of every leaf. The result 

 of these applications could be determined within an hour after they 

 were made, or as soon as the leaves became dry. Those nymphs that 

 were not hit and killed by the spray would be found running about 

 quite actively; thus the efficiency of the spray was quickly apparent. 

 It was found that a larger amount and a greater strength of the 

 tobacco liquid was required to kill the nearly full-grown nymphs, 

 and also that only a very small number of the winged adults was 

 destroyed by the spray. 



After the killing strength of the blackleaf tobacco extract had 

 been determined, several experiments covering areas of several acres 

 each were undertaken in a number of vineyards. On the vineyard 

 of Mr. H. H. Harper about 6 acres of the worst infested portion of 

 his vineyard was sprayed from July 14 to July 16, when the majority 

 of the nymphs were small. Blackleaf tobacco extract was applied 

 at a dilution of 1 gallon of the extract to 150 gallons of water. A 

 traction sprayer was used and a pressure of from 75 to 125 pounds 



1 Containing 40 per cent of nicotine. 



