12 DECIDUOUS FRUIT IXSECTS AXD INSECTICIDES. 



In comparing the sugar content of the samples from the sprayed 

 and the unsprayed plats it will be observed that the sample from the 

 unsprayed plat under serial No. 3154 showed a sugar content of only 

 8.61 grams per 100 c. c. as against 16.18 grams per 100 c. c. for sample 

 3153 from the sprayed plat. In other words, the sample of grapes 

 taken from the plat where the injury to the foliage of the vines by 

 the grape leafhopper was unchecked, by withholding the tobacco- 

 extract spray against the nymphs, contained only about one-half the 

 sugar content that was present in the sample taken from the vines 

 which were sprayed with the tobacco against this insect in the 

 nymphal stage. Samples under serial No. 3156 from the unsprayed 

 plat show a sugar content of 4.66 grams per 100 c. c. less than sample 

 No. 3155, taken from the sprayed plat, and sample No. 3260 from 

 unsprayed plat shows a sugar content of 6.37 grams per 100 c. c. less 

 than sample 3261, taken from sprayed vines in the same vineyard. 



In answer to an inquiry as to the approximate difference in value 

 of the fruit from these sprayed and unsprayed plats for use in making 

 wine or grape juice Prof. Alwood gives the following reply: 



In response to your question I may say that the sugar content of the three untreated 

 plats is so low that they would have no value whatever for making pure wine or unfer- 

 mented grape juice and could only be used for some low grade sophisticated products. 



Thus the analysis of these samples of fruit indicates that serious 

 injury to the foliage of the grapevine by the grape leafhopper greatly 

 impairs the quality of the fruit. A definite knowledge of this fact 

 furnishes an additional reason why the vineyardist should resort to 

 every practical means at his disposal for the control of this insect 

 whenever it is at all numerous in his vineyard - 



CONCLUSION. 



The field experiments made during the season of 1911 against the 

 grape leafhopper and recorded in this paper show that a single applica- 

 tion of the tobacco extracts applied against this insect in the nymphal 

 stage as a contact spray will reduce its numbers to such an extent 

 that the infested vines will remain in good foliage throughout the 

 season and mature a crop of high-quality fruit. 



As indicated by the variation in the time and rapidity in develop- 

 ment of the nymphs in 1910 and 1911, it is evident that no definite 

 date for making the spray application can be given. Where the 

 winged adults are at all numerous in the early part of the season the 

 vineyardist is urged to examine the underside of the grape leaves 

 toward the middle and the end of June and to observe the number and 

 size of the nymphs. The spray application to be most effective 

 should be made at about the time the first nymphs to hatch are near 

 the last molt. This is indicated by the length of the wing pads. 



