New York Agricultural Experiment Station. 721) 



tion was due not to the insects but to a disease or physiological 

 trouble, with quite similar symptoms. The differences between the 

 yellowing due to hoppers and that due to this " leaf blight ( ?)" 

 should be learned; since it is merely a waste of materials to 

 spray with nicotine for the latter trouble. Absence, or presence 

 of only small numbers of the hoppers, coupled with yellowing of 

 the leaves is of course a good indication that the insects are not 

 responsible ; and if the leaves show yellow and die at the margins 

 first, with dark areas along the midrib and veins, it is the " leaf 

 blight (?)" rather than "hoppers" that are to blame, for their 

 punctures lead to a quite uniform yellowing of the leaf, at first 

 in the form of minute yellowish dots. The veins also will have a 

 yellowish, punctuated appearance. 



The grape leaf-hopper, as it destroys or 

 Effect of makes useless much of the foliage, reduces 



hopper injury. the crop of fruit for the year of the attack 

 and weakens the vines ; but the most striking- 

 result of its work is to lower the quality of the fruit. Concord 

 grapes when well ripened are of a rich blue-black color; but 

 when " hoppers " infest the vines, the color changes to a purplish 

 or reddish hue. The sugar also is lessened and the acid increased, 

 so that grapes from badly injured vineyards become unfit for 

 making grape juice and unattractive for market. 



In each of the vineyards under experiment samples were taken 

 of grapes from sprayed and from unsprayed vines and the juice 

 pressed out and analyzed. In every set of samples the grapes 

 from the sprayed vines showed more sugar, the increases varying 

 from 8 to 68 per ct. in the different pairs of samples ; while 

 the unsprayed grapes had more acid than those from sprayed 

 vines in every case but one, the differences ranging from to 

 20.6 per ct. 



In selecting such comparison samples it is essential that the 

 grapes be taken from corresponding portions of the sprayed and 

 unsprayed vines, since grapes grown on the lower, shaded por- 

 tions of a vine are lacking in sugar and have an excess of acid as 

 compared with those grown on the upper parts of the vine. 



The work of 1912 on the grape leaf-hopper, 

 Summary. then, enforces the practices previously recom- 



mended — the destruction of winter refuges 

 of the insects, such as weeds, clumps of dead grass, brush, and 

 particularly clusters of fallen forest leaves ; getting rid of spring 

 food plants like raspberry, blackberry, wild strawberry, burdock, 

 etc. ; allowing suckers to remain on vines until spraying time ; and 

 thorough spraying with a nicotine preparation. 



