August, ’23] 
van dine: effects of leafhopper on grapes 
353 
stock and the various conifers, can very easily carry living larvae in the 
soil and matted roots to any distance over which the stock itself can be 
safely shipped. Stringent quarantine regulations affecting the ship¬ 
ment of nursery stock from infested territory have been, for several 
years, and are now being enforced by the Quarantine division of the 
Japanese beetle laboratory staff; so far as is now known, these regula¬ 
tions have been effective in preventing further dispersion through this 
means. 
THE EFFECT OF LEAF-HOPPER INJURY ON THE SUGAR- 
CONTENT OF GRAPES 
By D. L. Van Dine 
Pennsylvania State College, State College, Pa. 
Abstract 
The grape leaf-hopper, Erythroneura comes Say, is a major pest in the vineyards of 
the Pennsylvania grape belt along Lake Erie. During seasons of high leaf-hopper 
infestation, the grapes do not ripen properly. This condition seriously reduces the 
market value of the grapes for table use and for the manufacture of juice. The ex¬ 
tension department of Pennsylvania State College is furnishing a spray service to the 
grape growers for the control of vineyard insects and diseases under the direction of 
the author. The effect of a nicotine spray on th£ leaf-hopper, under the high leaf- 
hopper infestation found during the season 1922, was determined by a comparison of 
the sugar-content of grapes (as indicated by the Brix spindle) that received the 
nicotine spray with grapes that were not sprayed. The conclusion is that, in a 
season of severe leaf-hopper infestation, a nicotine spray applied to the vines during 
the period when the maximum number of nymphs of the first generation of leaf- 
hoppers are present, will permit the production of grapes of table quality. The work 
also demonstrates that the sugar-content of the grape juice, under conditions of high 
leaf-hopper infestation, is an index to the efficiency of the control measure. 
The primary injury to grapes by the leaf-hopper, Erythroneura comes 
Say, is the effect upon the quality of the product. Fruit from vines 
infested with leaf-hopper is low in sugar content, inferior in flavor, and 
improperly colored. Such grapes are not suitable for the table-grape 
market and are not wanted at the grape-juice factories. If any large 
proportion of the production is of such quality, the crop moves slowly 
at a low price. In a season of high leaf-hopper infestation the pro¬ 
duction of grapes of table quality depends upon efficient leaf-hopper 
control. 
There are numerous records relating to the effect of leaf-hopper in¬ 
jury upon the quality of grapes. Harris, 1841, (1) refers to the ex¬ 
haustion of grape vines by the continued interruption of the important 
functions of the plant due to the feeding of the leaf-hopper. Slingerland, 
1904, (2) states that leaves badly injured by the grape leaf-hopper die 
permaturely, thus preventing the proper coloring, ripening and sweeten- 
