Productivity of Concord vines infested with endemic populations of Eastern grape leafhopper, Erythroneura comes Say, was compared with that of uninfested vines in three field experiments from 1990 to 1995. Responses of vines to infestation levels ranging from 100 to 577 leafhopper days and peak leafhopper densities ranging from two to 14 leafhopper nymphs per leaf varied. Mean crop weight in vines not treated with insecticides was reduced by up to 4.9 kg/vine compared to sprayed vines. Effects on productivity sometimes carried over to subsequent crop years, but response of yield components to injury varied. In the season of injury, berry weight was the yield component most strongly affected. In subsequent years, leafhopper injury reduced bud fruitfulness, as measured by the number of berries per cluster and clusters per retained node. Soluble solids, adjusted for crop weight, were significantly affected in only one cropping cycle (out of 22). Yield reductions were only weakly correlated with infestation levels, as measured by leafhopper days and leaf injury ratings. Availability of adequate soil moisture and vine reserves is hypothesized to be an important determinant of the impact of leafhopper injury on Concord productivity in northeastern North America.
- Copyright 1997 by the American Society for Enology and Viticulture