New York State is the leading grape producer in the eastern US and third leading grape producer in the US. The generalist feeding invasive species Halyomorpha halys (Stål) is currently present in NY, although at relatively low densities. Our aim in this study was to determine how H. halys will affect grape production in NY if it becomes well established. We measured the impact of density, sex, and life stage of H. halys on Concord and Chardonnay grapevines by enclosing insects on a single grape cluster using a fine mesh bag. The insects remained caged on the clusters for 2 wk during and after the period of fruit set, after which damaged and undamaged berries were enumerated nondestructively. At this point, we found a strong positive correlation between density and both number and percentage of berries damaged for both nymphs and adults. In late summer, at harvest time, clusters were removed from the vines, damaged and undamaged berries were once again counted, and berries were weighed. Cluster weight for both Chardonnay and Concord cultivars decreased with increased density of adults. Furthermore, adult females were found to have a greater effect than adult males. In contrast to adult feeding, nymphs were found to have little impact on cluster weight. There was relatively little incidence of disease as a result of H. halys feeding. These results show that H. halys is potentially an economic threat to the grape industry in cool-climate regions, but only at high densities currently not observed.