A single larva may destroy 2 to 6 berries in a cluster, depending on berry size, and several larvae frequently inhabit a single cluster. At harvest, severely infected bunches may contain several larvae, and many of the berries may be completely hollowed. In many cases, bunches are covered with bunch rot fungi and infested with Drosophila spp. A protectant insecticide may be needed to prevent damage in areas heavily infested by grape berry moth. The number of spray applications depends on the amount of infested berries the grower is willing to accept.
Table grapes require more attention than grapes grown for juice.
To determine the percentage of clusters damaged, you should randomly inspect 100 clusters along the perimeter of the vineyard and 100 clusters toward the center of the vineyard. This method will tell you if treatment of the entire vineyard is necessary. Treatment of perimeter rows may be all that is necessary to control this pest. Cultural controls can be used to kill the overwintering pupae in leaves. Leaves can be gathered and destroyed in the fall, or leaves can be buried within the soil in the spring, two weeks before bloom, by rototilling or cultivating.