Grapes are webbed together and webbed to leaves. Dark green to purple worms, up to 3/8 inch long with dark brown heads, are found inside the grapes. White cocoons cling to the leaves under flaps of leaf tissue.
Destroy infested grapes. Stop turning the soil in late summer; clean up cocoons remaining on top of the ground along with all fallen grape leaves at the end of the season. This reduces the number of overwintering pests. The following year, treat plants immediately after bloom with an insecticide labeled for grape berry moth, following label directions.