What are these growing on my grape leaves?
This is so pretty. The first time I saw this tube gall was in graduate school. The galls are formed by small insects called midges. The galls look like tiny, red peppers hanging from the bottom of the grape leaf. Tube galls are caused by a midge, Cecidomyia viticola, which form on leaves after the insect deposits its eggs into the leaf tissue. The formation of the gall is the plant’s response to the presence of the egg in the tissue. The plant forms an outer coat to the egg and encloses it – basically protecting the egg until it exits.
The galls are cone-shaped and can be red or green or a combination of colors. They are small and generally no larger than ¼ of an inch long. The egg develops into a larva which will exit the gall, fall from the leaf to the ground and burrow into the soil. Once in the soil, the larvae will pupate then develop into an adult and start the process all over again.
Like most galls, grape gall midges seldom cause any real problems and generally do not reduce the number of grapes produced. Therefore, we do not recommend using chemicals, especially because of the risk of killing native pollinators and honey bees. Pruning galls is the best management practice – especially before you see any exit holes in the gall.