Hi I have 2 grapes plant on my yard, one leaf out of a thousand Grew thorns on its surface. I will like to know if anyone had seen this before, why and how? It may be bugs I don't know. Please help me get some answers. Thank you Victor
Prince George's County Maryland
Hi - These structures on the leaves are a type of gall. They are formed by the plant in response to very tiny insects that use the plant for part of their life cycle. This looks like grape tube gall, which is caused by a midge. It is not a serious problem for the plant and no control is necessary or recommended. This page from Ohio State University provides more information about galls on grapes. https://bygl.osu.edu/node/1278.