The mature larvae drop to the ground and remain there over the winter. A related midge species causes the marginal folds or leaf pockets that can be found on red oak or pin oak. Several small larvae may be found inside the swollen folds of the leaf. Caused by a small wasp, they typically appear on the leaves of valley oak and California white oak. These round, seed-like galls fall off leaves when mature.
Female wasps emerge in the spring from galls on the ground and lay eggs in opening buds.
After several weeks, small blister-like galls form on the young leaves. During the summer, males and females mate and females lay eggs in the mature leaves. The use of some products may not be legal in your state or country. Please check with your local county agent or regulatory official before using any pesticide mentioned in this publication.