Common Leaf and Twig Galls

Leaf infections called "galls" are bumps or growths caused as a result of the feeding and other activity of insects or mites. Powerful growth regulating chemicals produced by feeding insects or mites cause galls can occur on leaves, bark, flowers, buds, acorns, or roots. Although these galls may look like a serious problem, most are harmless to the overall health of the tree.

The Gall Discussion

Gall on Oak Leaf, About Forestry Forum Photo