Oak Galls: Cosmetic Issue, Rarely Harmful

Understanding Wasp-Induced Growths

Oak galls—caused by tiny cynipid wasps—are abnormal plant growths from insect chemicals. Leaf galls cause minimal harm. Twig galls (horned oak gall, gouty oak gall) can weaken heavily infested trees. Two+ year life cycles; adults lay eggs in expanding spring tissue.

Management

Chemical control is impractical. Rake/destroy infested leaves. Prune twig galls when small. Natural enemies usually regulate populations. Galls rarely kill trees.