Oak Leaf Galls: Harmless Wasp-Induced Growths

Tiny green, yellow, and red balls on oak leaf undersides in western Oklahoma. They rub off easily. The homeowner wonders if it's a disease or parasite.

What They Are

Insect galls—formed when a tiny wasp lays eggs and secretes chemicals that cause leaf tissue to swell around them. Each gall houses a single larva.

Impact

• No significant health effect on the tree.
• May cause premature leaf drop, but late in season it's inconsequential.
• Population varies yearly; often absent the next year.

Management

No treatment needed. Insecticide timing is difficult (must hit egg-laying). Cosmetic only.