Valley Oak Galls: Wasps, Sap & Falling Twigs Explained

Valley oaks dropping sap, green leaves with brown knobs (galls) in fall. The knobs are exit holes of gall wasps (Andricus spp.).

Life Cycle

• Wasp lays egg in bud → larva secretes chemical → gall forms.
• Larva develops inside → pupates → adult emerges, leaving empty gall.
• Galled twigs weaken and drop.

Management

• Control is impractical—wasps are tiny, timing is precise.
• Rake/destroy fallen galls to reduce population.
• Tree tolerates galls; no long-term harm.
• Consult arborist only if infestation is extreme and tree is high-value.

Live with it or remove the tree. Eradication is futile.