Leaf Galls on Scrub Oak: Harmless and Temporary

What They Are

Grape-sized, yellow-red balls on leaves = leaf galls caused by tiny gall wasps (Cynipidae). Wasp lays egg, secretes chemical → leaf forms protective gall around larva.

No Harm, No Treatment Needed

• Galls don't affect tree health.
• May cause early leaf drop if extremely numerous.
• Populations cycle wildly—next year may have none.
• Spray timing (pre-egg-lay) is nearly impossible.

Advice

Ignore them. Enjoy the ecological curiosity. No pesticide warranted.