Yellow Fuzz Balls on Oak Leaves: Gall Wasps, Even If Every Leaf

Every oak leaf in area has yellowish fuzz balls underneath. Owner doubts wasps—too many, too few wasps seen.

Confirmation: Gall Wasps

• Tiny wasps (Callirhytis)—hard to see.
• High population = high gall density.
• Life cycle: egg in bud → gall → adult emerges → lays in roots → next gen in leaves.

No Harm

Cosmetic leaf drop only. Population crashes naturally. Rake leaves to slightly reduce next year. No spray.