Oak Dropping Black Granules: Frass or Aborted Acorns?

Two Possibilities

1. Caterpillar frass: Coffee-ground-like droppings from leaf-feeding caterpillars. Look for chewed leaves. Feeding usually ends in one generation per year.
2. Aborted acorns: Immature acorns drop under stress (weather, drought). High tannin content stains concrete brown/green.

Stain Removal

• Try CLR (calcium-lime-rust remover) diluted.
• For stubborn stains, use muriatic acid (1:20 with water) with full safety gear.

Outlook

Caterpillar feeding stops naturally; acorn drop ceases when crop matures. No spray needed now.