Horned Oak Galls on Pin Oak: What They Are and What to Do

Horned Oak Galls on Pin Oak

If you notice hard, bark-colored balls on your pin oak branches that eventually sprout spikes, you're likely seeing horned oak galls. These abnormal growths are caused by a tiny gall wasp (Callirhytis cornigera) that lays eggs in the tree's tissue.

Identification

The galls range from quarter to half-dollar size, are woody and hard, and develop characteristic horns as they mature. They typically appear on smaller branches and twigs.

Impact and Management

While unsightly, horned oak galls rarely threaten the overall health of established trees. There are no effective chemical controls once galls have formed. Pruning heavily infested branches may improve appearance, but natural predators often keep populations in check over time.

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