Fact Sheet

Gall Wasps

Have you noticed bumps on oak tree leaves or swellings on twigs or leaves—
especially along the midrib of the leaves?

Your oak tree may have gall wasps.

The Problem

Gall wasps lay eggs in twigs or leaves, causing the tree to form protective galls around the larvae. Some larvae live inside twig galls for 2–3 years, while others create leaf galls that can distort leaves and reduce their ability to photosynthesize.

Symptoms and signs include:

Swollen, round galls on twigs or branches
Bumpy or irregular growths along the midrib veins of leaves
Deformed or curled leaves

Co-occurring issues or look-alike symptoms:
Two-lined chestnut borer.

The Vineland Prescription

Prune to remove galls and improve appearance.
Mulch and water to maintain vigor.

The Prognosis

Gall wasp treatment is generally not needed as the galls normally do not cause long-term damage.

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