Oak Leaf Galls: Harmless but Unsightly

What Are They?

The small green balls on shagbark hickory leaves and twigs are insect galls, not aphids. Tiny wasps or mites lay eggs and secrete chemicals that force the plant to form a protective structure around the developing larvae.

Impact and Management

• Galls rarely harm healthy trees.
• No effective spray once galls form—the insects are protected inside.
• Prune and destroy heavily galled twigs if practical.
• Fertilize with 10-10-10 at 1 lb per inch trunk diameter to maintain vigor.

Populations fluctuate yearly; often no galls appear the next season.