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Understanding Leaf Galls on Deciduous Trees in the Black Hills

What Are Leaf Galls?

Small, fuzzy, hard nodules on leaf undersides are typically insect-induced galls. Insects such as sawflies, midges, or mites lay eggs in leaf tissue, triggering abnormal plant growth that shelters developing larvae. The description matches willow gall (Pontania gallarum) but can occur on many species, including ash.

Impact and Management

Galls are cosmetic and rarely harm tree health. No treatment is necessary. If curious, slice a gall open to observe larvae. For peace of mind, maintain tree vigor with proper watering and mulching; healthy trees tolerate galling better.

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