Diagnosing Leaf Galls and Scale on Heritage Birch

What Are Those Wart-Like Growths?

The small, rough, wart-like bumps on your birch leaves are most likely insect galls—abnormal plant growths induced by tiny wasps, mites, or aphids. The insect lays eggs; the plant reacts by forming a protective chamber. By the time you see them, the insect has often left. Galls are unsightly but rarely harm tree health.

Distinguishing Galls from Scale

• Galls: Rough, irregular, often same color as leaf; part of leaf tissue; cannot be scraped off.
• Scale insects: Smooth, oval, distinct bumps that can be flicked off with a fingernail; often on stems and leaf veins; produce honeydew.

When to Worry

If the "warts" are smooth, oval, and on stems/branches, you may have scale infestation. Heavy scale can weaken the tree. Check for honeydew and sooty mold.

Management Options

1. Galls: No treatment needed. Rake and destroy fallen leaves to reduce next year's population.
2. Scale: Apply systemic imidacloprid soil drench in early spring. For immediate reduction, spray horticultural oil on dormant tree (late winter) to smother overwintering scales.
3. Aphids: If you see small, soft, green insects that squash easily, treat with insecticidal soap or systemic drench.

Getting a Definitive ID

If unsure, email clear close-up photos (top and bottom of leaves, stem close-ups) to a local extension service or certified arborist. Accurate identification ensures the right treatment.