Orange Growths on Japanese Maple Bark: Scale Insects, Not Disease

The Observation

Clusters of 1/16″ orange bumps on bark of an ‘Okagami’ Japanese maple. Owner fears a deadly disease.

Expert Evaluation

Photos reveal the bumps are scale insects (likely cottony maple scale or similar), not a fungus. Scales appear as tiny, immobile bumps; the orange color is the insect body or crawler stage.

Control

• Scrape off a few and examine with a lens—legs or crawlers confirm insect.
• Apply horticultural oil in dormant season (late winter) to smother overwintering stages.
• Or use a systemic like imidacloprid as a soil drench in spring.

Spread Risk

Scales can spread to other maples and woody plants. Monitor nearby trees.