Magnolia Scale: Bumps on Branches, Honeydew, Sooty Mold

Yellow magnolia in Ontario has greenish-gray blisters on lower branches with dark ooze inside. Owner asks if harmful.

ID: Magnolia Scale

Large soft scale (½″). Females pink-orange to brown with white wax; overwinter as dark nymphs. One generation; crawlers active July–August.

Damage

• Heavy honeydew → sooty mold, attracts insects.
• Severe infestation → branch dieback or tree death.

Control

• Timing: Target crawlers (July–Aug) with horticultural oil, insecticidal soap, or labeled insecticides (acephate, imidacloprid, etc.).
• Systemic: Imidacloprid soil drench (Bayer Advanced) applied weeks before crawler emergence.
• Cultural: Prune heavily infested branches; avoid over-fertilization.

Monitoring

Dead scales dry and don't bleed when crushed; new growth should look healthier.