Black Scaly Substance on Willow: Soft Scale Infestation

A large white willow by a lake has black, scaly buildup on leaf stems that rubs off as reddish-purple liquid. The owner suspects scale and asks about danger and winter die-off.

Confirmation: Soft Scale Insects

The description matches soft scale: protective waxy covering, honeydew excretion (the liquid), and sooty mold (black color). Scale insects suck plant sap, weakening the tree over time.

Scale Biology

• Two main groups: soft scale (waxy cover, easier to kill) and armored scale (hard shell).
• Eggs hatch into mobile crawlers—the only stage easily controlled.
• 7,000+ species; common on euonymus, magnolia, fruit trees, shrubs.

Control Options

1. Dormant oil in late spring before leaf-out (smothers overwintering stages).
2. Systemic insecticide: Bayer Advanced Tree & Shrub Insect Control (imidacloprid) applied as soil drench.
3. Consult a certified arborist for large trees.

Caution: Follow all label directions; avoid skin contact; store safely.