Diagnosing Sticky Sap and Green Growth on Pussy Willow

Two Separate Issues

A mature pussy willow exhibits sticky sap (honeydew) dripping onto the driveway and a green, powdery coating on the bark.

Cause 1: Sap-Feeding Insects

The honeydew is excreted by aphids or scale insects feeding on leaves and twigs. This sticky substance attracts ants, wasps, and sooty mold.

Treatment: Apply a systemic insecticide like Bayer Advanced Tree & Shrub Insect Control (imidacloprid) as a soil drench. Roots transport it to foliage, killing insects as they feed. Available at nurseries.

Cause 2: Lichens

The green powder is lichens—a symbiotic algae-fungus organism. They are epiphytes, not parasites; they use the bark for support only. Lichens indicate good air quality and a thin canopy but cause negligible harm.

Management: No control needed. Improve canopy density by fertilizing with 10-10-10 at 1 lb per inch of trunk diameter to shade limbs and reduce lichen growth naturally.

Summary

Treat the insects to stop the sap; ignore the lichens or address them indirectly through better tree vigor.