Treating Powdery Mildew on Holly Trees

Diagnosis and Control

Holly trees in Baltimore, MD with black spots, gray borders, and yellowing leaves likely have powdery mildew (despite the name, it can appear dark on holly).

Treatment Options

1. Sulfur or horticultural oil: Apply at first sign, repeat per label.
2. Systemic fungicide: Myclobutanil or propiconazole for severe cases.
3. Cultural: Improve air flow, avoid overhead watering, rake fallen leaves.

Professional Help

If uncertain, contact Maryland DNR Forest Service for a free forester visit.

Reference

Cornell Plant Clinic: Powdery Mildew Control.