Identifying and Treating Powdery Mildew on Paperbark River Birch

Symptoms and Diagnosis

A 20-foot paperbark river birch (Betula nigra) planted last year in northeastern Maryland shows wrinkled leaves with a white powdery coating on the undersides. This is classic powdery mildew, a common fungal disease that thrives in humid conditions with poor air circulation.

Management Strategies

1. Cultural controls: Improve air flow by thinning nearby vegetation. Avoid overhead irrigation; water at the base early in the day.
2. Fungicide applications: Apply a labeled fungicide (e.g., sulfur, neem oil, or a systemic like myclobutanil) at the first sign of infection. Repeat per label instructions, typically every 7–14 days.
3. Sanitation: Rake and destroy fallen leaves in autumn to reduce overwintering inoculum.

Long-Term Outlook

Powdery mildew rarely kills established trees but can weaken them and reduce aesthetic value. With consistent management, the birch should recover and develop greater resistance as it matures.

Additional Resource

For detailed control measures, see the Ohio State University fact sheet: Powdery Mildew on Ornamentals.