Rhododendron Diseases: Common Problems and Prevention

Rhododendron in bloom

Overview

Rhododendrons (Rhododendron)—flowering shrubs in the heath family (Ericaceae). Native to North America, Asia, Europe, Australia. Generally hardy but susceptible to a few diseases.

Common Diseases

Rhododendron wilt (Phytophthora root rot): Most common. Petal blight (Ovulinia azaleae) and powdery mildew also occur.

Symptoms

Wilt: yellowing leaves, drooping foliage, stunted growth. Petal blight: tiny rust/white spots on petals. Powdery mildew: white/gray leaf coating.

Causes and Timing

Mostly fungal/bacterial pathogens. Common during wet late spring/early summer conditions.

Other Issues

Iron deficiency: yellowing between leaf veins. Pests: lace bug, root weevils, black vine weevils.

Maintenance for Prevention

Plant in high, well-drained locations. Remove dead/dying foliage promptly to prevent disease spread.