Causes

• Any of four fungi infect azaleas with powdery mildew, say regional specialists Mary Kay Malinoski and David L. Clement of the Maryland Cooperative Extension Home and Garden Center. The fungi are Erysiphe cruciferarm, Microsphaera vaccinoii, Microsphaera penicillata and Sphaerotherca pannosa.
  
  

Spread

• Wind spreads fungal spores from infected azalea leaves to healthy ones. Leaf bud scales protect fungi during the winter, and the infection cycle repeats in the spring. The fungi are most active in cool, damp conditions.
  
  

Symptoms

• Infected azaleas have powdery white blotches on their leaves. In severe infections, both sides of the leaves may become completely white. Deciduous plants are more likely to suffer leaf drop than evergreen ones, caution North Carolina State University plant pathologists D. M. Benson and Tom Creswell.
  
  

Control

• Powdery mildew fungi have the worst effect on young azaleas in shade. Locate plants where they get some sun. Space them to provide adequate air circulation. Serious cases merit spraying with fungicide registered to treat powdery mildew.