Causal Agent:
Erysiphe cichoracearum, Sphaerotheca fuliginea - three races are known on cantaloupe

Distribution:
Worldwide

Symptoms:
All cucurbits are susceptible to powdery mildew, though it is less common on watermelon. The first signs of the disease appear as pale yellow spots on stems, petioles and leaves. Infection may occur on the upper or lower leaf surface. These spots enlarge, become covered with white spores and appear powdery. Infected leaves gradually turn yellow and eventually become brown and papery. Fruit infection, though rare, can occur on watermelon and cucumber. 

Conditions for Disease Development:
The fungus commonly overwinters on weeds, and is carried for long distances by air currents. Infection can take place without water on the plant surface, though high humidity (50-90%) is necessary. Disease development is favored by heavy plant growth, moderate temperatures, low light and dews.

Control:
Use resistant varieties. Where resistance is not available a good fungicide spray program can provide excellent control. Greenhouse plantings will benefit by avoiding practices that result in lush growth. Weed control and good sanitation practices will help in controlling powdery mildew.