Problem Identifier Unit Screen//v.w/ RR Template

Problem Identifier Unit Screen//v.w/ RR Template Powdery Mildew

Cucumbers, gourds, muskmelons, pumpkins, summer squash, watermelon, winter squash

Problem
The upper surfaces of the leaves are covered with a white powdery growth. Areas of the leaves and stems turn brown, wither, and dry. Fruit may be covered with the white powdery growth.

Analysis
This common plant disease is caused by either of 2 fungi (Erysiphe cichoracearum and Sphaerotheca fuliginea) that thrive in both humid and dry weather. The powdery patches consist of fungal strands and spores. The spores are spread by the wind to healthy plants. The fungus saps the plant nutrients, causing yellowing and sometimes death of the leaf. A severe infection may kill the plant. Since these powdery mildews attack several different kinds of plants, the fungus from a diseased plant may infect other types of plants in the garden. (For a list of powdery mildews and the plants they attack, see Powdery Mildews and Some of the Plants They Infect.) Under favorable conditions, powdery mildew can spread through a closely spaced planting in a matter of days or weeks.

Solution
Treat the plants with a fungicide containing chlorothalonil at the first sign of the disease. Continue treatment at intervals of 7 days as long as the disease is a problem. Grow varieties resistant to powdery mildew (see Slicing Cucumbers Resistant to Diseases).

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