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

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

Problem
Leaves and stems are covered with grayish white powdery spots and patches. These patches occur primarily on the upper surfaces of the leaves. The infected leaves eventually turn yellow and wither.

Analysis
This common plant disease is caused by a fungus (Erysiphe cichoracearum) that thrives 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 plant nutrients, causing yellowing and sometimes death of the leaves. A severe infection may kill whole plants. Since this powdery mildew attacks many different kinds of plants, the fungus from a diseased plant may infect other types of plants in the garden. (For a list of susceptible plants, see Powdery Mildews and Some of the Plants They Infect.)

Solution
Spray infected plants with a fungicide containing thiophanate-methyl. Spray at regular intervals of 10 to 12 days, or as often as necessary to protect new growth. This fungicide protects the new, healthy foliage, but will not eradicate the fungus on leaves that are already infected. Remove and destroy severely infected plants. Where practical, pick off diseased leaves. Clean up and destroy plant debris. Plant in a site having good aeration and exposure to early morning sun.

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