Peas: Powdery Mildew

Problem
A white powdery coating develops first on the upper surfaces of the lower leaves. Stems, pods, and other leaves may then become infected. Leaves may turn yellow and be malformed. Pods may be distorted, with dark streaks or spots.

Analysis
This common plant disease is caused by a fungus (Erysiphe polygoni) that thrives in both humid and dry weather. The powdery coating consists 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 leaf. A severe infection reduces pea yield considerably, and may kill the plant. Fall crops are most susceptible to serious damage; spring crops are attacked late in the season. Since this powdery mildew attacks many vegetables, the fungus from a diseased plant may infect other plants in the garden. (For a list of susceptible plants, see Powdery Mildews and Some of the Plants They Infect.) Under favorable conditions, powdery mildew can spread through a planting in a matter of days or weeks.

Solution
Treat plants with garden sulfur. Repeat at intervals of 7 to 10 days as needed. This fungicide does not cure infected leaves, but does protect healthy ones from infection.