Brownish spots on pea pod from powdery mildew infection.
The best method of control is prevention. Planting resistant vegetable varieties when available, or avoiding the most susceptible varieties, planting in the full sun, and following good cultural practices will adequately control powdery mildew in many cases. However, very susceptible vegetables such as cucurbits (cucumber, melons, squash, and pumpkins) may require fungicide treatment. Several least-toxic fungicides are available but must be applied no later than the first sign of disease.
In some cases, varieties resistant to powdery mildew may be available. If available, plant resistant varieties of cantaloupe, cole crops, cucumber, melons, peas, pumpkins, and squash. If you plant more susceptible varieties, you may need to take control measures.
Fungus species: Erysiphe cichoracearum
Controls: resistant varieties of lettuce, cucumber; water sprays; fungicides if necessary on squash and pumpkin
Fungus species: Erysiphe cruciferarum
Controls: not usually required
Fungus species: Erysiphe lycopersici
Controls: fungicides if necessary
Fungus species: Erysiphe pisi
Controls: resistant varieties; sprinkler irrigation
Fungus species: Erysiphe heraclei
Controls: tolerant varieties
Fungus species: Erysiphe polygoni
Controls: tolerant varieties
Fungus species: Leveillula taurica
Controls: rarely required; fungicides if necessary
Fungus species: Sphaerotheca fuliginea
Controls: resistant varieties for some; fungicides if necessary
Plant in sunny areas as much as possible, provide good air circulation, and avoid applying excess fertilizer. A good alternative is to use a slow-release fertilizer. Overhead sprinkling may help reduce powdery mildew because spores are washed off the plant. However, overhead sprinklers are not usually recommended as a control method in vegetables because their use may contribute to other pest problems.
In some situations, especially in the production of susceptible cucurbits, fungicides may be needed. Fungicides function as protectants, eradicants, or both. A protectant fungicide prevents new infections from occurring whereas an eradicant can kill an existing infection. Apply protectant fungicides to highly susceptible plants before the disease appears. Use eradicants at the earliest signs of the disease. Once mildew growth is extensive, control with any fungicide becomes more difficult. The products listed here are for home garden use. Commercial growers should consult the UC Pest Management Guidelines.