The Q&A Archives: Summer Squash

Question: The summer squash we got from you was doing very good. Now the leaves appear to have a milky film on them. I thought it was something that washed onto it but with watering the milky look is still there. What can I do?

Answer: What you describe may be powdery mildew, a fungal disease. Overcrowding, too much shade, or even hot days and cool night temperatures can all contribute to the development of this disease. To avoid, 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, 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. Several least-toxic fungicides are available, including horticultural oils, neem oil, jojoba oil, sulfur, and the biological fungicide Serenade. Be sure to apply according to label directions.

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