The Q&A Archives: White powdery growth on snap peas

Question: Each year my sugar snap peas develop a white, powdery growth on the leaves, which kills the vines before they're finished producing peas. What is this disease? Edwin Copeland Milo, ME

Answer: Powdery mildew is the problem, says Wilfred Erhardt, vegetable specialist at the University of Maine in Orono. This disease thrives in high humidity at temperatures of 80oF during the day and 60oF at night. What makes this disease so widespread is that, unlike other fungal diseases, it doesn't need the leaves to be wet to start an infection, Erhardt explains. The variety Sugar Snap is highly susceptible to powdery mildew. The best solution is to grow peas that are resistant, such as Sugar Ann or Sugar Bon, says Erhardt. This disease is also more of a problem in summer and fall, so plant your peas as early as possible in spring to mature a crop before the mildew becomes widespread, he adds. If your heart is set on growing Sugar Snap, you can try to prevent powdery mildew with weekly sprays of sulfur. Once you have the disease, however, sprays won't be effective, Erhardt says.

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