Powdery Mildew of Vegetables

Powdery mildews are caused by a variety of fungi, each specific to a host plant. It is recognizable by the white to gray powdery fungal growth on leaves and vines. Commonly infected vegetables are beans, squash, cucumbers, melons, pumpkins, beets, lettuce, peppers, tomatoes and onions. Since different fungi infect specific plants, it is not possible to spread from one species to another, for example, powdery mildew on beans will not affect squash. Severely infected leaves gradually wither and die; this premature loss of foliage results in poor fruit quality and quantity.

bean plant with powdery mildew
Infected plants usually appear coated with talcum powder or flower as shown on this bean plant.

powdery mildew on cucumber plant
An infected cucumber plant. Fungal growth can be found covering both leaf surfaces.

powdery mildew on onion plant
Some plants, such as tomatoes, peppers and onions, may have yellow colored leaf patches. Close-up view of powdery mildew on onion leaves.

pumpkin vine with symptoms of powdery mildew
Severely affected leaves can become dry and brittle, and then wither and die, as shown on this pumpkin vine.

squash plant with symptoms of powdery mildew
A squash plant with powdery mildew. Powdery mildews damage plants by decreasing photosynthesis and removing nutrients from the host plant.

powdery mildew on watermelon plant
A watermelon plant showing signs of powdery mildew. High humidity, shady locations, crowded planting, and/or poor air circulation promote spore germination.

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[Photos, left to right: Howard F. Schwartz, Colorado State University, Bugwood.org; Charles Averre, North Carolina State University, Bugwood.org; S. K. Mohan, Bugwood.org; Howard F. Schwartz, Colorado State University, Bugwood.org; Howard F. Schwartz, Colorado State University, Bugwood.org; David B. Langston, University of Georgia, Bugwood.org]