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.
Infected plants usually appear coated with talcum powder or flower as shown on this bean plant.
An infected cucumber plant. Fungal growth can be found covering both leaf surfaces.
Some plants, such as tomatoes, peppers and onions, may have yellow colored leaf patches. Close-up view of powdery mildew on onion leaves.
Severely affected leaves can become dry and brittle, and then wither and die, as shown on this pumpkin vine.
A squash plant with powdery mildew. Powdery mildews damage plants by decreasing photosynthesis and removing nutrients from the host 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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Identification and Control Information
- Integrated Pest Management for Home Gardeners: Powdery Mildew on Vegetables (PDF)—University of California
- Fact Sheet with Description and Control Options—University of Rhode Island Landscape Horticulture Program
More Information
- An Online Guide to Plant Disease Control—Oregon State University Extension
- Disease Prevention in Home Vegetable Gardens (PDF)—University of Missouri Extension
- Controlling Diseases in the Home Vegetable Garden (PDF)—University of Illinois Extension
[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]