Grape: Powdery mildew

Biology

Powdery mildew is a fungal disease which affects all aboveground portions of grapes. Leaves develop characteristic white to grayish patches of fungus on the underside. Both surfaces of shaded leaves may be affected. Young leaves are deformed and stunted, while older leaves may show some yellow spotting. Stems are infected while green and develop brown to black patches which later show as a reddish discoloration. Infected flowers fail to set fruit. Infected fruit develops grayish spots on the skin. These spots later appear russetted and the affected fruit may crack and drop. Disease development is favored by warm, dry weather. The spores are spread by wind, and the fungus overwinters on the bark or in infected buds. European cultivars (Vitis vinifera) are more susceptible than juice grapes. ‘Thompson Seedless’ is also affected.

Management Options

Use Integrated Pest Management (IPM) for successful plant problem management.

Non-chemical Management

Select non-chemical management options as your first choice!

• Orient plantings to minimize shading and maximize air flow through the canopy.
• Train and prune to provide good air circulation and light penetration.
• Remove suckers.

Chemical Management

IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides.

• Make first fungicide application when new growth is 6 inches long.
• Repeat applications at 10-to 14-day intervals. (Follow label instructions for timing and application intervals when using Spectracide IMMUNOX and Bonide Copper Spray or Dust.)
• Copper products provide only moderate control.
• Do not apply oils within 2 weeks of a sulfur application.
• Slight to severe foliage injury may occur on copper-sensitive varieties such as ‘Concord,’ ‘Delaware,’ ‘Niagra,’ and ‘Rosetti’.

Approved Pesticides

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.

• Bi-Carb Old-Fashioned Fungicide [Organic]
  Active ingredient: potassium bicarbonate [EPA registration number: 54705-10]
• Bonide Copper Fungicide Spray or Dust RTU [Organic]
  Active ingredient: basic copper sulfate [EPA registration number: 4-58]
• Bonide Liquid Copper Fungicide Concentrate/Organic Gardening
  Active ingredient: copper octanoate [EPA registration number: 67702-2-4]
• Monterey Liqui-Cop Copper Fungicidal Garden Spray
  Active ingredient: copper-ammonia complex [EPA registration number: 54705-7]
• Soap-Shield Flowable Liquid Copper Fungicide [Organic]
  Active ingredient: copper octanoate [EPA registration number: 67702-2-56872]
• ferti-lome Horticultural Oil Spray RTSpray
  Active ingredient: oil/pet distillate [EPA registration number: 48813-1-7401]
• Lilly Miller Sulfur Dust Fungicide/Insecticide Dust or Spray
  Active ingredient: sulfur [EPA registration number: 802-16]
• Monterey Horticultural Oil [Organic]
  Active ingredient: mineral oil/pet distillate light [EPA registration number: 48813-1-54705]
• Safer Brand Garden Fungicide/Flowers, Fruit and Vegetables Concentrate
  Active ingredient: sulfur [EPA registration number: 42697-37]
• Spectracide IMMUNOX Multi-Purpose Fungicide Spray Concentrate
  Active ingredient: myclobutanil [EPA registration number: 9688-123-8845]
• This list may not include all products registered for this use.

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