Powdery mildew attacks leaves, young shoots, and fruit. This fungal disease initially produces a light green, circular spot on either leaf surface. Later, a characteristic white, powdery coating of the fungus appears, typically on the underside of affected leaves. The affected leaves may become blistered and distorted. Leaves on young shoots are affected first. The shoots may also become covered with the fungus. Diseased tissues are often deformed and stunted. Infected fruits develop round, depressed areas which may not show any fungal growth. Older infections may cover the entire fruit. The fungus can overwinter on the plant or in debris on the ground. Powdery mildew is favored by high humidity, warm days, and cool nights.

Management Options

Non-Chemical Management

Space plantings and prune to provide good air circulation.
Plant in full sun.
Provide proper culture. Avoid heavy use of nitrogen fertilizer which promotes growth of susceptible, succulent shoots.
Rake and remove fallen leaves from beneath trees.
Avoid overhead watering, particularly when fruit is developing.
Carefully prune out and destroy severely infected shoots.
Remove infected suckers at base of tree.

Select non-chemical management options as your first choice!

Chemical Management

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

Apply when petals fall. Homeowners should not make foliar applications to trees over 10 ft tall. Consult a commercial pesticide applicator for treatment of trees and shrubs over 10 ft. tall.

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 reg no: 54705-10
Bonide Sulfur Plant Fungicide Micronized Spray or Dust RTU [Organic]
Active ingredient: sulfur | EPA reg no: 4-62
Hi-Yield Snake Eyes Dusting Wettable Sulfur
Active ingredient: sulfur | EPA reg no: 7401-188-34911
Lilly Miller Sulfur Dust Fungicide/Insecticide Dust or Spray
Active ingredient: sulfur | EPA reg no: 802-16
Monterey Horticultural Oil [Organic]
Active ingredient: mineral oil/pet distillate light | EPA reg no: 48813-1-54705
Spectracide IMMUNOX Multi-Purpose Fungicide Spray Conc
Active ingredient: myclobutanil | EPA reg no: 9688-123-8845
This list may not include all products registered for this use.

Images

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Caption: Powdery mildew on leaf Photo by: G.G. Grove
Caption: Powdery mildew on fruit Photo by: G.G. Grove

WSU Extension

Hortsense