WSU Extension


Bacterial leaf spot and dieback 
Leaf scorch 
Nectria canker 
Phyllosticta leaf spot 
Powdery mildew 
Tar spots 
Verticillium wilt 
Cottony maple scale 
Maple bladdergall mite 

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Caption: Powdery mildew on maple
Photo by: R.S. Byther
Maple : Powdery mildew
(revision date: 5/7/2015)

Powdery mildew of maple is a fungal disease which affects many hardwoods including maple, hazel, birch, and alder. On maples, a characteristic white, fuzzy or powdery growth appears on the upper or lower surfaces of mature leaves. Sometimes small black structures may be observed in the white areas. Shoots which develop late in the season may be distorted as a result of the infection.
Management Options

Non-Chemical Management
  • Watch for signs of infection during appropriate weather conditions (dry weather, warm days, and cool nights).
  • Pick off infected leaves, when practical, to prevent spread of the disease.
  • Gather and destroy fallen leaves.
  • Space plantings and prune to provide good air circulation.
Select non-chemical management options as your first choice!

Chemical Management

Apply when the first symptoms appear. 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.
  • Defend DF/Home & Garden Use/for Organic Gardening [Organic]
    Active ingredient: sulfur  |  EPA reg no: 62562-8
  • 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
  • Safer Brand Garden Fungicide/Flowers, Fruit & Vegetables Conc
    Active ingredient: sulfur  |  EPA reg no: 42697-37
  • 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.

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Caption: Powdery mildew on maple
Photo by: R.S. Byther