WSU Extension


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Caption: Powdery mildew on lilac
Photo by: C.R. Foss
Lilac : Powdery mildew
(revision date: 4/11/2018)

Powdery mildew is a fungal disease of the leaves. On lilac, it shows typical powdery gray-white growth on the upper leaf surface. Powdery mildew usually occurs fairly late in the season, and does relatively little damage to the plants. This disease is worse in summers with little rainfall and high amounts of fog or cloud cover.
Management Options

Non-Chemical Management
  • Hand-pick and destroy infected leaves and shoots.
  • Gather and destroy any diseased materials from beneath plants.
  • Plant species other than Syringa vulgaris which is the most susceptible to powdery mildew.
Select non-chemical management options as your first choice!

Chemical Management

Use just before symptoms are expected to occur or 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.
  • Bonide Fung-onil Multi-Purpose Fungicide Conc
    Active ingredient: chlorothalonil  |  EPA reg no: 60063-9-4
  • Bonide Infuse Systemic Disease Control
    Active ingredient: propiconazole  |  EPA reg no: 100-773-4
  • 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
  • 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 lilac
Photo by: C.R. Foss