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Caption: Powdery mildew on euonymus
Photo by: J.W. Pscheidt
  
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Euonymus : Powdery mildew
(revision date: 3/10/2017)


Biology
Powdery mildew is a fungal disease of the leaves of Euonymus japonica (evergreen euonymus). Characteristic patches of gray-white, powdery fungus are found in thick mats on the upper and lower leaf surfaces. Affected leaves may be distorted, turn yellow and drop. The disease is spread by wind-blown spores and is favored by shade and humid conditions with warm days and cool nights. The disease is inhibited by rainy weather, however. The fungus overwinters on leaf debris and on the host plant.
Management Options

Non-Chemical Management
  • Plant resistant species and varieties (E. japonica 'Patens' is very susceptible; variegated cultivars are seldom infected).
  • Plant in full sun.
  • Do not overfertilize. Powdery mildew prefers succulent new growth.
  • Space plants and prune to provide good air circulation.
  • Watch for signs of infection during appropriate weather.
  • Pick off and destroy (do not compost) infected leaves.
  • Collect and destroy leaf debris from under plants.
  • Spray upper and lower leaf surfaces with a strong stream of water. Spray only when leaves can dry quickly.
Select non-chemical management options as your first choice!

Chemical Management


If the disease has been severe in previous seasons, apply fungicides when disease is first observed. 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
  • 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 euonymus
Photo by: J.W. Pscheidt