Euonymus: Powdery mildew

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

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

Non-chemical Management

Select non-chemical management options as your first choice!

• 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.

Chemical Management

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

• 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.

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]
• Hi-Yield Snake Eyes Dusting Wettable Sulfur
  Active ingredient: sulfur [EPA registration number: 7401-188-34911]
• 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.