Azalea: Powdery mildew

categories: Azalea Azalea Diseases Ornamentals Shrubs

revision date: 2024-06-05 02:03

Biology

Powdery mildew on azalea forms a characteristic fuzzy white growth on upper or lower leaf surfaces. Entire leaves can be covered. In late summer and fall, small black specks may be found in the white areas. Powdery mildew is more severe on shaded plants. It is favored by the high humidity found in crowded plantings and damp locations.

Management Options

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

Non-chemical Management

Select non-chemical management options as your first choice!

• Prune and space plantings to allow good air circulation. Do not plant in extremely shaded or damp areas.
• Hand-pick and destroy mildewed leaves to control small amounts of infection.
• Rake and destroy fallen leaves year-round to reduce infection source. Do not compost diseased materials.
• Do not overwater or overfertilize plants, as the fungus prefers succulent new growth.
• Hose diseased plants with water when practical. This can help remove fungus and prevent new infections.

Chemical Management

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

• Begin applications when you first notice the disease on current-year leaves.
• If disease appears late summer, applications are not necessary on deciduous azaleas.
• Do not apply sulfur products when temperature is over 85F or within a few weeks of an oil spray.

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.