Rose: Powdery mildew

Biology

Powdery mildew is a fungus attacking leaves, stems, and flower parts. Usually young growth is most severely affected. Reddish, blister-like areas on the upper side of leaves are followed by powdery white growth, which can appear on either side of the leaf. Infected young leaves are often distorted. Flowers and stems also display the white growth. Some varieties of roses may drop infected leaves, while others are more resistant to powdery mildew. The disease is most active during cool, dry, cloudy weather.

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 disease-tolerant or disease-resistant varieties. (See list in PNW Disease Management Handbook.)
• Watch for signs of infection during appropriate weather conditions.
• Pick off infected leaves to prevent spread of disease.
• Gather and destroy all fallen leaves.
• Prune out and destroy infected canes at end of season to prevent overwintering of disease.
• Space plantings and prune to provide good air circulation.
• Avoid overfertilizing, which encourages susceptible new growth. If necessary, switch to a slow-release or lower-nitrogen formula.

Chemical Management

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

• Apply foliar fungicides during the growing season, starting in early season when young growth first appears.
• Do not apply oil products with or near a sulfur application.
• Sulfur is effective especially between 65 and 85 F, but may cause injury to plants if applied when temperatures are above 85 F.

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]
• Bonide Infuse Systemic Disease Control
  Active ingredient: propiconazole [EPA registration number: 100-773-4]
• Bonide Infuse Systemic Disease Control Lawn and Landscape
  Active ingredient: thiophanate methyl [EPA registration number: 53883-183-4]
• ferti-lome Liquid Systemic Fungicide II R-T-Spray
  Active ingredient: propiconazole [EPA registration number: 53883-184-7401]
• 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]
• This list may not include all products registered for this use.

Additional Images