Pear: Powdery mildew

Biology

Powdery mildew is a fungal disease found on twigs, leaves, blossoms, and fruit. New growth is particularly susceptible. The entire terminal may become covered with powdery mildew. Leaves develop a characteristic gray-white powdery growth, usually on the underside. Severe infections may spread to the upper leaf surface, as well. Dark brown to black fruiting bodies of the fungus can be seen around midsummer, while the whitish mycelia turn brown at this time. Infected leaves are often curled and distorted, while other infected tissues may become brittle and die back. Fruits may show patches of russeting after infection. Unlike apple powdery mildew, pear powdery mildew has not been observed overwintering in buds. Powdery mildew development is favored by high humidity, warm days, and cool nights.

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 varieties such as ‘Bartlett’, ‘Flemish Beauty’, and ‘Winter Nelis’.
• Prune out and destroy severely infected shoots when practical.
• Succulent new growth is often particularly susceptible to powdery mildew infection. Provide proper culture to prevent heavy flushes of new growth.

Chemical Management

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

• Apply fungicides when leaves are separating, just exposing bud cluster.
• Make applications at intervals recommended on product labels until weather dries.
• When in blossom, wait until 3⁄4 of petals have fallen before making applications.
• Oils should not be applied within two weeks of any sulfur application or necrotic foliage may result.
• Do not use oils when temperatures are below 50° F, above 90° F, or when plants are under heat or moisture stress.
• Do not use when foliage is wet as good coverage is essential.
• 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]
• ferti-lome Horticultural Oil Spray RTSpray
  Active ingredient: oil/pet distillate [EPA registration number: 48813-1-7401]
• 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.

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