WSU Extension

Hortsense

Crabapple : Powdery mildew
(revision date: 4/11/2018)


Biology
Powdery mildew of crabapple is typically seen on the foliage, but may also occur on twigs, blossoms, and fruit. Characteristic patches of white, powdery fungus develop on the leaves and terminal shoots. Infected young leaves often become deformed and curled. Infected shoot tips may be deformed or die back. Small black fungal fruiting bodies may develop in the white areas. Symptoms of fruit infection include white powdery growth and russeting (development of brown or rust-colored, corky patches on the fruit). The fungus may overwinter in infected buds.
Management Options

Non-Chemical Management
  • Plant trees in full sun.
  • Plant resistant varieties. Crabapples with good to excellent powdery mildew and scab resistance include 'Christmas Holly', 'Evereste', 'Golden Raindrops', M. baccata v. jackii, M. x zumi 'calocarpa', 'Molten Lava', 'Prairifire', 'Professor Sprenger', 'Sentinel', 'Sugar Tyme', 'White Angel', 'Winter Gem'.
  • Prune and destroy severely infected twigs and branches to reduce spread of disease.
  • Clean up and destroy fallen leaves from beneath infected trees. Powdery mildew can overwinter in infected leaf debris.
Select non-chemical management options as your first choice!

Chemical Management

Pesticide recommendations are for flowering (non-edible) crabapples. Apply fungicides when flower buds begin to expand, when flower buds are exposed, and when flower blossoms are present. Necrotic foliage may result if oil products are applied within 10 to 14 days of a sulfur application. Do not use oils below 50 degrees F., above 90 degrees F. or when plants are under heat or moisture stress. 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.
  • Bayer Advanced Natria Neem Oil Conc [Organic]
    Active ingredient: clarified hydrophobic extract of neem oil  |  EPA reg no: 70051-2-72155
  • Bi-Carb Old-Fashioned Fungicide [Organic]
    Active ingredient: potassium bicarbonate  |  EPA reg no: 54705-10
  • Bonide Fung-onil Multi-Purpose Fungicide Conc
    Active ingredient: chlorothalonil  |  EPA reg no: 60063-9-4
  • Bonide Infuse Systemic Disease Control
    Active ingredient: propiconazole  |  EPA reg no: 100-773-4
  • Defend DF/Home & Garden Use/for Organic Gardening [Organic]
    Active ingredient: sulfur  |  EPA reg no: 62562-8
  • ferti-lome Liquid Systemic Fungicide II R-T-Spray
    Active ingredient: propiconazole  |  EPA reg no: 53883-184-7401
  • 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
  • Ortho Max Garden Disease Control Conc
    Active ingredient: chlorothalonil  |  EPA reg no: 239-2522
  • R-T-U Year-Round Spray Oil
    Active ingredient: oil/pet distillate  |  EPA reg no: 6218-78
  • 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.
Images
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Caption: Powdery mildew on leaves
Photo by: R.S. Byther
Caption: Powdery mildew on leaf
Photo by: G.G. Grove