WSU Extension

Hortsense

Caption: Powdery mildew on photinia
Photo by: R.S. Byther
  
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Photinia : Powdery mildew
(revision date: 3/10/2017)


Biology
Powdery mildew is a fungal disease found on leaves and shoots of photinia. Characteristic patches of gray-white, powdery fungus are found in thick mats on the upper and lower leaf surfaces. The infected areas may develop fungal fruiting bodies which appear as small black specks on the white mats. Affected leaves may be distorted, turn yellow and drop. The disease is spread by wind-blown spores and is favored by shade, humid conditions, and warm days and cool nights. The fungus overwinters on buds of the host plant and in leaf debris.
Management Options

Non-Chemical Management
  • Plant in full sun.
  • Space plants and prune to provide good air circulation.
  • Watch for signs of infection during appropriate weather.
  • Prune and destroy severely infected leaves and twigs to reduce spread of disease.
  • Clean up and destroy fallen leaves from beneath infected trees.
  • Spray upper and lower leaf surfaces with a strong stream of water. Spray only when leaves can dry quickly.
  • Do not overfertilize. Powdery mildew is worse on succulent new growth.
Select non-chemical management options as your first choice!

Chemical Management


Apply when disease appears. Repeat applications at 7- to 10-day intervals if weather encourages disease (14-day intervals for Spectracide IMMUNOX). 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.
  • Monterey Horticultural Oil [Organic]
    Active ingredient: mineral oil/pet distillate light  |  EPA reg no: 48813-1-54705
  • 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.
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Caption: Powdery mildew on photinia
Photo by: R.S. Byther