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Caption: Powdery mildew on viburnum
Photo by: B.M. Johnson
  
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Viburnum : Powdery mildew
(revision date: 5/7/2015)


Biology
Powdery mildew of viburnum is a fungal disease which primarily affects young leaves and shoots. Affected plant tissues develop a powdery white growth of fungal mycelia. The fungus can be found on either leaf surface. The disease typically appears in the summer and reaches its peak in late summer, when tiny black specks may be observed among the white mycelia. Developing leaves may be somewhat deformed by severe infections. Powdery mildew is worst on plants in the shade. It is favored by a combination of warm days, cool nights, and humid conditions, but is inhibited by rain.
Management Options

Non-Chemical Management
  • Plant resistant varieties such as Viburnum burkwoodii 'Mohawk' and V. carlecephalum 'Cayuga'.
  • Plant in full sun.
  • Space plants and prune to provide good air circulation.
  • Remove and destroy heavily infected leaves and shoots.
  • Rake and destroy fallen leaves.
Select non-chemical management options as your first choice!

Chemical Management


Apply fungicides when conditions are favorable for disease. Do not use sulfur products. They cause black spots on leaves and defoliation. 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.
  • 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
  • GardenTech Daconil Fungicide Conc
    Active ingredient: chlorothalonil  |  EPA reg no: 67572-82-71004
  • 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
  • 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 viburnum
Photo by: B.M. Johnson
Caption: Powdery mildew on viburnum
Photo by: B.M. Johnson