Viburnum: Powdery mildew

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

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 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.

Chemical Management

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

• 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.

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 Fung-onil Multi-Purpose Fungicide Concentrate
  Active ingredient: chlorothalonil [EPA registration number: 60063-9-4]
• GardenTech Daconil Fungicide Concentrate
  Active ingredient: chlorothalonil [EPA registration number: 67572-82-71004]
• Monterey Horticultural Oil [Organic]
  Active ingredient: mineral oil/pet distillate light [EPA registration number: 48813-1-54705]
• Ortho Max Garden Disease Control Concentrate
  Active ingredient: chlorothalonil [EPA registration number: 239-2522]
• Spectracide IMMUNOX Multi-Purpose Fungicide Spray Concentrate
  Active ingredient: myclobutanil [EPA registration number: 9688-123-8845]
• This list may not include all products registered for this use.

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