Hydrangea: Powdery mildew
categories: Hydrangea Hydrangea Diseases Ornamentals Shrubs
last review date: 2025-06-28 12:23
Photo by: Dept. of Plant Pathology, NCSU
Biology
Powdery mildew is a fungal disease affecting leaves, young shoots, and flowers. White to grayish, powdery fungal growth develops on the top of the leaf and may also appear on tender shoots, buds, and flowers.
Leaves may also develop yellowish blotches or turn purplish brown, with a white powdery growth on the underside. Affected plant parts may be stunted and deformed. Severely infected leaves often drop from the plant, and shoots may die back.
Unlike other fungal diseases, powdery mildew does not require moist leaf surfaces for infection and is typically most prevalent during dry weather with warm days and cool nights. It thrives in conditions of high humidity, such as on plants in heavily shaded areas.
While powdery mildew may occur on other species of hydrangea, bigleaf or florist’s hydrangea (Hydrangea macrophylla) is most commonly affected.
Management Options
See "Using Integrated Pest Management (IPM) in the Landscape" for successful problem management techniques.
Non-chemical Management
Select non-chemical management options as your first choice!
- Avoid overfertilizing, which encourages susceptible new growth. If fertilization is necessary, use a slow-release or lower-nitrogen formula.
- Gather and destroy all fallen leaves.
- Pick off infected leaves and prune severely infected shoots to prevent spread of disease.
- Space plantings and prune to provide good air circulation.
- The cultivar ‘Veitchii’ is resistant to powdery mildew, while ‘Nikko Blue’ is susceptible. ‘Madame Emile Mouilliere’, ‘Forever Pink’, ‘Lilacina’ and ‘Holstein’ show intermediate susceptibility.
Chemical Management
IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides.
- Begin applications when conditions are favorable for disease.
- If necessary, repeat applications at weekly intervals or as label permits.
- Complete coverage including both upper and lower leaf surfaces is important, especially when using bicarbonates
Approved Pesticides
Examples of pesticides that are legal for home use in Washington State are listed below.
The list may not include all products registered for this use.
WSU Extension programs and employment are available to all without discrimination.
Evidence of noncompliance may be reported through your local Extension office.