There are several peony leaf diseases that can cause foliage to brown and die. The most common of these is Botrytis blight (gray mold) caused by the fungus Botrytis cinerea. This fungus can infect shoots, stems, leaves, and flowers anytime during moist periods in spring and summer. Another disease, caused by the fungus Cladosporium paeoniae, causes small red spots that can merge to form irregular purple blotches on leaves and stems. Red spot can lead to deterioration of peony foliage by late summer, as can several other leaf spots caused by fungi such as Alternaria, Cercospora, Septoria, and others. All of these fungal diseases of peony are favored by wet weather, and spring infections may eventually cause dieback later in summer.
Gardeners can reduce disease in the following ways:
- increase plant spacing to improve air circulation and keep humidity lower; prune away shading vegetation from nearby trees and shrubs;
- avoid wetting foliage when watering; and
- remove and destroy diseased foliage and blighted stems in the fall.
- Fungicides are available to help prevent peony foliar diseases. Check fungicide labels for timing and rates. Contact your local Extension office for fungicide recommendations.
