Peonies - Spots on Leaves
Question: Why do peony leaves and foliage develop spots and blotches and then die by late summer?
Answer: There are several peony leaf diseases which can cause foliage symptoms and death. 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, causing infected parts to turn brown and die. Another disease, caused by the fungus Cladosporium paeoniae, causes small red spots which can coalesce 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 other fungi. All of these fungal diseases of peony are favored by wet weather and infections begun in spring may eventually cause severe symptoms 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, remove and destroy diseased foliage and blighted stems in the fall. Fungicides are available for home garden use to help prevent peony foliar diseases. Check fungicide labels for timing and rates to use for peony diseases.
-Dr. John Hartman, Extension Plant Pathologist, University of Kentucky, Lexington