Black Spots on Peony Leaves
Why are the leaves on my peony turning black?
Botrytis and phyphthora blights can cause purple-black spots on the stems and leaves of peonies. Sanitation is often enough to keep this disease in check. Remove and dispose of infested plant debris in the fall. Add a 2 inch layer of mulch over the soil surface to keep soil borne fungi away from the plant. Use chemicals as a last resort in cases where sanitation has not worked and the disease has been an on-going problem. Apply a fungicide, such as copper, labeled for controlling this disease on peonies. Spray plants as the tips emerge and every 14 days through mid-June.