Botrytis Blight on Peonies and Roses
This fungal disease is most common in cool rainy as well as humid weather. The disease attacks a variety of ornamental and edible plants and often is specific to the plant part infected.
Look for the fuzzy gray growth and small back specs on the dead tissue.
Remove infected parts and place in a paper bag for disposal. And don't compost. Only clean up during dry weather as moisture helps spread the blight.
Ongoing sanitation, fall clean up and better weather is usually enough to keep this disease under control.
A bit more information: Several other fungal diseases can cause spots on the leaves and stems of peonies. These spots can be round and circular or irregular in shape. Stem cankers, sunken discolored areas, can cause twisting and even death of the stem. Sanitation is usually enough to manage these diseases on healthy established plants.