The fungus Botrytis cinerea may also infect stems, leaves, and buds. In wet weather, diseased plant parts become covered with a brown to gray coat of fungal spores. Stems, leaves, and buds when infected suddenly wilt and turn black color. In severe cases crown and root tissue may also show symptoms of rot. Controlling Peony Diseases.
Sanitary measures are the most effective means of controlling peony diseases.
Remove infected plant parts when they appear. In the fall, remove as much of the stalk as possible without injuring the buds. Fungicide sprays, such as Bordeaux mixture, basic copper sulfate, maneb, or mancozeb, are directed at protecting healthy plants. Diseased plants cannot be cured. Sprays need to be started in the spring as new shoots appear through the ground.