Herbaceous peonies, or Paeonia officinalis, and tree peonies, or Paeonia suffruticosa, are commonly cultivated in home gardens. Peonies, which grow best in cool climates, prefer full sunlight and well-drained soil. They are susceptible to several kinds of fungal infections.
Verticillium dahliae and Verticillium albo-atrum are soil-borne fungi that cause verticillium wilt in peonies. The Cladosporium paeoniae fungus causes peony leaf blotch, also known as stem spot or measles. The Botrytis cinerea fungus causes botrytis blight, while the soil-borne Phytophthora fungus causes phytophthora root rot.
Verticillium wilt enters peonies through their roots and clogs their water-transport systems, resulting in wilting and plant death. Leaf blotch is characterized by shiny purplish-brown spots on the upper leaf surfaces and reddish-brown streaks on stems. Botrytis blight covers new peony shoots and blossoms with a gray mold, killing plant tissue. Phytophthora blight, which attacks the roots, causes plant parts to blacken and wilt.
Fungicides are ineffective on verticillium wilt; removing diseased plants and replacing them with disease-resistant species helps to prevent the disease from spreading. Fungicides are effective on peony leaf blotch when used in combination with management practices, such as providing adequate air circulation and keeping the leaves dry. Preventive sprays help protect peonies from botrytis blight infections. Fungicides can help control phytophthora root rot if the roots are still healthy; planting peonies in well-drained soil with adequate air circulation helps prevent infections from occurring.