My Peonies Have Black Spots

Phytophthora blight and botrytis blight are fungal infections that attack peony plants. Symptoms of the diseases are black spots on the leaves, stems and buds. The treatment options vary according to the type of infection.

Types

The Phytophthora cactorum fungus causes phytophthora blight in peonies, while the Botrytis cinerea fungus causes botrytis blight. Both pathogens may remain dormant in the soil for years. They also survive in diseased plant matter. They mature during spring when weather conditions are cool and wet. Fungal spores spread through splashing rain and wind to infect new host plants.

Effects

Phytophthora and botrytis blight create leathery black areas of diseased plant tissue on the leaves, stems, shoots and buds of peonies. Plants infected with botrytis, also known as gray mold, also develop a thick gray mold on the diseased areas. Phytophthora usually attacks the roots or the shoots closest to the ground and causes diseased stems to fall over, while botrytis blackens young shoots, kills emerging buds and causes dieback in foliage.

Prevention/Solution

Phytophthora blight most frequently attacks plants that grow in poorly drained soil. Planting peonies in well-drained soil and watering plants from the ground rather than overhead will help prevent phytophthora blight. Peonies with diseased roots should be removed, along with the soil that surrounds the plant, and discarded. Removing diseased flowers and plant debris helps prevent the spread of botrytis blight. Both diseases are controlled using fungicides.

References

• University of Wisconsin Extension: Peony Disorders: Phytophthora and Botrytis Blights
• University of Minnesota Extension: Diseases of Peony
• Cornell University: Botrytis Blight of Peony
• Iowa State University Extension: Phytophthora Blight -- Peony