Several fungal organisms are capable of causing spots of varying sizes and colors on peony. These organisms may affect stems, leaves, bud scales, and flower petals. Most infections occur when the plant is still young and the leaf and stem tissues are very succulent. Spots may appear as small elongate reddish areas that enlarge to lesions with gray centers and reddish borders and may develop into extensive zonate cankers. Cankers on stems may cause twisting or, if the stem is very young, it may be killed. Spots on the leaf may occur along the veins as well as on the tissue between the veins and on the petioles. Buds also may be "blasted" (destroyed) when the bud scales and outer petals become infected.

Another disease appears as small, circular, red discolored spots occurring first on the leaves. A number of the spots may run together so that the leaves appear irregularly blotched. The under-surface becomes light brown (chestnut color) while the upper surface remains a dark glossy purple. On young stems the spots appear as reddish brown streaks. All parts of the plants may be infected and during severe drought conditions infected leaf cells are killed. Leaf and stem spots may be controlled best by removing old top material in the fall, cutting the stems at ground level and destroying those parts. Thorough sanitation should adequately control these diseases.