The peony comes from the genus Paeonia in the family Paeoniaceae and are herbaceous perennials. Some varieties are woody shrubs while others are trees. The plant variety grows from 2 to 4 feet high. The lightly scented flowers bloom in shades of red, pink or white and are about 6 to 8 inches in diameter. The leaves are dark green. Tree peony, or Paeonia suffruticosa, varieties can grow up to 7 feet tall but do not live as long. All peonies can be affected by different leaf diseases.
Mosaic Leaf Curl
The mosaic virus creates yellow blotches and rings on the leaves of the peony plant. The infected plants are not deformed in any way but must be destroyed to prevent the spread of the virus.
Botrytis blight is caused by the fungus Botrytis cinerea and affects not only the leaves but also the stems and buds. It is more prevalent in rainy cool weather. The fungus attacks early in spring, causing the leaves to develop unevenly shaped spots. The stalks turn colors at the bottom and wilt. The buds become covered with fungal spores.
The recommended control involves good sanitation practices. These include deadheading, or removing the flower after it has bloomed, and following good basic care practices for the plants. Fungicides are only partially effective on this fungus. To prevent the disease, copper sulfate can be applied in early spring when the shoots reach 6 inches tall.
Phytophthora blight is caused by the fungus Phytophthora cactorum and has very similar symptoms to Botrytis blight. The leaves are affected; however phytophthora does not produce the spore growth on the plant when it is excessively wet outside. The infected leaves can turn brown or black. Phytophthora can kill an entire plant. The infection starts in the roots and symptoms begin to appear all over. Fungicides do not help and if plants are truly infected they should be destroyed and new plants should not be planted in the same area.
Red spot is caused by the fungus Cladosporium paeoniae. The leaves develop red spots that can run together, forming odd-shaped purple splotches. By late summer the leaves will have deteriorated. As with most fungi, wet springs cause these diseases to thrive. Control involves improving air movement by good spacing when planted. Peonies do not like wet leaves so watering near the bottom of the plant is another good form of protection. It is also recommended to get rid of or throw away any infected leaves and stems.
Leaf and Stem Spots
There are many fungal organisms that cause spots on the leaves of peonies. They can affect the leaves by causing spots of different sizes and colors. They can also affect other parts of the plants. The spots on the leaves may appear at first to be small and reddish but then grow bigger and develop gray middles with red borders. Leaf spots can be controlled with good sanitation, including cutting stems down to the ground and destroying infected plant material.