There are large, brown spots on my peony leaves. What should I do?
Peony leaf blotch is probably responsible for the large, brown spots. Peony leaf blotch is caused by the fungus Cladosporium paeoniae. The disease is also known as red spot or measles. Typical symptoms include glossy purple to brown spots or blotches on the upper surfaces of the leaves. The disease may cause slight distortion of the leaves as they continue growth. Leaf symptoms are sometimes most apparent on the edges of older leaves. On stems, symptoms appear as long, reddish-brown streaks.
Peony leaf blotch is best managed through sanitation. The fungus survives the winter in infected plant debris. Diseased plant material should be removed in fall or early spring (before new shoots emerge). Cut off the stems at ground level. Remove the plant debris from the area and destroy it. Proper spacing and watering can help to minimize the severity of the disease. Space peonies 3 to 4 feet apart. When watering is necessary, avoid wetting the peony foliage. Fungicides can be used as a supplement to sanitation and good cultural practices.