Cut the stems at ground level in the fall or early spring to control peony leaf blotch. Before fresh shoots emerge, rake the area. Fungicides are available to aid in disease control, but they must be used in conjunction with other management measures. Avoid planting diseased plants as this will spread the blight.
Leaf blotch starts as yellow spots that turn brown and drop off of the leaf. This is a sign of infection. The spots usually appear on older leaves first, especially when it's hot outside. They can also appear on younger leaves if there is much stress at the time. Peony leaves have sharp edges and should not be handled with bare hands. Wear gloves when working with these plants.
If left untreated, peony leaf blotch can cause serious problems for the plant. New growth will be stunted until the next growing season. Even then, it's possible that the virus will spread to new leaves before they open. This could prevent healthy tissue from developing. The entire plant may become infected.
It's important to identify leaf blotch early so proper treatment can be given before more severe symptoms appear. Check leaves carefully for any yellow spots that might indicate infection. If you find one spot that has turned brown and dropped off, then that portion of the leaf is dead and should be removed. Do not use pesticides or other chemicals without first talking to your local agricultural department.
Checklist for Intersectional Peony Care
Peonies grow best in well-drained soil in full sun, away from huge shrubs or trees that might deprive them of water and nutrients. Soak the peony roots in water for several hours before planting. Work the soil up to a depth and width of 12" to 18", adding lots of compost as you go. Space plants 24 inches apart. Perennial peonies may be divided every three years to keep them vigorous.
When dividing perennials, it's important to try to maintain the original planting shape as much as possible. This helps the plants retain their identity and allows them to use natural growth processes such as sprouting and bud development, instead of being forced into early flowering by pruning off their side shoots. In addition, keeping the number of plants within reasonable limits ensures that they will be able to survive our sometimes-fickle climate. A few years ago, my husband and I divided up an entire perennial bed that had grown too large for our taste. We chose just four flowers and left the rest of the plants where they were, so that more offspring could grow up around the new plants. In fact, we've let some of those other individuals spread out across the yard over time because we know they'll provide more flowers next year!
Once the plant is divided, gently tease the roots apart from each other. If they're not already quite thin, work some sturdy scissors into the job. Place the divisions evenly around the parent plant, spacing them about 1 foot apart.