Peony Leaf Blotch: Effective Treatment and Management

Peony leaf blotch is a fungal disease caused by Graphiopsis chlorocephala. While the fungus is responsible for various diseases, the symptoms of peony leaf blotch are characterized by large, shiny, brown or purple lesions on the leaves. This disease is often confused with peony “red spot” and “measles,” which result in distinct red to reddish-black spots on the stems. It’s important to note that the symptoms of measles typically appear before the leaf blotch symptoms.

Peony Leaf Blotch

Peonies are also susceptible to Botrytis paeoniae, a gray mold fungus. This fungus can infect newly emerging shoots and cover them in a fine, velvety gray mold. It can also infect flower parts, resulting in bud blast and flower blight. In some cases, the fungal infections can spread down the stems, causing shoot blight.

Peony Botrytis

It’s important to mention that while searching online, you might come across mislabeled images or confusing information about these diseases. Peony leaf blotch and Botrytis blight have different disease cycles, although it’s not uncommon to find both diseases affecting the same plant.

Fortunately, neither peony leaf blotch nor Botrytis blight are considered fatal to garden peonies. However, they can significantly impact the aesthetic value of these plants in landscapes. Therefore, it’s essential to take steps to prevent and manage infections.

Effective Management Strategies

To effectively manage peony leaf blotch and Botrytis blight, it’s crucial to understand the disease triangle concept. The disease triangle consists of three conditions required for disease development: the presence of the pathogen, a susceptible plant host, and environmental conditions that support infection and disease progression. By eliminating just one of these conditions, you can prevent disease development.

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Disease Triangle

While reports suggest planting less susceptible peony varieties, scientific data evaluating disease susceptibility are limited. However, observations indicate that susceptibility may vary among different peony varieties. Other factors, such as micro-environments, can also influence infection levels within plantings.

Environmental management can help suppress these diseases. Avoiding overhead irrigation can reduce the risk of infection, although controlling natural rainfall is challenging. Fungicidal applications can be effective in suppressing the pathogens; however, success largely depends on the frequency of applications and weather conditions. For home gardeners and landscape management professionals, relying solely on fungicides is not recommended.

Disease Triangle - Pathogen

One of the most effective management strategies for peony leaf blotch and Botrytis blight is sanitation. Proper sanitation involves removing infectious tissues that harbor the fungi throughout the growing season and during winter. Here are the essential steps to follow:

Fall (right now!):

A. Cut and remove all top growth, ensuring everything is removed down to the soil line.

B. Rake and remove all mulch and plant debris from beneath the infected plants.

C. Add new mulch to a depth of no more than 2-3 inches to suppress the release of fungal spores in the following spring.

Spring:

Protect new shoots by applying a suitable fungicide labeled for peonies. Make sure the product label specifies the site (e.g., landscape) and that peonies are not listed as sensitive to the product. This protective measure requires one or two applications. While some gardeners have successfully managed peony leaf blotch without spring fungicidal applications, it’s advisable if there were heavy Botrytis infections during the previous season.

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During the Growing Season:

A. Remove and destroy any bloom buds, flowers, and stems showing signs of Botrytis infections. Consider dead-heading spent flowers.

B. Prune the plants selectively to improve air circulation, aiding leaf and stem drying.

C. Avoid overhead irrigation and utilize drip irrigation if available.

By following these steps and practicing proper peony plant care, you can effectively manage and reduce the impact of peony leaf blotch and Botrytis blight on your garden peonies.

For more information about peonies and professional assistance, visit Ames Farm Center.