Cut Flower Updates: August 15, 2025

Peonies bring abundant, profitable blooms to the cut flower farm each spring, but by late summer, you may begin to notice your plants looking worse for wear. This week, let’s explore a few common peony diseases and the symptoms that appear at this time of year.

Growers may begin to notice shiny, reddish-purple to brown lesions on the leaves of their peonies in late summer, and red spots or streaks on the stems. Leaves where lesions are present may be curled or distorted. This condition is known as peony leaf blotch, caused by the fungus Graphiopsis chlorocephala (formerly Cladosporium paeoniae).

Botrytis blight, caused by the fungus Botrytis paeoniae and other species of Botrytis, can also cause brown or blackish, irregular spots on leaves. Plant parts infected with Botrytis blight, also known as gray mold, will develop fluffy gray spores when moisture is present. It can be difficult to tell leaf blotch and Botrytis blight apart in the field – a laboratory diagnosis may be necessary. Luckily, neither disease is likely to cause significant damage or death of plants, unless disease pressure is severe.

Lastly, you may notice the white spores of powdery mildew appearing on peony leaves as we inch towards fall. This disease is caused by the fungus Erysiphe polygoni, which favors the high temperatures and low humidity of mid-late summer.

Many fungal diseases overwinter on diseased plant material, so management in future seasons depends on the sanitation measures you take this fall. We’ll create a more detailed post later in the season about how to cut back peonies and other herbaceous perennials in the fall to control diseases. For now, you can cut out the most heavily diseased portions of the plant and remove them from the field. Leave as much green, healthy foliage standing as possible to allow the plants to continue photosynthesizing through the end of summer. Remember to disinfect your snips often to avoid introducing fungal spores to new areas of the farm.

For more information on peony fungal diseases, visit this post from The Ohio State University: Garden Peony Clean-Up.