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Mold on Peonies

The cause of Peony mold along with the cure

By: Sandy Feather 2007
Penn State Extension


Q. What causes the leaves of my peonies to develop black spots and what can I do about this problem? When I cut back the bushes in the fall, I get rid of the branches and don't put them on my compost pile.

A. The black spots on the leaves sound like typical gray mold symptoms. This fungal disease is quite common on peonies, especially if we have cool, wet weather in early spring as they are poking up out of the ground. Gray mold is also known as botrytis, and it can spoil the flowers, too. Peonies infested with botrytis can have numerous flower buds that turn black and shrivel up before they get a chance to open. Those that do open may be brown and mushy inside, and not last very long.


Spread of the Disease

The dead flower petals are frequently covered with brownish-gray fuzz, which are the spores that spread the disease. Botrytis is spread by wind, splashing rain or irrigation water, and on tools or even your hands when you work on infected plants. The fungus survives on plant debris and can persist in the soil for many years.

Peonies in bloom
Pink Peonies in full bloom

Remove and dispose of all the decaying and infected plant parts. You are wise not to compost the diseased plant material. Clean up plant debris around your peonies during the growing season and again before putting the garden to bed in the fall. Cut herbaceous peonies to the ground and dispose of the cuttings when the tops have been killed back by frost. While you cannot keep them dry when it rains, avoid wetting the foliage when you water your peonies. Use soaker hoses or drip irrigation if possible. If not, use a watering wand and aim it at the soil under the peonies, rather than over the top of them.  It is helpful if they have full sun and good air circulation because that allows the foliage to dry quickly after rain or heavy dew.

 

Fungicide Applications

You can make also make fungicide applications as they begin to grow in the spring. Mancozeb (Dithane) and Cleary's 3336 (thiophanate-methyl) are labeled to control botrytis on peonies. Fungicide applications work best when applied preventatively, before you start to see leaf spots. Follow label directions regarding application rate and intervals between applications.

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