Powdery Mildew on Peonies #798447

Asked June 29, 2022, 9:13 AM EDT

Good Morning. My neighbor gave me some peonies last fall. We temporarily planted them in one garden until we extended the garden we wanted to plant them in. We transplanted them this spring. A few bloomed, but some were too small to produce flowers. Now most all of them are covered with powdery mildew (both on the top & bottom of the leaves and stems). The neighbor that gave them to us planted some in her yard too, but none of hers has this mildew. What is the best treatment for this? I've heard about making a Murphy Oil soap, baking soda, and water mixture and heavily spraying them with that, but it just seems that there would be something better to use. If they go untreated, could it harm the other plants I have in that garden (hosta, iris, tulips, fern peonies, other well established peonies, and daylilies). Thank you!!

Scott County Minnesota

Expert Response

Thank you for writing. 
This is a good resource of you.
I ignore this condition which is mainly about moisture.
Steve Miles Replied June 29, 2022, 2:46 PM EDT
Thank you for your reply.  I really appreciate it.

One question.  Would it hurt the peony plant if I were to cut it back now versus waiting until fall?  The powdery mildew is pretty bad on a couple of the smaller plants and I'd hate for the spores to travel and adhere to other plants in the garden.

Thank you & have a great weekend!

-----Original Message-----
From: Ask Extension <>
To: Gina Bresnahan <>
Sent: Wed, Jun 29, 2022 1:46 pm
Subject: Re: Powdery Mildew on Peonies (#0068378)

gabrez Replied July 01, 2022, 9:41 AM EDT
Thank you for writing back.
Here is good information for you.
Generally, one allows functional leaves to feed the roots for as long as possible to allow the root system to build for the next flowering season.  This is true with peonies as well.
Some plants should only be pruned in winter to prevent infections--this not the case with peonies.  
Bottom line: you can do some light pruning now for shaping the plant but wait until fall for major pruning.
Steve Miles Replied July 01, 2022, 11:06 AM EDT

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