powdery mildew - cut back ENTIRE plant to ground level .. ?

catalinaisle(6)October 7, 2010

Hi, Both of my peony plants have completely succumbed to what appears to be mildew (possibly botrytis, but I can't tell). I'll post more pictures later, but the whole plant is covered with velvety white stuff. Some stalks have fallen over flat on the ground! I've read on this and other websites "cut (infested) stalks back". (e.g. http://pubs.ext.vt.edu/450/450-602/450-602.html see cultural control.) If the *ENTIRE* plant is pretty much infected and therefore cut back to the ground level, does the plant then shoot out entirely new stems from the root next spring ... !!! ??? (If so, these plants hold the key to the fountain of youth?! :) Other than the sanitary precautions, do I need to take steps to protect the plant (essentially just the root system and stalks jutting out at ground level) - such as wrap the remaining stalks in burlap over the winter etc?

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calistoga_al ca 15 usda 9

Your soil around these plants is full of spores ready to infect new growth. Cut off all the mildew, in your case it sounds like all the above ground plant. Treat it like the disease it is and put it in your garbage, out of the garden. I would apply a good fungicide to the soil. I like the Bordeaux mix which is long lasting, in an attempt to prevent a reinfecting next year. Your plants will return with strength next year from the roots. While I am not gardening in your climate, I doubt you would need to cover your peonies for winter protection. Al

    Bookmark   October 8, 2010 at 10:08AM
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duluthinbloomz4

Calistoga is right - cut them down very close to the ground and clean up all cuttings as well any fallen leaves and stems. Here in zone 4 (considerably colder than your zone 6) peonies do not need any winter protection. They come up every year bigger and better. I've never had powdery mildew or botrytis on peonies so I can't speak to fungicides.

    Bookmark   October 9, 2010 at 3:02PM
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catalinaisle(6)

Can someone ID the type of peony I have from the photo?
I've read that bad air flow contributes to mildew problem. My flower bed is a bit thick at this point. Once I cut the plant back to ground, is now a good time to dig and split up the roots to improve air flow around the new plants in the spring ? Thank you!

    Bookmark   October 9, 2010 at 3:27PM
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calistoga_al ca 15 usda 9

If your peonies are so close together that they stay wet due to poor air circulation, one of them should be moved. Moving at this time is OK but does not call for dividing, unless the root is very large or you just want more plants. Most times a division will not bloom for a year or two. A herbaceous peony will grow to about a four foot diameter, so keep them far enough apart that the foliage from one plant does not mix with the neighboring peony. Al

    Bookmark   October 10, 2010 at 10:13AM
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catalinaisle(6)

Thank you, Calistoga. I've cut them all back down to ground. White powder was pervasive throughout. No visual symptoms of mildew on other neighboring plants such as hydrangeas and pachysandras. Turns out that three peony plants are within1-2 ft from each other. Next priority is to figure out and apply "Bordeaux mixture" to the perimeter.
They are currently in partial sun -to the west of house structure. Can they thrive in full sun - in south-facing flower bed?

    Bookmark   October 10, 2010 at 8:55PM
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calistoga_al ca 15 usda 9

Peonies here in the sunny Napa valley, better known for grapes, takes the full sun as long as they get adequate summer water. Apply your fungicide directly over the bare soil including the place where you removed or cut back the plants. The object is to KILL the remaining mildew spores remaining dormant just waiting for the right conditions to reinfect your susceptible plants. Al

    Bookmark   October 11, 2010 at 10:32AM
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