It's mildew. Other than the fact that it's unattractive it won't hurt anything. Humid conditions bring it on. Try and make sure your peonies have good air circulation around them next year. For this year, I'd just cut them back and not worry about it.

Diann
IA Z5a

Thanks Diann, when should i cut back and how far down.
dee

Cut it to the ground (its not a tree peony, right?) and discard all the leaves. Those leaves will all be dead in a few weeks, many people have already cut them off.

Mildew, which it sounds like, is encouraged by warm humid stagnant air and plants with dry roots. It is rarely fatal but can be very ugly and certainly doesn't do the plant any good. It will always arise in the right conditions but promptly clearing away infected leaves will help to keep it in check. Spraying when you see it is too late so most people don't bother.

Thanks Shrubs... does waiting til first frost before cuttting back help the plant for next season? if so, i should wait til then to cut, right? or does it not make a difference to the health of the plant? I really don't know much about peonies, so thanks for the help,
dee

I apologize if this is received/posted twice.
I encountered a similar situation recently. Leaves of the affected area was also covered in a black, tar-like substance.
Stems were unusually brittle, but the leaves were alive and green under the tar.
A day or two later, the oozing sap looked much darker than normal.
Any ideas/suggestions?

Certainly seems like my peonies are not suffering. But, I'd like some advise about how to wash the white from the peony so it doesn't look so creepy next to my walk.
(Nice forum! Thanks!)