You can always clean dead or decaying foliage off peonies, especially now when we're at the beginning of the end of the growing season. Don't leave the plant debris lying around to over-winter, dispose of it in your trash.

How are your peonies sited? They tolerate light shade but prefer full sun in rich, well drained soil with no competition from nearby shrubs and trees that might have aggressive root systems. Good air circulation around peonies helps keep them healthy too.

Thanks Duluthinbloom,
I'll cut back and remove the foliage from the garden.

I have 6 single peonies planted in my main perennial bed and this is the first summer in 25 years that this fungus? has affected 2 of the plants. Both are in full sun. We've had an very wet summer and this bed is crowded with other perennials.
Thanks

You're welcome.

Cool, wet weather in the spring, followed by lots of summer rain or continuous days of drizzle can cause some peony problems. Can't do much about rainfall, but if you water during any dry spells, best not to wet the leaves. Maybe moving some of the crowding perennials away a little will help the air circulation - that, along with cutting the peonies down in the fall and disposing of all the debris might be about all you can do. That will probably result in the peonies coming up clean and healthy next season.

If it is a fungus, the fungicides aren't terribly effective unless they're used early - so I've read. I'm no expert, but like you, have had peonies for many years. So far no problems, knock on wood.

Jacqui Ontario,
I too have the same problem!
Infact, I had it last year too. I am new to gardening and didn't know what to do, so I didn't do anything! (well I actually did cut them down to the ground in the fall as they were just too ugly to look at and I thought they were dead and gone, for sure.)

Anyway to my delight, this Spring, they came back as happy, healthy and pretty as can be. So I thought to my self, hmmmmm... they are doing well and survived what ever that was, I'm going to leave them be.

Here we are, in the fall and they have it again. I bet they have had the brown leaves for a while now, though.
It really looks to be a major infestation, whatever it is. It can't be healthy for my other surrounding plants (roses) either.

I don't want to spray, as I try not to do that. I guess I'll do nothing again, and hope they return happily in Spring?

We had a very wet summer this year, so that might contribute, but even last year, which was very hot and dry, it seemed to be worse. Can it be that this is just how Peonies look at the end of the season??

Good luck and I'll follow and let you know if I learn anything more!

Tulipsmiles