It looks to possibly be Botrytis blight. If so remove affected parts and apply a suitable fungicide. Am I remembering correctly that this was your beautiful white/yellow?

^^ Yes, that is her.

I thought it might be phytophthora blight, but I am not sure, I'm not well-versed on plant diseases. I thought Botrytis had a greyish fuss? I don't see any of that on her.

In her prime:

when did you move.. and how did you dig it.. and move it .. and how did you plant it????

refresh my memory how long ago that was ... and tell us how you dug and moved and planted it ...

i never had any luck with tree peony ... i usually blamed MI winters ,...

and it always intrigues me.. how disease and bugs.. find stressed plants ... hence i am wondering if it ever fully recovered from teh move????

ken

I moved it 2 years ago. It was fine last year. It got hit this year.

Tree peonies are very tough plants, I doubt our MI winters did them in - maybe something else in your environment. Like if I can't this funk under control, she's a goner...

If it is happening right now, it is the normal time of year for the greenery to die off for the winter. That is what mine look like when they die back for winter. In the past, when I have moved mature tree peonies, the above ground plant eventually died off and new scions pushed up out of the ground the next spring. There will be some normal die off of wood and just trim it off. Otherwise, let the foilage fall off.

Looks a wee bit fungal to me, too mxk3...my leaves generally go yellow then drop very cleanly and rapidly. However, I would certainly hold fire until next April/May before condemning it as they generally are tough and robust plants. Might be tempted to do a copper spray, now and at bud break next year.

It started mid-summer, then progressively worsened.

Clean up around it really well and next spring hit it with a good fungicide and ground around it a couple of times.