mine got powdery mildew and started turning brown at the edges. Did the same last year and lost the leaves ultimately. it has to be the excess rain and not as much sunshine. This year, I sprayed neem oil a few times and eventually chopped off the leaves. It can either grow some now and make more food before frost or sulk, I don't care......

Just an FYI peonies do not have green foliage all year round. Like many plants they go dormant in the fall.

Once, the go dormant, ie the leaves turn brown, cut them back to ground level.

Just a reminder that tree peonies are NOT cut back to the ground.