These symptoms you are seeing (distortion, elongated twisting growth) are characteristic of herbicide injury rather than a disease. There are some herbicides used for lawn and landscape weed control that work as growth regulators, which can result in unusual growth if they come in contact with non-target plants. Some herbicide products can volatilize and drift on wind currents from applications nearby, so even if you did not apply an herbicide in the vicinity of this particular plant, it is possible that damage can occur from an herbicide application nearby. 

There is not much you can do about this type of injury, other than trim out the distorted portions of the plant. The following pages go into more detail about herbicide damage on landscape plants.

https://extension.umd.edu/resource/herbicide-damage-flowers

https://extension.umd.edu/resource/herbicide-damage-trees

Christa

You're welcome.

Thank you for sending these close-up photos. The symptoms you found on these stems are consistent with a fungal disease -- possibly white mold or gray mold (Botrytis). Verticillium wilt can occur in peonies as well but it looks to our plant pathologists like white or gray mold, more likely.  

Our recommendation is the same; prune out those affected stems and discard them. If you are curious, you could put a piece of the symptomatic stem in a Ziplock bag with a moist paper towel and keep it near a window for a few days and see if it develops white or gray mold sporulation. (Our plant pathologists are curious, but you may have already cut/discarded those pieces already). 

Christa

You're welcome, Diane. Let us know how it goes and feel free to send us more photos if you see sporulation and want to have us take a look.

Christa