A few possibilities.

Given the appearance of yours -- Many perennials will die out in the middle (the donut look) when they have matured to the point where they need to be divided. I've been told that when a perennial looks spectacular, it's probably time to divide it for the next season.

Have you seen any vole tunnels? Liatris is a favorite food for them.

Crown or stem rot or root-knot nematodes-- if the entire plant is afflicted.

Cameron

Yes, we do have voles and my husband is trying to get rid of them. This is a plant from a division last year, so it is not an old plant. Wondered about some kind of rot problem because of this "forever cloudy and rainy" weather. Not sure what to do given this. Any suggestions?

I would rip out the affected part and make the crown clean if possible,perhaps using a little sulphur on the wounds. Then hope for the best. That's what I've sometimes done to irises. No experience with Liatris though, the roots of nearly all of them have been totally eaten by rodents(1 Liatris left)

Hi

I was just wondering if you found a solution to the wilting of your Liatris plant?? I have one (first Year) and growing great till the other day. Now one by one a steam is wilting and dying. I'm afraid that by the end of the week I will lose the whole plant! Help please anyone... Thank you

Too much water. Liatris is a prairie plant. It does not like too much water or fertilizer.

If it's voles, they are eating away at the roots, and the plant will slowly and inexplicably die. If you tug at the stalks of the plants the roots will feels "loose", and the soil may seem disturbed or fluffy around the root ball.

Several years back I had a terrible problem with voles in the 2 garden beds in front, and they ate all my Kobold. Now I sprinkle a castor oil solution I read about on the Hosta forum on those beds when necessary. This works unbelievably well and it lasts for months! Do a search on this forum for "voles castor oil" or such and some threads will no doubt come up.