You don't have a problem with moles or voles do you? I had an echinacea that was planted last year, did great in beginning of this spring then went brown. A vole or mole ate the roots right off! It was eaten from the ground up!
Otherwise, just keep it evenly moist, not overwatered. maybe give it some shade for a few days and see if it improves. Have you been fertilizing it? Don't give it too much nitrogen which can make them floppy and weak.
Maybe others have some ideas too.

Actually yes, we have a HUGE mole problem. I never even thought of that! Now that you mention it, the other day when I was watering I noticed a hole near my foundation right between my coreopsis and my columbine - all of the water was running into it. Now that the coreopsis is almost totally dead I wonder if he'll move on to my other flowers. Any suggestions on keeping them out of a specific area? There's no way we can afford a grub prevention on our entire lawn - it's quite large.

Get a =^..^= or =^..^=, =^..^=.

Problem solved! :)

Moles are carnivores, they eat worms, bugs and grubs, not plants.

Actually I wasn't sure of the difference between moles and voles, and after doing some research I believe we have both. Voles do eat plants and roots, and they leave smaller holes without mounds of dirt around them - that's what I found in my flower bed. (The larger holes with mounds are mostly in my grass.) So any thoughts on getting rid of voles? Although I'm sure my cat would love it, I won't let him outside - too much traffic. :)

We have golphers..are those moles? My cats do a good job but they make tunnels around the flowers and I have to go in there and step on them to pack the flower again. Now I make it an evening habit to walk around in there just to see if there are any new tunnels. When they dig the tunnels, they also dig up the plant. Grrrr.

i buy moonbeam every year even though it'sa perennial

my plants do the same thing as yours

look great when planted then turn brown and die

so sad as i really love this plalnt

if anyone has the reason why i would love to hear from you

i have no moles or voles just bunnies

thanks