My coneflowers seem to be afflicted with stem and root rot
It was a long cold winter and spring was slow to come. When it did we had unusually cool temperatures and seemingly endless rains. Now that summer has arrived it is hot and humid and the rain continues. These have been perfect conditions for fungus to thrive.
The first symptoms appeared in late spring. A full stem of foliage turned brown and the flower heads drooped. Seemed like classic symptoms of under watering. If you have read much of this website, you will see repeatedly "withhold water until the problem is identified"! In this case, with all our rain I did not suspect the problem was lack of water. I removed the complete stem that had died back and continued to monitor.
The fungus is likely Sclerotinia sclerotiorum, sclerotinia stem and root rot, often just referred to as crown rot. This fungus usually originates in wet soil but can also be moved through the air. It can afflict a variety of plants and manifest different symptoms. For echinacea, the plant will often continue to grow and bloom, so just when you think you have the problem licked the flower heads droop again.
My cluster of three plants looked pretty good for a while, then the wilted look appeared again. And another stem wilted completely and had to be removed. This cycle is continuing and I do soon need to make a decision.
Continue to monitor, removed dead stems, and hope my other coneflowers and perennials are not afflicted.
Treat with a fungicide, which may require repeated applications.
Remove the plants entirely.
I do try to avoid using chemicals but of course sometimes they are necessary but should be used cautiously. And before using a chemical fungicide I would want to be certain of the diagnosis. I am loathe to destroy plants because, of course, gardeners always nurture their young back to health! I do have sincere concerns however about this fungus spreading. Ugh! Right now, still monitoring and destroying dead foliage (Don't EVER put diseased foliage in the compost!).
Watch and wait, hope for recovery