Last year I planted three Pow Wow cone flowers; two are blooming beautifully, and the third, well... look for yourself. Any ideas as to what is going on with the middle one?
Likely aster yellows disease. You'll want to remove the whole plant to avoid infecting the others.
Here is a link that might be useful: Diseases on echinacea
Eek! Get rid of it ASAP. Aster yellows is terrible.