If you can post a shot I could be "diagnosed" better. But in general, asters yellow will cause the blooms to have green petals and/or miniature green blooms will grow from a flower's cone. Many times the plant's leaves will look perfectly fine.

Mites can cause a wide range of cone distortion issues but they won't cause the two issues noted above.

http://cubits.org/echinaceas/articles/view/426/

http://www.clemson.edu/extension/hgic/plants/landscape/flowers/hgic1182.html

http://urbanext.illinois.edu/focus/per_echinacea.cfm

For the life of me I cannot figure out how to put pictures into my message. Other than the one I can upload using the browse button on the message form here. I took some pictures of my affected coneflowers. I really hope I don't have to destroy them, as it seems that ALL my coneflowers are affected.
Why is it that my friend about 20 miles away has coneflowers in abundance, she is constantly thinning them out and giving them away. While I have to struggle and fight to keep mine alive, THEN when I finally have some nice looking plants, all of a sudden they look like this.....
I added a link to my flicker site showing the pictures I took.

Jenny p

Here is a link that might be useful: Echinecea photos

The tell-tell sign your plant has asters yellow is the deformed double flower. You are best to take the plant out immediately.