If it's aster's yellow.. then yes you will have to destroy it.. roots and all. Just make sure it's not just mite damage with is very prevalent this year as well. Below is a site where you can compare the two issues.

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

Thank you kindly for your response and link. I appreciate it. It's hard for me to say goodbye!