Hi Janet,

The photos you shared this week are classic symptoms of Aster yellows. However, there is a chance the distortion of the flower is caused by a mite. 

What does the rest of the plant look like? Is it otherwise healthy? Do the leaves look strong and green? Aster yellows typically effects the entire plant, weakening it and/or making it look unhealthy, maybe yellow or distorted leaves. Mites typically only attack the flower. 

This website from Missouri Botanical Garden has good information and images. 

More information and photos from Ohio State University. 

Personally, I would remove this plant from my garden. Aster yellows is spread by leafhopper insects and I wouldn't want to take the risk of it spreading to other plants (Aster yellows impacts a shocking number of plants). However, before you pitch the plant, if you would like a definitive diagnosis, you can send in the plant to the MSU Plant and Pest Diagnostics lab. 

Lindsey K. Kerr, MS, MHP (she, her, hers)
Consumer Horticulture Educator
Michigan State University Extension