Hi!

This is a symptom of Aster yellows disease, which causes a general yellowing and stunting of the plant. This disease is spread in the field by Macrosteles fascifrons, the aster leafhopper. 

The best way to manage this disease is first through early detection of infected plants. Remove infected plants as soon as they are diagnosed to prevent spread to nearby healthy plants. There is no cure for infected plants.

You can learn more about this disease and management of it on our Asters Yellows page. 
https://extension.umd.edu/resource/aster-yellows-disease-flowers

Jamie