Coneflower yellow aster disease. Does this have anything to do with Aster flowers/shrubs? I had to dig out about 40+ coneflowers last year. I have 2 shrub asters and I also had some aster flowers I started from seed last year. I noticed on my Fireworks Aster seed packets it says not to plant where I had asters previously.
If you google aster yellow disease it will give you sites with lists of plants that are hosts and are affected and it is a long list. I couldn't find any information listing asters as the cause. It seems to be caused by a tiny phytoplasma, similar to a bacteria, and is spread from plant to plant by leafhoppers. There is no known cure but removal of affected plants is recommended. Oat straw mulch and removal of weeds like dandelion might help.