Aster yellows can affect any plant in the asteraceae family. It is spread by leafhoppers. I had it in my yard one hot summer and lost quite a few coneflowers. The flowers turn weird looking and the foliage will start to yellow and the plant looks sick.
I also have some mites every year, and they can cause all kinds of weird distortions on the flowers. They're not deadly though. I generally just cut off obviously infected blossoms when I notice them, and trash them. But overall the plant doesn't look as sickly as with aster yellows.
Karen
