|spotted cucumber beetle (Diabrotica undecimpunctata howardi)|
Take a good look at your larger flowered asters. If the ray petals are missing or mangled, you probably have an infestation of cucumber beetles. I've been hand-catching and squishing the little buggers, but there has to be a better way, short of growing only small flowered ex-asters and goldenrods. The only suggestions for organic controls I've come across are floating row covers (not going to work for ornamental plants), and yellow sticky traps, which I fear might trap bees.