I hope it is ok to post this late. Have you seen the insects yet? One we are having a terrible time with is the Corn Rootworm Beetle, a relation of the Cucumber Beetle. The larvae must feed on corn to survive, but in the adult stage, they feed on different parts of corn, and move on to other plants. It is said they prefer yellow composites like sunflower and others, but I have seen them on nearly every native plant I grow.
Are you any where near an agricultural area? I have corn up to my property line on two sides this year, plus right across the road, so it was a worse infestation than normal.
Here's a picture of one. They are a tannish yellow, but as they age, they become more green.