Hi, Well Black-eyed Susans always get pretty ratty looking by this time of year. There is a whole host of insects who enjoy them and the plants themselves are slowing down for the fall. I doubt those whitish bugs you are seeing in the soil are to blame. It's more likely grasshoppers, crickets, beetles, etc. At this late time of year I would not spray because your plants won't look that good anyway, plus you may kill good bugs such as butterflies who also like these plants. In late summer, you'll just see this as a natural process these plants go through.