Thanks for your question.

These are aphids on your Black Eyed Susans. Although I cannot with complete confidence identify the specific species, I believe they might be what is commonly called a Sunflower Aphid (Aphis helianthi). As its name suggests, another host for this aphid are sunflowers. This is not surprising as both belong to the same botanical family, the Asteraceae.

While unsightly, these bugs do not cause significant damage to your plants. They should disappear within a couple of weeks. If you want to get rid of them, do NOT attempt to use chemical insecticides, since several different types of beneficial insect pollinators would be killed in the process. Simply wash these aphids off your plants with a forceful stream of water from a hose. They will be unable to climb back onto the plants.

Insecticidal soaps can be effective means to help control certain insects including aphids, but they do have limitations. Insecticidal soaps are contact insecticides, since they plug breathing holes in the outside of the insect. Carefully read the label on any commercial product you might purchase to be sure it is effective against aphids

Here is some additional on these and related points:

https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=18009

https://extension.umd.edu/resource/aphids-flowers/

https://extension.umd.edu/resource/aphids-trees-and-shrubs/

https://extension.umn.edu/yard-and-garden-insects/aphids

As I said, you are not dealing with a significant problem. Good luck. Please get back to us with any further, related questions.

Thanks for your response.  A bit of advance warning.  You may continue to see aphids on your plants even after your hosing.  New adult aphids will arise from immature aphids that may still be on your plants.  In other words, hosing off aphids may be part of your daily routine for at least another week, perhaps even longer.  A female aphid can produce young without having to mate with a male.  Rather a unique situation.  These young can be as many as 12 to 15 per day/female aphid.  Their reproductive prowess is huge!

Good luck.  Be persistent.  I have high confidence that your plants will survive.

Glad to be of assistance.  Thanks again for consulting with our forum.