Thank you for reaching out to the UVM Extension Master Gardener Helpline with your questions, Al!

Your photograph and the completed worksheet are 
very helpful.

It looks like you have a classic case of aphids on your heliopsis.  There are many varieties of aphids -- and the "red" ones DO like heliopsis.  I fought this fine battle with some of my heliopsis last year -- so far the same plant is free & clear this year. :-)  

Aphids are soft bodied insects that suck the sap from plants. They can reproduce quickly, but a lot of our beneficial insects and birds love to eat aphids. We don't see aphids doing long term damage to the plant if corrected quickly (within a month or so of them first showing up in large numbers).

Here's a link to a fact sheet from the University of Minnesota's Extension service on the "brown" (often perceived as "red") abrosia aphid:

https://apps.extension.umn.edu/garden/diagnose/insect/garden/beetles/small/aphid.html

Even if this is not the exact species of aphid that you are battling, the information remains pertinent.   Be sure to click on the "More Information on Aphid Species" link to read about this pest's life cycle and how to manage outbreaks.

Here is a much more detailed fact sheet from the University of Maryland:

https://extension.umd.edu/resource/aphids-home-gardens/

 Note, in particular:  "Key Points" and "Aphid Management Tactics."

You'll read that spraying the aphids (with a strong spray) is the first line of defense; many of us find this helps and I recommend it, but it may not cure the problem entirely.  Still:  you may find it's enough -- if repeated often -- to reduce the population to tolerable levels. 

Key, to me, is to try to address the problem without killing off the beneficial insects/predators that feed on aphids. (Keep in mind that MOST insects are beneficial to our gardens.....we just focus on the pests.)  I found that the problem was localized for me....so if you have several clumps of heliopsis, you might consider cutting off any particularly badly infested portions of the plant (the tips were especially loaded in my case -- so I combined aphid removal with pruning to get a sturdier, broader set of flowers :-) and disposing of that material.  If you decide you need to resort to something stronger than the spray from your hose:  consider Neem oil -- it's a natural (tree-based) oil that stops the aphids from feeding.  This, too, takes some persistence and time but is less harmful to the "good guys" you want to keep in your garden.  If you are not averse to manual intervention, you can don gloves and easily kill these soft-bodied pests as part of your battle plan.

Most important for the future:  clean up all plant debris this fall (and as it dies before then).  Aphids can overwinter and we don't want to give them a place to lay their eggs. I cut my infected heliopsis right down to the ground and raked up all debris.

You might also notice, in the University of Maryland article, that overfertilizing with nitrogen can encourage aphids because it tends to push plant growth quickly resulting in tender (and delicious) new growth stems that aphids can puncture.   So avoid high nitrogen, quick releasing fertilizers as studies have shown these fertilizers can boost aphid populations.

I hope this helps and that you, too, will be eyeing your heliopsis next year with gratitude for the lack of aphids!

-- Robilee Smith