when is your first frost ..

and do they die back to the ground ...

i would suggest that if they have been there for 4 years ... they dont need anything to help them 'heal' ... and i surely would not be ferting them in fall ..

are you 100% sure on the bug ID?

and i would not expect the same bug plague next year ... seems like you just had a bumper crop this year.. but you dont mention any of the previous 4 years ...

ken

The first frost usually isn't for at least another couple of weeks to a month. (mid-late October)

Yes, they die back to the ground, but I leave the dead stems as they are, over the winter and prune them back in the spring when I start seeing new growth at the base of the plant.

Yes, I am positive they are aphids. I've even noticed a lady bug or two feasting on them. (just not nearly enough ladies to make a difference)

No, I've not had a problem with bugs in previous years. Not every year, but I do remember planting Petunia's around them at least once or twice - not knowing they are aphid-deterrent plants - so perhaps I need to do that for next year?

The only thing different this year is that I added 8 new Gaura bushes to my existing 3. I'm not so much worried about my established bushes, just the newbies.

Especially at this time of the year, I'd use a brisk spray of water from the hose to dislodge aphids from perennials.

Aphids are seldom a problem here, and then only on an occasional annual planting.