Many thanks for all the thoughts expressed here. I do believe it’s time to use some stronger chemicals and I stopped by our local agriculture supply store for advice and bioweapons. The clerk tried directed me to Pramitol. The person thought it might be just what I need and claimed it can kill pretty much anything green, most things that aren’t and might be able to give cancer to igneous rocks. Don’t spill it on yourself, don’t breathe it, try not to even look at it.
The clerk also echoed freckafree’s autumn application advice. Her advice was to quit trimming them back and let them get as big and green and leafy as possible over the summer. Hose them down with the Pramitol mid-September and hope for the best.