My onondagas have been fine, but the trilobums were first hit by borer two years ago. I think it was due to drought stress. Since I don't supplemental water on an ongoing basis and won't be using chemicals, I have come up with plan B plants. I also cut the trilobums off at the ground as an experiment to see if the new growth would be luckier (Yes, they are re-sprouting). Really attractive shrub, but if the problem is too severe to live with, then I'll pick an alternate.

If you want to keep trying with it, you might be willing to cut off at ground level and get some pyrethin on hand. All my research turned up that as the only significantly effective treatment. Good luck.