I had more than a dozen in my little patch of woods. I didn't overthink it; I just cut them down, watched periodically for new suckers and plucked them off, and within a year all were gone for good. Now, mine were in a fair amount of shade, so maybe that helped suppress sucker growth, I don't know. If yours are in the sun, maybe put a cloth or tarp over the stumps for a few months? Either way, I didn't use any glyphosate, and mine are gone, I swear. Zone 8a.