Hey Dave! I would use Glyphosphate..its whats in Round-up, but the generic forms work well and is MUCH cheaper. Southern States has got it, thats where I purchase mine. Gly-4 is what its called at this SS. It takes awhile for it to start killing the weeds 5 to 10 days but the weeds/grass will surely die. Also it works best in warm temperatures 70 degrees and higher. Good luck!