Sandburrs are tough to keep gone. One application of premergeant has never got rid of them as far as I have seen. As many apps in one season as is allowed is more like it and start early at that. Several years of premergeant apps will be needed. If MSMA is legal to use in Texas then it may help keep sandburs down. The best success I know of is premergeant early and again later with Dimension, lots of fertilizer and grass mowed as high as possible.