How can I kill sand burrs/grass burrs?

[wilburn cox]

Several years ago I used a product (can't remember brand) that was very effective for killing these pesky burrs. EPA got involved and took it off the market. We have 4 acres and have grass burrs. I use Round UP in a small Windex spray bottle but this also gets on the near by grass.
Is there a product that will kill these burrs and not harm grass??

Any help will be appreciated. We live near Stephenville TX. Finally getting much needed rain, grass is sprouting and also the grass burrs.

thanks in advance;
Red Cox