Getting Rid of Weeds in Horse Pasture

Cut the weeds. You can use a trimmer if it has a metal blade, or, for more exercise, use a weed whip or a machete (spelling?). Don't try to do it all at once though. With rain and luck, the grass will grow. You don't say how large your field is, but a lawn mower might take care of some thick patches. Cut them off and keep cutting them off, and also chop at them with a well sharpen hoe. I realize these ideas are labor intensive, but they don't cost much and will provide exercise.