My main concern is what about the horses while I am killing the bitterweed. My second concern is there a better way to kill bitterweed other than roundup. I have it in my pasture bad, it is from one side to the other and it looks like the only grass growing in my 6 acre pasture is back in the woods. The bitterweed is tall enough to spray without hitting other plants, but will the horses eat the bitterweed when the plant is dead??