I have a Formosa tree in my front yard, that I have been trying to kill for the last 10 or 11 years. As you might guess, each time that I cut it down, it comes back with a vengence. In the last year or so, it has come up in a few other areas of the yard (one about 145 feet away from the original plant). It was already a good sized tree when I bought this property, but it was planted nest to the road (In the outlying county). When the highway department mows the edge of the road, they use their boom mounted mower to trim it back away from the road, and this causes new stalks to grow. I need something that will kill the root system and not just the stump(s), or the surrounding plants