Hi, Here's what I do. I cut the tree down to ground level and while the cut is still fresh, I "paint" the exposed cut with a brush-killing herbicide. You want to add the herbicide to the cut fairly quickly after you cut the tree down so that it absorbs the brush killer. Also, this does not work in the winter when the tree is dormant. You want to do this while the tree is growing. Brush killers are commonly available at most garden centers.