Use a lopper or saw if need be to cut through the trunk close to the ground. Then immediately apply a product called Tordon RTU (RTU = ready to use - active ingredient Picloram) to the perimeter of the trunk such that the outer inch or two of the wound is treated. So, if your tree is a foot in diameter, the outer 2" of the wound surface gets treated. If your trees are less than 4" in diameter, the entire wound surface gets treated. It is far better than glyphosate (Round-Up) or tree/brush killer. One and done. You can paint it on with a disposable foam brush.
Al
