This invasive specie is hard to kill. I would cut it back in early spring to weaken the plant. In fall cut it back again and apply an herbicide containing glyphosate to the stumps. It may return the following year, so repeat the process. Eventually it will run out of gas. Concentrates work better than ready to use products - one is Bonide Concentrated KleenUp Weed Killer. They also come in different strengths. Look for 41 percent. Read the directions carefully. This chemical will kill anything it touches. I you have valuable plants in the area do not spray it, apply with a paint brush. Good Luck Nancy and Happy Yardening.