Ortho Brush-b-gon is readily found at garden centers. It costs about $10 a bottle, and it contains Triclopyr. I like staghorn sumac as a native ornamental, but use the Brush-b-gon to control it so it doesn't take over. Staghorn Sumac is a native prairie plant, and in nature is controlled by prairie fires. It is spread by rhizomes (undeground root system), so it is difficult to get rid of unless you dig up the entire root system. You need to get rid of an entire colony in order to eliminate it. Burning doesn't get rid of it, but controls it. Cutting and burning actually stimulate the plant to produce more shoots.
It also requires full sun in order to survive, so if you cut it back and plant something in the area that will shade the area, new shoots will be unable to flourish, and will eventually die. This may be an option for someone who wants to avoid chemicals.