The trunk piece dies faster when you cut it close to the surface, eliminating much of the wood with a saw, axe or machete. Leave a piece no taller than 1 foot above ground for you to have some surface to apply the poison to.
To create a path for the herbicide to travel to the roots, drill five 1-inch-wide, 1-foot-deep holes around the side of the stump. Space them evenly for the chemical to be distributed uniformly. After you drill the lateral holes, create five additional 1-inch-wide holes on the top surface of the stump. Hold the tool at a 45-degree angle as you drill as far into the wood as it takes for each pair of lateral and upper holes to intersect.
Garden supply shops sell different brands of powder stump removers, most of which have potassium nitrate as the active ingredient. After you choose a product, drop 3 ounces of the powder in each of the five holes on the top surface. Fill them with water to release the chemical and begin the breakdown process. It is important to note that stump removers are formulated to kill year-old and older stumps.
Six weeks after you treat the wood with stump remover, the trunk piece will feel soft, a sign that what is left of the cut plant is dead. Cut up the stump above ground and discard the pieces. If you want, dig around the area the trunk occupied until you reach the dead root system and pull it out with your shovel.