"Smoking it out" means that you get a chemical from your garden center--find the largest and most successful one in your area as they have been around and know what works in your area--and use that per label directions. The directions are usually to drill a couple of holes in the center of the root, put the chemical in the root to kill it, and wait a couple of weeks while the chemical works it's way through the root. Then you can put something to start a fire in the hole, light it, and let the fire burn the root to ashes. I tried this on a willow tree and the roots just kind of laughed at it but then willow trees are known as being hard to kill and difficult to remove.