Q: Our pergola is covered with wisteria and has gotten so rotten we are cutting it down. How do we kill the large wisteria vine?

A: The big wisteria will be a problem for years. Roots near and far from the original trunk will continuously send up sprouts. There’s not much you can do to prevent them. Right now, cut the wisteria trunk at ground level, bore a hole in it and dribble some glyphosate (Roundup, etc) into the hole. Spray glyphosate onto the surface of the fresh cut at the bark line. The chemical will be sucked back into the root system for a small distance but I’m positive it won’t kill the entire root mass. You’ll just have to remove sprouts as soon as you spot them for at least three years, thereby eventually starving the roots and killing them.