You might try this. I had a bad patch. I wasn't about to try digging it up. I cut the stems just below a joint and poured double strength Weed-b-Gon down in the the tube. It was taken down into the root and the root died. It never came back either. I had tried just spraying it. It didn't work. I don't know if it would contaminate the soil as the root died if you wanted to plant a garden there.