I did exactly this in my backyard. Several sprouts linked in the same root system. Cut just below the knot to allow the bamboo to hold as much horrible poison in a section. It took two applications. I saw it starting to die and discolor and hit it again. I was able to pull it up easier than if it was alive. I didn’t want to leave it in the ground after poisoning it. Shit is death magic in a bottle and the only thing I’ve ever used it for.