I just picked up a job to clear out a backyard filled with bamboo plants that are close to 8 feet tall. I have never had to do this but I told the lady that I would start out with a chain saw and level it close to the ground. She would like it dug out by the roots, but as far as I can tell, this type of plant has shoots coming out of roots that grow horizontal. Would Roundup work in killing these plants once their cut? She says she has tried Roundup, but it didn't work. Any ideas?