Right. A good 15 years ago i got a small bamboo from b&q it said clump forming on the tin, fast forward until last month and it had grown savage, spreading at will and was around 8 feet high. It had engulfed one of my buddliea. I decided enough was enough and onto the interweb and read to cut it back to about 10 inches  then let sprout again and spray it to give it the old heave ho. I attacked it with the chainsaw and I have  now noticed some green shoots coming through, I did try