Cut it. Pour Tordon on the cut end. Tordon can be purchased at Big R, Rural King, etc. plus it is a neat shade of blue!
Go to your local CO-OP and try "reward" its not listed for bamboo but it kills everything and its safe in run off waters. They recommend adding a "surfactant" to it but adding a tsp (per gal) of plain lemon dish soap has the same effect. Just add it after adding water...sudds you know. Last I check a gallon goes for a couple hundred but this is real stuff.
It's an aquatic herbicide and you pay more for that, and it is no longer safe for water when you use detergent as a surfactant, as detergent is not listed on the label. You must use a non ionic surfactant to be within label restrictions.
Garlon 3A can be used as well around water with a non ionic surfactant. But for his application see my earlier post.
Napalm
Napalm