How do I kill Bamboo that is now about 30ft high?

Very difficult to kill. Best to dig up what you can and use bush killer on any that start back.up. roots run horizontal throughout garden

cut it off fill the center holes with Round-Up then any new leaves that sprout asap spray with Round-Up----Round-up.....it's absorbed thru plant leaves then into stem/stalk then root system killing plant. you need to add food coloring so you can tell where you are spraying ,hold sprayer down on plant leaves you are spraying,don't spray in wind/slightest breeze,don't get in wet solution(it dries quickly),wear disposable gloves.....follow the safety instructions on bottle it has always said "hazardous" the safety instructions have always been on containers. no special mix of it,buying concentrate & mixing yourself is best but it comes premixed. just respray asap if you see any new growing and do not let plants get flowers/seeds to spread even more. the more you kill just the tops the more the roots/rhizomes spread underground. just look for new plants starting and spray it before it gets out of control.get a good 2 gallon pump sprayer and not a back pack,because if it leaks on you well you could be joining all the civil suits of people who did not heed hazardous warnings.

Cut down what you can. Dig a trench around the bamboo about 12" deep. Pour rock salt in the trench and wet it down. Use vegetation killer on the shoots. The trench will prevent underground growth/spreading.

Just hope we have the strength to dig down, I feel Bamboo should be outlawed for residential gardens along with the Prickly Pear, we had the P Pear, growing wild in 1950's and now it's a terrible problem on the Qld side of the Qld /Nsw border, and Queensland doesn't seem to want to do anything about these huge PPear tree/bushes..