How do you get rid of Japanese knotweed?

To destroy any Japanese knotweed remains on site, allow the cut canes to dry out, then burn them. On no account add them to your normal household waste. When digging out, remove as much root as possible, then repeatedly destroy the regrowth by mowing the area short.

NO....OMG Don't mow it you will only increase the growth it's like pruning it. It just grows more underground. You've already seen what happens when you cut it off. If that "herbicide injection" was not a Glysophate it won't do anything. Whenever you see new growth spray it with Round-Up, round up is absorbed into leaves then thru stem into root system killing plant. Be diligent looking for new growth, spray when it has a few leaves so it can be absorbed & douse it heavily. Get the concentrate and mix it yourself keeping the sprayer handy so when you see it you can spray it.Use some food coloring in the Round-Up so you can see where you have applied it;use sprayer on stream;do not spray when there is breeze or wind;hold sprayer on stream down onto leaves/stem you are spraying so it makes full contact;don't get in wet spray;wear gloves;if you spill any dilute with lots of water and some dish soap;get yourself nice 1-2 gallon sprayer(not a back pack they have been know to leak on peoples backs , YIKES no wonder people got cancer) Round up is a chemical and if you follow safety instructions use it wisely you'll be fine. Japanese Knotweed one more invasive species that got planted instead of some plant that is natural local to area. The plant, which can grow from three to 15 feet tall, has bamboo-like stems and is sometimes called Japanese bamboo. As with many invasive plants, knotweed thrives in disturbed areas and once established can spread rapidly, creating monoculture stands that threaten native plant communities.

A good solution for killing a Japanese knotweed is a good weed killer spray that is safe to use and is safe around kids and pets when used as directed.