Here you go Roundup for Japanese Knotweed.

Thanks @Tropical_Willie. It sounds like a nightmare though, from what I hear. It goes through bricks! etc. Here is a random article.
http://www.mirror.co.uk/news/japanese-knotweed-everything-you-ever-4328310
3. Kill it with chemicals

You can turn to chemicals, especially treatments containing glyphosate, but beware: it can take up to five years’ treatment to finally be rid of the pesky plant.

Professional treatments can set you back thousands of pounds.

I set my goats on it, they love the stuff.

I much prefer goats to horrible toxic chemicals from Monsanto! There are companies that let you rent goats for such purposes, such as Rent A Goat and Rent a Ruminant.

@wildpotato and @Zaku The thing is that’s good for the seller and renters of goats, it doesn’t get rid of the problem once and for all.

Here is another article.
http://goo.gl/4zXbfw