There is a lot talked about how Japanese knotweed has no natural predators in the UK – which results in its rampant growth and rapid rate of spread. People talk about the psyllid aphid and the leaf spot fungus. Some people even pick and eat JK in the early growing season, before it branches. This vodka recipe, for example, is a pretty creative use of knotweed. If you keep cutting early growth, then it’s possible the plant will exhaust all of its stored nutrients and die – although how long this would take is anyone’s guess.
The one thing I would say is that you will need to be very careful when harvesting – as it’s an offence to cause Japanese knotweed to grow (more info here). The part of the plant most likely to re-grow is the root – but in theory, any living part of the plant could re-grow.
So if you’re harvesting JK for vodka, just cut the stems cleanly and cook whatever you use – don’t dispose of it in your normal compost or with recyclable food waste. If you have any leftover bits you don’t know what to do with, then boiling or burning them is probably a safe bet.
Anyway, back to biological control; I have been doing some hard research in to the matter, and I have found that JK actually does have natural predators in the UK – see below for conclusive proof!