According to this article:

> This BBC article from 2010 points out that Japanese knotweed isn't really a problem in its native country - while common, the plant "doesn't rage out of control like it does in the UK, thanks to natural predators that keep it in check".

> In Japan, knotweed has many natural predators in the form of nearly 200 insect species and a variety of fungi. Certain psyllids (plant lice) have proven to have an appetite for Japanese knotweed sap - the organisers of the Chelsea Flower Show have looked at using psyllids to keep Japanese knotweed at bay, and one species (Aphalara itadori) has even been released into the wild in an effort to combat the UK's knotweed problem.

https://www.taylor-weed-control.co.uk/news/post/what-eats-ja...