Japanese knotweed is a thug of a plant capable of growing a foot a week at this time of year; it spreads rapidly from underground rhizomes; erodes riverbanks, leading to flooding; smothers other plants; blocks drains and wreaks such havoc on homes and gardens that it blights property prices. It is estimated that controlling Japanese knotweed costs the UK economy about £170m each year. An entire industry has been built on trying to control the plant, using at least 15 different active control methods. There is, however, no impartial study of how effective any of these treatments are.
Scientists at Swansea University recently concluded the world’s largest field trial over five years on tackling Japanese knotweed. Their depressing assessment is that eradicating the plant using weedkillers is useless, and so too are physical methods such as covering up and cutting down knotweed.
Instead of eradication, though, they say that knotweed can be controlled and managed using glyphosate-based herbicides, which are significantly better than all other herbicide groups currently used. Most importantly, the glyphosate needs to be applied at the right time of year, allowing lower doses to be used. However, glyphosate is a controversial herbicide, potentially carcinogenic and harmful to the environment.
