Can you kill off knotweed? No, you can knot!
IF you’ve spent years battling a Japanese knotweed invasion on your property, the news probably won’t come as a surprise.
There is officially nothing you can do to get rid of it, a major study has concluded. Swansea University researchers spent five years testing 21 methods of destroying knotweed, including various mixtures of herbicides promoted by gardening companies. None were found to eliminate the blight effectively.
The findings will do nothing to cheer up those who have been refused mortgages because of Japanese knotweed on their property. Homeowners face bills of up to £20,000 to remove the rampant invader before they can sell up, and the Government estimates it costs £166million a year in treatment and home devaluations. It is also unlawful to allow knotweed, which can grow 4in a day in summer, to spread or to dispose of it incorrectly.
Even digging out a small infestation is generally not a successful solution – major roots from which regrowth occurs can be as much as 7ft below ground.
Professor Dan Eastwood, lead researcher on the study, said they had focused on finding evidence of ‘what actually works’ and warned of ‘unscrupulous companies offering expensive and ineffective treatment solutions’.
Dr Dan Jones, an invasive plant species consultant, said the data showed ‘eradication is not possible’, but added: ‘Hopefully over the longer term we may move towards [changing] that by using new chemicals we’re looking at.
‘But it’s not a question of eradication, it’s a question of sustained control and management and wellinformed control and management.’ He added that claims made by companies that they could quickly eradicate the problem with herbicides ‘have now been proven to be false, based on our experiments’.
The study found the best chemical to control its growth was glyphosate, a controversial herbicide that environmentalists claim is linked to cancer. Japanese knotweed – Fallopia japonica – was brought to Britain by the Victorians as an ornamental garden plant and to line railway tracks to stabilise the soil.
But it has no natural enemies in the UK, whereas in Asia it is conPest: trolled by fungus and insects.