By Nic Seal, Founder and MD of Japanese knotweed firm Environet UK.
New research released in April by Swansea University’s Professor Dan Eastwood and Dr Dan Jones, has called into question the claim that Japanese knotweed can be eradicated. Yet the research focuses almost entirely on herbicide methods of treatment, without properly investigating excavation methods which physically remove Japanese knotweed from the ground and, if done properly, are 100% effective.
Many of the research findings mirror Environet’s own experiences in the field of Japanese knotweed, gained during a 15 year period treating over 1,900 sites. However, the research has been interpreted by some as meaning Japanese knotweed cannot be eradicated, which is extremely misleading and quite simply wrong. It can be eradicated, as proven by the vast majority of projects Environet and other professional knotweed companies have completed, and guaranteed.
It is possible to completely kill knotweed using herbicide, if applied correctly. The time it takes will depend on site conditions and in particular the maturity of the plant and the size of its underground rhizome system. Smaller infestations can be killed in two years, larger ones may take three or more years.
The problem with herbicide treatment is that it’s virtually impossible to verify with any level of confidence whether the herbicide treatment has been totally effective. No regrowth does not necessarily mean that the plant is dead – it’s quite likely to be just dormant, ready to grow when ground conditions are altered. For that reason, it should be considered a method of ‘control’.
However, the research paper does give a misleading conclusion as it does not consider well proven physical removal methods, and by implication suggests these give no better level of control.
Environet developed its patented Xtract™ method in 2008 method, and has been using it successfully ever since to remove the viable rhizome from the ground, ensuring that the plant cannot regrow. Such is its success that the method has been adapted for residential properties, called the Resi Dig-Out™ method.
Excavation achieves complete eradication, which is why it is growing in popularity, despite the higher cost. If no visible rhizome remains in the ground, there will be no regrowth and there is no risk of dormancy.