This week, there was an article published by BBC News (and subsequently more media outlets) with the headline ‘knotweed cannot be eradicated’, in reference to the release of the University of Swansea’s Japanese knotweed treatment field trial results.
The headline was unfortunately misleading and not completely in context to the basis of the trials and the results gained. Another case of the media slightly sensationalising a story.
The result paper from the field trials was published online on the 23rd April. The research investigated the use of various types of herbicide, application techniques and timings of application. It’s important to note however that it did not explore excavation methods.
It identified that glyphosate-based herbicides were the most effective on knotweed and there was an optimal time to apply them. The optimal regimes were able to obtain effective control of the knotweed over a 3 to 5-year period. These optimal regimes are those currently used by Japanese Knotweed Ltd in its herbicide treatment programmes.
It confirmed that eradication or control of Japanese knotweed using herbicide in a short space of time (i.e. one season, as claimed by some unscrupulous companies) is not possible.
It also found that although the optimal herbicide treatment regime had been able to successfully control the plant (preventing above ground growth) it had not been possible to remove the viability from every part of the plants underground rhizome (stem) system. The plant can’t be classified as eradicated until all the viability has been removed.
However, in most residential situations and situations where there are no plans for a change of land use (i.e. no development) the inability of herbicide to removal all the viability does not matter. Our sustained herbicide management plans control knotweed to the satisfaction of property owners and interested third parties (such as mortgage lenders), with the works covered by an Insurance Backed Guarantee.
Japanese Knotweed Ltd achieves complete eradication of knotweed when it is required through excavation. The excavation of knotweed is provided where there is a planned change of land use (i.e. development) or where long-term herbicide treatment and control is not desirable. There are varying methods of excavation and waste disposal which are deployed according the logistics of a site and any development plans.
The advice for land/property owners given below comes from the Swansea University Field Trial website page and correlates to the advice Japanese Knotweed Ltd has been providing its clients for years:
- Ignore the hysteria - your house will not fall down. Knotweed can be controlled using glyphosate at the right time of year, though this can usually take three to five years. However, we don't recommend you do this yourself – we have seen mortgages declined because of botched treatment undertaken by homeowners.
- Knotweed is a resilient weed that cannot be controlled by one herbicide treatment in a single year, a claim frequently made by unscrupulous companies. Any treatment strategy should be long-term and target both the above-ground and extensive below-ground parts of the plant.
- Effective treatment centres on working with the biology of the plant and targeting the correct herbicide when the plant is vulnerable to its effects, from summer into late autumn (depending on the weather).
- Calling out a weed control company to control knotweed is not the same as calling out a plumber. We would expect the plumber to get the work done soon, if not immediately. If you call out a company in spring to control knotweed, quite rightly, you will need to wait until later in the year to get the best results – this will save you time, money and hassle in the long-term.
- Once knotweed has been effectively controlled using herbicide don't disturb this land by digging, for example, as it is likely to come back; even if the above-ground parts of the plant are dead, the below-ground rhizome system probably isn’t. Again however, don’t panic, if it comes back, call the contractors to regain control.
- Don't try digging out the knotweed yourself, it is easy to miss parts of the root and spread it and you cannot dispose of this plant material along with your garden waste – in fact, it is illegal to do this.
If you have any concerns over the content of the BBC News article, please contact us. We’re happy to answer your questions.