What are the Best Methods for Removing Japanese Knotweed
There are several treatment methods available for Japanese knotweed removal, the right one for you and your site will depend on your circumstances.
More information and advice on removing Japanese knotweed from Commercial Development sites.
More information and advice on removing Japanese knotweed from Residential Gardens.
What's your objective - Japanese knotweed eradication or control?
Are you looking for complete eradication (implying either complete destruction or removal) or control (preventing further spread and damage)? In most circumstances, especially on development sites and in most gardens, complete knotweed eradication should be the objective. Where complete eradication is an unattainable goal e.g. knotweed along a watercourse originating from knotweed upstream, a control programme (consisting of a herbicide treatment programme) may be a more realistic objective.
What Japanese knotweed eradication methods are available?
If the affected ground is not going to be disturbed (e.g. by construction or landscaping works) AND you have plenty of time (at least one growing season, possibly more) before you want to achieve eradication then an in-situ herbicide method may be suited. If not, you need to consider a physical removal method.
In-situ Herbicide Treatment
Herbicide treatment can result in eradication, although it is difficult and best left to a specialist in Japanese Knotweed eradication. The minimum time required is one growing season (typically May through to October) involving several applications of herbicide. This can either be applied by foliar spray, or in environmentally sensitive areas by stem injection.
There is always a risk that viable rhizome remains after herbicide treatment so if you are likely to disturb the soils in the area, and re-growth cannot be tolerated, then you should look at a physical removal method.
Physical removal methods involve the excavation of all infested soil under expert supervision (typically to depth of 2m or more) followed by, either treatment, or disposal of that material. In certain circumstances complete excavation may not be possible (e.g. restricted access, underground obstructions such as roots from trees protected by TPO, underground services, presence of groundwater).
What physical removal methods are available?
Once excavated the options for the further treatment or disposal of the excavated soils are:
Xtract™ is a method developed by Environet in 2008, with patents granted in the UK and USA, with patents pending in Europe and Canada. The process separates and removes viable rhizome from the soil, the offending rhizome is taken off site and destroyed, leaving the processed soil to be re-used on site. Xtract™ is a very quick process so should prevent delays to construction. It has minimal environmental impact, since no infested soil is sent to landfill and no herbicide is used. See more on Xtract™ ...
In very limited circumstances Xtract™ may not be appropriate (e.g. infested soils are contaminated with materials that pose a risk to health). In these circumstances other removal options will need to be considered.
Stockpile & treat (Bund method)
Knotweed infested soil is excavated from construction critical areas and stockpiled in a location on site for subsequent herbicide treatment. It relies upon a large area of the site being available for knotweed treatment in a quarantine area for at least 12 months, in which time herbicide can be applied. The problem with this method is usually space, in that the soil should be spread out to a thickness of only 500mm to achieve eradication in 12 months, so seldom finds favour with developers. See more on our Stockpile & Treat method ....
On-site cell burial relies upon the containment of viable rhizome within a very large cell lined with root barrier on all sides, top and bottom. Cell burial for Japanese knotweed should be considered as a control rather than eradication strategy. We consider there to be better methods. See more on Cell Burial ...
Supervised dig & dump
Dig and dump is recommended as the method of “last resort” by the Environment Agency. If this method is to be used it pays to have a specialist supervising the work to not only ensure that all legal requirements are met, but also to ensure ALL, but ONLY, Japanese knotweed infested soil is removed. Expert supervision can result in significantly reduced volumes, thereby saving cost. See more on our Supervised Dig & Dump ...