What are the options for Japanese knotweed removal?
There are many treatment methods available for Japanese knotweed removal, some are tried and tested, and there should be at least one that suits your circumstances.
What is the objective - Japanese knotweed control or eradication?
The first consideration is “What is the Objective?” i.e. 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, complete knotweed eradication is usually the objective. Where complete eradication is an unattainable goal e.g. knotweed along a watercourse originating from knotweed upstream, a control programme may be a more realistic objective.
Japanese knotweed control
If the objective is control then in-situ herbicide treatment is likely to be the most appropriate and economic solution where infested soils are not being disturbed.
Where soils are being disturbed, control can also be achieved using root barriers and an on-going herbicide treatment programme.
Japanese knotweed eradication
Where the objective is eradication timeframe needs to be considered.
Eradication using herbicides
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 (typically to depth of 2m or more) and then 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). In these circumstances a combination of root barrier and herbicide treatment may be appropriate.
Assuming the Japanese knotweed infested soils can be excavated then one needs to consider the options for the further treatment or disposal of the excavated soils.
If a large area of the site can be utilised for knotweed treatment then it may be possible to stockpile the material 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 approx 500mm to achieve eradication in 12 months. See more on our Stockpile & Treat method ....
If space is not available, then on-site processing of the soil using Xtract™ will be an economic solution. This process removes viable rhizome from the soil, so that the soil can 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. 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 either on site cell burial, or dig & dump (consign material to landfill) will be the options. See more on Xtract™ ...
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. See more on Cell Burial ...
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 ...
Disputes relating to Japanese knotweed due to "encroachment" > >