Total Japanese Knotweed Removal
Treating Japanese Knotweed
There are a number of different treatment options available however these are largely dependent on site specific factors such as site size , time-lines and location.
Soil Sifting Method (Screening)
Knotweed Control Ireland can screen Knotweed infested soils and remove all viable rhizome material including other visible contaminants.
The eradication proposals comprise excavation and treatment of soils on site to eradicate Japanese Knotweed and render the soils suitable for reuse as fill at the site within a relatively short period. The preferred treatment option is to screen the soils on site to remove any rhizomes, together with the application of a suitable herbicide to eliminate the risk of any future re-growth. In areas of the site where excavation is not possible, other treatment schemes should be considered.
Infested soils are typically excavated using an excavator (4 -13- 23 ton), capable of digging to at least 3-5.5 metres deep. The excavation work is supervised by our experts to ensure the soil containing rhizome`s, crowns and roots is completely Knotweed free. The rhizomes are traced right back in all directions. Knotweed Control Ireland trace the root system to the very tip of the root-cap and keep photo-records to show this.
The excavated infested soils may further undergo a screening process in a portable vibration machine specially adapted to separate the Japanese knotweed rhizome from the soil.
The remaining soil is clean and free from all Knotweed plant material this treated soil can be re-used on site.
Note - current Best Practice Guidelines from the Environment Agency state that soil cleaned in this way should not be reused off site. If the intention is to move the soil, then waste legislation applies and the material must be consigned as knotweed infested and will require special removal license from National Park and Wildlife Services.
The Knotweed rhizomes and root material are extracted and bagged on site, this material can then be brought for incineration. In some cases the Knotweed material can be left to dry on a porous ground barrier and an exemption to burn the Knotweed on site is applied for.
Treatment takes a matter of days/weeks depending upon the quantity of material being processed. The site is left in a clean and safe state ready for development works to commence.
Note to Developers: If Japanese Knotweed is found on your site do not cut or dig up the plant. We strongly advise that the site is not scrapped back before a Knotweed surveyor inspects the area first. Recently (Late 2019) developers have received letters from local planning offices asking that Invasive Plant Surveys should be carried out before site enabling works commence.
Where Japanese Knotweed infested areas are not going to be disturbed by work or are located on site boundaries the following measures should be implemented:
Fence off the area – (exclusion zone should be 7m from the outer plant stem to allow for extensive root structure)
Erect signage and restrict access (‘Japanese Knotweed infested area – Keep Out’)
Brief the site team
The Bund Method
The bund method can be considered where burial or cell formation is not feasible due to insufficient depth. The principle of the bund method is to move the Japanese Knotweed impacted soils to an area of the site that is not in use.
This area needs to be set aside for between 18-24 months (potentially longer for larger bunds).The knotweed infestation should be treated with herbicide prior to excavation and left for 2-4 weeks to allow the herbicide to take effect.
All bunds should be located at least 50m away from watercourses.
The relocated knotweed contaminated ground can be stored in three ways and you the client can choose the preferred method:
STOCKPILE: Usually used so that it can be treated with herbicide, with the eventual aim of re-using this material on-site (this material will always remain classed as controlled waste if removed from site). The stockpile should therefore be less than 1m in height so that herbicide treatment can be as effective as possible (i.e. buried knotweed rhizome that does not produce surface growth cannot be treated with herbicide).
BUND: The knotweed spoil can be used to form a landscape bund. It will be accepted that there may be buried dormant knotweed material within the bund. It will also be accepted that the bund will be subject to long term chemical treatment of emergent knotweed (which may impact on plants and grass grown upon the bund).
CUT AND FILL: It may be desirable to relocate the knotweed contaminated spoil so it resides at ground level. This is done by forming a cutting into which the knotweed is deposited. The arising clean spoil from the cutting formation can be re-used on site or removed from site as clean material or even as-dug topsoil with a commercial value!
A Knotweed Management Plan (KMP) will be used to record the position of the relocated knotweed with this being marked upon as-built site drawing. This will help prevent potential future disturbance of these locations. If these works are part of a site development project the KMP should then be included in the Operations and Maintenance (O&M) Manuals.