Japanese Knotweed Eradication
Written by Administrator
Wednesday, 06 October 2010 15:58

Knotweed is an invasive plant species not native to the UK. It was introduced as an ornamental plant and has proliferated, due to it’s rapid growth and hardy nature, through the spread of soil contaminated with rhizome fragments. It displaces native species, reduces biodiversity, blocks paths and damages concrete and tarmac surfaces and it’s deliberate growth or release is listed in The Wildlife ( NI ) Order 1985 as an offence.




Treatment Options

Knotweed is notoriously difficult to destroy and, due to it’s rapid spread, must be targeted in a controlled fashion. The specific methodology for treatment is dictated primarily by timescale, but also by the size of the site. Dependent upon the project timetable there are a number of effective treatment strategies for the destruction of the plant.

< 1 Year – Dig & Dump – Any Site

Herbicide treatment can take 3 years before destruction is achieved. With shorter timescales, a more immediate solution is necessary which generally involves removal of all knotweed structure and associated soils. Targeted excavation of knotweed containing soils removes all traces of the plant from within and beneath the targeted footprint. Mechanical screening of the soils further reduces the volume for transfer from site, delivering considerable cost saving over traditional dig and dump. The excavation is reinstated with clean soils and capped.

<1 Year – Bunded Onsite Treatment – Space Considerations

Where space facilitates, creation of an artificial contained bund provides an onsite treatment facility for Knotweed contaminated soils. The agreed footprint containing the plant is excavated and transferred to the bund for treatment with herbicide until complete destruction is achieved. Soils are then tested and, once proven clean, may be used for reinstatement onsite or elsewhere. The timescale for the entire treatment process is up to 3 years.

<1 Year – In-Situ Capping – Any Site

The knotweed is treated with herbicide and capped in-situ after a shallow dig to remove the surface plant structure. The combination of the chemical treatment and physical barrier precludes further vertical growth of the plant, protecting the integrity of future surface infrastructure.

 <1Year – Onsite Cell Placement – Space Considerations

Impacted soils and plant structure are excavated and transferred for permanent encapsulation in a cell within the site boundary. The cell can be lined and capped with low permeability clay to contain the rhizomes after treatment with herbicide.

2-4 Years – In-Situ Stem Injection – Any Site

Neat herbicide solution is injected through the wall of each stem individually in order to destroy the surface and subsurface plant mass. Repetition of the process over the course of multiple growing seasons is key to the success of this strategy. This is our most cost effective and least intrusive strategy for the control of knotweed and is ideal where project timetables permit.