Japanese knotweed control

Japanese knotweed can be controlled using customised work programmes that kills the weed on site or eradicated by its physical removal. Control programmes usually cost much less than the more immediate solution offered by eradication but may take longer to complete.

Japanese knotweed control is achieved using:

Herbicide programmes

Operator treating knotweed

Often the cheapest, simplest option for most situations. Herbicide programmes, typically consist of a series of treatments in the first year with inspection and 'as required' treatments for a further minimum of three years. Follow up care is vital; the Environment Agency and pesticide manufacturers state quite clearly that herbicide programmes to effectively control Japanese knotweed takes a minimum of three years. Any shorter term measures are not acceptable as knotweed may enter a dormant state for some years if the control programme is not subsequently managed correctly.

Safety with herbicides is paramount. A contractor may only use trained, competent and qualified staff to apply herbicides. The minimum qualification for operators is the NPTC PA1 and PA6a (both are required).

Herbicide programmes can be very cost effective but must be monitored; a need that takes a longer time to be sure of the final, long term result for the client.

Costs for a three-year programme are typically from £600.00 + VAT; final costs having to reflect the degree of knotweed spread, geographical location, presence of other factors (such as surface water or environmentally sensitive areas).

Control methods, may be the most relevant for many sites; domestic, commercial or construction. The Knotweed Company uses only BASIS qualified advisers able to select the most appropriate herbicide for use on our customers' sites and fully qualified, experienced staff to carry out the work.

Variations on the herbicide method include the mechanical or manual removing (also known as sifting or sieving) of the larger rhizomes in the surface layers and either onsite incineration or offsite disposal (to licensed tip). This method does not remove all the knotweed from the soil and must be used in conjunction with an herbicide programme.

Site visits to discuss all options are critical and will be arranged to suit your needs.

Stockpile (bund) method

Stockpiling methods are used in combination with herbicide programmes. Japanese Knotweed contaminated soil is re-located to another part of the site, spread out into a thin layer (500mm is normally regarded as suitable) and treated following a herbicide programme; a quick and cost effective solution for many development sites.

Most suitable for larger sites, where an area of land for the relocated knotweed may be used for several years, while the herbicide programme is undertaken.

Costs vary with site, volume of soils to be moved and other factors that will need to be discussed.

Vertical root barriers

Vertical root barrier being installed to site boundary, following full excavation of the Japanese knotweed.

Vertical root barriers are used to minimise the risk of an infestation from an adjoining property spreading across the boundary. Other uses of root barriers - are to protect buildings or structures from being damaged – particularly to line foundations if knotweed is in the vicinity. However although vertical barriers comply with Environment Agency recommendations, the Japanese Knotweed Control Company would only advise the use of this method with an appropriate herbicide programme.

Costs of installing root barriers are variable and demand on site visits, discussions and planning. It must be noted that they may need be installed to a depth of nearly 2m (or deeper; one of many factors that will affect final costs).

Barriers may not be suitable for all locations; if installation would risk structural damage to properties, for example, then an alternative method of control will be offered the client.

All methods must be individually priced. Control measures for smaller infestations of knotweed may be discussed on the telephone but site visits are normally arranged and more detailed quotations offered.

Site visits are normally not charged but, due to the expertise of this company, full technical reporting in some instances, may require an agreed charge with the client before that visit.

Reduced level excavation

Shallow (300mm) excavation of infested rear garden.

Root barrier installed over excavation.

Clean top soil being placed onto the root barrier.

Reduced level excavation is perhaps one of the most underused methods; simple, adaptable, reliable and suitable in many situations. Essentially a layer of soil (which includes the Japanese knotweed) is removed and taken to a licensed landfill site. The depth of this layer may vary, but may typically be 300mm. Following this removal, a root barrier is placed over the excavated surface and up the exposed sides of the dig out. Excavations adjacent to a building or structure may demand either the barrier to be heat welded to its surface or left in contact. Backfill of excavated areas must only be done with knotweed free soil, aggregate or rubble.

Reduced level excavation is used on large or small areas.

Herbicide programmes are used to control invasive shoots of knotweed that may emerge in subsequent years from the properties boundaries.

All methods must be individually priced. Control measures for smaller infestations of knotweed may be discussed on the telephone but site visits are normally arranged and more detailed quotations offered.

Site visits are normally not charged but, due to the expertise of this company, full technical reporting in some instances, may require an agreed charge with the client before that visit.