There are a number of invasive weeds which pose a threat to habitats but only japanese knotweed poses the additional threat of causing physical damage to buildings and infrastructure. It provides little benefit to indigenous flora and fauna and will restrict / destroy local habitats including waterways. It is an offence under the Wildlife & Countryside Act 1981 to allow or to spread japanese knotweed. It is also considered a controlled waste and falls under waste compliance legislation such as The Environmental Protection (Duty of Care Regulations) 1991 as amended.
The plant was introduced by the Victorians as an ornamental plant and only female plants were imported. Therefore, it only spreads by vegetative means, normally via underground rhizomes (roots). It grows only between April and October and remains dormant through the winter months. Above ground growth dies back with the on-set of frosts and will not cause spread after this time. It is most happy on disturbed ground or near water. It was used extensively to stabilise steep railway embankments. It will grow and spread indefinitely unchecked and has been reported to extend up to 7 m below ground level. Restricted, it will penetrate and cause extensive damage to tarmac, concrete, paving, foundations, brickwork and services.
Early identification and action are imperative to ensure compliance with applicable legislation and ensure works are completed in a cost effective and sustainable manner. This is best served through the production and adherence to a japanese knotweed management plan.
On confirmation that japanese knotweed is present, there are really only three options available and which are summarised below and confirm the advice as contained in the Environment Agency Code of Practice for the Management, Destruction and Disposal of Japanese Knotweed.
Herbicide treatment represents the most cost effective and sustainable approach but also entails the longest timescale. Systemic herbicide is applied to the above ground growth and is taken in by the plant and into the main rhizome system, ultimately killing the plant. Complete eradication can take up to three years although this timescale can be influenced by external matters. For example, excavating the knotweed and re-stockpiling in a controlled area can stimulate additional above ground growth thus increasing surface area to which herbicide can be applied and shorten the treatment time. Alternatively, weaker herbicides should only be used near water and which can extend treatment time.
Excavation & Deep Burial on Site
The Environment Agency has adopted a pragmatic and sustainable approach to the management of japanese knotweed in their COP and will permit deep burial on-site. However, this needs careful planning and control to minimise risk of re-growth and detrimental impact to subsequent re-development. Deep burial will normally be completed in combination with an element of herbicide treatment.
Off Site Disposal
Whilst complete excavation and offsite disposal represents the quickest method and provides the greatest confidence of complete eradication, it is normally also the most expensive and least sustainable option.
VertaseFLI encompass all elements of japanese knotweed and other invasive weed management. We have completed hundreds of projects to hundreds of hectares all over the UK. This includes initial site inspection and assessment, preparation of management plans, herbicide treatment, on-site and offsite disposal and cross boundary protection. We have even completed underpinning works to buildings damaged by Japanese Knotweed where an appropriate management plan was not adopted before re-development.
View some of our Japanese Knotweed case studies here