Invasive Non-Native Species – Japanese Knotweed – successful control

Our team are trained to recognise Invasive Non-Native Species [ also called INNS ]  on survey sites and advise on issues with their control.

One of the most pernicious, we encounter is Japanese Knotweed, which is an Asian species originating as a garden escape, spread via root fragments of its rhizomes, often from fly tipping or contaminated topsoil. Once established the underground rhizomes, according to The Environment Agency Guidelines, can grow to a depth of 3m [10 feet’] or more and up to 7m [22’ feet] away from the plant. The bamboo-like stems with their distinctive ‘heart-shaped’ leaves can reach up to 3m [10’ feet] high.

Once established it causes serious problems and its’ dense thickets will swamp out other vegetation and penetrate through tarmac and concrete, sometimes damaging foundations and buildings. Control and eradication of the plant is therefore legally required e.g. the Environmental Protection Act 1990, and planning permission will require an eradication programme for infestations.   Quick remedial action is advisable to ensure that the incidence of Knotweed does not hinder a potential development plot or lead to more costs later on. Treatments to eradicate it include herbicidal spraying, root barrier membranes and dig-and- disposal to landfill.  To prevent its’ spread, all parts of the plant and any soil contaminated with the rhizome are classified as controlled waste, and can only be removed and disposed of by a licensed waste control operator, making it an expensive approach.

Norfolk Wildlife Services recently worked on behalf of a client to gain planning permission for a brownfield riverside site.  The project involved detailed assessment for reptiles, bats and riverine ecology, but the presence of Japanese Knotweed was quickly detected during the initial walkover by NWS staff.  Having assessed the extent and implications to the project,  Norfolk Wildlife Services recommended herbicide spraying over a two-year available period, using an approved method for riverside situations.   Successful control was confirmed during return visits and the client was pleased with the outcome, which avoided the cost of expensive landfill disposal and delays during construction.

Invasive species are relatively uncommon in East Anglia, but other species that we encounter are New Zealand Swamp Pygmyweed, Himalayan Balsam, American Mink and Turkish Crayfish.  We also have some very large unwanted ghost carp looking for a new home! Local knowledge allows for a quick assessment of any issues.

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