Japanese Knotweed Control and Eradication

Japanese knotweed is a highly invasive plant that can cause extensive damage to property where it is growing.

Where this nasty invasive plant is on development sites, it can delay the construction process by several years and indirectly costing a lot of money to the land owner and the developer. The invasive weed has an extensive rhizome system extending some seven meters laterally from the visible Japanese knotweed plant and up to three meters deep from the crown. A spectacular spread of knotweed will occur by disturbing the soil containing the annoying plant, as fragments of rhizome weighing less than one gram will regenerate into a new plant infestation, growing to a height of around three meters in one growing season. Consequently, Japanese knotweed infestations are increasingly found throughout the United Kingdom, Europe and America, and, as the invasive weed does not have any natural predators, the problem is escalating to the extent that DEFRA now estimate the cost of Japanese knotweed eradication within the United Kingdom to be between one and a half and two point six billion pounds.

The invasive weed is listed under Schedule 9 of the Wildlife and Countryside Act 1981, making it an offence to cause the knotweed or allow it to spread in the wild.

All parts of this invasive plant, and any soil contaminated with its rhizome, are classified as Japanese knotweed “controlled waste” requiring all the Japanese knotweed “duty of care” requirements under the Environmental Protection Act 1990.

The plant has no respect for property boundaries and it can cause many neighbour disputes.

Japanese knotweed solutions to eradicate the plant can involve neighbours thereby causing differences of opinion with its control. Japanese knotweed is regarded as more serious than a nuisance and any invasive plant affecting boundaries should be destroyed. Often the control and eradication of the plant in this instance can cause complications. Insisting on Japanese knotweed removal or Japanese knotweed eradication is a common law right but expensive to instigate.

The Environment Agency’s Knotweed Code of Practice “Managing Japanese Knotweed on Development Sites” is a useful reference guide and outlines the various options for Japanese knotweed removal.

Due to the legislative regime of Japanese knotweed and highly invasive nature of the plant, ignoring Japanese knotweed is not an option.

Careful management of Japanese knotweed infested material is required to prevent its spreading. The volume of Japanese knotweed infested material can be surprisingly large due the extent of horizontal and vertical penetration of the rhizome system into the soil.

Japanese knotweed treatment options can often fall into two categories with Japanese knotweed removal - in situ treatment or physical removal of all viable Japanese knotweed rhizomes.