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How to Eradicate Japanese Knotweed

Updated on June 24, 2013
Japanese Knotweed
Japanese Knotweed | Source

Japanese Knotweed - Troublesome Weed

Originally introduced into the UK by the victorians during the 19th Century from Japan as an attractive ornamental plant, it gradually became an invasive weed, due to the fact that all its natural predators back in Japan are not present in this country.

Japanese Knotweed (Fallopia japonica) is a clump-forming perennial, producing tall bamboo-like stems, reaching approx 2m high by early summer. Leaves are up to 14cm in length, creamy white tassels are produced during late summer and early autumn, approx 15cm long, before dying back to below ground level during winter.

How does Japanese Knotweed Spread?

This invasive plant spreads by strong underground stems (rhizomes) rather than seeds and can reproduce from small 1cm sections of the root. It can grow a metre in a month, penetrate concrete and tarmac with ease, thus causing damage to buildings and roads.

In the UK it is illegal to “plant or otherwise cause to grow in the wild” Japanese Knotweed under ‘The Wildlife and Countryside Act 1981. It is down to landowners to control these plants, but they don’t have to remove them. However, causing the plants to spread by removing or disposing of them incorrectly would be illegal.

How to Control Japanese Knotweed

Non-Chemical Control

Digging out established plants by hand should be done with extreme care, so that no part of the plant is left in the soil. All parts of the plant should be disposed of at a licensed landfill site (details can be found from your local authority), under no circumstances should it be included with domestic household waste. Alternatively, allow any plant parts to dry out before burning.

If you have a large clump of Japanese Knotweed it may be necessary to employ contractors with machinery that are able to excavate and mechanically remove any rhizomes from the soil.

Also, studies have shown, cutting back the stems four times a year can significantly reduce the vigour of the plants. The first cut should be carried out when the first shoots appear and the last cut just before the stems die down for the winter (September or October). To achieve complete control using this method may take some time. Cut stems should be thoroughly dried before being burnt or taken to landfill.

Chemical Control

Control of Japanese Knotweed by chemical herbicides is best done by professional contractors who are able to use stronger chemicals than those available to the amateur gardener, and they have the best equipment to achieve good control, such as injectors.

Herbicides are best applied in the autumn, prior to the plant dying down for the winter. This ensures the maximum amount of chemical is taken down into the root system; control may still take three years before it stops growing back.

Trials have shown that combining herbicide treatments and digging is one of the most effective methods of control. By injecting herbicide into the stems and then subsequently cultivating the ground will break up the rhizome into smaller pieces, thus stimulating any dormant pieces into leaf reader for further herbicide application.

Biological Control

After years of trialling, a plant sucker (psyllid) is being released in the UK, at a number of trial sites, as a natural biological control and if successful it will be released more widely.

Further information

If you require further information on control and disposal of Japanese Knotweed, then either contact an approved contractor or your local authority.

by Alistair Olver

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    • unknown spy profile image

      IAmForbidden 5 years ago from Neverland - where children never grow up.

      maybe this is the same weed used to see in some of the lots. hard to break and always coming back.

    • lifehealpraise profile image

      lifehealpraise 5 years ago from South Florida

      Great information and very useful. There was a similar looking plant in my garden that I thought was very pretty, but my husband insisted we remove it because it was a weed and it was really starting to take off up the coconut tree towards the roof. I look forward to more of your hubs!