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