What is Japanese Knotweed?

Japanese Knotweed (Fallopia japonica) was first introduced to Britain by the Victorians as an ornamental plant – and was actually awarded a gold medal at a prestigious flower show. It is referred to under its previous name of Polygonum cuspidatum in The English Flower Garden by John Murray. In the 1907 edition it is cited as “easier to plant than to get rid of in the garden”.

In its native countries of Japan, North China, Korea and Taiwan, the weed presents nowhere near the problem it now poses across Europe, America and New Zealand. With its natural habitat being on the slopes of volcanoes, it is no surprise that the less harsh and more fertile environment of Britain has allowed this plant to flourish to extreme proportions. Furthermore, outside of Asia, the plant has no natural biological enemies to check its spread. In Japan, for example, at least 30 species of insect and 6 species of fungi live on the plant.

This plant is perennial and extremely invasive. It thrives on disturbance. The tiniest piece can re-grow, and has been spread by both natural means and by human activity. It soon overruns riverbanks, railway embankments, road verges, gardens and hedgerows, threatening the survival of other native plant species and in turn insects and other animal species.

In riparian areas, high water flows disperse fragments of the plant downstream where new colonies form. In the past, fly-tipping and transportation of soil containing rhizome fragments have been a major cause of spread, particularly in the urban environment. Green waste recycling schemes are also sites of potential contamination which is a cause for concern. Local Authorities, including those in Devon, are desperate to find ways of eradicating this serious pest.

Huge sums are being spent in the UK controlling the weed. In 2004, a DEFRA review of non-native species policy stated that a conservative estimate for the costs involved in eradication would be £1.56bn. The aggressive spread of the plant following its first escapes into the wild in the 19th Century resulted in it occurring in most parts of the UK (except Orkney) and eventually being listed in the Wildlife and Countryside Act 1981 as a pest species. All parts of the plant are considered as controlled waste under the Waste Regulations.

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How to identify Japanese Knotweed

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