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13 November 2014

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You are in: Guernsey > Nature > Nature Features > Japanese knotweed

Japanese knotweed growing on the cliffs

Japanese knotweed growing on the cliffs

Japanese knotweed

Some gardens in Guernsey (and across the British Isles) have become overgrown with this fast growing, invasive plant and in 2009 Guernsey's States looked at ways to get rid of it.

Japanese knotweed is a tall plant with large green leaves and a very thick stem. The stem looks like a green and brown bamboo stem with reddish spots and can grow up to ten centimetres a day with a total height of between three and four metres.

Knotweed stems

Knotweed stems

Commerce & Employment's Head of Plant Protection, Terry Brokenshire, described the plant as "invasive", he said: "It is not native to Guernsey and it grows very vigorously and smothers the are so native plants can't get a hold."

As well as damaging other plants Terry added that "it can damage foundations of buildings, grow through walls and lift tarmac".

The plants can be removed by simply cutting them down, but they will continually grow back Terry warned, he also said that if the plants are cut and any bits of them fall on the ground they can very easily take root and new plants will grow smothering even more areas.

Terry said, "The best way is to use chemicals" and that there are suitable ones available to both the professional and amateur gardener.

Knotweed stems with red markings

Knotweed stems with red markings

Another method that has been proposed by the British authorities is to bring in an insect from Japan which would destroy the plants.

A similar system is used by local tomato farmers in greenhouses but for the knotweed the insects would have to be released outside. This form of biological control could cause issues with damage being caused to other plants, however Terry said initial tests "look very safe indeed".

Terry added that this sort of problem had been caused by man who had spread the plant around the globe and that "in its wild natural state in Japan its fine".

last updated: 28/07/2009 at 15:51
created: 28/07/2009

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