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Relentless invader stalks UK construction projects

JAPANESE KNOTWEED is posing increasing problems for UK construction projects.

The invasive plant is capable of penetrating asphalt, walls, foundations and drainage pipes. It is extremely hardy and can thrive in almost all soil conditions, including contaminated ground on brownfield sites.

Dense areas of growth on riverbanks impede water flow, ditches become blocked, flood defences are affected by the root system and in the autumn dead material washes into waterways, blocking culverts.

Controlling the weed is costly and time consuming because the Environmental Protection Act 1990 classes it as a controlled waste.

A long programme of chemical control can be effective but it is not practical where a developer wants to go ahead with building.

Believed to have been introduced from Japan in the early 19th century as a garden plant, Knotweed grows rapidly to a height of 2m to 3m.

It spreads easily by seed, cut stems or underground, via its strong and extensive root system, which can be up to 2m deep. It is a successful competitor, replacing existing vegetation and dying back in the winter to expose loosened and easily eroded soil.

South Wales appears to be a black spot for the problem; the Welsh Development Agency has published guidelines for its control and Swansea council has appointed a Japanese Knotweed officer.

Scientists from Loughborough University have produced a Japanese Knotweed Manual.

Elcot Nurseries, which provides soft landscape solutions for construction and civil engineering, has now set up a specific division to deal with the increasing problem of Knotweed.

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