The Environment Agency calls it “indisputably the UK’s most aggressive, destructive and invasive plant”. Japanese Knotweed has vigorously invaded a range of habitats and with no natural enemies in Britain (such as predators and diseases) it has colonised and dominated habitats at the expense/exclusion of native plants. Japanese Knotweed forms tall thickets and a lush green canopy that excludes light, shading the area below. Native plants can rarely compete with this invasive species and local plant biodiversity is reduced.
Japanese Knotweed is particularly well-suited to growth along riverbanks and has colonised roadsides, railways and derelict industrial lands. Rivers, hedgerows, roadsides and railways form important wildlife corridors for native plants and animals to migrate and disperse along, and large infestations of Japanese Knotweed can block these routes for wildlife. When Japanese Knotweed colonises riverbanks it can create problems in terms of flood management. It increases the risk of riverbank erosion when the dense growth of the plant dies back in the autumn exposing bare soil. It can also create a flooding hazard if the dead stems are washed into the streams and clog up the channel.
Japanese Knotweed is able to colonise a variety of urban environments. Due to its ability to exploit weaknesses in construction materials, such as concrete and tarmac, new knotweed growth can cause serious damage to buildings, hard surfaces and infrastructure. Once established underneath or around the built environment, it can be particularly hard to control; the stout rhizomes are notorious for pushing through asphalt, building foundations, concrete retaining walls and even drains, causing significant damage. As a result, Japanese Knotweed has caused some problems in the residential housing market and the difficulty
in treating Japanese Knotweed has seen some historical reluctance to lend. Mortgage lenders will expect the presence of Japanese Knotweed to be noted on a residential valuation report. According to a report in the daily mail thousands of house sales are being hit by the spread of Japanese Knotweed and in one of the worst cases the value of a four-bedroom house in Hertfordshire was virtually wiped out after it dropped from £305,000 to £50,000 due to the damage caused. The weed had spread along the brick walls, forcing its way through flooring and had sprouted over skirting boards. It was on the brink of collapsing.
“At the Olympic site in East London the RHS reports the cost of removing and disposing of Japanese Knotweed to be estimated at £70 million.”
The Environment Agency calls Japanese Knotweed “indisputably the UK’s most aggressive, destructive and invasive plant”
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