Article - The River Blog

Japanese knotweed – why is it a problem?

Author: Jeanette Dyson
Categories: Invasive species

It’s the time of year when Japanese knotweed rears its invasive head. This non-native plant has deservedly gained a notorious reputation over recent years for reducing biodiversity, damaging building foundations and even landing Network Rail with a bill for thousands of pounds after being successfully prosecuted for allowing Japanese knotweed to spread to neighbouring land.

The law and Japanese knotweed

Landowners, homeowners or businesses, are legally responsible for controlling Japanese knotweed on their premises.

It is illegal to cause Japanese knotweed to grow in the wild. And if you have Japanese knotweed on your property, you must not allow it to spread to neighbouring properties. If this happens, it is classed as a private nuisance and you could be prosecuted under civil law.

Before prosecution, however, landowners with a Japanese knotweed problem will be given the opportunity to address the issue.

Japanese knotweed and property prices

If Japanese knotweed is discovered within 7m of your property, it can affect property prices. It can also affect your ability to sell your property. Some mortgage lenders will not offer mortgages on properties that have Japanese knotweed within 7m.

So what is Japanese knotweed and how can it be controlled?

How to identify Japanese knotweed

Japanese knotweed is a tall herbaceous plant with bamboo-like stems. The leaves are shield-shape, and flat bottom where they attach to the stem.

Leave are attached either side of the leaf stem in an alternating pattern. This gives the stem a distinctive zig-zag.

The main stems are hollow and speckled purple.

Shoots look very similar to bamboo shoots.

You can download the Non-Native Species Secretariat sheet to help you identify Japanese knotweed.

Why do we need to control Japanese knotweed

Japanese knotweed can grow into dense thickets which crowd out other species. This reduces diversity and reduces the prevalence of native plants that wildlife rely on for food and shelter.

This non-native plant, which was originally introduced into this country as an ornamental plant in the 19th century, also contributes to riverbank erosion. This increases the likelihood of flooding.

The strong rhizomes, can grow deep underground, helping it to spread quickly and easily. These root-like stems can grow through cracks in concrete and tarmac and have been reported to damage buildings and make property difficult to sell.

It’s particularly important to control Japanese knotweed alongside riverbanks. The plant can be spread downstream by flowing water, colonising the riverbank as it goes.

How to control Japanese knotweed

NEVER cut, burn or pull Japanese knotweed. Fragments of rhizomes will quickly regrow into new plants, causing the Japanese knotweed to spread further.

Japanese knotweed can only be treated by licensed operatives and disposed of at licensed waste management sites.

If you suspect that you have Japanese knotweed on or near your land, report it to your local authority. If you spot Japanese knotweed on or close to the River Holme catchment – which includes the Holme, Ribble, New Mill Dike, Magbrook, Dog Dike and many more – please let us know.

We have trained specialists, with the equipment and expertise to treat Japanese knotweed. This is done by spraying the plant and/or injecting the stems with pesticides.

We offer Japanese knotweed stewardship programmes for landowners. In return for a donation, we can control Japanese knotweed on your land.

Anyone joining our Japanese knotweed stewardship programme will receive a certificate stating that they have taken steps to control the spread of this invasive species.

Download our Japanese knotweed control leaflet on our projects page.

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