JAPANESE knotweed is blighting areas of East Lancashire, with particularly high levels in Blackburn. 

An interactive map shows the density of infestations across the UK, showing hotspots.
In Blackburn, there are 385 reported occurrences of the invasive species within 4km of the town centre. 

There have been 244 occurrences in Accrington, 206 in Rawtenstall, 205 in Burnley, 126 in Colne and 113 in Clitheroe. 

The notorious plant can grow four inches a day in summer, and its roots or rhizomes spread far underground causing structural damage to buildings.

The UK's most common plant pest, it has been scuppering house sales for decades because mortgage lenders are cautious with properties affected by it. 

The online map, produced by Environet UK, allows people to search by postcode to discover the number of reported sightings nearby or to report any new sightings.

Adam Walmsley, project officer at Clitheroe-based Ribble Rivers Trust, said East Lancashire does have a lot of Japanese knotweed compared to areas of North and West Lancashire because it is more urban.

He said: “The Japanese knotweed is associated with development, so it will be grow if you move soil and rubble around from housing developments.

“It is more prevalent in urban areas such as Blackburn with a high population and will also lie near river banks.

“We did have an invasive species project to try and tackle this but the funding hasn’t been continued.” 

The interactive map was created by Nic Seal, of Environet UK, who said: “This heatmap will enable us to build a nationwide picture of the Japanese knotweed problem and give the general public the information they need to assess the risk locally, particularly when buying a property.”

Knotweed hotspots are marked from yellow through to red depending of the severity of infestation.

The Victorians introduced Japanese knotweed as an ornamental plant but it now grows rampantly along railways, waterways, in parks and gardens and is notoriously difficult to treat.

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The Environment Agency brands it as “indisputably the UK’s most aggressive, destructive and invasive plant.”

Another non-native plant to be wary of is giant hogweed, which is toxic and can cause skin burns if you come into direct contact with it.

Mr Walmsley said: "Giant hogweed is also becoming more prevalent in the Calder and Darwen catchment areas and will mainly grow on river banks."