Nature Features

Himalayan balsam may sound and look exotic, but it's an unwelcome visitor here in Devon, where it is starting to take over some of our riverbanks.

In some places the invasive weed is crowding out native species, leading to erosion.

This summer, the Environment Agency and volunteers from the conservation charity Devon Wildlife Trust are surveying the River Dart and its tributaries to assess the extent of the problem.

And in one location, 25 volunteers have been tackling the weed head-on by going 'balsam bashing' at a stream near Totnes.

Himalayan Balsam

This site was chosen as it was the highest point on the stream that had been colonised, so once cleared, it should not be reseeded from upstream plants.

Himalayan balsam has been introduced to this country by members of the public, who have unwittingly been dropping seeds in areas because the weed looks nice in full bloom.

Unfortunately, the weed spreads rapidly and takes over native species - and that's bad news for the home grown plants.

It is also causing erosion on riverbanks. The balsam dies back during the winter months and the native species are being driven out.

Sediment scoured from the banks is deposited on the riverbed, burying the clean gravels essential for many fish and invertebrates.

The battle against the weed is under way

Through the wildlife trust's Dart Catchment Project, the charity is mapping the extent of the problem on the tributaries of the Dart to direct future management of the weed.

On each stream, they have been identifying the highest upstream point where the plant is found, to assess the viability of controlling the weed. 

Jeremy Bailey at the Environment Agency said: "There is no quick fix, because the seeds of the plant remain viable for about two years.

"There needs to be a catchment-wide approach involving everyone who is interested in the River Dart and its tributaries if we are going to be successful in the long term."

Members of the public are being asked to inform the Devon Biodiversity Records Centre if they spot the weed, by clicking on 'Send in your Sightings' at www.devonwildlifetrust.org - the trust's website is linked from this page.