Action on invasive species in Calderdale

Invasive species are outcompeting our native plants and increasing our flood risk – but we can all help tackle the problem.

Close up of Japanese knotweed flowering
Managing invasive species

Managing invasive species is an important part of reducing flood risk and creating a more biodiverse Calderdale.

Himalayan balsam and Japanese knotweed dieback over autumn and winter and leave the earth bare. This means rainwater flows more quickly over the ground, increasing the risk of flooding. Removing invasives allows our beautiful native species to revegetate and thrive, ensuring that the land is covered all year round. This helps to slow the rainwater down on its journey to the river and stop soil from being washed away.

A sign that reads 'Attention, invasive plant, Japanese Knotweed'
Working in partnership

Work to combat invasive species along watercourses in Calderdale is led by the Calder INNS sub-group. This group brings together a wide range of partners to ensure a strategic approach to identifying and treating invasives.

Treatment of Japanese knotweed has been carried out by Yorkshire Wildlife Trust and by the River Stewardship Company on behalf of the Environment Agency. Forus Tree and Calder Future have carried out extensive removal of Himalayan balsam in the Calder Valley. Some landowners have also removed Himalayan balsam as part of the Landowner Grant Scheme to reduce flooding.

Although Giant hogweed doesn’t contribute to flood risk we are also working to control this invasive in Calderdale as it can be damaging to human health if the sap comes into contact with skin. Treatment of giant hogweed is carried out by the River Stewardship Company on behalf of the Environment Agency.

Invasive species warning sign
How you can help

There are lots of different ways you can help us to take action on invasive species in Calderdale. To learn more about why action is needed please visit our Invasive Species page.

Report sightings

The biggest difference you can make is to report sightings of invasive species on the INNS Mapper app and website. This is particularly important for Japanese knotweed and Giant hogweed as you should not try to remove them yourself - they require professional treatment. To do this, you can:

  • Learn what to look for – these identification sheets are a great way to familiarise yourself with what invasives look like
  • Download the INNS Mapper appthe app is free to download and use
  • Report sightings – on the new the INNS Mapper app and website

If you are not able to use INNS Mapper you can also email the Yorkshire Wildlife Trust at and send your report to them.

Himalayan balsam seeds
Get involved in the action

There are some fantastic volunteer groups such as Slow the Flow and Forus Tree tackling invasive species across Calderdale. Join a volunteering day to help to clear invasives and create natural flood management measures. Take a look at our News Page for upcoming volunteer opportunities.

Bash the balsam!

Summer is the peak season for ‘balsam bashing’. Himalayan balsam has a very shallow root system so it can easily be pulled out of the ground and then snapped. If this is done before the plant goes to seed it can be an effective way of stopping the spread.

The Yorkshire Invasive Species Forum and Yorkshire Wildlife Trust have produced this guide to help you pull Himalayan Balsam safely. Please don’t pull Himalayan Balsam once the flower has become a seed head – if the seed pod bursts this will spread the seed over several meters.

Treat knotweed on your land

It’s important not to try to remove Japanese knotweed yourself as doing so can actually increase the spread of the plant. Treatment needs to be carried out by professionals and takes several years to be fully successful. If you have Japanese knotweed on your land and require advice or guidance you can contact the Yorkshire Wildlife Trust at

Raise awareness

Help us get the word out about invasive species in Calderdale. Download these resources to share through your own networks:


Social media graphics

Himalayan balsam in flower
Projects in Calderdale

An exciting new initiative is taking place in Calderdale to tackle invasive species.

Led by Calderdale Council, an experimental trial with CABI (Centre for Agriculture and Bioscience International) is underway at a site near Todmorden. The trial involves a natural control method which hopes to reduce the impacts of Himalayan balsam.

In 2006, CABI began studying different types of natural control methods which exist in balsam’s native range of the Himalayas. A rust fungus was observed and selected as the test subject in an experimental trial and, in 2010, a specific species of rust fungus was exported to a quarantine facility for in-depth safety testing.

Since 2015, this rust has been introduced to 47 sites throughout England and Wales. The site in Todmorden has been remarkably successful, showing the second most promising results of the test sites. Further studies and possible release of the rust will take place at this site; however, it is hoped that the rust is now established on site and will spread from the site using airborne transmission.

This will hopefully help reduce the spread of Himalayan balsam without spending lots of time and effort pulling up individual plants.

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