Spring Special: Identifying non-native invasive species

Simon Watts
April 26, 2021

Spring sees green shoots appearing along our riverbanks but not all of them are welcome. Some of the plants (or flora) you find along our rivers are "non-native invasive species." These were brought to the United Kingdom from around the world and have spread causing harm to the environment. You can help protect native species and river visitors by learning how to identify and report them.

Himalayan Balsam

Top Trumps card for Himalayan balsam

Himalayan balsam is controlled by pulling plants before they go to seed. It is a popular summer activity with our volunteers.

The seeds are spread by flood water. We focus on controlling it high up catchments to prevent its spread or on sites with high ecological value.

As the first true pair of leaves appears you can see the distinctive serrated edges. It has orchid pink flower.

It is widespread throughout the middle Aire catchment but less so in the Upper Aire.

Two leaves sit in a graphic that divides text

Japanese knotweed

Japanese knotweed is controlled by injecting stems with pesticide. We treat Japanese knotweed along Bradford Beck. YorGreenCIC treat it in the Bradford area.

Japanese knotweed has heart shaped leaves and a tall stem that looks like a cross between rhubarb and bamboo. It can reach over head height and regrow from fragments of roots.

Reporting it through the Yorkshire Wildlife Trust INNS Mapper site is the most effective way to ensure it is treated.

Two leaves sit in a graphic that divides text

Giant hogweed

Identifying giant hogweed seedlings is challenging as they can be confused with native hogweed species.

Giant hogweed looks like an enormous cow parsley. It is significantly larger and can reach heights between 1.5m and 5m with a spread of between 1 and 2m. Leaves are jagged and lobed and a flower spike formed in the second year before setting seed.

Their stems are green with purple blotches and stiff, white hairs. The leaves are huge (up to 1.5m wide and 3m long) and is deeply divided into smaller leaflets. Flowers appear in June and July.

Reporting it through the Yorkshire Wildlife Trust INNS Mapper site is the most effective way to ensure it is treated. In Leeds, this is done by the River Stewardship Company.

Two leaves sit in a graphic that divides text

Signal crayfish can be found throughout the catchment. There is currently no viable method of control in the United Kingdom.

Large specimens can sometimes be seen from bridges or found under rocks. It is illegal to trap or fish for them without a license from the EA.

Pockets of native white-clawed crayfish populations still remain within the Aire catchment. The best way to protect them is careful biosecurity to prevent the spread of signal crayfish.

How to report them

Both Japanese Knotweed and giant hogweed can be reported through the Yorkshire Wildlife Trust INNS Mapper site is the most effective way to ensure it is treated. You have to create an account to do this. In our next blog we will take you through the process of reporting.


© Copyright Aire Rivers Trust 2020
The Aire Rivers Trust is a company limited by guarantee registered in England and Wales No: 07464227 and a Registered Charity No: 1145609
Registered Office at: 38 Morton Lane, East Morton, Keighley BD20 5RS
Top linkedin facebook pinterest youtube rss twitter instagram facebook-blank rss-blank linkedin-blank pinterest youtube twitter instagram