A call to arms has come from the Yorkshire Invasive Species Forum which needs volunteers to seek and destroy immigrant plants.

Aggressive imports such as Japanese Knotweed and the New Zealand pygmyweed are a problem on waterways.

And conservation charity Yorkshire Wildlife Trust, which heads the Forum, wants people to help fight the spread of such harmful plants along the Rivers Aire and Calder.

Jon Dunster, project officer for Yorkshire Invasive Species Forum, said: “Invasive plants are one of the biggest threats to biodiversity today as they outcompete our native species and cause riverbank erosion which can contribute to flooding risk.

“In addition to this they can clog-up waterways which can affect river-users such as canoeists and anglers. It has been proven that controlling their numbers is effective, so long as it is carried out as part of a river catchment wide co-ordinated programme.

“But to achieve a co-ordinated control programme and make a difference to invasive plant populations the Trust needs the help of volunteers – there are just too many to go it alone.”

The Forum wants people to join its ‘Plant Tracker’ teams which will carry out visits to spots within the river catchment to look for key plant species.

In the catchment for the rivers Calder and Aire five plants in particular pose the biggest threat to botanical security: floating pennywort, giant hogweed, Himalayan balsam, Japanese knotweed and New Zealand pygmyweed.

Those with no prior knowledge of them will be briefed in plant recognition and how to log their findings.

To find out more about the invasive species project run by Yorkshire Wildlife Trust and the plant species causing problems in Yorkshire visit ywt.org.uk/invasives. And to enquire about volunteering on the project e-mail volunteering@ywt.org.uk.