CABI supports floating pennywort weevil release in Barnsley, UK

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29 August 2023, UK: A joint venture between Yorkshire Water and the Environment Agency has funded the release of a biocontrol agent at a site in Barnsley, Yorkshire, UK, to help tackle one of our most invasive aquatic plants – floating pennywort.

In July 2023, the weevil was introduced into a large pond owned by Barnsley Metropolitan Borough Council, as part of ongoing field trials by CABI.

If successful It is hoped that this biocontrol agent will contribute to the national strategic approach to floating pennywort management, providing a long-term and sustainable solution and mitigating the impacts of this highly invasive weed.

Floating pennywort is a highly damaging non-native plant that was first introduced to Britain as an ornamental pond plant in the 1990’s. In the wild, this species can grow up to 20cm a day and rapidly forms dense floating mats of weed across waterbodies.

These crowd out native species, block light impacting on the aquatic ecosystem, interfere with activities such as angling, paddling and sailing, and potentially increase the flood risk. In Yorkshire, it affects a number of canals and rivers, including the River Calder, the Calder & Hebble Navigation and the River Don.

Conventional treatment is by the application of chemicals (glyphosate) or physical removal of the plant using boats or volunteers. Whilst this can minimise the impact of this invasive plant, the pennywort is rarely cleared completely and can often return year after year. It is also very difficult to treat pennywort when it is growing amongst native vegetation.

The answer may lie with the Floating Pennywort Weevil (Listronotus elongatus). This insect was approved as a biocontrol for release into the wild in England in autumn 2021, after a decade of safety and efficacy testing by CABI.

Andy Virtue, from the Environment Agency, said, “We have been working in partnership for years to try to keep this highly invasive plant species under control. We have done well to minimise the spread of floating pennywort in Yorkshire, however there are clear impacts where it is unfortunately present. We hope the introduction of the weevil will provide way of tackling this invasive plant and minimise its impact on our watercourses.”

Djami Djeddour, Senior Scientific Officer, CABI, said, “These weevil releases are the culmination of a decade of research by CABI, together with South American collaborators in the native range of floating pennywort, to identify the safest and most damaging natural control for this pernicious weed. We’re very pleased to be working in partnership in Yorkshire to try to establish weevil populations and bring floating pennywort under long term control.”

Dr Steph Bradbeer, from Yorkshire Water, said, ‘Working in partnership is so important for tackling invasive non-native species across Yorkshire, which pose a risk to the environment and wildlife. One of these invasive species is floating pennywort, which if unchecked, can grow up to 20cm a day and cause significant problems in slow-flowing watercourses and impact draining systems.

“This collaborative project to release the floating pennywort biocontrol at a site in Barnsley is very exciting and we hope the release of these specialist weevils will provide a way of managing floating pennywort.”

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