Invasives Blog

As part of UK Invasive Species Week 2021, we bring you – thanks to our friends at the Angling Trust – this collection of photos taken at the launch of a national campaign to tackle the highly invasive floating pennywort from blighting Britain’s rivers and lakes.

Floating pennywort – first found in the wild in England in the 1990s – can grow at an incredible 20cms a day from tiny fragments to form dense mats that cover the water’s surface. These can block out light, stifle native plants, and make rivers and lakes unsuitable for insects and fish.

The dense rafts can also make waters inaccessible to anglers and present a flood risk when plant mats build up around sluices and drains.

The event was an opportunity to see first-hand the benefits of working collaboratively to tackle floating pennywort (Hydrocotyle ranunculoides). It is anticipated that later this year, a specialist weevil native to South America – Listronotus elongatus –will be released into the wild to provide a sustainable way to halt the spread of the species.

This follows extensive research undertaken by CABI to determine the suitability of the species for release and presents one of several biological controls that are being used to assist in invasive species management.

As part of the campaign launch, Djami Djeddour, Senior Scientific Officer at CABI, joined the Angling Trust and the Herts and Middlesex Wildlife Trust on a visit to the Colne Valley where she met the Colne Valley Fisheries Consultative to help clear a dense mat of floating pennywort.

You can read the full story ‘CABI expertise supports national campaign to control invasive floating pennywort on Britain’s rivers and lakes’ here. Meanwhile enjoy the photos below courtesy of the Angling Trust.

Representatives from the Angling Trust point out the dense mat of floating pennywort which not only causes havoc for local anglers but can also reduce the availability of oxygen in the water, threatening fish and invertebrates, choking drainage systems and crowding our native water plants.

Did you know? Floating pennywort has been banned for sale in the UK since April 2014.

Regular cutting from May-October will prevent complete dominance and help manage this plant.
According to Plantlife, Hand pulling (or spot chemical treatment) should follow cutting to reduce re-growth. Pulling is likely to work best on small infestations rather than larger areas.
Djami lends a hand with the floating pennywort – some of which was taken back to CABI’s laboratories in Egham, UK, to act as ‘weevil food’. Usually the material is piled up away from the river to rot down.
A tasty meal for Listronotus elongatus but a nuisance for anyone else.
The team didn’t bargain for this invasive American red signal (Pacifastacus leniusculus) crayfish – first introduced to Great Britain in 1976.
Listronotus elongatus weevil controlling floating pennywort – currently being researched in the laboratory for potential future release (Credit: CABI).

Read more about CABI’s work to ‘control floating pennywort in a safe and sustainable way’ from the project page.

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