South American weevils on the River Soar are helping to eradicate Floating Pennywort. More...

The Canal & River Trust is working with the Centre for Agriculture and Bioscience International (CABI) to use Argentinian weevils to control invasive Floating Pennywort, Hydrocotyle ranunculoides, which has been called "the worst aquatic weed in the UK". Originating from Central and South America, the plant arrived in the UK in the late 1980s as an ornamental plant for the aquatic trade. It didn't take long for it to escape cultivation and spread rapidly in English and European waterways, forming dense mats, reducing the availability of oxygen in the waterways, crowding out native water plants and posing a risk to wildlife and livestock. Floating Pennywort can grow up to 20cm per day and can regenerate from tiny fragments. With restrictions on chemical use near water, management requires sustained and laborious mechanical and manual clearance which can increase spread if the plant is fragmented. 

Since 2011 CABI has been investigating biological controls for Floating Pennywort. After a decade of extensive research and reviews, the Argentinian weevil, Listronotus elongatus, was identified as the best candidate and this summer controlled releases took place at a number of locations, including the River Soar. The release sites will be monitored over the next 12 months to continue gathering data and evidence. Watch this space! 

Photo: CABI