Removal of Hydrocotyle ranunculoides in England (GB)
Hydrocotyle ranunculoides (Apiaceae, EPPO A2 List) originates from North America and was introduced in the United Kingdom in the 1980s by the aquatic nursery trade. The plant is recorded in the wild in 35 sites in southern England and Wales, and is thought to have accidentally escaped from aquaria and garden ponds. It forms dense interwoven mats of vegetation on the water surface and out competes most native aquatic plants. It also causes desoxygenation of the water, affecting fish and invertebrate populations and choking drainage channels. The plant has proven to be difficult to control because of its rapid growth (up to 20 cm a day) and its ability to regrow from a single node.
In September 2004, dykes contaminated with H. ranunculoides along approximately 1 km were reported to the authorities by a surveyor of the Gillingham Marshes. The official authorities visited the site with all relevant partners and decided in October 2004 to take action to manage the invasive plant. It was removed using a mechanical digger in early February 2005. This was followed by extensive hand-picking by official staff and volunteers conducted at least once a month throughout the growing season (March till September 2005 and 2006). This step was essential to completely remove the floating fragments created by the digger. In addition, a mesh grid was set up to prevent floating fragments to spread. After removal, plants were disposed on the site to dry out and die as it was the most economic and ecological option, and piles were monitored on a monthly basis. If regrowth is observed, glyphosate treatments will be applied with the permission granted by the authorities.
The removal of H. ranunculoides has been a success at Gillingham Marshes but requires ongoing monitoring and intensive hand-picking as it has not been completely eradicated. The native aquatic vegetation is re-establishing. This experience highlights that rapid action and coordination between partners was essential for success.
Kelly A (2006) Removal of invasive floating pennywort Hydrocotyle ranunculoides from Gillingham Marshes, Suffolk, England. Conservation Evidence 3, 52-53.