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Providing evidence to improve practice

Individual study: Control of floating pennywort Hydrocotyle ranunculoides by hand removal along the River Can, Essex, England

Published source details

(2004) Control of floating pennywort. Environment Agency


Floating pennywort Hydrocotyle ranunculoides (native to North America) is an invasive alien plant to in the UK. used in garden ponds. It was introduced into the UK via the aquatic nursery trade and was first noted growing in the wild in 1991. By 2000, it had escaped into the wild and was growing prolifically along parts of the Rivers Can, Chelmer and Blackwater in Essex. If left uncontrolled, it was considered that the floating pennywort could cause severe ecological damage, cutting off oxygen from the water and impeding flows and navigation. It is resistant to most herbicides approved for use in water, and when cut mechanically, fragments break off and quickly root and grow again. An experiment was undertaken to assess whether hand removal could be effective as an eradication method.

Study site: The attempted H.ranunculoides took place along a stretch of the River Can in Essex, southeast England. The Environment Agency's Ecological Appraisal team led the project with assistance from the Environment Management team. The work was undertaken by the Agency's Emergency Work Force (EWF).

Hand removal: During 2001 an experiment was undertaken to assess whether hand removal (cutting and removal of the pennywort) could be effective as an eradication programme. Stems were cut close to the substrate and cut material removed for disposal on land.

By September 2001, the hand-cleared stretch of the River Can was largely clear of the weed. However minor regrowth was and without regularly clearance it is considered that it may recolonise over time. The hand clearance method has since continued downstream for several kilometres as a stop gap until other eradication methods are available.

A new trial is planned for 2004 to determine if the method can be combined with mechanical removal followed by spot treatment with herbicide.

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