Floating pennywort: Physical removal

Overall effectiveness category Likely to be beneficial
Number of studies: 2
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How is the evidence assessed?

Effectiveness

40%
Certainty

40%
Harms

not assessed

Calculating overall effectiveness category

Background information and definitions

Manual or mechanical removal of floating pennywort Hydrocotyle ranunculoides with manual removal of any visible remaining fragments may offer a tool for localised population eradication. For example, it is reported that floating pennywort has been eradicated from the upper reaches of the River Chelmer and the River Lee by removing as much plant biomass as possible then handpicking remaining fragments (Newman & Duenas 2010). It is important to carefully manage any mechanical removal efforts as floating pennywort demonstrates high regeneration capacity, and is able to regenerate from small shoot fragments (Hussner 2008).

Hussner, A. (2008) Ökologische und ökophysiologische Charakteristika aquatischer Neophyten in NordrheinWestfalen. Dissertation, Heinrich-Heine-Universität, Düsseldorf, 192 pp.

Newman J.R. & Duenas M.A. (2010) Information sheet: control of floating pennywort (Hydrocotyle ranunculoides). Centre for Ecology & Hydrology, Wallingford, UK. 3pp.

Study locations

Key messages

A study in Western Australia found that following a two-week program of physical removal of floating pennywort, the rate of growth exceeded the rate of removal.
A study in the UK, found that removal using a mechanical digger and monthly picking by hand greatly reduced the cover of floating pennywort but did not completely eradicate it.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

A before-and-after study from 1991 to 1992 in a river in Western Australia (Ruiz-Avila & Klemm 1996) found that a two-week program of physical removal did not reduce floating pennywort Hydrocotyle ranunculoides biomass. Following the removal program in late 1991, by September 1992 the estimated biomass of floating pennywort in the river had increased from an initial 175 tonnes to 420 tonnes. Control attempts in 1991 involved a two-week programme of physical removal by cutting the floating mats of floating pennywort with sickles from small boats. The mats were then pushed by small boats to an aquatic harvester, floated to the bank and removed by a backhoe. Follow up maintenance control was continued until January 1992, when growth rates exceeded the rate of removal.
Study and other actions tested
Referenced paper
Ruiz-Avila R.J. & Klemm V.V. (1996) Management of Hydrocotyle ranunculoides L.f., an aquatic invasive weed of urban waterways in Western Australia. Hydrobiologia, 340, 187-190.
A study in 2005-2006 by the Broads Authority at Gillingham Marshes, Suffolk, UK (Kelly 2006) found that removal of floating pennywort Hydrocotyle ranunculoides using a mechanical digger and extensive hand picking, along with monitoring, greatly reduced the cover of floating pennywort but did not completely eradicate it. Hand-picking was undertaken at least once a month (usually every fortnight) throughout the growing season (March – September 2005-2006 ongoing). In addition, a mesh grid was added to the upstream end of the water pump at Gillingham Marshes to try to prevent floating fragments from entering and infesting the River Waveney, adjacent to the marshes. To dispose of the pennywort, it was piled on the site and monitored for regrowth. Monthly monitoring of the pile was undertaken and if signs of growth were observed, they were sprayed with the herbicide glyphosate.
Study and other actions tested
Referenced paper
Kelly A. (2006) Removal of invasive floating pennywort Hydrocotyle ranunculoides from Gillingham Marshes, Suffolk, England. Conservation Evidence, 3, 52-53.

Please cite as:

Aldridge, D., Ockendon, N., Rocha, R., Smith, R.K. & Sutherland, W.J. (2020) Some Aspects of Control of Freshwater Invasive Species. Pages 555-87 in: W.J. Sutherland, L.V. Dicks, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2020. Open Book Publishers, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

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This Action forms part of the Action Synopsis:

Control of Freshwater Invasive Species

Related Actions

Actions	Effectiveness	Studies	Category
Floating pennywort: Combination treatment using herbicides and physical removal Action Link	Unknown effectiveness (limited evidence)	1	Synopsis Link
Floating pennywort: Public education Action Link	No evidence found (no assessment)	0	Synopsis Link
Floating pennywort: Use of liquid nitrogen Action Link	No evidence found (no assessment)	0	Synopsis Link