Action: Crassula helmsii: Use a combination of control measures
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- One before-and-after study at a single pond in the UK found covering Crassula helmsii with carpet, followed by treatment with the herbicide glyphosate, killed 80% of the plant.
Because of the difficulty of controlling C. helmsii, a combination of control methods may be required to fully eradicate the species from a site (Dawson & Warman 1987, Leach & Dawson 2000, EPPO 2014). These could include a combination of mechanical removal, covering with lightproof barriers, and the use of herbicide. For example an integrated approach of mechanical removal (turf-stripping) and herbicide was used at a site in the UK, leading to an initial reduction in C. helmsii, although the species recolonized when treatment stopped and no quantitative data were provided (Clarke 2009).
Clarke S. (2009) A summary of three different approaches to the treatment of non-native invasive species Crassula helmsii at protected sites. Proceedings of the 41st Robson Meeting, 17-18 February 2009, Centre for Ecology and Hydrology, Wallingford, UK, 14-17.
Dawson F.H. & Warman E.A. (1987) Crassula helmsii (T. Kirk) cockayne: Is it an aggressive alien aquatic plant in Britain? Biological Conservation, 42, 247-272.
EPPO (2014) PM 9/19 (1) Invasive alien aquatic plants. EPPO Bulletin, 44, 457-471.
Leach J. & Dawson H. (2000) Is resistance futile? The battle against Crassula helmsii. Journal of Practical Ecology and Conservation, 4, 7-17.
Supporting evidence from individual studies
A before-and-after study in 2002-2003 at a single pond in Surrey, UK (Anonymous 2004) reported that covering C. helmsii with carpet strips followed by the application of glyphosate reduced the area of the plant, although no statistical tests were carried out. One year after glyphosate application approximately 80% of C. helmsii had been killed. In autumn 2002, strips of carpet were placed over C. helmsii and weighted down wherever possible on the pond edge and in shallow water. In July-August 2003 the carpet was removed and the glyphosate-based herbicide Roundup was applied twice.