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Providing evidence to improve practice

Action: Crassula helmsii: Use hot foam to control plants Control of Freshwater Invasive Species

Key messages

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Supporting evidence from individual studies


A replicated, controlled study in 2011-2014 at waterbodies in the New Forest, UK (Ewald 2014) reported that treatment with hot foam did not reduce cover of C. helmsii, although this was not tested statistically. Average coverage of C. helmsii was 56% before and 60% at the end of the hot foam treatment, compared to 63% and 70% respectively at control sites. The study also found that coverage of native plant species fell from 31% to 14% at treatment sites and from 17% to 14% at control sites over the trial period. A biodegradable agent composed of plant oils and sugars was applied as a very hot foam (above 97 °C for 2 s) to five ponds twice during autumn 2011 and autumn 2013. No treatment occurred in 2012, and two ponds were only partially treated in 2011 and 2013, because of high rainfall. Aquatic dye treatment was additionally applied to these two ponds. C. helmsii coverage was assessed in five random 0.25 m2 quadrats within each treatment area in winter and summer from 2011-2014, and also in seven control ponds.



A before-and-after study in 2003 at waterbodies in a nature reserve in South Yorkshire, UK (Bridge 2005) reported that spraying with hot foam partially destroyed C. helmsii, although statistical tests were not carried out.  Approximately 50% of C. helmsii was killed by the treatment, but only the top layers of the plant were affected. Biodegradable ‘Waipuna’ hot foam, an organic compound of corn and coconut sugars, was sprayed three times between September and November 2003. No information about the size of area treated or monitoring was provided.


Referenced papers

Please cite as:

Aldridge, D., Ockendon, N., Rocha, R., Smith, R.K. & Sutherland, W.J. (2019) Some aspects of control of freshwater invasive species. Pages 569-602 in: W.J. Sutherland, L.V. Dicks, N. Ockendon, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2019. Open Book Publishers, Cambridge, UK.