Action: Crassula helmsii: Use hot foam to control plants
Key messagesRead our guidance on Key messages before continuing
- One replicated, controlled study in the UK found that treatment with hot foam, along with other treatments, did not reduce cover of Crassula helmsii. One before-and-after study in the UK found that applying hot foam partially destroyed C. helmsii.
Hot foam has been used proposed as an approach for controlling vegetation. A biodegradable, plant-based foam allows heat to remain in contact with plant surfaces for a longer period than using hot water, with the aim of rupturing plant cells and killing the plant.
The use of hot water to control C. helmsii is discussed in ‘Use hot water’.
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.
- Ewald N.C. (2014) Crassula helmsii in the New Forest. Final report on the status, spread and impact of this non-native invasive plant, and the efficacy of control techniques following a 3 year trial. Freshwater Habitats Trust report.
- Bridge T. (2005) Controlling New Zealand pygmyweed Crassula helmsii using hot foam, herbicide and by burying at Old Moor RSPB Reserve, South Yorkshire, England. Conservation Evidence, 2, 33-34