Crassula helmsii: Use hot foam to control plants

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

Effectiveness

20%
Certainty

50%
Harms

not assessed

Calculating overall effectiveness category

Background information and definitions

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’.

Study locations

Key messages

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.

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 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.
Study and other actions tested
Referenced paper
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 (Oxford) report.
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.
Study and other actions tested
Referenced paper
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.

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

All the journals searched for all synopses

This Action forms part of the Action Synopsis:

Control of Freshwater Invasive Species

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