Action: Crassula helmsii: Decontamination to prevent further spread
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- One controlled, replicated container study in the UK found that submerging Crassula helmsii in hot water led to higher mortality than drying out plant fragments or a control.
C. helmsii is able to rapidly regenerate from small fragments of plant, and is also highly tolerant of drying out (Dawson & Warman 1987). This means it can easily be spread between water bodies, for example on equipment used for fishing or other watersports. Effective methods to decontaminate equipment, such as hot water or bleach, are therefore important in minimising the spread of C. helmsii.
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.
Supporting evidence from individual studies
A replicated, controlled container experiment in 2013-1014 in the UK (Anderson et al. 2015) found that exposure to hot water led to higher mortality of C. helmsii fragments compared to drying treatment or a control. Submerging C. helmsii in hot water caused 90% mortality 1 h after treatment, and all plants were dead after 1 day. Hot water followed by drying did not result in additional mortality (80% mortality after 1 h). Drying treatment only led to partial mortality (20% after 8 days and 50% after 16 days), and all fragments in the control group survived for 16 days. Two hundred and forty 60 mm plant fragments were placed in mesh bags and submerged in 14 °C water for 1 h to simulate an angling trip. Hot water samples were then submerged in 45°C water for 15 min. Samples in the drying treatment were put on plastic trays in a room with circulating air. Control samples were placed in unsealed plastic bags to hinder drying. Mortality was assessed after 1 h and 1, 2, 4, 8 and 16 days using a FluorPen.