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Providing evidence to improve practice

Action: Crassula helmsii: Use dyes to reduce light levels 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 aquatic dye, along with other treatments at some sites, did not reduce cover of C. helmsii, although no statistical tests were carried out. Average coverage of C. helmsii was 72% before and 75% at the end of the dye treatment, compared to 63% and 70% respectively at control sites. The study also showed that coverage of native plant species fell from 17% to 11% at treatment sites and from 17% to 14% at control sites over the trial period. Several other treatments (mechanical removal, herbicide, hot foam) were also used at some sites during this trial. A combination of Dyofix blue and black pond dyes were applied to six ponds on 5-6 occasions between August 2011 and December 2013. 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.


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.