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Providing evidence to improve practice

Individual study: Crassula helmsii: Attempts at elimination using herbicides

Published source details

Dawson F.H. (1996) Crassula helmsii: Attempts at elimination using herbicides. Hydrobiologia, 340, 241-245


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Crassula helmsii: Chemical control using herbicides Control of Freshwater Invasive Species

A controlled container experiment in 1988-1994 in southern England, UK (Dawson 1996) reported that control of C. helmsii varied between herbicide types, although no statistical tests were carried out. Treatment of low-biomass, underwater C. helmsii with diquat reduced biomass by 100%. Submerged C. helmsii biomass was also reduced by diquat-alginate (97% reduction), dichlobenil (66%) and terbutryne (48%). Glyphosate caused the greatest biomass reduction in trials on plants above the water (82%). Emergent C. helmsii biomass was also reduced by asulam (66%), 2,4-D amine (55%) and dalapon (51%). Trials of higher herbicide concentrations on higher biomass of C. helmsii showed that diquat and diquat alginate reduced biomass by at least 85% at all concentrations. However even at the highest concentration, C. helmsii was not eliminated. The biomass reduction caused by glyphosate was lower and more variable (between 5% and 80%). Fourteen 0.25 x 0.25 m turfs were grown in either deep or shallow water in 300 l tanks. Low-biomass trials used 13-16 kg/m2 fresh weight C. helmsii and took place in October 1988 and summer 1989 and 1990. High-biomass trials took place in spring 1993 and 1994 using up to 50 kg/m2 C. helmsii. Glyphosate and diquat were applied between 1x and 50x usual concentration. Trials lasted 5-12 weeks.