Herbicide control of submerged bog moss (Mayaca fluviatilis Aubl.).

Bog moss, Mayaca fluviatilis Aubl., is an invasive perennial aquatic plant native to Central and South America, the Caribbean and the United States. Sold as an aquarium plant for many years, bog moss is now naturalised in Sri Lanka, Singapore and three locations in Australia. It can grow either fully submerged as semi-floating mats in water up to 2 m in depth or as a semi-terrestrial plant on the margins of wetlands. The mats can block drains and irrigation channels, contribute to water-logging in adjacent cropland, impede recreational activities, endanger swimmers and threaten biodiversity. Bog moss mats which break free during flooding can damage bridges and moored boats. Despite a variety of management techniques, effective control remains elusive. Our objective was to examine the efficacy of subsurface application of ten herbicides, registered in Australia or the USA for aquatic weed control, which could also be applied to emergent foliage. A replicated microcosm study was conducted in 2-L aquaria beginning in January 2011. The maximum and one-fifth labelled rates of bispyribac, dichlobenil, diquat + guar gum, endothal, flumioxazin, glyphosate, imazapyr, metsulfuron, triclopyr and carfentrazone were applied to the water column of each designated microcosm. One hundred and twenty days after treatment (DAT), bispyribac, dichlobenil and glyphosate proved ineffective with biomass reductions of less than 40%. The higher application rates of triclopyr, flumioxazin, endothal and diquat gave >90% biomass reductions of bog moss at 120 DAT. Regrowth occurred in at least one replicate regardless of herbicide, indicating multiple applications may be necessary to provide longer term plant control. Future research should identify effective rates for triclopyr, endothal, imazapyr, metsulfuron, flumioxazin, carfentrazone, diquat + guar gum and possible timing of applications to maximise treatment efficacy.