2019 ASHS Annual Conference

Florida’s waters are routinely invaded by new exotic plants. Two new invaders are redroot floater (Phyllanthus fluitans) and feathered mosquitofern (Azolla pinnata). Redroot floater, a dicot, was first reported in a Desoto County canal attached to the Peace River in 2010. Feathered mosquitofern, a true fern, was first collected in Florida’s waters in Palm Beach County in 2007. Despite their very different botanical classifications, both species can survive out of the water on damp soil, form floating dense mats and cause ecosystem harm by attenuating light and oxygen in the water column. They also interfere with boating, fishing and swimming. Current distribution of both species is primarily southern Florida, but range expansion is likely, so it is critical to identify control methods for these species. We evaluated efficacy of 35 foliar herbicide treatments (single aquatic herbicides or combinations of two herbicides) in greenhouse trials with four replicates per treatment. We applied treatments to robust populations of plants in 68L mesocosms and monitored them for 6 weeks after treatment, then recorded percent coverage and conducted a destructive harvest. Dried plant material was weighed to determine reduction in biomass compared to untreated controls (UTC). Twenty-nine of the 35 treatments reduced biomass and coverage of these species by 90% compared to UTC. Exceptions were 7.7 or 3.9 oz/acre fluridone, 8 oz/acre topramezone, 48 oz/acre glyphosate, and 8.6 or 13.5 oz/acre carfentrazone.