The Rest of the Story: Three Years of Research With “Natural” Herbicides and Aquatic Plants

The 2019 Florida Fish and Wildlife Conservation Commission (FWC) “pause” in herbicidal aquatic weed control spurred interest in evaluating the efficacy and selectivity of alternative products for invasive species management in aquatic systems. We investigated the activity of a range of concentrations of acetic acid, d-limonene and combinations of the two products after foliar applications to selected invasive floating and native emergent plants. Plants were co-cultured in 68L mesocosms until floating plant coverage was > 80%, then treated once with a single product or combination (plus surfactant). Four replicates were prepared for each treatment and all plants were maintained for 8 weeks after treatment. Plants were then evaluated for visual quality, destructively harvested and placed in a forced-air drying oven for 2 weeks to determine reduction in biomass compared to untreated control (UTC) plants. In most cases, native emergent plants were not seriously damaged by treatments. Floating invasive species were adequately controlled (>80% reduction in biomass) by some treatments. However, these treatments are not yet labeled for aquatic use and deployment of these treatments at scale would result in a 16-fold to 47-fold increase in material costs alone. These data reveal that alternative products may be useful for aquatic weed management but more research – including field trials – is necessary to confirm these results.