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Investigation of Reduced Herbicide Rates and Tank Mixes Applied Via Submersed Injection for the Selective Control of Cuban Bulrush (Oxycaryum cubense)
Proceedings of the 2020 Mississippi Water Resources Conference

Year: 2020 Authors: Turnage G., Byrd J.

Cuban bulrush (Oxycaryum cubense) is a perennial invasive aquatic plant species native to South America that is spreading across the Southeastern US. Cuban bulrush can block boat launches, impede navigation along river channels, negatively affect drainage canals, and degrade fishery habitat by lowering dissolved oxygen under plant mats. Cuban bulrush is capable of outcompeting and displacing native and other invasive species for resources thereby disrupting ecosystem processes. During initial colonization, it exists as an epiphytic species utilizing other aquatic plants or structures for habitat. Limited data exist concerning effective chemical control (herbicides) methods for controlling Cuban bulrush. This project was conducted over two years to 1) screen potential herbicides for selective control of Cuban bulrush (year 1) and 2) investigate tank mixtures of herbicides active on Cuban bulrush for selective control (year 2). In year 1, herbicides were identified that provided short-term selective control of Cuban bulrush grown with American lotus; herbicides were applied at the maximum rate allowed. No herbicide provided long term reduction of Cuban bulrush or American lotus. In year 2, reduced rates (half the maximum label rate) and tank mixtures of two systemic (triclopyr and fluridone) and two contact (flumioxazin and carfentrazone-ethyl) herbicides from year 1 were examined for control of Cuban bulrush and two native plant species, cattail and hardstem bulrush. Emergent Cuban bulrush was reduced 92% by triclopyr, 88% by carfentrazone-ethyl, 100% by triclopyr+flumioxazin, and 100% by triclopyr+carfentrazone-ethyl when compared to reference plants at 8 weeks after treatment (WAT). At 44 WAT, all treatments deliver greater than 94% control of Cuban bulrush compared to reference plants. Submersed Cuban bulrush was reduced 86% by triclopyr and 93% by triclopyr+flumioxazin when compared to reference plants at 8 WAT. At 44 WAT, all treatments delivered greater than 93% control of Cuban bulrush when compared to reference plants. In year two, herbicides did not reduce biomass of native plants at eight weeks after treatment (WAT). Hardstem bulrush was not affected by herbicide treatments at 44 WAT while cattail biomass was reduced by multiple treatments. These data suggest that triclopyr alone and in combination with flumioxazin can selectively control both emergent and submersed Cuban bulrush tissues over the short-term, but any herbicide or herbicide combination used here can deliver long term control. These treatments provided selective long-term control of Cuban bulrush when growing with American lotus and hardstem bulrush but not cattail.

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