Evaluation of fluazifop-P-butyl and sethoxydim for Hymenachne amplexicaulis control in mixed and monotypic emergent plant communities

摘要

West Indian marsh grass, Hymenachne amplexicaulis, is an invasive grass species that forms monotypic stands in Florida's freshwater marshes. It is typically managed using broad-spectrum herbicides that can have significant non-target impacts. Grass-specific herbicides (graminicides), sethoxydim and fluazifop-P-butyl, represent an opportunity to control H. amplexicaulis and reduce nontarget impacts. Plots were established in a monotypic H. amplexicaulis stand in November 2017 by applying fluazifop-P-butyl at 0.42 or 1.12 kg ha~(-1) or sethoxydim at 5.04 kg ha~(-1) each with MSO at 1 % v/v. Both graminicides significantly reduced H. amplexicaulis cover by 85% to 90% at 6 mo after initial treatment (MAT1), but by 9 MAT1, this control fell to 52 to 68%when compared to nontreated plots. Plots were retreated with the same herbicide treatments in August 2018 to assess longer-term efficacy. At 11 mo after second treatment (20 MAT1), graminicides reduced H. amplexicaulis cover by 75 to 88% and increased plant diversity, measured by Simpson's Diversity Index (D), compared to nontreated plots. At a second site with low H. amplexicaulis cover (3%), the same treatments maintained low H. amplexicaulis cover but did not eliminate the plant. D was not impacted by these graminicides, and there were few differences in D when treated and nontreated plots were compared by functional groups including monocotyledonous nongraminoid, dicotyledonous, and graminoid plants. Few differences emerged in functional groups between herbicide-treated and non-treated control plots. Functional groups were not affected by graminicide treatment over time beyond seasonality of examined species. These studies indicate both graminicides may be effective in controlling West Indian marsh grass while maintaining or improving plant diversity.