Control of West Indian marsh grass with glyphosate and imazapyr

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West Indian marsh grass (Hymenachne amplexicaulis [Rudge] Nees), hereafter referred to as WIMG, is a non-native invasive species present in at least 14 counties of central and south Florida. This perennial grass species out-competes native vegetation and is capable of rapid spread by both seeds and vegetative tissue. Experiments were conducted to determine the optimal timing and herbicide strategy for WIMG in natural areas and to determine the effect of water depth on WIMG control with herbicides. Glyphosate (N-(phosphonomethyl) glycine) at 4.2 kg ai/ha, imazapyr (2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1-H- imidazol-2-yl]-3-pyridinecarboxylic acid) at 1.1 and 1.7 kg ai/ha, and glyphosate + imazapyr at 4.2 + 1.1 kg ai/ha provided at least 90% control 3 months after treatment (MAT) at Myakka River State Park and the St. John's River. However, by 6 MAT regrowth of WIMG resulted in only 70% control with glyphosate alone, which was significantly lower than all other treatments. Although timing did not have an impact on WIMG control, it did appear to have some impact on reestablishment of native species. The reestablishment of native species may have been impacted more by the extreme drought conditions following the fall application in 2006. Water depth does not appear to influence control of WIMG with these herbicides. Regardless of water depth, glyphosate + imazapyr reduced WIMG biomass by as much as 97% compared to the untreated control. These data indicate that excellent control of WIMG can be obtained using glyphosate, imazapyr, or a tank-mix of these herbicides at any time during the growing season.

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Journal of Aquatic Plant Management

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