Effectiveness of Three Postemergence Herbicides in Controlling an Invasive Annual Grass, Microstegium vimineum

Effective control of Nepalese browntop (Microstegium vimineum) is important to land managers in the eastern United States because invasions can suppress native vegetation, thus decreasing vegetation diversity and habitat quality for many wildlife species. We evaluated the effectiveness of herbicides with varying selectivity (glyphosate, imazapic, and clethodim) at full rates and half rates (based on labeled rates for annual grass control) on the control of japangrass and their effects on non-target vegetation. We conducted our experiment in three forested areas in east Tennessee. We measured species coverage using point transects before treatment, 60 days after treatment (60DAT), and one year after treatment (1YAT). Japangrass coverage 60DAT was similar for all six treatments (0%-8%), but differed from coverage in control plots (83%). The coverage of japangrass in all treatments was less than control plots 1YAT (10%-35% vs. 68%). However, full rates of glyphosate (2qt/ac) and imazapic (8oz/ac) were most effective in controlling japangrass 1YAT (17% and 10%, respectively). Percent coverage of non-target vegetation 60DAT and 1YAT were similar among the treatment and control plots. Our results suggest full rates of glyphosate and imazapic are the most effective postemergence options to control japangrass. Multiple applications should be evaluated across years and sites to gain a better understanding of the long-term effects of herbicide applications.

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