Evaluation of Herbicide and Disking to Control Invasive Bluestems in a South Texas Coastal Prairie

Abstract

Conservation and restoration efforts of native grasslands are being hindered by invasive, exotic plants. Exotic bluestem grasses (Bothriochloa and Dichanthium spp.) have become increasingly invasive throughout the rangelands of the central and southern Great Plains, United States. Accordingly, the aim of this study was to evaluate the efficacy of glyphosate, imazapyr, and imazapyr + glyphosate treatments with or without disking to remove exotic bluestems from a south Texas coastal prairie. We evaluated three different control regimens: 1) herbicide treatments only, 2) herbicide treatments followed by two diskings (H + D), and 3) disking followed by herbicide treatments (D + H). Percent exotic bluestem, native grass, and forb cover were visually estimated at 0 (pre-treatment: May 2006), 20, 52, and 104 wk after treatment (WAT). The herbicide-only and H+D regimens were ineffective at controlling exotic bluestems. However, exotic bluestem cover in herbicide-treated plots of the D+H regimen was significantly lower (P#0.05) compared to control plots and most treatment plots of the herbicide-only and H+D
regimens up to 52 WAT. Control regimens did not notably facilitate an increase in native grass cover from pre-treatment levels, but native grass cover remained the highest, and increased the most, in some imazapyr-treated plots of the herbicide-only and D+H regimens, respectively. In the H+D and D+H regimens, disking resulted in a flush of forb cover (up to 50%) at 52 WAT; yet forb cover was #5% in these plots by 104 WAT. Exotic bluestem cover recovered back to, or was greater than, pretreatment levels among most treatment plots across all three control regimens at 104 WAT. This study suggests that follow-up control measures are needed to suppress the re-invasion of exotic bluestems after initial control efforts. Additional studies are needed to evaluate other strategies to control exotic bluestems in rangelands of the central and southern United States.