Limpograss (Hemarthria altissima) Tolerance to Hexazinone

Field trials were conducted in 2013 and 2014 to investigate the tolerance of limpograss to increasing rates of hexazinone. Dose-response curves were generated using linear and quadratic regression models to determine the hexazinone estimated dose (ED) required to provide 10% (ED10) and 20% (ED20) of visual injury and herbage mass reduction. The ED10and ED20for visual estimates of injury were estimated to be 0.05 and 0.14 kg ai ha-1at 60 d after treatment (DAT). Regarding forage herbage mass reduction, the ED10and ED20were estimated to be 0.07 and 0.19 kg ai ha-1in 2013, whereas in 2014, the ED10and ED20were estimated to be 0.03 and 0.06 kg ai ha-1, respectively. The significant difference in herbage mass reduction between 2013 and 2014 was likely due to rainfall patterns, which possibly promoted hexazinone leaching in 2013 and consequently, less activity. Overall, hexazinone resulted in high degrees of limpograss injury across all response variables in both years; therefore, smutgrass control in limpograss pastures with hexazinone may not be a viable option. The presence or absence of smutgrass should be considered before limpograss establishment as there is no viable herbicide to selectively remove smutgrass from limpograss swards.