<i>Sporobolus indicus</i> var. <i>pyramidalis</i> management in response to hexazinone rates, rainfall, and application timing in Florida pasture systems

Abstract Rainfall is the main driving factor for soil-active herbicides, influencing their incorporation, leaching, and absorption. Studies were conducted to determine the effects of simulated rainfall and hexazinone application rates on giant smutgrass [ Sporobolus indicus (L.) R. Br. var. pyramidalis (P. Beauv.) Veldkamp] control and the impacts of application timing and rates on S. indicus var. pyramidalis in the field. Greenhouse experiments were established in Florida between 2017 and 2018, comprising hexazinone application rates of 0.56 and 1.12 kg ai ha −1 , and seven simulated rainfall accumulation volumes (0, 6, 12, 25, 50, 100, and 200 mm), distributed in a completely randomized design with four replicates and a non-treated control. Field experiments were conducted in a split-plot arrangement, wherein main plots were application timings at 1-wk intervals, subplots were two hexazinone application rates (0.56 and 1.12 kg ha −1 ) and a non-treated control, distributed in a randomized complete block design, with four replicates. In the greenhouse experiment, 49 and 92 mm were required to obtain 50% visual control and 35 and 82 mm to reduce biomass by 50% for hexazinone rates of 0.56 and 1.12 kg ai ha −1 , respectively. Field experiments showed that hexazinone peak efficacy was from mid-June to mid-August when applications were followed by 10 to 75 mm of rainfall during the first 7 d after treatment. The recommended rate of hexazinone at 1.12 kg ai ha −1 should be applied, as it has an extended window of optimum application timing.