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 Sporobolus indicus var. pyramidalis control, and the impacts of application timing and rates on Sporobolus 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, where main plots were application timings at one-week 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 DAT. 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.