Fluridone use in furrow-irrigated rice: Palmer amaranth control and crop response

Abstract Rice cultivated under furrow irrigation faces weed management challenges due to the aerobic conditions that favor the emergence of terrestrial weeds such as Palmer amaranth. Fluridone was recently registered for use in rice production, offering an alternative site of action for Palmer amaranth control. Four site-years of field experiments were conducted in 2022 and 2023 in furrow-irrigated rice to assess Palmer amaranth control and crop tolerance to fluridone applied preemergence alone or with various postemergence treatments. The experiment was a randomized complete block design with a split-plot arrangement and four replications. The whole-plot factor was the postemergence treatment, while the subplot factor was fluridone applied preemergence at 0, 84, 168 (1× labeled rate), and 336 g ai ha −1 . Postemergence treatments included no herbicide, a single florpyrauxifen-benzyl application at 6 wk after rice emergence(WAE), and a weed-free control. The 2× rate of fluridone caused the greatest visual injury compared with the 0.5× rate across site-years at 2 and 5 WAE, ranging from 8% to 34%. The 1× and 2× rates of fluridone provided the greatest reduction in Palmer amaranth density 4 wk after treatment (WAT). However, the effect diminished or became less prominent by 8 WAT. Palmer amaranth density at rice harvest was reduced in most instances after a follow-up application of florpyrauxifen-benzyl, and seed production had diminished by ≥94% compared to its absence. Regardless of the fluoridone rate, rough rice grain yield was not affected under weed-free conditions. These findings suggest that integrating fluridone with a subsequent florpyrauxifen-benzyl application enhances Palmer amaranth management in furrow-irrigated rice compared to using fluridone alone. However, sequential applications are needed for successful Palmer amaranth control.