Evaluation of Residual Herbicides Across Multiple Rice Production Systems

A field study was conducted in 2019, 2020, and 2021 at the LSU Agricultural Center H. Rouse Caffey Rice Research Station (RRS) near Crowley, LA. to evaluate the crop safety and potential weed control of very long chain fatty acid (VLCFA) inhibiting herbicides in Louisiana rice production. The study evaluated the use of acetochlor, dimethenamid, s-metolachlor, and pyroxasulfone applied preemergence (PRE), delayed PRE (DPRE), and the two- to three- leaf, early postemergence (EPOST) rice growth stage. In general, rice injury decreased as application timing was delayed with the least amount of rice injury occurring when the VLCFA inhibiting herbicides were applied EPOST. However, barnyardgrass and red rice control also decreased as the application timing was delayed from PRE to EPOST. A field study was conducted in 2020 and 2021 at the RRS to evaluate the use of graminicide PRE in acetyl Co-enzyme A carboxylase (ACCase) resistant rice. Quizalofop, clethodim, pinoxaden, fluazifop, and sethoxydim were evaluated for crop injury and grass weed control in ACCase-resistant rice. No herbicide evaluated injured rice at an unacceptable level with injury from 2 to 4%. Results from this study suggest that the ACCase inhibiting herbicides do have some residual activity on barnyardgrass and red rice; however, from 14 d after treatment (DAT) to 21 DAT the residual activity decreased significantly. Of the herbicides evaluated, these results suggest that ACCase herbicides within the aryloxyphenoxypropionate family appear to have more residual activity than ACCase herbicides in the cyclohexanedione or phenylpyrazolin families. Two separate field studies were evaluated in 2021 at two locations on the RRS to evaluate early season applications of florpyrauxifen and a prepackaged mixture of halosulfuron plus prosulfuron in water-seeded rice production. In each study florpyrauxifen and halosulfuron were applied at two rates and applied to the soil surface 48-hours prior to the seeding flooding and seeding (SURFACE), directly onto the pregerminated seed 24-hours following seeding and immediately after removal of the seeding flood (SEED), and at pegging (PEG). Data suggests that both florpyrauxifen and halosulfuron plus prosulfuron have a fit in water-seeded rice production. Due to crop injury, both herbicides should be avoided when the pregerminated seed is exposed on the soil surface following the removal of the seeding flood. These data suggest that florpyrauxifen may be a better POST option, whereas halosulfuron plus prosulfuron may be a better PRE option in water-seeded rice production