Weedy Rice Control When Using Single and Sequential Applications of Oxyfluorfen.

Weedy rice in Arkansas is resistant to HRAC/WSSA group 1 and 2 herbicides that are commonly used for control. The ROXY® Rice Production System (RRPS) provides tolerance to herbicides containing oxyfluorfen. Oxyfluorfen is a Herbicide Resistance Action Committee/Weed Science Society of America (HRAC/WSSA) group 14 herbicide labeled for preemergence (PRE) and postemergence (POST) applications in many crops. Oxyfluorfen currently is not labeled for use in rice; however, the Roxy trait in the RRPS allows for applications of the herbicide. During the 2021 and 2022 growing seasons, two independent field trials were conducted at the University of Arkansas System Division of Agriculture's Rice Research and Extension Center near Stuttgart, Ark. The first experiment was designed to determine if there was a rate response for weedy rice control associated with oxyfluorfen applied POST at the 2-leaf growth stage of weedy rice. The second experiment was designed to determine the optimal rate of oxyfluorfen to use PRE and POST in a sequential program when the maximum annual rate could not exceed 1.5 lb ai/ac. For the rate response experiment, oxyfluorfen (ALB2024) was POST-applied at 0.5, 0.75, 1, 1.25, or 1.5 lb ai/ac when the weedy rice reached the 2-leaf growth stage. In the sequential application experiment, mixtures of clomazone and oxyfluorfen (ALB2023) (0.3 plus 0.5, 0.75, or 1 lb ai/ac, respectively) were applied PRE, followed by a POST application of oxyfluorfen that resulted in the total amount of the herbicide applied being 1.5 lb ai/ac. Weedy rice control for all treatments ranged from 57 to 73% for the rate response experiment at 35 days after treatment. In the sequential application experiment, oxyfluorfen applied PRE resulted in 46 and 70% weedy rice control at the lowest (0.5 lb ai/ac) and highest (1 lb ai/ac) oxyfluorfen rates, respectively. At 14 days after the final treatment, 78 to 81% weedy rice control was observed for all treatments when oxyfluorfen was applied sequentially. Oxyfluorfen could potentially serve to suppress weedy rice in a RRPS; however, oxyfluorfen alone will not be able to achieve complete control. [ABSTRACT FROM AUTHOR]