Gowan Company recently registered benzobicyclon, a WSSA Group 27 herbicide, as a postflood option in rice. It is the first 4-hydroxyphenylpyruvate dioxygenase-inhibiting herbicide commercially available in mid-southern U.S. rice production. In 2018 and 2019, field experiments were conducted across multiple sites in Arkansas to determine if the addition of benzobicyclon to quizalofop- or imidazolinone-resistant rice herbicide programs would improve weedy rice control. Across site-years, one application of quizalofop, either at the 1- or 3-leaf rice stage, followed by benzobicyclon applied postflood, provided comparable weedy rice control to two sequential applications of quizalofop, which is a standard herbicide program in quizalofop-resistant rice. Additionally, treatments containing quizalofop or quizalofop followed by benzobicyclon injured rice ≤5% at 28 d after the postflood application. Across site-years, at 28 d after the postflood application of benzobicyclon, all treatments containing a full-season herbicide program followed by benzobicyclon postflood provided comparable or improved weedy rice control when compared to two sequential early postemergence applications of imazethapyr. In both experiments, rice treated with benzobicyclon yielded comparably or better than treatments containing the standard herbicide program for each system. Findings from this research suggest that the use of benzobicyclon in quizalofop- and imidazolinone-resistant rice systems could be an additional and viable weedy rice control option for rice producers.

Information on performance of sequential treatments of quizalofop-P-ethyl with florpyrauxifen-benzyl on rice is lacking. Field studies were conducted in 2017 and 2018 in Stoneville, MS, to evaluate sequential timings of quizalofop-P-ethyl with florpyrauxifen-benzyl included in preflood treatments of rice. Quizalofop-P-ethyl treatments were no quizalofop-P-ethyl; sequential applications of quizalofop-P-ethyl at 120 g ha−1 followed by (fb) 120 g ai ha−1 applied to rice in the 2- to 3-leaf (EPOST) fb the 4-leaf to 1-tiller (LPOST) growth stages or LPOST fb 10 d after flooding (PTFLD); quizalofop-P-ethyl at 100 g ha−1 fb 139 g ha−1 EPOST fb LPOST or LPOST fb PTFLD; quizalofop-P-ethyl at 139 g ha−1 fb 100 g ha−1 EPOST fb LPOST and LPOST fb PTFLD; and quizalofop-P-ethyl at 85 g ha−1 fb 77 g ha−1 fb 77 g ha−1 EPOST fb LPOST fb PTFLD. Quizalofop-P-ethyl was applied alone and in mixture with florpyrauxifen-benzyl at 29 g ai ha−1 LPOST. Visible rice injury 14 d after PTFLD (DA-PTFLD) was no more than 3%. Visible control of volunteer rice (‘CL151’ and ‘Rex’) 7 DA-PTFLD was similar and at least 95% for each quizalofop-P-ethyl treatment. Barnyardgrass control with quizalofop-P-ethyl at 120 fb 120 g ha−1 LPOST fb PTFLD was greater (88%) in mixture with florpyrauxifen-benzyl. The addition of florpyrauxifen-benzyl to quizalofop-P-ethyl increased rough rice yield when quizalofop-P-ethyl was applied at 100 g ha−1 fb 139 g ha−1 EPOST fb LPOST. Sequential applications of quizalofop-P-ethyl at 120 g ha−1 fb 120 g ha−1 EPOST fb LPOST, 100 g ha−1 fb 139 g ha−1 EPOST fb LPOST, or 139 g ha−1 fb 100 g ha−1 EPOST fb LPOST controlled grass weed species. The addition of florpyrauxifen-benzyl was not beneficial for grass weed control. However, because quizalofop-P-ethyl does not control broadleaf weeds, florpyrauxifen-benzyl could provide broad-spectrum weed control in acetyl coenzyme A carboxylase–resistant rice.

Benzobicyclon is the first 4-hydroxyphenylpyruvate dioxygenase-inhibiting herbicide pursued for commercial registration in U.S. rice production. A study was conducted in 2015 and 2016 to evaluate the response of eight rice cultivars to post-flood application timings of benzobicyclon at 494 g ai ha-1 (proposed 2X rate). ‘Caffey’, ‘CL151’, ‘CLXL745’, ‘Jupiter’, ‘LaKast’, ‘Mermentau’, ‘Roy J’, and ‘XL753’ were evaluated in response to applications of benzobicyclon. The highest level of visible injury was observed in LaKast at 7% in 2015. No visible injury was detected among other cultivars either year at 2 weeks after treatment. In 2015 and 2016, no more than a four-day delay to reach 50% heading occurred across all cultivars. Rough rice yield was not affected by any of the post-flood application timings of benzobicyclon. A second study was conducted in 2016 at three locations throughout Arkansas to investigate the tolerance of 19 tropical japonica (inbred and hybrid) and two indica inbred cultivars to a premix containing benzobicyclon at 494 g ai ha-1 and halosulfuron at 72 g ai ha-1 applied 1 week after flooding. The tropical japonica cultivars have excellent crop safety to benzobicyclon while application to the indica cultivars, Rondo and Purple Marker, expressed severe phytotoxicity. Benzobicyclon caused less than a 2 d delay in heading to the japonica cultivars. Rough rice yield of the tropical japonica cultivars was not affected by benzobicyclon while yields of both indica cultivars were negatively affected. Benzobicyclon can safely be applied to drill-seeded tropical japonica inbred and hybrid cultivars in a post-flood application without concerns for crop injury. Benzobicyclon should not be used on indica cultivars as it will cause severe injury, delayed heading, and yield loss.

Rice cultivar, growth stage at application, or both may influence rice tolerance to quinclorac. Field studies were conducted to compare the response of five rice cultivars ‘Bowman’, ‘Cheniere’, ‘CL161’, ‘Cocodrie’, and ‘XL723’ to postflood quinclorac applications. Quinclorac at 0.56 kg ai ha−1 was applied 2 and 4 wk after flood (WAF). Pooled across quinclorac application timings, no differences in maturity were detected among the cultivars in 2008, but maturity of Cheniere and XL723 were delayed compared with CL161 and Cocodrie in 2007. Maturity of Cheniere and XL723 was delayed in 2007 compared with 2008. Pooled over cultivar, maturity was similar for 2 and 4 WAF applications in 2007 but was delayed for 2 WAF treatments in 2008. Regardless of year, postflood quinclorac applications reduced rough rice yield of all cultivars except Bowman. Cheniere and XL723 had lower rough rice yields compared with other cultivars in 2007; however, in 2008, rough rice yields of Cheniere, CL161, Cocodrie, and XL723 were similar, but still lower, than that of Bowman. Pooled over cultivar, postflood quinclorac reduced rough rice yields more when applied 4 WAF than at 2 WAF during both years. Our results demonstrate that Cheniere and XL723 are less tolerant than Bowman is to postflood quinclorac applications and that all evaluated cultivars are more susceptible to quinclorac applied at later developmental stages. Consequently, if circumstances necessitate a postflood quinclorac application, the herbicide should be applied no later than panicle initiation and should not be applied to Cheniere or XL723.