Tolerance of Southern US Rice Cultivars to Benzobicyclon

Abstract

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 19tropical japonica(inbred and hybrid) and twoindicainbred cultivars to a premix containing benzobicyclon at 494 g ai ha-1and halosulfuron at 72 g ai ha-1 applied 1 week after flooding. Thetropical japonicacultivars have excellent crop safety to benzobicyclon while application to theindicacultivars, Rondo and Purple Marker, expressed severe phytotoxicity. Benzobicyclon caused less than a 2 d delay in heading to thejaponicacultivars. Rough rice yield of thetropical japonicacultivars was not affected by benzobicyclon while yields of bothindicacultivars were negatively affected. Benzobicyclon can safely be applied to drill-seededtropical japonicainbred and hybrid cultivars in a post-flood application without concerns for crop injury. Benzobicyclon should not be used onindicacultivars as it will cause severe injury, delayed heading, and yield loss.