Effect of rice leaf stage on tolerance to benzobicyclon in a drill‐seeded production system

Abstract

AbstractBenzobicyclon is a new postflood‐applied herbicide that was registered for use in U.S. rice (Oryza sativa L.) in 2021 by Gowan Company. Therefore, research was conducted to evaluate tolerance of commonly grown rice cultivars to benzobicyclon. In 2018 and 2019, field experiments were conducted near Stuttgart, AR to evaluate the influence of growth stage on rice tolerance to benzobicyclon, and to evaluate pure line and hybrid rice tolerance to benzobicyclon following repeated use of acetolactate synthase‐inhibiting herbicides. In one of two years, rice growth stage (leaf number) at application impacted tolerance to benzobicyclon. In 2018, the two‐leaf application of benzobicyclon was generally more injurious to the rice cultivars, ‘CL153’, ‘Diamond’, ‘PVL01’, and ‘CLXL745’ than when applied at four‐leaf or tillering growth stages. In the second year, all rice cultivars, except ‘Rondo’, were not injured by benzobicyclon applied at any growth stage. In both years, benzobicyclon applied to indica rice cultivar Rondo elicited ≥97% crop injury, regardless of application timing. Findings from these experiments suggest that rice cultivar tolerance can vary across environments and that smaller‐sized rice could be more prone to injury than when applications occur at a typical timing for a postflood‐applied herbicide. In general, four‐leaf and tillering rice will exhibit sufficient tolerance to benzobicyclon. It is especially not recommended to apply benzobicyclon on rice cultivars that have a predominant indica‐type genealogical background. Benzobicyclon following repeated applications of acetolactate synthase‐inhibiting herbicides to the pure line cultivar CL153 and the hybrid cultivar CLXL745 did not pose increased risk for injury to rice.