Optimizing Benzobicyclon Efficacy in Drill-Seeded Rice

The repetitive use of the same herbicide sites of action in U.S. rice has led to the evolution of resistance in several weeds. Growers need to integrate multiple sites of action by mixing herbicides for effective weed control. Benzobicyclon is being developed as a post-flood herbicide for U.S. rice. As a Group 27 herbicide, benzobicyclon will offer a new site of action to rice producers in the U.S. Research was conducted in 2015 and 2016 to evaluate benzobicyclon efficacy based on weed size at application, flood depth, weed spectrum, tank mix with post-flood herbicides, and use rate. The greatest efficacy with benzobicyclon often occurred when applied to small weeds in a 15 cm flood depth. Barnyardgrass control with benzobicyclon was greater at 371 g ha-1 than at 247 g ha-1. Amazon sprangletop and acetolactate synthase-resistant rice flats edge were controlled completely with benzobicyclon at 247 g ha-1 at the early timing at both 5 cm and 15 cm flood depths. The addition of benzobicyclon at 247 g ha-1 to post-flood herbicides generally increased barnyardgrass and sprangletop spp. control. Benzobicyclon at 247 g ha-1 added to halosulfuron at 53 g ha-1 increased barnyardgrass control. The addition of benzobicyclon at 247 g ha-1 to other post-flood herbicides such as halosulfuron at 53 g ha-1, imazamox at 45 g ha-1, and cyhalofop 280 g ha-1 increased red sprangletop and Amazon sprangletop control (>90%). The addition of benzobicyclon to post-flood herbicides will broaden and improve the spectrum of weed control in US rice.