Spray deposition, adjuvants, and physiochemical properties affect benzobicyclon efficacy

Abstract

Benzobicyclon is a new pro-herbicide being evaluated in the Midsouth United States as a post-flood weed control option in rice. Applications of benzobicyclon to flooded rice are necessary for efficacious herbicide activity, but why this is so remains unknown. Two greenhouse experiments were conducted to explore how herbicide placement (foliage only, flood water only, foliage and flood water simultaneously) and adjuvants (nonionic surfactant, crop oil concentrate, and methylated seed oil [MSO]) affect herbicide activity. The first experiment focused on importance of herbicide placement. Little to no herbicidal activity (<18% visual control) was observed on two- to four-leaf barnyardgrass, Amazon sprangletop, and benzobicyclon-susceptible weedy rice with benzobicyclon treatments applied to weed foliage only. In contrast, applications made only to the flood water accounted for >82% of the weed control and biomass reduction achieved when benzobicyclon was applied to flood water and foliage simultaneously. The second experiment concentrated on adjuvant type and benzobicyclon efficacy when applied to foliage and flood water simultaneously. At 28 days after treatment, benzobicyclon alone at 371 g ai ha−1 provided 29% and 67% control of three- to five-leaf barnyardgrass and Amazon sprangletop, respectively. The inclusion of any adjuvant significantly increased control, with MSO providing near-complete control of barnyardgrass and Amazon sprangletop. Furthermore, we used the physiochemical properties of benzobicyclon and benzobicyclon hydrolysate to derive theories to explain the complex activity of benzobicyclon observed in our study and in field trials. Benzobicyclon applications should contain an oil-based adjuvant and must be applied to flooded rice fields for optimal activity.

Benzobicyclon efficacy is affected by plant growth stage, HPPD Inhibitor Sensitive 1 (HIS1) expression and zygosity in weedy rice (Oryza sativa)

“…Benzobicyclon was applied at 0, 23, 46, 93, 185, 371 (1×), 742, and 1,484 g ha −1 . Methylated seed oil (MSO; Leci-Tech, Loveland Products, Loveland, CO, USA) was added to all treatments at 1% v/v to optimize performance of the herbicide (Brabham et al 2019). Treatments were applied using a research track sprayer equipped with two 1100067 flat-fan nozzles and calibrated to delivered 187 L ha −1 .…”

“…Expression in roots was not investigated, because previous research (Maeda et al 2019) as well as findings in our pilot study (data not shown) indicated HIS1 expression in roots is minimal. Higher expression in the whorl is favorable, because benzobicyclon hydrolysate has ideal physicochemical properties for phloem mobility (Brabham et al 2019).…”

Rice tolerance to multiple applications of florpyrauxifen‐benzyl alone and followed by benzobicyclon

“…& Schltdl.) (Brabham et al., 2019; McKnight et al., 2018). Hydrolysis of benzobicyclon in water is necessary to provide sufficient weed control, as evident by foliar applications providing 1% weedy rice control, whereas treatment of both foliage and water can increase control to 88% (Brabham et al., 2019).…”

Migration behavior of benzobicyclon hydrolysate and associated influencing factors in different agricultural soils

“…This herbicide inhibits the activity of p-hydroxyphenylpyruvate dioxidase and affects the synthesis of plastoquinone, thereby influencing the biosynthesis of carotenoids and causing leaves chlorosis (Van Almsick 2009). Owing to its broad spectrum and high activity, BZB has been widely used to control annual weeds, sedges, gramineous weeds, and broadleaf weeds in paddy fields globally (Brabham et al 2019, McKnight et al 2018. As a pro-herbicide, BZB itself is inactive, but is rapidly hydrolyzed in flooded paddy fields to become its active form with herbicidal activity, benzobicyclon hydrolysate (BH) (Williams &Tjeerdema 2016).…”