Abstract
AbstractBenzobicyclon 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.
Highlights
In the United States from 2006 to 2017, rice was planted on an average of 1.16 million ha, 75% of which was located in the Midsouth (Arkansas, Louisiana, Missouri, and Mississippi) (USDANASS 2018)
Barnyardgrass seeds were obtained from Azlin Seed Service (Leland, MS); Amazon sprangletop seeds were collected from field plots at the Rice Research and Extension Center near Stuttgart, AR; and the weedy rice seed was a subsample of multiple accessions known to be susceptible to benzobicyclon (Young et al 2018a)
Plant dry weights of weedy rice, Amazon sprangletop, and barnyardgrass were reduced by 78%, 77%, and 68%, respectively, when benzobicyclon was applied simultaneously to foliage and flood water (Table 1)
Summary
In the United States from 2006 to 2017, rice was planted on an average of 1.16 million ha, 75% of which was located in the Midsouth (Arkansas, Louisiana, Missouri, and Mississippi) (USDANASS 2018). The second experiment focused on the efficacy of benzobicyclon (371 g ha−1) applied with or without adjuvants to foliage and flood water simultaneously. Benzobicyclon (371 g ha−1) was selectively applied to flood water and/or plant foliage where, under our experimental setup, we assumed benzobicyclon and the hydrolysate active form were available for uptake only via the deposition method.
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