Abstract
AbstractDowny brome, feral rye, and jointed goatgrass are problematic winter annual grasses in central Great Plains winter wheat production. Integrated control strategies are needed to manage winter annual grasses and reduce selection pressure exerted on these weed populations by the limited herbicide options currently available. Harvest weed-seed control (HWSC) methods aim to remove or destroy weed seeds, thereby reducing seed-bank enrichment at crop harvest. An added advantage is the potential to reduce herbicide-resistant weed seeds that are more likely to be present at harvest, thereby providing a nonchemical resistance-management strategy. Our objective was to assess the potential for HWSC of winter annual grass weeds in winter wheat by measuring seed retention at harvest and destruction percentage in an impact mill. During 2015 and 2016, 40 wheat fields in eastern Colorado were sampled. Seed retention was quantified and compared per weed species by counting seed retained above the harvested fraction of the wheat upper canopy (15 cm and above), seed retained below 15 cm, and shattered seed on the soil surface at wheat harvest. A stand-mounted impact mill device was used to determine the percent seed destruction of grass weed species in processed wheat chaff. Averaged across both years, seed retention (±SE) was 75% ± 2.9%, 90% ± 1.7%, and 76% ± 4.3% for downy brome, feral rye, and jointed goatgrass, respectively. Seed retention was most variable for downy brome, because 59% of the samples had at least 75% seed retention, whereas the proportions for feral rye and jointed goatgrass samples with at least 75% seed retention were 93% and 70%, respectively. Weed seed destruction percentages were at least 98% for all three species. These results suggest HWSC could be implemented as an integrated strategy for winter annual grass management in central Great Plains winter wheat cropping systems.
Highlights
Weed control in wheat agroecosystems is imperative to prevent yield losses due to competition for light, nutrients, physical space, and water (Van Heemst 1985)
High densities of jointed goatgrass increase the risk of gene flow between these two species, leading to a potential for herbicide-resistance traits to transfer from wheat to jointed goatgrass (Donald and Ogg 1991; Gaines et al 2008; Hanson et al 2005; Mallory-Smith et al 2018; Zemetra et al 1998)
Selective POST herbicides available for feral rye and jointed goatgrass control in wheat are limited to imazamox (Tan et al 2005) (Group 2, Clearfield® wheat) and quizalofop-p-ethyl (Anonymous 2019; Ostlie et al 2015)
Summary
Weed control in wheat agroecosystems is imperative to prevent yield losses due to competition for light, nutrients, physical space, and water (Van Heemst 1985). Major winter annual grass weed species threatening wheat productivity in the western United States are downy brome, feral rye, and jointed goatgrass (Fleming et al 1988; Lyon and Baltensperger 1995). Feral rye densities at 40 plants m−2 and downy brome at 65 plants m−2 can cause 60% and 20% yield loss in winter wheat, respectively (Pester et al 2000; Stahlman and Miller 1990). The most common weed-control practices in wheat cropping systems are tillage, crop rotation, and herbicides (Daugovish et al 1999) Combining these strategies has substantially decreased winter annual grass densities and increased wheat yield (Lyon and Baltensperger 1995; Young et al 1994). Selective POST herbicides available for feral rye and jointed goatgrass control in wheat are limited to imazamox (Tan et al 2005) (Group 2, Clearfield® wheat) and quizalofop-p-ethyl (quizalofop) (Anonymous 2019; Ostlie et al 2015)
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