The Impact of Herbicide Application and Defoliation on Barley Grass (Hordeum murinum subsp. glaucum) Management in Mixed Pasture Legumes

Allison Chambers,William Brown,Jane Kelly,Wayne Robinson,John Broster,Leslie Weston,Paul Weston

doi:10.3390/agronomy10050671

Abstract

Barley grass (Hordeum murinum subsp. glaucum.) is an annual weed associated with grain revenue loss and sheep carcass damage in southern Australia. Increasing herbicide resistance led to a recent investigation into effective integrated weed management strategies for barley grass in southern Australia. Field studies in Wagga Wagga, New South Wales (NSW) during 2016 and 2017 examined the effect of post-emergent herbicide applications and strategic defoliation by mowing on barley grass survival and seed production in a mixed legume pasture. Statistically significant differences between herbicide-only treatments in both years showed propaquizafop to be more than 98% effective in reducing barley grass survival and seed production. Paraquat was not effective in controlling barley grass (58% efficacy), but led to a 36% and 63.5% decrease in clover and other weed biomass, respectively, after 12 months and increased lucerne biomass by over three-fold after 24 months. A single repeated mowing treatment resulted in a 46% decline in barley grass seedling emergence after 12 months and, when integrated with herbicide applications, reduced other weed biomass after 24 months by 95%. Resistance to acetyl-CoA carboxylase (ACCase)-inhibiting herbicides observed in local barley grass populations led to additional and more focused investigation comparing the efficacy of other pre- and post-emergent herbicides for barley grass management in legume pastures. Haloxyfop-R + simazine or paraquat, applied at early tillering stage, were most efficacious in reducing barley grass survival and fecundity. Impact of defoliation timing and frequency on barley grass seedlings was also evaluated at various population densities, highlighting the efficacy of repeated post-inflorescence defoliations in reducing plant survival and seed production. Results highlight the importance of optimal environmental conditions and application timing in achieving efficacious control of barley grass and improving pasture growth and biomass accumulation.

Highlights

IntroductionReduced fertiliser use [5,6,7], the prevalence of soil acidity [8], continuous grazing, and drought conditions over time led to a decline in legume productivity across southern Australia [1,9]
Lucerne (Medicago sativa) is the most widely grown perennial pasture legume in southern Australia [1], supplying a livestock feed source [2,3], facilitating the high growth rates and carcass weights desired by prime lamb markets [4], and often the only quality forage available in dry seasons.Agronomy 2020, 10, 671; doi:10.3390/agronomy10050671 www.mdpi.com/journal/agronomyReduced fertiliser use [5,6,7], the prevalence of soil acidity [8], continuous grazing, and drought conditions over time led to a decline in legume productivity across southern Australia [1,9]
Significant differences in barley grass seedling emergence counts (F = 8.2, df = 2, 8; p < 0.001) due to mowing alone were noted after 12 months (Figure 2)

Summary

Introduction

Reduced fertiliser use [5,6,7], the prevalence of soil acidity [8], continuous grazing, and drought conditions over time led to a decline in legume productivity across southern Australia [1,9]. The propagules and seeds produced by some grasses are problematic to livestock producers, due to their lodgement within animal tissue causing significant carcass damage and further welfare, production, and economic impacts at the farm and processing level [12]. Given the recent upward trend in Australian sheep meat prices [13], carcass damage due to grass seed penetration continues to pose significant challenges to the profitability of the Australian sheep industry.

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Discussion

Conclusion