Jointed goatgrass (Aegilops cylindrica): A Review

Abstract

In 1994, the National Jointed Goatgrass Research Program was initiated with funding from a special USDA grant. The 15-yr program provided $4.1 million to support jointed goatgrass (Aegilops cylindricaHost.) research and technology transfer projects in 10 western states. These projects resulted in approximately 80 refereed manuscripts, including journal articles and extension publications. The research covered various topics related to the biology and ecology of jointed goatgrass as well as its management and control in wheat (Triticum aestivumL.) production systems. This review summarizes the research on jointed goatgrass published after Donald and Ogg’s 1991 review, most of which was conducted as part of the USDA-funded National Jointed Goatgrass Research Program. Specific topics that were studied and reviewed here includeA. cylindricagenetics, especially as it relates to gene flow and hybridization rates with wheat and fertility of the resulting hybrids; vernalization requirements; seed dormancy, longevity, and germination requirements; competitiveness with wheat; and herbicide resistance acquired through evolution or gene flow from wheat. With respect to management, a wide variety of practices were evaluated, including various tillage types and frequencies; crop rotations, especially diversified wheat production systems that include spring-seeded annual crops; competitive wheat cultivars, seeding dates, seeding density, and row spacing; fertility management, including nitrogen application timing and placement; and field burning. Finally, many studies evaluated the use of herbicides, especially the introduction of imazamox in imidazolinone-resistant wheat cultivars, as well as comparison of adjuvant systems and application timings. In addition to the many management practices that were studied individually, several integrated management systems were evaluated that combined crop rotations, tillage, and herbicide programs. Between 1993 and 2013, weed scientists in 14 western states estimated that jointed goatgrass infestations decreased by 45% to 55% and attributed the reduction to the implementation of more diverse crop rotations, improved cultural practices, and use of imazamox-resistant wheat technology. This is evidence that the practical implications of the National Jointed Goatgrass Research Program have been successfully implemented by growers throughout the western United States.

Winter annual grass control and crop safety in quizalofop‐resistant wheat cultivars

“…To address the inconsistency in feral rye control with imazamox, cultivars with two homoeologous mutations for imazamox resistance (e.g., Haley et al., 2012) were introduced to improve feral rye control using higher imazamox rates with methylated seed oil (MSO) as an adjuvant (Nakka et al., 2019). Jointed goatgrass infestations across the western US were estimated to have dropped from 45 to 55% due to implementation of crop rotations and use of imazamox‐resistant wheat with imazamox (Mallory‐Smith et al., 2018).…”

Seed retention of winter annual grass weeds at winter wheat harvest maturity shows potential for harvest weed seed control

“…POST herbicides are at a high risk for resistance evolution due to their frequent use in these cropping systems. Currently, no cases of herbicide resistance in Colorado have been reported for downy brome, feral rye, or jointed goatgrass (Heap 2019); however, downy brome and jointed goatgrass imazamox resistance cases were reported in Montana and Washington, respectively (Kumar and Jha 2017;Mallory-Smith et al 2018). A modelling study considering an integrated management approach (e.g., PRE, POST, and HWSC) indicated the frequency of resistance alleles could be eliminated or greatly reduced in weed populations and that weed density decreased to two plants m −2 (Somerville et al 2018).…”

“…An additional threat posed by jointed goatgrass is the potential to hybridize with wheat. 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).…”

An ALA122THR substitution in the AHAS/ALS gene confers imazamox‐resistance in Aegilops cylindrica

“…cylindrica infestations are found in 3 million hectares of land and can reduce yield by up to 25% in dense populations, resulting in an estimated economic cost of $145 million per year 3 . It is well adapted to reduced tillage systems, and can be found infesting winter wheat‐fallow rotations throughout the western United States 2,3 . In winter wheat, there are very limited herbicide options for Ae.…”

“…Since the development of IMI‐resistant winter wheat and the use of imazamox, the technology has become the primary method growers use to manage Ae. cylindrica in winter wheat 3 …”