Agronomic surveys of summer weed species are necessary to identify future research directions for optimal weed control, but usually focus on agricultural fields in a single season. To survey all species in the absence of weed control measures and determine species variability between seasons, a survey of 133 sites was conducted on roadsides adjoining agricultural fields throughout the Western Australian grainbelt in early 2015 and repeated in 2016 and 2017. The survey identified 144 species, but only 19 species were evident at more than 10% of sites. The most common species were weeping lovegrass [Eragrostis curvula (Schrad.) Nees], fleabane (Erigeron sp.), windmillgrass (Chloris truncata R. Br.), and wild radish (Raphanus raphanistrum L). The survey highlighted that weed species incidence varied between years. For example, C. truncata incidence was 30% in 2015 and 55% in 2016, while stinkgrass [Eragrostis cilianensis (All.) Vignolo ex Janch.] ranged from 20% in 2015 to 50% of sites in 2017. Conversely, density of individual species on the roadside was usually low, and density remained consistent between years. The survey highlighted multiple weed species that will require further research to optimize management programs. Raphanus raphanistrum and wild oat (Avena fatua L.) in particular are an issue for growers, as these species are highly detrimental winter weeds, and the survey demonstrates that they can also be common summer weeds. Control of these species with nonselective herbicides in summer as well as winter is likely to exacerbate the development of herbicide resistance.
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Vol. 67 • No. 5