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The introduction of harvest weed seed control (HWSC) techniques and associated machinery has enabled the routine use of an alternative weed control technology at a novel weed control timing in global grain cropping fields. Driven by the significant threat of widespread populations of annual ryegrass (Lolium rigidum ) with multiple-herbicide resistance, in the 1990s Australian growers and researchers developed techniques to target, at grain harvest, the seed production of annual ryegrass and other important weed species. The HWSC approach to weed management is now routinely used by a majority of Australian grain producers as an integral component of effective weed control programs. Here we detail the development and introduction of current HWSC systems and describe their efficacy in Australian grain production systems. The use of HWSC has likely contributed to lower annual ryegrass population densities and thus mitigated the impacts of herbicide resistance as well as slowing further evolution of resistance. In addition, low weed densities enable the introduction of site-specific weed control technologies and the opportunity to target specific in-crop weeds with non-selective alternative weed control techniques. With an awareness of the evolutionary potential of weed species to adapt to all forms of weed control, there is an understanding that HWSC treatments need to be judiciously used in grain cropping systems to ensure their ongoing efficacy. The successful use of Australian developed HWSC systems has attracted global interest and there is now a considerable international research effort aimed at introducing this alternative weed control approach and timing into the world’s major cropping systems.

Avena is a problematic weed of cropping regions of southern Australia and many areas of the world. In 2010, a random survey was conducted across 14million hectares of the Western Australian grain belt to monitor the change in herbicide resistance levels by comparing resistance frequency results with a survey conducted in 2005. Screening Avena populations with herbicides commonly used to control this weed revealed that 48% of Avena populations displayed resistance to the commonly used acetyl-Co A carboxylase-inhibiting herbicides, which was lower than that found in 2005 (71%). The broad-spectrum herbicides glyphosate and paraquat provided good control of all Avena populations. Resistance to acetolactate synthase-inhibiting herbicides and to flamprop were detected for the first time in Western Australia in this survey. Therefore, a wide range of weed management options that target all phases of the cropping program are needed to sustain these cropping systems in the future.

Transgenic glyphosate-resistant canola was first commercially grown in Western Australia (WA) in 2010, providing an opportunity to obtain important baseline data regarding the level of glyphosate resistance in weeds following the exclusive use of glyphosate for in-crop weed control. In this study, two surveys (2010 and 2011) were conducted across the 14Mha of the grainbelt of WA. The 2010 survey was carried out at the late-flowering stage of glyphosate-resistant canola, whereas the 2011 survey was conducted at an earlier growth stage (6–8 leaves), ~2–3 weeks after the second in-crop glyphosate application. During the surveys, 239 fields were visited, representing an estimated combined area of 24000ha. The 2011 survey alone represented a subsample of 23% of the total glyphosate-resistant canola planting in the WA grainbelt for that season. Glyphosate resistance was identified in one population of wild radish (Raphanus raphanistrum L.) and in eight annual ryegrass (Lolium rigidum L.) populations. None of the tested capeweed (Arctotheca calendula (L.) Levyns) populations were glyphosate-resistant. In this survey, no populations of barley grass (Hordeum spp.), brome grass (Bromus spp.), wild oat (Avena spp.) or small-flowered mallow (Malva parviflora L.) survived glyphosate application. Despite a long history of pre-seeding and fallow glyphosate use in WA, this survey found that glyphosate still provides excellent in-crop control of most species; however, some resistance is evident, requiring diverse weed control techniques to limit their spread.

Random surveys conducted in the Western Australian (WA) grain belt have shown that herbicide-resistant Lolium rigidum and Raphanus raphanistrum are a widespread problem across the cropping region. In 2010, a random survey was conducted to establish the levels of herbicide resistance for common weed species in crop fields, including the minor but emerging weeds Bromus and Hordeum spp. This is the first random survey in WA to establish the frequency of herbicide resistance in these species. For the annual grass weed Bromus, 91 populations were collected, indicating that this species was present in >20% of fields. Nearly all populations were susceptible to the commonly used herbicides tested in this study; however, a small number of populations (13%) displayed resistance to the acetolactate synthase-inhibiting sulfonylurea herbicides. Only one population displayed resistance to the acetyl-coenzyme A carboxylase-inhibiting herbicides. Forty-seven Hordeum populations were collected from 10% of fields, with most populations being susceptible to all herbicides tested. Of the Hordeum populations, 8% were resistant to the sulfonylurea herbicide sulfosulfuron, some with cross-resistance to the imidazolinone herbicides. No resistance was found to glyphosate or paraquat, although resistance to these herbicides has been documented elsewhere in Australia for Hordeum spp. (Victoria) and Bromus spp. (Victoria, South Australia and WA).