Herbicide Resistance in Summer Annual Weeds of Australia's Northern Grains Region

For more than two decades, glyphosate has been relied on to control summer annual weeds in fallow systems in Australia's northern grains region. With numerous cases of glyphosate resistance reported in weed species collected from this region, there are concerns about the future viability of this herbicide. A random seed collection survey of summer weeds was conducted between 2016 and 2018 with the aim of determining the frequency and distribution of resistance to glyphosate and other herbicides commonly used for summer weed control. Glyphosate resistance was ubiquitous in fleabane, with all collected populations resistant to this herbicide. Glyphosate resistance was also prevalent in feathertop Rhodes grass, windmill grass, and awnless barnyard grass, with resistance detected in 68%, 58%, and 36% of populations, respectively. Only 14% of sowthistle populations collected between 2013 and 2108 were resistant to glyphosate. Resistance to haloxyfop was detected in feathertop Rhodes grass, albeit at a low frequency (2%). Other herbicides, such as 2,4-D amine, propaquizafop, and clethodim, provided good control of the broadleaf and grass weeds tested. The results from these surveys conducted between 2013 and 2017 provide a first glimpse of the state of herbicide resistance in key crop weeds for Queensland and the northern region of New South Wales. It is clear that farmers and agronomists need to consider incorporating non-chemical weed management tactics to promote the sustainability of current herbicides.

Automated summary

Glyphosate has been widely used to control summer annual weeds in fallow systems in Australia's northern grains region, but the increasing cases of glyphosate resistance in weed species have raised concerns about its future viability. A seed collection survey conducted between 2016 and 2018 revealed that glyphosate resistance was widespread in fleabane and prevalent in feathertop Rhodes grass, windmill grass, and awnless barnyard grass. Only a small percentage of sowthistle populations showed resistance to glyphosate. Other herbicides, such as 2,4-D amine, propaquizafop, and clethodim, provided effective control of the tested broadleaf and grass weeds. The survey results highlight the need for farmers and agronomists to incorporate non-chemical weed management tactics to ensure the sustainability of herbicides.