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

Abstract

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.

An Analysis of Miscible Displacement and Numerical Modelling of Glyphosate Transport in Three Different Agricultural Soils

“…The leaching of glyphosate in sandy soils without macropores was also reported by other studies [14][15][16]. Structured soils [17] with macropores can enhance pesticide transport rates, and glyphosate (and AMPA) has been reported to leach from subsurface sites [10][11][12]. Glyphosate leaching has been reported to be severe in gravelly soils with coarse textures [24,25].…”

“…Several commercial products contain this active ingredient, including Roundup, widely used in genetically modified crops. In soil materials, glyphosate shows extreme solubility, mostly because of the presence of aluminium oxides and iron oxides in the compound, along with a low pH value [3][4][5][6][7][8][9][10][11][12]. The amount of glyphosate in soil has been shown to vary according to pH, iron and aluminium oxides, and soil structures as well as the timing and activity of glyphosate application [3,8,[12][13][14][15][16].…”

Looking beyond Glyphosate for Site-Specific Fallow Weed Control in Australian Grain Production

“…Glyphosate was generally more efficient than any of the individual herbicides assessed in these studies, with the implication that this herbicide will continue to be relied on for SSWC despite a proliferation of glyphosate resistance throughout northern Australian cropping regions [13]. In this study, glyphosate was the only treatment to control C. virgata (Table 4) and has previously been at least comparable to a variety of alternate treatments on a susceptible C. virgata biotype [11].…”

“…The ever-present threat of glyphosate resistance [13] dictates the need for further research aimed at identifying alternatives. This should include investigating the use of increased application rates, above those used in this investigation (Table 3), to control large summer fallow weeds.…”

“…Very many cases of glyphosate-resistant weeds have now been reported in the northern grains region [10][11][12]. A recent herbicide resistance survey in the northern region found that, of the sampled populations, 14% of sowthistle (Sonchus oleraceus) and 68% of feathertop Rhodes grass (Chloris virgata) were resistant to glyphosate [13]. Cases of glyphosate resistance in C. virgata [14] have also been reported in the southern grains region.…”