Glyphosate resistance is an increasing threat to sustainable and profitable cotton production in Australia. Currently, five weed species, found in several hundred populations, have been confirmed as glyphosate resistant in the cropping region of Queensland and New South Wales. The situation is becoming more complicated, as new research has discovered that both target site and several different non-target site resistance (NTSR) mechanisms can be responsible for glyphosate resistance, as has been established in Australian barnyard grass. Weed populations with some NTSR mechanisms may also have the potential to develop cross resistance to other important herbicides used or potentially used in cotton systems, and stress may activate NTSR mechanisms.

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Glyphosate-tolerant cotton varieties have been grown for over a decade, and other transgenic herbicide-tolerance traits are being introduced. This will likely result in future varieties with a ‘trait stack’ tolerant to several herbicides, such as glyphosate, glufosinate and dicamba. These will provide both new control tactics but also potential risks.

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The overall aim of this new project is to minimise the adverse impacts of glyphosate-resistant weeds or potential impacts of multiple-resistant weeds on the cotton industry. This will be achieved by firstly increasing our knowledge of glyphosate-resistant and multiple-resistant weeds by understanding the drivers for resistance in current and future cotton farming systems. Then, new tactics for weed control in future herbicide-tolerant cotton crops will be evaluated. Finally, new management strategies for glyphosate-resistant weeds and to avoid multiple herbicide resistance will be developed.

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The research will integrate studies on weed ecology, glyphosate-resistance mechanisms, and both chemical and non-chemical control tactics, using molecular tools and gene expression, spatial modelling, risk assessments, and in-depth pot and field experiments on key weeds. In addition, development of improved management strategies, a decision support tool with the ability to evaluate weed control economics and weed identification app will lead to improved practices for managing glyphosate-resistant weeds and reducing the risk of multiple resistance in trait stacks.