Non-target-site-based resistance should be the centre of attention for herbicide resistance research: Alopecurus myosuroides as an illustration

Non-target-site-based resistance (NTSR) mechanisms can confer unpredictable resistance to herbicides with different chemistries or modes of action. In two French fields, 18% and 40% individual plants of Alopecurus myosuroides (black-grass), respectively, were resistant via NTSR to all the most effective herbicides approved for A. myosuroides control in wheat (fenoxaprop, clodinafop, pinoxaden, iodosulfuron+mesosulfuron and pyroxsulam) and to the broad-leaf-selective herbicide quizalofop. Pinoxaden and pyroxsulam had never been applied to these populations. In the absence of new herbicide modes of action, this renders a purely chemical control of A. myosuroides in winter cereals much more complex in these fields. A segregation analysis showed that multi-resistant phenotypes were endowed by multiple NTSR genes, underlining the complexity of NTSR. Yet, despite the threat posed to weed control, our lack of knowledge on NTSR is obvious. NTSR should therefore become the priority in herbicide resistance research.