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RESEARCH PRODUCT

Adapting cropping system to delay herbicide resistance. A simulation study

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Weeds have evolved resistance to numerous herbicides, and their management becomes increasingly expensive and difficult. Here we (1) adapted the existing weed dynamics simulation model AlomSys to account for target-site resistance to acetyl-coenzyme A carboxylase (ACCase)-inhibiting herbicides in Alopecurus myosuroides by integrating wild and mutant target-site resistant (TSR) genotypes, mutations, fitness costs and seed immigration, and (2) ran simulations testing different crop management practices for their ability to delay resistance evolution and/or control of TSR plants. Simulations of an oilseed rape/winter wheat/winter barley rotation showed that TSR plants exceeded 1 plant/m² approximately 22, 7 and 7 years after introducing one, several or many selective herbicides, respectively. Reduced herbicide rates or spraying conditions had no effect on the selection of TSR plants; adding spring pea to the rotation, yearly mouldboard ploughing, occasional ploughing before wheat or rapeseed delayed resistance by 14, 12, 7 and 3 years, respectively. Allele proportions also changed, e.g. ploughing selected a hitherto rare TSR allele presenting improved pre-emergent growth.