Mechanisms of glyphosate resistance and response to alternative herbicide‐based management in populations of the three Conyza species introduced in southern Spain

BACKGROUND In perennial crops, the most common method of weed control is to spray herbicides, and glyphosate has long been the first choice of farmers. Three species of the genus Conyza are among the most problematic weeds for farmers, exhibiting resistance to glyphosate. The objectives of this study were to evaluate resistance levels and mechanisms, and to test chemical control alternatives in putative resistant (R) populations of Conyza bonariensis, Conyza canadensis and Conyza sumatrensis. RESULTS Plants from the three R populations of Conyza spp. survived high doses of glyphosate compared with plants from susceptible (S) populations. The rate of movement of 14C glyphosate out of treated leaves in plants from S populations was higher than in plants from R populations. Only plants from the R population of C. sumatrensis contained the known target site 5‐enolpyruvylshikimate‐3‐phosphate synthase mutation Pro106‐Thr. Field responses to the different alternative herbicide treatments tested indicated injury and high effectiveness in most cases. CONCLUSIONS The results indicate that non‐target site resistant (NTSR) mechanisms explain resistance in C. bonariensis and C. canadensis, whereas both NTSR and target site resistant (TSR) mechanisms contribute to resistance in C. sumatrensis. The results obtained in the field trials suggest that the resistance problem can be solved through integrated weed management. © 2018 Society of Chemical Industry Non‐target‐site resistant (NTSR) mechanisms explain resistance in C. bonariensis and C. canadensis, whereas both NTSR and target‐site resistant (TSR) mechanisms contribute in C. sumatrensis. Resistance can be solved through Integrated Weed Management.