Chemical control of herbicide-resistant Lolium rigidum Gaud. in north-eastern Spain

Abstract

Lolium rigidum Gaud. is one of the most common weed species in winter cereals in north-eastern Spain, with populations that have evolved resistance to herbicides becoming more widespread since the mid-1990s. Nine trials on commercial fields with herbicide-resistant L. rigidum were conducted during the cropping seasons 2001-2002 to 2003-2004, testing the efficacy of 20 herbicides and mixtures pre- and post-emergence and as sequential applications. Weed populations chosen had different resistance patterns to chlortoluron, chlorsulfuron, diclofop-methyl and tralkoxydim, representative of the resistance problems faced by farmers. In pre-emergence, prosulfocarb mixed with trifluralin, chlortoluron or triasulfuron was effective on six populations. In post-emergence, iodosulfuron alone or mixed with mesosulfuron gave the best results but did not control three resistant populations. At Ferran 1, none of the herbicide combinations reached 90% efficacy. The diverse efficacy patterns of the different populations demonstrate the need for detailed knowledge of the populations before using herbicides. Moreover, the unexpected insufficient efficacy of the new herbicide iodosulfuron prior to its field use shows the need to combine herbicides with other non-chemical weed control methods to control resistant L. rigidum in north-eastern Spain.