Current status in herbicide resistance in Lolium rigidum in winter cereal fields in Spain: Evolution of resistance 12 years after

Abstract

Lolium rigidum Gaud. is the most prevalent and damaging grass weed of winter cereals in Spain. L. rigidum infestations are frequently treated with herbicides and, consequently, populations have evolved resistance. In 2012–2013 a random survey was conducted across cereal cropping areas of the Castilla-León and Cataluña regions to establish the distribution and frequency of herbicide resistance in L. rigidum populations to chlortoluron (Photosystem II inhibitor), chlorsulfuron (Acetolactate synthase inhibitor) and diclofop-methyl (Acetyl CoA Carboxylase inhibitor), commonly used herbicides for L. rigidum control in Spain. The results of this survey were compared with the results of a previous survey conducted in 2000–02. Resistance to PSII and ALS-inhibiting herbicides was common: 51% and 92% of the accessions collected from Castilla-León and Cataluña respectively were resistant to chlortoluron, while 75% of accessions from both regions were resistant to chlorsulfuron. Resistance to ACCase was more widespread in Cataluña, where 83% of accessions were classified as resistant, than in Castilla-León where 74% of the populations were still classified as susceptible to diclofop-methyl. These results show that resistance levels to all three herbicides had increased in Castilla-León since 2000 and to chlortoluron and chlorsulfuron in Cataluña. The accessions were also treated with the double dose (2X) of each herbicide. The percentage of L. rigidum that now exhibits multiple herbicide resistance has increased considerably, especially in Cataluña where 75% of the accessions were resistant to multiple herbicides, therefore herbicide sustainability and resistance management present a great challenge.