April 2017 Update

Alopecurus myosuroides 101 verified cases. Most of these cases are seed samples sent by farmers or consultants on suspicion of resistance. They have been tested in pot experiments including a susceptible and a resistant reference population. In most cases fenoxaprop-P, flupyrsulfuron and cycloxydim have been tested, in some cases also pendimethalin and/or prosulfocarb. From 2013 mesosulfuron + iodosulfuron (Atlantis) and florasulam + pyroxsulam (Broadway) have also been included in some of the test. In most cases we find resistance to fenoxaprop and flupyrsulfuron but not to cycloxydim. Around 10% of the samples were less susceptible to pendimethalin or prosulfocarb than the susceptible reference population. Resistance to ACCase inhibitors seems to be caused by an altered target site at the 1781 position in approximately 20% of the resistant populations, while resistance to other SoA more likely seems to be due to enhanced metabolism. Reports from practice indicate increasing resistance to Atlantis and Broadway. Genotyping has been conducted for some of the samples by IDENTXX and Bayer CropScience. The most common mutation is at the 1781 position (Ile to Leu) and seems to be present in around 10% of the resistant populations.  A survey on untreated plots in agricultural fields all over Denmark showed that A. myosuroides was resistant in 30% of the fields (to be presented in Denver in May). References: Keshtar E. (2015): Ecological fitness, molecular basis and selection of resistant blackgrass (Alopecurus myosuroides) biotypes. PhD dissertation, Department of Agroecology, Aarhus University. Keshtkar E., Mathiassen S.K., Moss S.R., Kudsk P. (2015): Resistance profile of herbicide-resistant Alopecurus myosuroides (black-grass) populations in Denmark. Crop Protection, vol. 69, 83-89.