Greenhouse and laboratory experiments were conducted to investigate the response of winter wheat, and two diclofop-methyl–sensitive (OR and KG) and four diclofop-methyl–resistant (EP, GT, RBG, and JB) Italian ryegrass biotypes to the experimental herbicide mixture AE F130060 03 (an 8.3:1.7 mixture of the experimental sulfonylurea herbicides AE F130060 00 and AE F115008 00). AE F130060 03 at 15 or 18 g ha−1 without the safener AE F107892 reduced biomass of winter wheat 10 to 14%, whereas applications made with AE F107892 did not reduce wheat biomass. AE F130060 03 at 15 or 18 g ai ha−1 was more effective than diclofop-methyl in reducing biomass of one diclofop-methyl–sensitive Italian ryegrass biotype and all four diclofop-methyl–resistant biotypes. However, differential responses to AE F130060 03 at 15 and 18 g ha−1 occurred among diclofop-methyl–resistant biotypes. AE F130060 03 at 15 or 18 g ha−1 reduced biomass of OR, KG, EP, and GT from 61 to 84% but reduced biomass of RBG and JB biotypes only 35 to 52%. Absorption, translocation, and metabolism experiments were conducted to further investigate differential response of diclofop-methyl–sensitive KG and diclofop-methyl–resistant JB to AE F130060 00. Absorption, translocation, and metabolism of AE F130060 00 in winter wheat treated with or without the herbicide safener AE F107892 were also included for comparison. Foliar absorption of [14C]AE F130060 00 was influenced only by plant species because Italian ryegrass biotypes absorbed at least three times more AE F130060 00 than did wheat 12, 36, and 72 h after treatment (HAT). No more than 9% of absorbed radioactivity translocated into shoots and roots of either species during the experiment. Greatest overall metabolism occurred in winter wheat treated with the safener AE F107892. Seventy-two HAT, relative amounts of parent AE F130060 00 in Italian ryegrass biotypes were nearly 1.8 times greater than that in wheat that received AE F107892 and nearly 1.5 times greater than that in unsafened wheat. However, obvious differences in herbicide metabolism between diclofop-methyl–sensitive KG and diclofop-methyl–resistant JB were not evident. We hypothesize that differential sensitivity to AE F130060 00 in these biotypes is most likely due to a less sensitive acetolactate synthase, although further research is required to confirm this hypothesis.
Nomenclature: AE F130060 03, 8.3:1.7 mixture of AE F130060 00, proposed common name mesosulfuron-methyl, 2-[(4,6-dimethoxypyrimidin-2-yl carbamoyl)sulfamoyl]-4-methanesulfonamido-p-toluic acid, and AE F115008 00, proposed common name iodosulfuron-methyl-sodium, 4-iodo-2-[3-(4-methoxy-6-methyl-1,3,5-triazin-2-yl)ureidosulfonyl]benzoic acid); AE F107892, proposed common name mefenpyr-diethyl, 1-(2,4-dichlorophenyl)-4,5-dihydro-5-methyl-1H-pyrazole-3,5-dicarboxylic acid; diclofop-methyl; Italian ryegrass, Lolium multiflorum Lam. LOLMU; winter wheat, Triticum aestivum L. ‘Pioneer 26R24’.