Effect of Mesosulfuron Rate and Formulation on Wild Oat (Avena Fatua) Control and Malt Barley Tolerance

Experiments were conducted in 2005 and 2006 near Huntley, Montana to evaluate two formulations of mesosulfuron-methyl for the control of wild oat in malt barley. The two formulations differed due to the amount of safener, mefenpyr-diethyl, that each contained. Formulation 1 and 2 contained mesosulfuron-methyl and mefenpyr-diethyl at a 1 : 2 and 1 : 6 ratio, respectively. The two formulations were applied alone at two rates or in combination with other small grain herbicides that are typically used for broadleaf weed control. The low and high rate of formulation 1 contained 7.8 and 10.1 g ai/ha of mesosulfuron-methyl and 15.6 and 20.2 g ai/ha of mefenpyr-diethyl, respectively. The low and high rate of formulation 2 contained 2.5 and 3.1 g ai/ha of mesosulfuron-methyl and 15 and 18.6 g ai/ha of mefenpyr-diethyl, respectively. These treatments were compared to a standard treatment of fenoxaprop and a nontreated control. In 2005, formulation 2 applied alone at the low and high rates caused barley injury of 7 and 11% at 21 days after treatment (DAT) and 4 and 7% at 56 DAT, respectively. Applications of formulation 1 caused barley injury that was 9 and 17 percentage points greater at 21 DAT and 12 and 18 percentage points greater at 56 DAT than barley injury from applications of formulation 2 when these herbicides were applied alone at the low and high rate, respectively, in 2005. In both years, formulation 1 applied alone at either rate injured barley more than fenoxaprop at 21 and 56 DAT. In both years, formulation 1 and 2 applied alone controlled wild oat between 85 and 96% at 21 DAT and between 92 and 98% at 56 DAT. Regardless of rate, wild oat control with either formulation was similar to that provided by fenoxaprop at 56 DAT. In 2005 and 2006, barley yield was equivalent between treatments of formulation 1 or 2 and that produced by barley treated with fenoxaprop. No difference in the percentage of plump kernels occurred between treatments of formulation 2 and fenoxaprop. The percentage of plump kernels was reduced 6 to 7 percentage points with treatments containing formulation 1 compared to treatments containing formulation 2. Overall, formulation 2 was effective for the control of wild oat in malt barley. Low levels of malt barley injury occurred with this treatment; however, barley successfully recovered by harvest, and yield and kernel size were equivalent to barley treated with fenoxaprop. Nomenclature: mefenpyr-diethyl, [diethyl 1-(2,4-dichlorophenyl