Mesosulfuron Reduces Hard Red Wheat Early Season Growth.

Mesosulfuron is a sulfuonylurea herbicide used to control annual grass weeds in winter wheat. It is formulated with the safener mefenpyr to achieve crop tolerance. The objective of the study was to evaluate early crop growth and development of various winter wheat varieties treated with mesosulfuron applied alone, with mesosulfuron applied with bromoxynil plus MCPA in mixture, and mesosulfuron applied with pyrasulfotole plus bromoxynil in mixture, as mesosulfuron has reportedly caused injury when applied under adverse conditions. Studies were established in Davenport, Dayton, Fairfield, and LaCrosse, WA in 2009 and in Pullman, WA in 2009, 2010, and 2011. The experimental design was a randomized complete block, strip plot with four replications. Main plots were six winter wheat varieties (‘Bauermister’, ‘Eltan’, ‘Eddy’, ‘Madsen’, ‘ORCF-102’, and ‘Bruehl’) and sub-plots were three herbicide treatments (mesosulfuron alone, mesosulfuron with bromoxynil plus MCPA, or mesosulfuron with pyrasulfotole plus bromoxynil) and a non-treated control. Applications were made in 2009 to trials in Dayton, Lacrosse, and Pullman on March 26; to the trial in Davenport on April 16, and to the trial in Fairfield on May 20. In 2011, an application was made in Pullman on April 19. Five plants were harvested from the nontreated plots of each variety on the day of treatment to determine the above ground dry biomass. Five plants were also harvested from all replicates of each treatment 14 and 21 days after treatment (DAT). Injury ratings were recorded at those intervals. Hard red wheat derived lines ‘Eltan’ and ‘Eddy’ were very sensitive to mesosulfuron, while all other varieties were less sensitive. Mesosulfuron applied with bromoxynil plus MCPA increased injury, while mesosulfuron applied with pyrasulfotole plus bromoxynil was similar to mesosulfuron applied alone. Both pyrasulfotole plus bromoxynil and bromoxynil plus MCPA are formulated as emulsifiable concentrates, and likely increase mesosulfuron absorption. However, pyrasulfotole plus bromoxynil contains a small amount of mefenpyr, the same safener in formulated mesosulfuron. The additional safener decreases injury in ‘Eltan’ and ‘Eddy’.