Winter wheat response to preplant applications of aminocyclopyrachlor.
Field studies were conducted in Wyoming and Nebraska in 2007 through 2009 to evaluate winter wheat response to aminocyclopyrachlor. Aminocyclopyrachlor was applied at rates between 15 and 120 g ai ha-1 6, 4, and 2 mo before winter wheat planting (MBP). Redroot pigweed control was 90% with aminocyclopyrachlor rates of 111 and 50 g ha-1 when applied 4 or 2 MBP. Aminocyclopyrachlor at 37 g ha-1 controlled Russian thistle 90% when applied 6 MBP. At Sidney, NE, winter wheat yield loss was >10% at all aminocyclopyrachlor rates when applied 2 or 4 MBP, and at all rates >15 g ha-1 when applied 6 MBP. At Lingle, WY, >40% winter wheat yield loss was observed at all rates when averaged over application timings. Although the maturing wheat plants looked normal, few seed were produced in the aminocyclopyrachlor treatments, and therefore preharvest wheat injury ratings of only 5% corresponded to yield losses ranging from 23 to 90%, depending on location. The high potential for winter wheat crop injury will almost certainly preclude the use of aminocyclopyrachlor in the fallow period immediately preceding winter wheat.