LAUSR

Abstract: The objectives of this study were to evaluate the efficacy of a new premix of iodosulfuron (6%)/thiencarbazone (45%) applied alone or tank-mixed with 2,4-D, dicamba, glyphosate, or metribuzin in the fall and (or) early spring followed by preemergence (PRE) and postemergence (POST) herbicide applications for control of glyphosate-resistant giant ragweed and their effect on corn yield. Field experiments were conducted in no-till corn fields infested with glyphosate-resistant giant ragweed (20–30 plants m-2) near Clay Center and McCool Junction, NE, in 2013 and 2014, respectively. A premix of iodosulfuron/thiencarbazone applied alone or in split applications in the fall and early spring controlled glyphosate-resistant giant ragweed <60% and resulted in a density of 14 giant ragweed plants m-2, which was comparable to the untreated control at 28 d after early spring treatment (DAEST). Metribuzin or 2,4-D applied alone resulted in <75% giant ragweed control at 28 DAEST; however, 2,4-D or dicamba tank-mixed with iodosulfuron/thiencarbazone provided ≥92% control. Treatments including 2,4-D or dicamba led to 85%–98% reduction in giant ragweed biomass at 28 DAEST. A follow-up application of a premix of isoxaflutole/thiencarbazone tank-mixed with atrazine applied PRE was not effective, although a POST application of tembotrione + atrazine resulted in >91% control at 28 d after postemergence treatment. The premix applied alone did not provide effective control of giant ragweed in corn primarily because lack of residual activity.