Preemergence Herbicide Premixes Reduce the Risk of Soil Residual Weed Control Failure in Corn

Abstract

Widespread occurrence of herbicide-resistant weeds and more variable weather conditions across the US has made weed control in many crops more challenging. Preemergence (PRE) herbicides with soil residual activity have resurged as the foundation for early-season weed control in many crops. Field experiments were conducted at Janesville and Lancaster, WI in 2021 and 2022 (4 site-years) to evaluate the weed control efficacy of solo (single site of action [SOA]) and premix (two or more SOAs) PRE herbicides in conventional tillage corn. Treatments consisted of 18 PRE herbicides plus a non-treated check. At Janesville-2021, S-metolachlor + bicyclopyrone + mesotrione, atrazine + S-metolachlor + bicyclopyrone + mesotrione, and clopyralid + acetochlor + mesotrione provided >72% giant ragweed control. At Janesville-2022, none of the PRE herbicides evaluated provided >70% giant ragweed control due to the high giant ragweed density and the lack of timely rainfall. At Lancaster-2021, atrazine, dicamba, and flumetsulam + clopyralid provided <45% waterhemp control, but the remaining treatments provided >90% control. At Lancaster-2022, the efficacy of some PRE herbicides was reduced due to the high waterhemp density; however, most herbicides provided >75% control. At Lancaster-2021 and 2022, only dicamba and S-metolachlor did not provide >75% common lambsquarters control. PRE herbicides containing SOA group 15 provided >75% control of giant foxtail. Across weed species, PRE herbicides with two (78%) and three (81%) SOAs provided higher weed control than PRE herbicides with a single SOA (68%), indicating that at least two SOAs PRE result in better early-season weed control. The efficacy of the PRE herbicide treatments evaluated herein varied according to the soil seed bank weed community composition and environmental conditions (i.e., rainfall following application), but the premixes were a more reliable option to improve early-season weed control in conventional tillage corn.