Palmer amaranth, a dioecious summer annual weed species, is the most troublesome weed in agronomic crop production systems in the United States. Palmer amaranth resistant to photosystem (PS) II- and 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors is of particular concern in south central Nebraska. The objectives of this study were to determine the effect of PRE followed by POST herbicide programs on PS II- and HPPD-inhibitorresistant Palmer amaranth control, crop yield, and net economic return in conventional corn. A field study was conducted in 2014, 2015, and 2016 in a grower's field infested with PS II- and HPPD-inhibitor-resistant Palmer amaranth near Shickley in Fillmore County, Nebraska. A contrast analysis suggested that mesotrione S-metolachlor atrazine applied PRE provided 83% Palmer amaranth control at 21 d after application compared to 78 and 72% control with pyroxasulfone fluthiacet-ethyl atrazine and saflufenacil dimethenamid-P, respectively. Most of the PRE followed by POST herbicide programs provided ≥85% Palmer amaranth control. Based on contrast analysis, POST application of dicamba diflufenzopyr provided 93% Palmer amaranth control compared to 87, 79, and 42% control with dicamba, dicamba halosulfuron, and acetochlor, respectively, at 28 d after POST. All PRE followed by POST herbicide programs, aside from mesotrione S-metolachlor atrazine followed by acetochlor (2,530 to 7,809 kg ha-1), provided 9,550 to 10,500 kg ha-1 corn yield compared with 2,713 to 6,110 kg ha-1 from nontreated control. Similarly, PRE followed by POST herbicide programs, except for mesotrione S-metolachlor atrazine followed by acetochlor ($191 and $897 ha-1), provided similar net return of $427 to $707 ha-1 and $1,127 to $1,727 ha-1 in 2014 and 2015-16, respectively. It is concluded that herbicide programs based on multiple sites of action are available for control of PS II- and HPPD-inhibitor-resistant Palmer amaranth in conventional corn.
Nomenclature: Acetochlor; atrazine; dicamba; diflufenzopyr; dimethenamid-P; fluthiacet-ethyl; halosulfuron; mesotrione; pyroxasulfone; saflufenacil; S-metolachlor; Palmer amaranth, Amaranthus palmeri S. Wats; corn, Zea mays L.