Economics of Management of Photosystem II‐ and HPPD‐inhibitor‐Resistant Palmer amaranth in Corn

CORE IDEAS: Glufosinate + dicamba had similar Palmer amaranth control as glufosinate. Glyphosate + dicamba had similar control as glyphosate. Pre‐emergence followed by post‐emergence and post‐emergence‐only programs had similar control. A Palmer amaranth biotype resistant to photosystem (PS) II‐ and 4‐hydroxyphenylpyruvate dioxygenase (HPPD)‐inhibitor in continuous seed corn production fields in southcentral Nebraska is a management challenge for corn growers. Field studies were conducted on a grower’s field in 2014 through 2016 near Shickley in Fillmore County, Nebraska to determine the efficacy of herbicide programs for control of resistant Palmer amaranth, net economic return, and yield of glyphosate‐ and glufosinate‐resistant corn. Based on contrast analysis, pyroxasulfone + fluthiacet‐ethyl + atrazine applied pre‐emergence (PRE) had the highest (95%) Palmer amaranth control compared with saflufenacil + dimethenamid‐P, mesotrione + S‐metolachlor + atrazine (91 to 92%), and acetochlor + clopyralid + flumetsulam (87%) at 21 d after PRE in 2014 to 2015. Glufosinate or glyphosate alone, or tank‐mixed with dicamba applied post‐emergence (POST)‐only or aforementioned PRE herbicides followed by POST programs had 89 to 99% control at 28 and 72 d after POST in 2014 to 2015. Corn yields and net returns were higher where PRE followed by POST and POST‐only herbicide programs were used compared with PRE‐only programs in glufosinate‐ and glyphosate‐resistant corn in 2014 and 2016. In 2015, corn yields and net returns were similar where PRE‐only, POST‐only, and PRE followed by POST herbicide programs were used in glufosinate‐ and glyphosate‐resistant corn. Results of this study suggest that effective PRE followed by POST herbicide programs are available for controlling PS II‐ and HPPD‐inhibitor‐resistant Palmer amaranth in corn and growers need to adopt an integrated weed management approach to reduce the chances of evolution of herbicide‐resistant weeds.