Target site resistance to acetolactate synthase inhibitors in a fall panicum (<i>Panicum dichotomiflorum</i> Michx.) accession from Wisconsin and its response to alternative herbicides

Abstract Owing to the lack of effective POST herbicide options, producers typically rely on nicosulfuron as main grass in sweet corn production systems. In 2019, a Wisconsin producer reported fall panicum control escapes after spraying nicosulfuron. Seeds from mature plants were collected (1) measure response acetolactate synthase (ALS)-inhibiting herbicides, (2) elucidate resistance mechanism, and (3) evaluate its alternative herbicides. Greenhouse laboratory investigations conducted assess ALS-inhibiting herbicides mechanism. Dose–response results showed that was highly resistant with ratio &gt;12.9-fold (survived rates &gt;254 g ai ha −1 , or 8× field label rate). Molecular genetic studies indicated there are multiple ALS gene copies due mutation one copy, resulting an Asp-376-Glu amino acid substitution. Additional greenhouse experiments indicate clethodim (105 ), quizalofop-p-ethyl (70 ae glyphosate (864 glufosinate (650 ) options manage ALS-resistant (&gt;90.0% 96.8% biomass reduction) rotational years. The 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting isoxaflutole mesotrione tembotrione (92 tolpyralate (39 did not provide control. Because these commonly used for weed corn, more required combinations HPPD-inhibiting other sites action Herein we confirm first case United States.