Investigating the Efficacy of Selected Very-Long-Chain Fatty Acid-Inhibiting Herbicides on Iowa Waterhemp (Amaranthus tuberculatus) Populations with Evolved Multiple Herbicide Resistances

Very long chain fatty acid (VLCFA)-inhibiting herbicides (Herbicide group (HG) 15) have been applied to corn and soybean fields in Iowa since the 1960s. The VLCFA-inhibiting are now more frequently control multiple herbicide-resistant (MHR) waterhemp (Amaranthus tuberculatus Moq. J.D. Sauer) populations that ubiquitous across Midwest United States as resistance is not widespread. Waterhemp has evolved resistances from seven sites of action (HG 2, 4, 5, 9, 14, 15, 27), six-way confirmed. Thus, objective this study was determine if selected less sensitive when additional herbicide traits within population. Dose–response assays were conducted a germination chamber efficacy three (acetochlor, S-metolachlor, flufenacet) on MHR populations. An herbicide-susceptible, three-way, four-way, five-way population responded treatments differently; however, several four-way exhibited ratios greater than 1 treated with acetochlor S-metolachlor. Selected subjected dose–response assay field using same herbicides, all achieved 80% at maximum labeled rate. results experiments provide evidence some may exhibit decreased susceptibility but generally, these remain efficacious