LAUSR

BACKGROUND Amaranthus palmeri S. Wats is among the most problematic annual broadleaf weed species in the USA, including in Kansas. In late summer 2015, seeds of an A. palmeri population (MHR) that had survived field-use rates of 2,4-D were collected from Barton County, KS, USA. The main objectives were to: (i) confirm and characterize 2,4-D resistance in a MHR population; (ii) characterize the resistance profile of the MHR population in relation to a multiple herbicide-susceptible (MHS) population to glyphosate, chlorsulfuron, atrazine, mesotrione, fomesafen; and (iii) determine the effectiveness of alternative POST burndown herbicides for controlling MHR population. RESULTS The MHR population had 3.2-fold resistance to 2,4-D. In addition, the MHR population also exhibited multiple resistance to glyphosate (11.8-fold), chlorsulfuron (5.0-fold), atrazine (14.4-fold), and mesotrione (13.4-fold). Furthermore, the MHR population also showed reduced sensitivity to fomesafen (2.3-fold). In a separate study, dicamba with glyphosate, atrazine or fluroxypyr + 2,4-D, and paraquat alone or with atrazine, metribuzin, saflufenacil or 2,4-D provided ≥ 99% injury to the MHR population. Similarly, saflufenacil alone or with atrazine, metribuzin or 2,4-D, and glufosinate alone or with glyphosate + 2,4-D, and glyphosate + dicamba, and a premix of bicyclopyrone + atrazine + mesotrione + S-metolachlor also effectively controlled the MHR population. CONCLUSION This research confirms the first global case of an A. palmeri population from Kansas with multiple resistance to 2,4-D, glyphosate, chlorsulfuron, atrazine and mesotrione, and reduced sensitivity to fomesafen. Dicamba, glufosinate, paraquat, and saflufenacil alone or in tank-mixtures with PRE herbicides effectively controlled this MHR population. © 2019 Society of Chemical Industry.