Multiple-herbicide-resistant waterhemp control in glyphosate/glufosinate/2,4-D-resistant soybean with one- and two-pass weed control programs

Abstract

Waterhemp control in Ontario has increased in complexity due to the evolution of biotypes resistant to five herbicide modes of action (Groups 2, 5, 9, 14, and 27). Four field trials were carried out over a two-year period in 2021 and 2022 to assess the control of multiple herbicide-resistant (MHR) waterhemp in glyphosate/glufosinate/2,4-D -resistant (GG2R) soybean using one- and two-pass herbicide programs. S-metolachlor/metribuzin, pyroxasulfone/sulfentrazone, pyroxasulfone/flumioxazin, and pyroxasulfone + metribuzin applied preemergence (PRE) controlled MHR waterhemp similarly 46, 63, 60, and 69%, respectively at 8 weeks after postemergence (POST) application (WAA-B). A one-pass application of 2,4-D choline/glyphosate DMA POST provided greater control of MHR waterhemp than glufosinate. Two-pass herbicide programs of a PRE herbicide followed by (fb) a POST herbicide resulted in greater MHR waterhemp control compared to a single PRE or POST herbicide application. PRE herbicides fb glufosinate or 2,4-D choline/glyphosate DMA POST controlled MHR waterhemp 74 to 91% and 84 to 96%, respectively at 8 WAA-B. Two-pass herbicide programs of an effective PRE residual herbicide fb 2,4-D choline/glyphosate DMA POST in GG2R soybean can effectively manage Group 2, 5, 9, 14, and 27-resistant waterhemp.