Effect of herbicide programs on control and seed production of multiple herbicide–resistant Palmer amaranth ( Amaranthus palmeri ) in corn resistant to 2,4-D/glufosinate/glyphosate

Multiple herbicide–resistant (MHR) Palmer amaranth is among the most problematic summer annual broadleaf weeds in Nebraska and several other states. A new MHR corn cultivar (resistant to 2,4-D/glufosinate/glyphosate, also known as Enlist corn) has been commercially available in the United States since 2018. Growers are searching for herbicide programs for control and reduce seed production of MHR Palmer amaranth among Enlist corn crops. The objectives of this study were to evaluate herbicides applied preemergence, early postemergence, or preemergence followed by (fb) late postemergence for the management of MHR Palmer amaranth in Enlist corn fields and to assess their effect on Palmer amaranth biomass, density, seed production, and corn yield. Field experiments were conducted near Carleton, NE, in 2020 and 2021, in a grower’s field of Enlist corn infested with acetolactate synthase–inhibitor/atrazine/glyphosate–resistant Palmer amaranth. Herbicides applied preemergence, such as flufenacet/isoxaflutole/thiencarbazone-methyl, acetochlor/clopyralid/flumetsulam, or acetochlor/clopyralid/mesotrione, provided 75% to 99% control of Palmer amaranth 30 d after preemergence. Preemergence fb late postemergence herbicides resulted in 94% Palmer amaranth control 90 d after late postemergence, reduced weed density to 0 to 8 plants m −2 30 d after late postemergence, and reduced biomass to 2 to 14 g m −2 15 d after late postemergence compared to preemergence-only (59% control, 0 to 15 plants m −2 , and 4 to 123 g m −2 ) and early postemergence–only herbicides (78% control, 6 to 30 plants m −2 , and 8 to 25 g m −2 ). Based on contrast analysis, Palmer amaranth seed production was reduced to 14,050 seeds m –2 in preemergence fb late postemergence herbicide programs compared with 325,490 seed m –2 in preemergence-only and 376,750 seed m –2 in early postemergence–only programs. Based on orthogonal contrast, higher corn yield of 12,340 and 11,730 kg ha −1 was obtained with preemergence fb late postemergence herbicide programs compared with preemergence-only (10,840 and 11,510 kg ha −1 ) and early postemergence–only programs (10,850 and 10,030 kg ha −1 ) in 2020 and 2021, respectively.