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

Abstract

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