Annual weed competitiveness as affected by preemergence herbicide in corn

Competitiveness of weeds that survive a PRE herbicide application (escaped weeds) might be altered because of herbicide injury. As a result, potential crop yield loss may be reduced. Field experiments were conducted at Ashland Bottoms, KS, in 2001 and 2002 and at Rossville, KS, in 2002. The objectives were to quantify corn growth and yield response to Palmer amaranth or velvetleaf competition, with or without isoxaflutole (0.03 kg ha⁻¹) or flumetsulam (0.04 kg ha⁻¹) application, and to determine seed production of Palmer amaranth or velvetleaf as affected by PRE herbicide. Palmer amaranth and velvetleaf densities ranged from 0 to 6 and 0 to 32 plants m⁻¹ of corn row, respectively. At Ashland Bottoms in 2002, corn height at tasseling decreased with increasing Palmer amaranth (1.58 cm weed⁻¹ m⁻¹) and velvetleaf (1.32 cm weed⁻¹ m⁻¹) density when no herbicide was applied. With flumetsulam application, each increase in velvetleaf density reduced corn height by 0.4 cm. Escaped Palmer amaranth and velvetleaf were shorter than untreated plants at corn tasseling. At Rossville in 2002, Palmer amaranth that escaped isoxaflutole or flumetsulam application caused 13% corn yield loss (YL) at a density of 3 plants m⁻¹. In contrast, corn YL from untreated Palmer amaranth at the same density was 30%. At Ashland Bottoms in 2002, velvetleaf that escaped flumetsulam caused 3% corn YL at a density of 3 plants m⁻¹ compared with 38% YL caused by untreated velvetleaf at the same density. Seed production of Palmer amaranth was independent of density or herbicide treatment, whereas production of velvetleaf seed increased with density, with or without flumetsulam. The study showed that corn YL from both Palmer amaranth and velvetleaf that escaped a PRE herbicide was less than from untreated weeds, but seed production by escaped weeds was similar to that of untreated weeds.Nomenclature: Flumetsulam; isoxaflutole; Palmer amaranth, Amaranthus palmeri S. Wats., AMAPA; velvetleaf, Abutilon theophrasti Medicus, ABUTH; corn, Zea mays L., ‘DKC53–34RR’, ‘Asgrow RX740RR’.