Multi-tactic strategies to manage herbicide-resistant waterhemp (<i>Amaranthus tuberculatus</i>) in corn–soybean rotations of the U.S. Midwest

Abstract Field experiments were conducted over 2 yr (2019 to 2020) at two locations in Iowa evaluate multi-tactic strategies for managing multiple herbicide–resistant (MHR) waterhemp [ Amaranthus tuberculatus (Moq.) Sauer] a corn ( Zea mays L.)–soybean Glycine max (L.) Merr.] rotation. The effect of three herbicide programs on A. control was tested (2019). effects the prior year’s weed control, cereal rye Secale cereale L.) cover crop, and soybean row spacing (38-cm vs. 76-cm wide) density, biomass, seed production (2020). A program used with sites action provided only 35% MHR compared ≥97% by action. In soybean, adequate (≥90%) crop use or narrow rows reduced density more than 60% 3 9 wk after planting (WAP) inadequate (30%) no crop. Cover narrow-row 44% WAP wide-row soybean. Inclusion single tactic, herbicides corn, biomass harvest least 24% combination all tactics 80%. conclusion, diverse targeting life-cycle stages can make substantial contributions management populations.