Integrating early spring‐planted barley or oat for Palmer amaranth management in soybean

Abstract Fall‐planted cover crops (CCs) are widely used for weed suppression, but CC establishment challenges after fall harvest in temperate regions necessitate alternative approaches. The objectives of this study were to evaluate the integrated effect of spring‐planted barley or oat CC and herbicide programs for CC biomass production, Palmer amaranth ( Amaranthus palmeri S. Watson) suppression, and soybean [ Glycine max (L.) Merr] yield. Field experiments were conducted during 2023–2024 in an irrigated no‐till soybean in south central Nebraska. A split‐plot design with early spring planted (i) barley ( Hordeum vulgare L.) CC, (ii) oat ( Avena sativa L.) CC, and (iii) no cover crop (NCC) as main factors and sub‐factors included five herbicide programs: (i) nontreated, (ii) pre‐emergence (PRE) only (PRE‐only), (iii) post‐emergence (POST) only (POST‐only) (iv) PRE followed by POST herbicide (PP), (v) PRE followed by POST plus residual herbicide (PPR). Barley or oats were drill‐planted a month before soybean planting. Oat produced 42% more biomass than barley in 2023 (1.44 Mg ha −1 ) and 102% more biomass in 2024 (3.47 Mg ha −1 ). In 2023, CCs had no effect on Palmer amaranth at CC termination. In 2024, oat and barley without PRE herbicide reduced Palmer amaranth density by 89% and 83% and biomass by 90% and 92%, respectively, compared to NCC without PRE herbicide. At 4 weeks after POST herbicide application, oat‐nontreated treatment reduced Palmer amaranth density by 80% and biomass by 64%, while barley‐nontreated had similar results compared to NCC‐nontreated. Soybean yields were not affected by CCs but improved by integrating with herbicide program, with PPR treatment (4.12 Mg ha −1 ) yielding 225% higher than the nontreated control. It is concluded that spring‐planted oat CC integrated with herbicides can be included in Palmer amaranth management program in soybean.