Combined effects of spring-planted cover crops and residual herbicide on weed suppression and subsequent wheat yield in the semiarid Central Great Plains

Abstract Cover crops (CCs) are a component of the integrated weed management strategies for controlling herbicide-resistant weed biotypes. A field study was conducted at Kansas State University Agricultural Research Center near Hays, KS, from 2021 to 2024 to determine the effect of spring-planted CCs in combination with residual herbicide on weed suppression during fallow phase and subsequent wheat yield in a no-till winter wheat ( Triticum aestivum L.)–grain sorghum [ Sorghum bicolor (L.) Moench]–fallow rotation in the semiarid Central Great Plains (CGP). The study site had a natural seedbank of glyphosate-resistant (GR) kochia [ Bassia scoparia (L.) A.J. Scott] and Palmer amaranth ( Amaranthus palmeri S. Watson). A mixture of CCs (oats [ Avena sativa L.]–barley [ Hordeum vulgare L.]–spring peas [ Pisum sativum L.]) was spring-planted in no-till sorghum stubbles and terminated at the oats heading stage. Four treatments were tested: (1) weedy fallow (no CC and no herbicide), (2) chemical fallow (no CC but glyphosate + flumioxazin/pyroxasulfone + dicamba), (3) CC terminated with glyphosate, and (4) CC terminated with glyphosate + flumioxazin/pyroxasulfone. Across 3 yr, CC at termination reduced total weed density by 78% to 99% and total weed biomass by 93% to 99% compared with weedy fallow. Weed suppression by the CC terminated with glyphosate plus flumioxazin/pyroxasulfone continued for at least 90 d with reduced total weed density of 52% to 80% and total weed biomass reduction by 70% compared with weedy fallow across 3 yr. No differences in subsequent wheat grain yield between CC treatments and chemical fallow were recorded in 2021 to 2022 and 2022 to 2023; however, in 2023 to 2024, chemical fallow and CC terminated with glyphosate + flumioxazin/pyroxasulfone had greater wheat yield than CC terminated with glyphosate only. These results suggest that integration of spring-planted CC with residual herbicide may help suppress GR B. scoparia and A. palmeri in the CGP.