Legacy effects of winter cover crops on weed population dynamics in subsequent winter grain crops

Sustainable weed management requires integrated strategies. Cover crops (CCs) in crop rotations are an effective tool for weed suppression; however, information on their legacy effects on weed dynamics in subsequent grain crops remains limited. This study evaluated the legacy effects of five winter CC treatments: black oat (Avena strigosa), red oat (Avena byzantina), hairy vetch (Vicia villosa), Persian clover (Trifolium resupinatum), and a black oat–hairy vetch mixture on weed dynamics in subsequent barley (Hordeum vulgare) and wheat (Triticum aestivum). The legacy effects of CCs were dynamic and year-dependent. Before CC termination, most treatments reduced weed reproduction by 75–88% compared with the fallow control. This suppressive effect persisted during the post-soybean fallow, where grass-based treatments (black oat, red oat, and the mixture) produced the greatest residue cover and reduced weed cover by up to 90%. However, legacy effects on weed infestation in subsequent grain crops differed between years. In 2023, the high competitive ability of barley masked treatment differences. In contrast, during the less competitive 2024 wheat season, black oat reduced final weed cover by 58%. Overall, CC legacy effects provided effective weed suppression, although their magnitude depended on residue persistence, crop competitiveness, and environmental conditions.