Field research was conducted at Siedlce University of Natural Sciences and Humanities in 2019–2021. The objective was to determine the effects of bacterial formulations and cover crops on the biomass, number and species composition of dominating weeds prior to spring barley harvest. The field trial involved two factors: A – bacterial formulations: I – control, II – nitrogen-fixing bacteria ( Azospirillum lipoferum Br17, Azotobacter chroococcum), III – nitrogen-fixing bacteria ( Azospirillum lipoferum Br17, Azotobacter chroococcum) + phosphorus-solubilizing bacteria ( Bacillus megaterium var, phosphaticum, Arthrobacter agilis), IV – nitrogen-fixing bacteria ( Azotobacter chroococcum) + plant growth-promoting rhizobacteria (PGPR) ( Bacillus subtilis, Bacillus amyloliquefaciens, Pseudomonas fluorescens); B – cover crops: control without a cover crop, red clover, red clover + Italian ryegrass, Italian ryegrass. Spring barley was harvested in late July. Weed samples were collected just before harvest to determine the fresh and dry matter of weeds as well as their number and species composition. The research demonstrated conclusively that an application of bacterial products combined with cover crops contributed to a significant reduction in the weight and number of weeds including dominating species such as Chenopodium album, Sinapis arvensis, Tripleurospermum inodorum and Elymus repens. Superior weed control was achieved in spring barley grown in combination with Azotobacter chroococcum + PGPR and a mixture of red clover and Italian ryegrass as a cover crop.