The population dynamics of different bacterial groups with antifungal properties was investigated in comparison with total bacteria based on colony forming units for successful biological control of the soil‐borne pathogenVerticillium dahliaevar.longisporumStark causing tracheomycosis of oilseed rape. This is the first report about bacterial population densities of a plant with a winter annual life cycle. Population densities of colony forming bacteria of oilseed rape (Brassica napusspp.oleiferaMetzg. Sinsk.) were significantly lower in autumn and winter than in spring and summer. The number of antifungal bacterial populations like fluorescent pseudomonads,Bacillus spec.(spores) andStenotrophomonas maltophiliaalso increased during life cycle. The percentages of antifungal isolates were 7 % on average and relatively stable during time of investigation as estimated by a bioassayin vitro.The antifungal mechanisms of 10 different isolates of each selected taxonomic group were investigated. The mechanisms were specific for each isolate. All of these selected strains showed antifungal activity againstV. dahliaevar.longisporum in vitroand therefore, they were evaluated as potential biocontrol agents against this pathogen.