Single-strain biocontrol agents often look promising when tested against single-strain pathogens. When confronted with a biodiverse field population, however, biocontrol is inconsistent. This study implies that biodiversity of the crown rot pathogen Colletotrichum musae leads to strain discrimination by antagonists which results in variable biocontrol of the disease. Broad host-range mycoparasites of fungi of the crown rot disease complex of banana (C. musae, Fusarium moniliforme and Botryodiplodia theobromae) which attacked at least two of the pathogen genera, exhibited significant differences in aggression against different strains of C. musae, the main pathogen. Antagonists acted via several different mechanisms, i.e. parasitism, antibiosis or competition, simultaneously. The relative importance of each mechanism differed with the individual mycoparasites. Strain discrimination was correlated to differential susceptibility to one or more minor mechanism(s). When as many as four antagonists were combined into one inoculum, they complemented rather than antagonised each other. Biocontrol efficiency increased with the number of antagonist strains combined. Therefore, strain mixtures should be sought to control the crown rot disease complex of banana.