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After a wild-type isolate of Epicoccum purpurascens was exposed to shortwave ultraviolet light, several new strains were recovered which were improved in sporulation, fungicide tolerance, and performance in suppression of white mold caused by Sclerotinia sclerotiorum. The efficacy of E. purpurascens in controlling white mold of snap bean (Phaseolus vulgaris) was assessed in greenhouse and field trials. White mold was significantly reduced in both greenhouse and field trials when 2-4 sprays of E. purpurascens conidial suspensions (in 1% malt extract) were sprayed onto the plant surface during the flowering period. Germination of E. purpurascens conidia on senescent petals was greater than on younger flowers. Addition of malt extract to conidial suspensions improved germination on flowers and increased colonization of emerging flowers. Application of E. purpurascens did not accelerate senescence of bean leaves or affect pod yield of bean in greenhouse trials. Mycoparasitism of S. sclerotiorum by E. purpurascens was found only rarely in in vitro tests and was not observed on flower disks. Production of inhibitory compounds by E. purpurascens was the most important mechanism in suppression of white mold but competition for nutrients also appeared to play a role in biocontrol. The influence of nutrients on conidial germination, growth, sporulation and production of antifungal compounds by E. purpurascens were also investigated.