The ubiquitous entomopathogenic fungusBeauveria bassiana(Balsamo) Vuillemin was applied to whorl-stage corn plants,Zea maysL., by foliar application of a granular formulation of conidia and by injection of a conidial suspension. Plants were analyzed at harvest for presence ofB. bassianaand for the amount of tunneling by laboratory-reared European corn borer larvae,Ostrinia nubilalis(Hübner). In 1989, 98.3% of the foliarly treated plants, 95.0% of the injected plants, and 33.3% of the nontreated plants were colonized byB. bassianaat harvest. In 1988, there were no significant differences between treatment effects onO. nubilalistunneling in plants. In 1989, when environmental conditions were more conducive to fungal growth, tunneling was significantly greater in the control plants, followed by the injected and foliarly treated plants. When applied to foliage,B. bassianaprovided the greatest amount ofO. nubilalissuppression. The entomopathogenic fungus colonized the corn plant at whorl stage, moved within the plant, and persisted to provide season-long suppression ofO. nubilalis.