The field experiment was carried out in 2009–2011 year, in Niziny village, near the city of Przemysl. The aim of the studies was to evaluate the effectiveness of Isaria fumosorosea for the control of Ostrinia nubilalis. Two protection treatments were used: seed dressing with spores of the entomopathogenic fungus and spraying plants during vegetation with spore suspension. The results showed, that the application of I. fumosorosea may reduce the damage caused by larvae of European corn borer (O. nubilalis) in stem and cob in comparison to unprotected plants.