Corn lodging due to bent or broken stalks results mostly from feeding by the European corn borer, Ostrinia nubilalis (Hübner), and from stalk rot infections. Stalk rot of corn (Zea mays L.) is caused in southwestern Ontario mainly by Gibberella zeae (Schw.) Petch (Fusarium graminearum Schwabe), which attacks roots during the summer and invades the bases of the stems as the plants mature (Gates and Mortimore 1972). Several studies in the U.S.A. reported an association between the rot and the borer. Christensen and Schneider (1950) recorded severest stalk rot with highest borer infestation and found that inbred lines usually free from rot became susceptible when infested by the borer. Chiang and Wilcoxson (1961) reported a higher incidence of rot in plants artificially inoculated with Fusarium graminearum and borer larvae than in those inoculated with F. graminearum alone. A recent study in Iowa (Jarvis et al. 1982) showed that the greatest stalk rot damage occurred in high borer infestations. Carson and Hooker (1981), however, were unable to relate the incidence and severity of rot to corn borer infestation. In their 3-year study, the least rot occurred in the year of severest borer infestation. Since observations in corn fields in southwestern Ontario also indicated that there might not be a direct relationship between severity of stalk rot and severity of corn borer infestation, further studies were undertaken.