The plant pathogen Fusarium graminearum is most recognized for causing fusarium head blight (FHB) in barley. The overall impact of FHB results from the combination of significant yield loss, and mycotoxin contamination in infected grain. In malting, the environmental conditions that stimulate barley germination also facilitate new fungal growth which can lead to production of mycotoxins thereby contributing to malt quality defects. Two crucial elements that impact Fusarium growth during malting are defensive plant compounds such as phenolic acids, and the presence of other microbes that also colonize barley and may compete with Fusarium. To investigate the relationships among these variables, laboratory-scale malting experiments were performed using barley variety AC Metcalfe in the presence or absence of F. graminearum and of Geotrichum candidum, a well-known inhibitor of pathogenic moulds. The addition of G. candidum in steeping water successfully suppressed F. graminearum growth in malting however, it did not significantly affect DON accumulation. The concentrations of soluble-free and insoluble-bound phenolic acids were analyzed in barley, green malt, and malt, in the presence or absence of both fungi using HPLC revealing ferulic acid and p-coumaric acid as most abundant phenolics. The principal source of differences in phenolic acid content came from the malting process, while impacts due to fungal presence were minimal. In-vitro bioassays measuring inhibition of fungal growth in the presence of phenolics demonstrated a dose-dependent effect where higher phenolic concentrations resulted in greater growth reduction of fungal mycelia. Interestingly, we observed the disappearance of these phenolic acids in the presence of F. graminearum in liquid culture. Understanding the effects of defensive compounds in the presence of competing microbes will suggest new approaches to the mitigation of F. graminearum.