In vitro evaluation of azole fungicide sensitivity in Fusarium langsethiae , F. tricinctum , F. poae and F. sporotrichioides populations from Irish oats

Abstract BACKGROUND Fusarium head blight (FHB) in oats represents a significant challenge to crop production and food safety, primarily because of mycotoxin contamination. In this study, 286 Fusarium isolates, representing in majority F . langsethiae , and small numbers of F. tricinctum , F. poae and F. sporotrichioides , obtained from commercial Irish oat crops in 2022 were evaluated in vitro for their sensitivity to three azole fungicides: prothioconazole‐desthio (PDZ), tebuconazole (TBZ) and mefentrifluconazole (MFZ). A microtitre plate assay was used to generate dose–response curves and to determine their half‐maximal effective concentrations (EC 50 ) to each of the three fungicides. RESULTS Differences in fungicide sensitivity and evidence of moderate cross‐resistance among the azole fungicides tested, particularly in F. langsethiae , were detected. Specifically, isolates were overall more sensitive to PDZ, while sensitivity differences between fungicides and partial cross‐resistance between MFZ and TBZ were statistically significant. These results were supported by a principal component analysis and a cluster analysis that confirmed F. langsethiae isolates were least sensitive to MFZ, this fungicide being responsible for the highest amount of variability in the population. CONCLUSION Given that oats are used in human consumption and animal feed, these findings underscore the critical need for ongoing resistance monitoring to maintain food safety standards aligned with European Union regulatory requirements. © 2026 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.