Sensitivity of Irish Pyrenopeziza brassicae populations to methyl benzimidazole carbamate ( MBC ), quinone outside inhibitor ( QoI ) and succinate dehydrogenase inhibitor ( SDHI ) fungicides

BACKGROUND: Light leaf spot, caused by Pyrenopeziza brassicae, is an economically damaging disease of winter oilseed rape in north‐western Europe. Disease control relies upon the use of foliar fungicides, with the azoles the main class of fungicides being used. Changes in the sensitivity to azole fungicides have been reported for Pyrenopeziza brassicae populations across Europe. Therefore, there is a need to investigate the use of fungicides having alternative modes of action for control of this disease, although methyl benzimidazole carbamate (MBC) fungicides are no longer approved for use in the European Union (EU). Little information is available on the sensitivity of Pyrenopeziza brassicae to fungicides with alternative modes of action, with only a small number of Irish Pyrenopeziza brassicae isolates previously screened against such fungicides. This study investigated the sensitivity of three collections of Irish Pyrenopeziza brassicae isolates (representative collection, 2019 collection and 2020 collection) to MBC, quinone outside inhibitor (QoI) and succinate dehydrogenase inhibitor (SDHI) fungicides. RESULTS: Different levels of sensitivity of Pyrenopeziza brassicae populations to the MBC, QoI and SDHI fungicides were detected. Three phenotypes of sensitivity (sensitive, moderately insensitive, insensitive) to MBC were identified, with the sensitive phenotype still predominant in Ireland. No differences in sensitivity to QoI and SDHI fungicides were found and no cytb mutations associated with reduced sensitivity to QoI fungicides were detected by sequencing. CONCLUSION: The results suggest that, despite different levels of sensitivity to MBC fungicides, no sensitivity shifts to QoI or SDHI fungicides were identified in Irish Pyrenopeziza brassicae populations. However, continuous fungicide sensitivity monitoring and integrated management strategies using fungicides with different modes of action are necessary to sustain long‐term effective control of Pyrenopeziza brassicae. © 2025 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.