Cereal breeding in Ireland took place in the early twentieth Century to establish native Irish oat cultivars with higher grain yields. However, the production of Irish cultivars declined rapidly from 1973 as the import of international, commercially bred oat cultivars increased which were tested for suitability to Irish climatic conditions. A collection of these heritage oat accessions has been maintained by the Department of Agriculture, Food and the Marine (DAFM). In this study, we investigated a collection of heritage oats for possible resistance to powdery mildew caused by the fungal pathogen Blumeria graminis f. sp. avenae (Bga). We identified Bga resistance in two historical oat accessions (Tyrone 1994 and Sandy). This resistance was mediated by high levels of papillae formation and/or encasements to an Irish single spore isolate. However, intermediate resistance was observed when using a range of Bga isolates.