Sclerotinia sclerotiorum is a plant pathogenic fungus that causes Sclerotinia stem rot in oilseed rape. In Sweden, the disease causes severe crop loss that varies by year. Previous studies have shown a relationship between the proportion of infected petals and disease incidence in infected fields in places with high humidity levels before and during flowering. In this study, the aim was to develop a technique to detect S. sclerotiorum and other fungi pathogens in the petals of oilseed rape from naturally infected fields by using nanopore sequencing from Oxford Nanopore Technologies. DNA was extracted from the petals of oilseed rape and subsequently amplified by performing PCR after optimizing the optimal annealing temperature. Using the forward primer ITS1catta and the reverse primer ITS4ngsUni, these primers targeted the ITS region, which is used as a marker for the identification of fungi. The resulting Amplicon concentrations varied. Five amplicon PCR samples were selected for MinION sequencing. These samples were selected since they had the best purity levels. Finally, bioinformatic analysis was done with Kraken2 and the Pavian tool and compared with UNITE databases. The result showed hundreds of thousands of reads were recovered from the Ascomycota and Basidiomycota fungi divisions; S. sclerotiorum was observed in one field sample; other Sclerotiniaceae species like Dumontinia tuberosa, Botrytis cinerea, and Sclerotinia bulborum were detected in two fields; and many other fungal pathogen species affecting rapeseed crops in Sweden were successfully detected. MinION was successful in identifying S. sclerotiorum and other plant pathogens.