Data for: Deep Learning–Based Identification of Visually Similar Foliar Diseases in Field-Grown Barley

High-throughput assessment of foliar diseases remains one of the main constraints in breeding programs targeting improved resistance. Most existing deep learning datasets focus on single pathogens and controlled imaging conditions, which limits their usefulness in realistic field scenarios where several visually similar diseases often appear together. To support research on robust multiclass disease segmentation, we assembled a high-resolution image collection of barley flag leaves naturally infected with two economically significant pathogens: brown rust (Puccinia hordei) and ramularia leaf spot (Ramularia collo-cygni). The dataset reflects the complexity of field-grown plants, including mixed infections, heterogeneous symptom expression, senescence-related discolouration, and substantial class imbalance. Leaves were collected from 62 barley genotypes cultivated in field trials in Estrées Saint Denis (France) and in Irlbach/Paitzkofen (Germany) during developmental stages corresponding to Zadoks 50–69. In total, the dataset contains 336 annotated leaves, which were subsequently converted into 3,632 image patches.