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English walnut (Juglans regia) has become an important crop in Chile, representing 11.5% of the total area of fruit trees, surpassed only by grapevine. As the Chilean walnut industry rapidly expands, young orchards are at risk from the emergence of new fungal diseases. Botryosphaeriaceae and Diaporthaceae fungi have been recognized as main causes of wood diseases in walnut, with symptoms of dieback, canker, and blight. In winter 2017, samples were collected from different orchards in Valparaíso and Maule regions. Fungal isolates recovered were cultured, characterized morphologically, and identified using DNA sequence analyses. Three species (Neofusicoccum parvum, Diplodia mutila, Diplodia seriata) were characterized in Botryosphaeriaceae and two (Diaporthe cynaroidis, Diaporthe australafricana) in Diaporthaceae. Pathogenicity tests showed that N. parvum was the most aggressive species to walnut. This study confirmed the presence of pathogenic Botryosphaeriaceae and Diaporthaceae in J. regia that should be considered an increasing risk for the growing Chilean walnut industry.