Investigation of Abiotic and Biotic Factors Associated With the Outbreak of Japanese Larch (Larix kaempferi) Dieback in the Republic of Korea

Japanese larch (Larix kaempferi) is a native East Asian species valued for its adaptability to moderate climates and high-quality timber, making it a popular plantation tree in the Republic of Korea. In 2022, a severe dieback affecting Japanese larch, with symptoms ranging from needle drop to complete tree death, was observed in the largest seed orchard in Korea. This damage poses a significant threat to the orchard's productivity and seed quality. This study aimed to identify and characterise the causes of dieback through physiological and pathological approaches. We found evidence of drought stress and reduced growth in damaged trees, particularly from 2019 to 2022. Additionally, we isolated two potential pathogens, Pestalotiopsis kenyana and Aureobasidium pullulans, both of which were able to cause disease in detached needles and could be controlled using various fungicides. These findings improve our understanding of Japanese larch disease ecology and will aid in developing effective management strategies for this disease.