Abstract Climate change has already been acknowledged to have destabilizing effects on tree health. In addition to increased abiotic disturbances, trees are increasingly negatively impacted by the emergence of fungal pathogens. Lecanosticta acicola , the causal agent of brown spot needle blight (BSNB), affects pines and is considered invasive in Europe. In October 2025, typical symptoms of L. acicola , brown circumferential lesions with a yellow halo, were observed on an urban tree, Pinus mugo . The pathogen was isolated from surface-sterilized needles, and morphological and molecular identification confirmed it as L. acicola . Here, we report the first observation of the invasive pathogen L. acicola on the non-native host P. mugo in Finland. Lecanosticta acicola is classified as a Quality Plant Pest by the Finnish Food Authority and as no suitable plant protection methods are currently available in Finland, this finding is of particular significance. The detection of this pathogen highlights a potential threat to forestry and emphasizes the need for preventive strategies to limit its spread, including eradication, breeding and improved integrated pest management (IPM) practices in nurseries.
Terhonen et al. (Mon,) studied this question.