Pine Needle Pathogen Lecanosticta acicola Spreads Into Native Scots Pine (Pinus sylvestris) Stands in Latvia

Lecanosticta acicola, the causal agent of brown spot needle blight, is a known pine needle pathogen. During the past decades, it has spread in Northern Europe, including the Baltics, where it has mainly infected exotic pines. This study presents novel data on the occurrence of the pathogen on introduced, as well as on further spread of the pest to the native pine species in Latvia. In the autumn of 2022, infection of L. acicola was discovered on several young native Scots pine (Pinus sylvestris) stands throughout Latvia, and in a commercial nursery, thus signifying the transition to a native host with high potential for wider expansion. The transmission of the pathogen to the local pine populations could accelerate the spread of the pathogen and decrease the vitality of pines in the Baltics in the future. The fungus was identified by molecular PCR-based methods; conidia were found only on a few pines in surveyed stands, as symptom severity was still low (mostly latent infection). Nevertheless, the observed behaviour of the pathogen implies the establishment and presumed invasion in the native forest areas, and thus the emergence of additional forestry risks.