Development and Impact of Diseases in Potato Crops under Changing Climatic Conditions in the Northwest of the Russian Federation

This study presents results from a two-year monitoring program (2023-2024) on two key fungal diseases affecting potato: Alternaria blight (Alternaria solani Sorauer) and late blight (Phytophthora infestans (Mont.) de Bary). The research was conducted in the experimental field of the Federal State Budgetary Scientific Institution All-Russian Institute of Plant Protection (VIZR) in St. Petersburg. The spread and severity of these pathogens were analyzed in relation to specific agroclimatic conditions during the growing seasons, which determined their respective severity. Long-term meteorological data from the Hydrometeorological Center of the Russian Federation for St. Petersburg—which confirm a regional warming trend—were utilized. Our findings indicate that increasing average summer temperatures correlate with a rise in the damage potential of Alternaria blight in potato. By the end of the 2023 growing season, disease development exceeded 40%. Under very warm, sunny, and relatively dry conditions that year, yield losses from A. solani reached 22%. In contrast, late blight development was negligible in 2023. Conversely, during the hot but rainy 2024 season, no Alternaria blight symptoms were observed. However, late blight development reached 100% by the end of the growing season, resulting in yield losses of 73%.