Airborne Plasmopara viticola Sporangia: A Study of Vineyards in Two Bioclimatic Regions of Northwestern Spain

Downy mildew, caused by Plasmopara viticola, is one of the most destructive diseases affecting grapevines, particularly in areas with bioclimatic conditions that favor its development, such as northwestern Spain. This study examined the presence of P. viticola sporangia in three vineyards located in two distinct bioclimatic regions (ultra-oceanic and subcontinental) over two consecutive years (2023 and 2024) using Hirst-type volumetric samplers. The relationship between P. viticola and grapevine phenology, along with meteorological variables, was analyzed to help develop effective strategies for managing this disease. Spearman correlation analysis showed that temperature was the most influential variable in all vineyards. However, water-related variables (relative humidity and precipitation) showed stronger correlations in the ultra-oceanic vineyard, which also had the highest sporangium concentrations. Principal Component Analysis revealed that sporangium concentrations in the ultra-oceanic region were most strongly associated with relative humidity and wind speed. In contrast, sporangium concentrations in the subcontinental vineyards were more closely related to temperature, dew point, and wind speed (in Alongos), as well as wind speed (in Alongos and Cenlle). PCA results clearly differentiated the two bioclimatic zones. These findings provide valuable insights that can improve downy mildew management in vineyards in northwestern Spain.