Plasmopara viticola

Plasmopara viticola is the oomycete that causes grapevine downy mildew, one of the most destructive diseases of vineyards in warm, humid climates. It overwinters as oospores in fallen leaves and soil, then produces zoospores that spread by rain and wind, causing yellow oil-spot lesions on leaves with white fungal growth on the underside. First recorded on American grapevines in 1834 and later introduced to Europe, it proved especially damaging to the more susceptible European wine grape Vitis vinifera, cutting French production by as much as half in some years and prompting the development of the Bordeaux mixture fungicide in 1885.