Scientific term: Plasmopara viticola, Peronospora
Genus/ Division: Mock mushroom, egg mushroom (Oomycota)
Slightly purple or white-gray mealy coatings form on the underside of the leaf. Either oil spots or red colored areas (see picture) are visible on the upper side of the leaf.
The consequence of the infestation is withering and dying of the leaves and eventually the whole vine. The grapes are then also no longer suitable for consumption.
The wind carries the spores and spreads the disease.
Viret, Olivier, Werner, Siegfried, Pierre-Henri, Dubuis, and Katia, Gindro. "Echter Mehltau".Eidg. Departement für Wirtschaft, Bildung und Forschung WBF, Agroscope, AMTRA, Version von (2014).