Powdery mildew

The disease manifests as the appearance of a grayish-white 'powdery' coating on the surface of leaves, shoots, inflorescences, and berries. A characteristic symptom is 'flag shoots' — stunted shoots with curled leaves emerging from infected buds. When berries are affected, their skin becomes necrotic and cracks, which often triggers secondary infections, while reddish-brown spots remain on the matured vine.

The development of the pathogen does not require liquid moisture; it spreads actively at temperatures from +20°C to +35°C and a wide range of humidity. The fungus persists in buds, on shoots, or in plant debris in the form of mycelium and cleistothecia. High humidity is not a mandatory condition, so infection outbreaks are often observed during hot and dry weather.

A cultivar's resistance to powdery mildew is a genetically determined trait associated with the use of genes from wild American grape species. During variety trials, the level of resistance is determined using a point scale based on field observations under natural epiphytotic conditions or through artificial inoculation methods. The final rating depends on the specific climatic conditions of the region, the level of infection pressure, and the cultivar's ability to withstand pathogen accumulation.