Downy mildew of grapevines

The disease manifests as the appearance of "oily" yellow-green spots on young leaves, on the underside of which a white fuzzy sporulation bloom forms under high humidity. On older leaves, a necrotic "mosaic" spotting forms, and affected inflorescences and young berries become covered in bloom, after which they turn brown, dry out, and fall off. On shoots, the disease is characterized by the appearance of gray or brown spots and possible curling of the tips.

The development of the pathogen is strictly limited by moisture, as infection occurs only in a droplet-moisture environment at air temperatures above +10°C, with an optimum in the range of +20...+25°C. In dry and hot weather, the development process slows down or stops completely. The primary source of infection is oospores that have overwintered in fallen foliage.

Varietal resistance is based on the genetic characteristics of species of the genus Vitis and is implemented through mechanisms of a rapid biochemical reaction aimed at creating barriers for the pathogen, or through anatomical hypersensitivity that interrupts the parasite's development cycle. Resistance assessment in breeding is carried out on a 5-point scale, where values from 0 to 2 points correspond to immune or highly resistant varieties, and 4–5 points indicate susceptibility requiring mandatory protection.