A heavy infection may lead to shedding of the affected leaves and bursting of grapes. There may be up to a 60% harvest loss. When the first infection is visible, the disease become difficult to control.
Powdery mildew (grapevine) [Uncinula necator]
The fungus is very common in Europe but does not occur every year or with equal intensity at every site. Warm weather and dense, leafy populations enhance the risk of infection, the first infections can occur in mid-May.
Pattern of damage
Upper sides and undersides of leaves are covered with a mealy gray-white fungal layer (Picture 1). A whitish fungal cover can also be seen on the green grapes (Picture 2). All green plant parts may be affected. In the course of the summer, the affected spots turn dark gray.