Symptoms
Yellowish, translucent, irregular spots on the upper surface of the leaves. White powdery growth on lower surface of the leaves. Downy damaged leaves become brown and dried leads to premature defoliation. Whitish growth of fungus on berries which later becomes leathery and shrivel and further development of soft rot symptoms.
Disease cycle
It is an obligate parasite and survives in active phase in evergreen grapevines. Oospores are the main source of survival on leaves and shoots lying on the soil. Under favourable conditions oospores will germinate and infect the lower leaves of the plant. Then the sporangia are formed which later detached from the leaves by wind and causes infection to new plants. Sporangium germ tube forms zoospores which enter the host through lenticels and stoma. Rain, wind, water and others are the mode of spread of the pathogen.
Management
Suitable spacing, proper sanitation, removal of leaves at ground level to avoid infection.
Spray Veni GoKlean at the rate 1.25 to 1.5 ml per litre of water at 12-15 days intervals as preventative spray and or after recognition of the disease symptoms.