Powdery mildew

Symptom

The disease initially appears as whitish powdery patches on the green parts of the grapevine. As the infection progresses, the white fungal growth becomes denser, giving the surface a dull, powder-dusted appearance. Leaves affected by the pathogen gradually change from green to reddish-brown or black. These symptoms are more prominent on the fruit clusters and peduncles. Severely infected leaves often become deformed, lose their natural color, and show reduced vigor. When the disease attacks the flower clusters, fruit set is significantly reduced. Infection at the young fruit stage causes berries to drop prematurely. On maturing fruits, symptoms include uneven growth, deformation, surface cracking, or deep scarring. Fully ripened berries are rarely affected. If the disease invades the rachis of grape clusters, it causes restricted growth, brittleness, and poor fruit quality. Under severe infestation, the fungal colonies develop into patches that appear grayish-white to black.