Grape Downy Mildew
Grape Downy Mildew (Plasmopara viticola) occurs whenever it is warm and wet during the growing season.
The fungus attacks all green tissue, especially the leaves. The leaf lesions appear as yellow or reddish brown areas on the upper sides of the leaves with a corresponding white downy fungal growth on the leaf underside. Eventually the lesions grow to infect the majority of the leaf leading to defoliation.
Upper Leaves
Yellow or reddish-brown areas
Lower Leaves
White downy fungal growth
Young berries are infected with a white fungal growth that superficially looks similar to Powdery Mildew. The older berries remain hard with a light green to red appearance. Eventually the infected berries will drop.
Older berries remain hard with a light green to red appearance
Older berries remain hard with a light green to red appearance