Seasonal development and life cycle
Grape downy mildew occurs mainly in regions where it is warm and wet during the vegetative growth of
the vine. Limited rainfall in spring and summer generally reduces the spread of the disease in California.
In most regions the fungus survives the winter mainly in fallen leaves. The fungus may also survive in
buds and shoot tips. The pathogen is dispersed by splashing rain and wind. The infection process can
take less than 90 minutes. Infection generally occurs in the morning and the incubation period is about
4 days. Downy mildew is favored by all factors that increase the moisture content of soil, air, and host
plant. Epidemics are promoted principally by rain and irrigation practices. | 
Downy
mildew fungus on leaf |
