Definition - What does Powdery Mildew mean?
In the context of viticulture and vineyard management, powdery mildew is a fungus that lives on the flaky bark of wine vines and appears as a light dusting of white powder on the leaves. There are many different types of powdery mildew that can infect a plant, once the powdery mildew has infected a plant, it can be almost impossible to remove the mildew, so viticulturists have to set-up the vineyard to prevent powdery mildew.
WineFrog explains Powdery Mildew
Powdery Mildew is a common disease that can attack wine vines. It will survive from season to season, and while it is hard to get rid of, viticulturists can implement good vineyard practices to reduce the risk of powdery mildew attacking wine vines. Powdery mildew likes moisture and shade, so keeping plants spaced properly where they can get adequate sun and dry out thoroughly after rain or irrigation helps to keep the vines healthy and free of powdery mildew.