Oidium

In reference to wine, "oidium" is a fungal disease that has the ability to cause severe damage to the vine. The mildew attacks multiple parts of the vine, including the fruit, leaves, and shoots. This type of fungi does not require moisture and is found in dryer climates, such as California, where other fungi fail. The smell, taste, and color of wine is negatively affected when made with infected grapes. Also known as "powdery mildew". Growers control mildew by applying copper sulfate sprays or various forms of sulfur.