Powdery mildew is a fungal disease of grape vines which, unlike most fungal diseases, thrives in dry climates. Also called oidium, it occurs in most of the wine regions of the world. This is the most troublesome fungus disease of grapes in California by far. It can be controlled by timely application of sulfur dust directly onto the vine leaves and immature fruit. New fungicides have been introduced in recent years which greatly improve a vine's recovery from severe attacks. (Wine/Other)