Master Gardener: What’s wrong with a grapevine coated in powder

Q: I have a 7-year-old grapevine that just started to produce fruit; however, the fruit looks like it might have some kind of fungus. It is coated with a white powder and has cracks. I heard that I should dust it with sulfur after it flowers – is this correct?
A: Powdery mildew is a common problem for grape growers. There are several different species of fungi that cause this problem, but the treatment is the same for all fungus species.
Powdery mildew fungus requires moist conditions to p