Our 5-yr old Chardonnay is still in the mitten stage, only a few broke buds. At least we do not see the risk of frost in the 10-day forecast... Once they broke buds, the first disease to be considered is Phomopsis. It is because a) Phomopsis produce spores from previously infected canes, cordons, and trunks, b) the spores are active even in 40's, and c) young leaves and clusters are susceptible to infection. The best approach is use of Mancozeb, captan, or Zirum as a protective application. QoI fungicides such as Abound and Pristine works too, but you want to keep them for later in the season.