Last night, we had several rain events which accounted for about 5 hours of wetness. Average temperature during that period was about 60F, and total amount of precipitation was 0.17 inches. It could be a light infection event for Phomopsis, powdery mildew ascospore discharge, and downy mildew infection. (little too short for black rot infection)
I went back to the vineyard and took a look at the leaf lesions I showed here on Friday.
Sure enough, there are sprangiophores (a tree-like structure containing spores) coming up from the underside of the leaf. As I mentioned in Friday's entry, it takes 1-2 weeks to develop spraongiophore, thus, the infection probably took place during 5/16-17 rains (I wrote 17-18th, but it was 16-17th).
We are expecting few more chances of rains during this week. If your vines are close to bloom or blooming, please be ready to protect your vines.