The Sight of One Flower Blooming

We went to the vineyard on Wednesday, June 17 and while checking up on our vines, we saw this one grape flower in bloom! It was on a Chardonnay plant. Excitedly, we checked our other plants, the Chenin Blanc and the Auxerrois, but it was only on this one Chardonnay that the flower had blossomed.
The grape flower in bloom is something of an anomaly because the grape flower bud is formed with a calyptra or cap which consists of the grape flower petals. The grape flower is a perfect flower, meaning that they have both the female (stigma) and male (stamen) parts and can self pollinate. This calyptra covers the reproductive organs of the grape flower. When the grape flower "blooms", the calyptra falls off. After seeing this one grape flower, I looked every day to see if our other grape flower buds were blooming.
When they pop, they pop at once. On Saturday, June 20, we saw nothing and then on Monday, June 22, many of the flowers were in bloom. All of our varieties, Auxerrois, Chenin Blanc and Chardonnay were in bloom, so I took photos and photos and photos and among the ones I took, I found the blossoms in various stages of shedding their calyptra.

Between Saturday when we saw no flowers in bloom and Monday, when we saw many flowers in bloom, there was a rain event in our area which brought us 3/4-inches of rain. Rain can have a detrimental effect on fruitset due to the following reasons:

• Temperature is an important factor in germination and growth of the pollen tube. Fruitset is greatly reduced when temperatures fall below 65^oF or exceed 100^oF
• Cold temperatures, rainfall or high humidity are often associated with incomplete detachment of the calyptras leading to reduced fruitset
• Rain can dilute the stigmatic fluid and interfere with germination of the pollen grains

We'll keep these things in mind as our season unfolds. So far, it has been an unusually cool summer.
References:
1. 1. Nick K. Dokoozlian, Grape Berry Growth and Development.