Rain at Flowering

This year, our Chardonnay was precocious and bloomed beginning around June 15th. In my previous blog, I tabulated all the rain days that we've been having and on June 16th, we had 1-3/4 inches of rain. Rain during bloom can lead to a condition called millerandage or "hens and chicks" where the berries are of unequal size. What we saw this year with our Chardonnay was something worse. Since many of the Chardonnay plants were in more than 30% bloom, many of the flowers seem to have been aborted.
Vitus vinifera vines are perfect flowers (hermaphrodites) meaning that they contain both male and female organs. They are self pollinating and don't require bees to pollinate them. But rain during flowering can dilute the stigmatic fluid and interfere with germination of the pollen grains.¹ We believe that this condition is what happened to some of our Chardonnay this year:

The aborted flowers can become a problem through the season if it remains on the rachis (the main axis of the grape bunch or what you have left after you eat all of the grapes). The growing grapes will trap the flower "trash" and this becomes a reservoir for all types of fungal and bacterial diseases.
To ensure that we can harvest these Chardonnay, I have been going through each bunch and cleaning the rachis of the unfertilized, spent flowers. First I tried it with a brush, but that didn't quite work, so now I gently tap each rachis so that the spent flowers fall off. The picture shown on the right is cleaned Chardonnay cluster, compare it to the picture above which had all the spent flowers near the rachis.
References:
1. Nick K. Dookozlian, Berry Growth and Development.