Coulure
Also known as "shatter." During flowering in the spring, wind and rain as well as chemical deficiencies can keep grapevine flowers from being properly fertilized, causing these flowers to drop off the cluster. This dropping of flowers is called coulure. Since each flower is responsible for a grape, the cluster of grapes that eventually forms is loose and missing grapes. If the improperly fertilized flower stays attached, it produces a puny, seedless grape called a "shot" grape. Although the yield is reduced, there is a corresponding benefit—loose clusters that allow for increased air circulation are less susceptible to rot in humid conditions.
