Annual Growth Cycle of Grapevines - Fruit Set

Fruit Set

The stage of fruit set follows flowering almost immediately, when the fertilized flower begins to develop a seed and grape berry to protect the seed. In the Northern Hemisphere, this normally takes place in May and in the Southern Hemisphere in November. This stage is very critical for wine production since it determines the potential crop yield. Not every flower on the vine gets fertilized, with the unfertilized flowers eventually falling off the vine. The percentage of fertilized flowers averages around 30 but can get as high as 60 or be much lower. Climate and the health of the vine play an important role with low humidity, high temperatures and water stress having the potential of severely reducing the amount flowers that get fertilized. Coulure occurs when there is an imbalance of carbohydrate levels in the vine tissues and some berries fail to set or simply fall off the bunch. Varieties like Grenache and Malbec are prone to this abnormal fruit set. Millerandage occurs when some fertilized flowers do not form seeds but only small berry clusters. Grape berry size depends on the number of seeds so berries with no seeds will be significantly smaller than berries containing seeds. On one cluster there may be berries of various sizes which can create problems during winemaking due to the varying "skin to pulp" ratio among the grapes. This can be caused by vine disease, such as fanleaf, or by a boron deficiency in the vine. Gewürztraminer and the Chardonnay clones IA and Mendoza are both prone to millerandage.