(pronounced coo-LYUR) is the French word for the result of a metabolic and weather conditions that causes the failure of the grapes to develop after flowering. In English the word shatter
is used. This condition may occur due to extended rains or frigid weather during the flowering season. It also occurs in vines that have little sugar content in their tissue. Flowers stay closed and are not fertilized. Thus the vines are not pollinated and the grape fails to develop and it falls off. Coulure can also cause irregular bunches of grapes which are less compact than normal. These bunches are more sensitive for diseases. The yield of a vine with coulure will decrease substantially.
Coulure is triggered by periods of cold, cloudy, rainy weather or very high out-of-season temperatures. The condition is manifested in the Spring. Varietals with high proclivity to couloure are Grenache, Malbec, Merlot, and Muscat Ottonel. Other causes of coulure may be vineyard conditions and practices, pruning too early or too severely, excessively fertile soils or overuse of fertilizers, and improper selection of rootstocks or clones.