coulure

Coulure is a horticultural term describing the failure of fruit set after flowering, most often observed in grapevines. It denotes a condition in which a proportion or the whole flower cluster does not develop into fruit, leading to reduced yields and loose, incomplete clusters. The term originates from French and is used in viticulture and pomology; it is one of several disorders that affect successful pollination and fruit set. A related but distinct phenomenon is millerandage, in which fertilization occurs but berry development is irregular, producing many small berries.

Causes: Coulure is strongly linked to environmental stress during flowering, especially cool or damp weather that inhibits pollen germination and pollen tube growth. In grapes, cool springs, high humidity, and insufficient warmth can prevent ovule fertilization. Other contributing factors include nutritional or water stress, strong vine vigor with imbalanced carbohydrate supply, and management practices that delay or damage flower development. Pests or diseases affecting flowers or pistils can also cause coulure.

Impact and management: Coulure reduces crop yield and can alter berry size distribution. Management strategies include selecting cultivars or clones with better flowering performance in a given climate, ensuring adequate soil moisture and balanced nutrition during the pre-bloom period, and practicing vineyard canopy management to reduce humidity around the clusters and improve pollination conditions. Protecting vines from frost during bloom and minimizing drought or heat stress can also help.