Vineyard Irrigation: A Balancing Act with Consequences

<h3>Abstract</h3> <h3>Background and goals</h3> The water balance of a grape berry determines its final size and has implications for yield and quality. However, how water moves into and out of a berry and how water movement is affected by grapevine water status remains controversial. This synopsis examines the available evidence to develop suggestions for vineyard irrigation management. <h3>Methods and key findings</h3> Studies published over the past 20 yr have firmly refuted the notion that ripening grape berries become hydraulically isolated from the vine. Instead, the berries’ high demand for sugar leads to a massive increase in phloem inflow that requires discharge of surplus water via berry transpiration and xylem backflow to the leaves. Although berry size becomes unresponsive to short-term changes in soil moisture, ripening berries will shrink gradually when vines are water-stressed. Conversely, the berries’ propensity to absorb surface water can result in berry splitting, leading to berry expansion or shrinkage, and thus dilution or concentration of berry contents, depending on weather conditions. <h3>Conclusions and significance</h3> Unlike rainfall, irrigation during grape ripening does not dilute grape composition–unless it is supplied by overhead sprinklers. This Insight argues that while some water deficit is desirable for high-quality grape production, growers should focus mostly on preveraison water deficit for maximum benefits.