Effects of automated fruit-zone irrigation cooling and basal leaf removal on physiology and performances of field grown Sauvignon blanc and Barbera grapevines

Berry dehydration and sunburn are growing concerns for wine grapes cultivated in warm climates. An underexplored method to address this is localized water nebulization at the cluster level for cooling. In 2024, a trial was conducted on Sauvignon blanc (SB) and Barbera rows in Northern Italy, comparing two factors at two levels each: uncooled control (C) versus cooled vines (CL), and non-defoliated (ND) versus defoliated vines (D). Basal defoliation was performed at veraison, while automated cooling was implemented using one fogger per vine, positioned about 10 cm above the cordon, and activated when the air temperature exceeded 33 °C and relative humidity was below 55%. The foggers had a flow rate of 11.2 L/h, with intermittent cooling cycles of 1 min off and 2 min on. Throughout the season, leaf gas exchange, water status, surface cluster temperature, yield components, and grape composition at harvest were measured in both varieties. Out of 51 potential activation days, the system operated on 44 days (86.3%), delivering a total of 145 mm and 183 mm in Sauvignon blanc and Barbera, respectively. The maximum cooling effect on clusters, ranging from − 6 to − 9 °C, was observed when comparing the C-D (warmest) and CL-ND (coolest) treatments, with cooling efficiency unaffected by the presence or absence of basal leaves. Both cooling and maintaining leaf cover effectively reduced cluster sunburn. In Sauvignon blanc, leaf gas exchange and water status were minimally impacted, whereas in Barbera, cooling significantly enhanced leaf function during summer. In Barbera, while ND vines exhibited enhanced sugar and color accumulation at harvest compared to D vines, the CL vines had lower total anthocyanins and phenolics at harvest than C vines, regardless of their unit of expression. This supports the hypothesis that the significant decrease in surface cluster temperature achieved by cooling might not suffice to improve berry pigmentation if berry skin wetting is prolonged, and as a result of an apparent VPD drop, berry transpiration and ripening may be delayed.