Late-season source limitation practices to cope with climate change: delaying ripening and improving colour of Cabernet-Sauvignon grapes and wine in a hot and arid climate

The current rise in temperatures is hastening grape ripening, resulting in unbalanced wines with high alcohol content but poor colour, aroma and phenolic composition. Late-season canopy manipulation practices aimed at reducing the size of the photosynthetic apparatus after veraison have been shown to delay ripening in cooler climates. However, these methods have not directly been compared in regions with high irradiance and temperature, where berry composition is negatively affected by late fruit exposure. In this two-year Cabernet-Sauvignon trial, we compared the application of pinolene (P) to late shoot topping (T) and late above-bunch zone leaf removal (LR), all performed during the late stages of ripening, with an untreated control (C). Vine water status was monitored weekly from the time of treatment application until harvest. Gas exchange was monitored only in 2021, from treatment application through to harvest. Berry samples were collected to measure berry weight, total soluble solids, pH, titratable acidity, and the anthocyanin profile. At harvest, we assessed yield components, rated sun damage on clusters, and produced experimental wines. Wine colour and chemical characteristics were evaluated. The application of P scarcely improved gas exchange and stem water potential. Conversely, LR and T increased water potential but did not affect leaf gas exchange. T was the only treatment that significantly decreased sugar accumulation, followed by P, which showed some effect although not significant. Grape yield was not altered, despite the use of P resulted in a lower berry weight in 2022. Canopy manipulation increased lighting conditions in the canopy and caused a significant presence of damaged fruits, especially in LR. Berry anthocyanins were not affected, but LR resulted in a lower concentration of total anthocyanins in the wine and altered the anthocyanin profile. P increased wine acidity, while LR and T improved wine colour. This study suggests that late-season canopy management can effectively control ripening speeds and improve the composition of grapes and wines. However, it is essential to avoid grape overexposure by employing the appropriate techniques to ensure grape quality is not compromised.