Vine Performance and Phenology Postponement in Cane-Pruned Chardonnay Vines Grown in a Temperate Climate: The Effects of a Delayed Winter Pruning

In a global warming context, the advancement and compression of maturity in early ripening grape varieties suited to sparkling wine making can easily expedite harvest within the first two weeks of August (in northern Italy). Such earliness, albeit safeguarding acid retention, involves potential suboptimal grape composition and triggers logistical issues related to grape harvest and delivery. Hence, this three-year study beginning in 2020 was conducted on cane-pruned Chardonnay vines, grown in the Franciacorta district of Lombardy, to assess if a single-step delayed winter pruning was able to postpone vine phenology and ripening, without harming yield potential. Control (C) vines pruned midwinter were compared with those subjected to late winter pruning (LWP), performed when the apical shoots growing on the unpruned canes had reached the 2-3 unfolded leaf stage (T1) as well as 7-8 days later (T2). In 2022, a fourth treatment was added, consisting of a two-step procedure with finishing performed at T1 (LWP-two canes). Vegetative growth, yield components, ripening dynamics, and maturity at harvest were followed in each year of this study. Budburst delay induced by LWP treatments across seasons varied between 4 and 9 days, whereas harvest was postponed by 5–14 days. The extent of delay was especially pronounced in 2020, when the removed leaf area (LA) was also found to be the highest. The higher the removed LA, the higher the yield constrain was in the concomitant year. In 2020 and 2021, despite the harvest delay, LWP vines were able to assure full matching with desirable features in must composition, set at total soluble solids (TSS) of about 18°Brix and a titratable acidity (TA) of at least 8 g/L. In the very hot and dry phase of 2022, none of the treatments facilitated the required ripening status, while data showed that an even earlier ripening would not have allowed the harvest to reach the minimum TSS level. Notably, even in 2021 and 2022, when the removed LA was quite low, a delaying effect was prompted in the seasonal trends of all main ripening parameters. This suggested that besides the amount of LA removal, other unknown factors drive the postponement of ripening. In 2022, the behavior of added-treatment LWP-two canes was found to be quite similar to that of the C vines. Depending upon the desired yield level and local climate feature, the protocol entailing a single-step late winter pruning, performed at any time between the T1-T2 time window used in this study, is deemed as effective in achieving a significant harvest delay while maintaining or even improving the compositional patterns recorded for midwinter pruned vines.