A one-year study was conducted in the Central Coast of California at a commercial vineyard to evaluate the effect of supplemental irrigation on dry-farmed Vitis vinifera L. cv. Zinfandel with varying vine ages during the 2021 growing season. The experimental block was historically dry-farmed on own-rooted Zinfandel vines, older vines were replaced as production quality decreased with a genetically identical scion grafted onto St. George (Vitis vinifera Scheel) rootstock. Six total treatments were included in this study, with Young vines (5 to 12 years old), Old vines (40 to 60 years old), and Control (2:1 ratio of old to young vines, and representation of the block). Each vine age treatment included both non-irrigated and irrigated vines, the total vine sample contained half irrigated and half non-irrigated. Irrigation was manually applied at véraison and véraison + 4 weeks, based on age-specific ETc, and to replenish 95% ETc. Results indicated no significant changes in phenological progression, leaf senescence, and physical berry analysis caused by supplemental irrigation during key developmental stages. Vine age was the primary driver of significant variation observed for most parameters. However, irrigated vines had slightly higher phenological progression leading up to harvest, although not statistically significant. Due to this minor trend, irrigated vines in each vine age group were harvested before the non-irrigated vines starting with young, control, and old vines. Additionally, lower leaf water potential was found at pre-dawn during the second irrigation application at véraison + 4 weeks. Applying supplemental irrigation during the growing season resulted in no significant impacts on vine performance. Results suggest the potential for implementing a dry-farmed management in vineyards to help adapt to climate changes and water scarcity issues.

A two-year study was conducted at a commercial vineyard in California’s Templeton Gap AVA to evaluate the effect of vine age on viticultural, enological, and sensory attributes of Vitis vinifera L. cv. Zinfandel grapes and wines. The experimental block was dry farmed, conventionally managed, with own-rooted Zinfandel vines that, when determined unproductive, were replaced with new vines of genetically identical scion plant material grafted onto St. George (Vitis rupestris Scheele) rootstock. Treatments included Young vines (5 to 12 years old), Control (representative proportion of young to old vines in the block), and Old vines (40 to 60 years old). Results indicated Young vines progressed more slowly during berry formation and more rapidly during berry ripening than Old vines. Due to variation in the timing of sugar accumulation, Old vines were harvested 21 days after Young vines in 2019, and 9 days after in 2020. Old vines produced, on average between both seasons, 3.7 kg more fruit per vine than Young vines. Old vines also produced, on average between both seasons, 22.8 more clusters per vine than Young vines (5.41 tons/acre and 2.64 tons/acre, respectively). The larger vine capacity observed was attributed to Old vines having more arm, spur and dormant bud positions per vine than Young vines, in addition to larger trunk circumference and diameter. Vine age also had an effect on vine vegetative growth, with Old vines producing shorter internodes (25.5% decrease) and smaller shoot diameters (29.3% decrease) compared to Young vines. Young vines had higher mid-day stomatal conductance and tended to have higher mid-day photosynthetic rates, although no differences in corresponding pre-dawn measurements were found. While root architecture was similar between age groups, Old vines displayed greater rooting depths. Young vine wines had lower pH and titratable acidity than Old vine wines. Old vine wines were defined by a wider array and intensity of aromatics, including raisin, orange peel, black fruit and spices relative to Young vine wines which were defined by wet topsoil and pomegranate aromas. These results suggest the potential for greater yield and improved wine quality when extending the longevity of Zinfandel vineyards.