A trial was conducted in the hot climate of central California to assess the interactive effects of pruning systems and deficit irrigation methods on canopy architecture, yield, water productivity, and phenolic composition of Zinfandel under exceptional drought for three years. The pruning systems were cane-pruned (CP, six canes with eight nodes), spur-pruned (SP, 22 two-node spurs), and mechanically-pruned (MP, 100 mm hedge). The deficit irrigation treatments were sustained deficit irrigation (SDI) at 80% of crop evapotranspiration (ETc) from budbreak to leaf fall and regulated deficit irrigation (RDI) at 80, 50, and 80% of ETc between budbreak and fruit set, fruit set to veraison, and veraison to leaf fall, respectively. The research vineyard received 87, 30, and 27% of the 10-year average winter precipitation in years 1, 2, and 3 of the study. In year 1, the combination of CP and RDI was recommended based on reproductive and reduced water footprint. In years 2 and 3, the combination of MP and SDI was recommended based on sustainable yield, optimum leaf area to fruit ratio, and greater flavonol, flavan-3-ol monomers, and anthocyanin concentrations in berry skin. Recommended leaf area to fruit ratio and Ravaz index productivity indices were adjusted based on results for this hot climate region to reach commercial maturity for the cultivar studied. The study provides information to help growers identify combinations of pruning systems and deficit irrigation methods that may optimize reproductive, vegetative, and water productivity while accumulating commercially acceptable flavonol, flavan-3-ol monomers, and anthocyanin concentrations in berry skin in hot climates under exceptional drought.

Funding Support: American Vineyard Foundation