Comparison of Sustained Deficit and Pre- and Postveraison Regulated Deficit Irrigation on Malbec and Syrah Grapevines

The objective of this study was to compare the effect of sustained deficit irrigation and regulated deficit irrigation strategies on the yield components and berry composition of two winegrape cultivars (Vitis vinifera L.) that differ in their hydraulic behavior. Malbec and Syrah grapevines were grown in southern Idaho under arid conditions and were drip-irrigated weekly from fruit set until harvest to supply 35 or 70% of estimated vine water demand that was delivered either as a sustained amount (35, 70) or the amount was altered at veraison (3570, 7035). In both cultivars, the 7035 and 35 treatments produced fruit with a greater concentration of anthocyanins and phenolics than the 3570 and 70 treatments. In both cultivars, the yield of the 7035 treatment was similar to 30% greater than the 35 treatment and similar to 15% lower than the 70 treatment. The 7035 treatment was provided similar to 58% more water than the 35 treatment and similar to 20% less water than the 70 treatment. In both cultivars, the 3570 and 7035 treatments had a similar ratio of yield reduction to water savings, similar carbon isotope composition, and similar seasonal average weekly midday leaf water potential. The 3570 and 35 treatments had greater bud injury (low pruning weight and low cluster number per vine) and slower recovery from injury than the 7035 and 70 treatments after exposure to an extreme cold weather event. Despite inherent differences in carbon isotope composition, the 70 and 7035 treatments offer the best potential in both cultivars for sustained productivity under challenging climatic conditions.