2013 ASHS Annual Conference

Water scarcity, impaired water quality, decreased soil quality, and aberrant weather are listed among the top risks to grape production in the western United States (Thrupp et al., 2008). Grapes are the highest value fruit crop produced in the United States, and all grape products combine to generate an estimated $162 billion impact on the American economy each year. Perhaps the most important issue associated with global warming for California is related to water availability (Weare, 2009). California's warmer winters and springs have led to reduced snow-pack, increasing the seasonality of water flows and directly affecting the ability to grow plants, produce food, and support growing populations (Allen-Diaz, 2009). This report describes results from two years of deficit irrigation of table grapes grown in the San Joaquin and Coachella Valleys. The objective was to determine the effects and limits of deficit irrigation strategies on vine development, yield, and grape quality for table grape production. Starting in 2011, two 0.9 ha plots in California were selected, one in Delano in a ‘Crimson Seedless’ late maturing table grape and, the other one in an early season table grape, ‘Sugraone’ in Mecca. Rows (west–east oriented) contain 32 vines spaced 2.1 m apart within the row and 3.6 m between rows. The plots contained 3 rows with the middle row being the data row. The vines are drip irrigated with one lateral on each vine row with three emitters per vine each discharging 3.8 L/hour. Three irrigation treatments were used: T1 as the normal grower practice (GP) and two deficit irrigated treatments, T2 and T3, as a percentage reduction of GP during specific growth stages. In 2011, no differences between treatments in terms of yield were achieved in any location even with reductions of applied water of 5% and 10% for T2 and T3, respectively, for both varieties. During 2012, the ‘Sugraone’ harvest data demonstrated largest yields for T2 and no effect in ‘Crimson Seedless’ even with reductions near to 22% less water in the entire season. In terms of fruit quality, positive effects were found for deficit treatments, achieving highest values for soluble solids in ‘Sugraone’ T2, both years, and ‘Crimson Seedless’ T3 in 2011. Improvements in color development were also significant in this late season table grape both years, parameter extremely important in this variety.