Issue link: http://winesandvines.uberflip.com/i/830382
June 2017 WINES&VINES 49 PRACTICAL WINERY & VINEYARD GRAPEGROWING I t's often thought that if some is good, more must be better. But that axiom does not apply to regu- lated deficit irrigation, according to research conducted by Washington State University (WSU) scientists. Regulated deficit irrigation is a management strategy used by grapegrowers to fine-tune canopy development and improve fruit-quality attributes. 1 "Though some water stress can often help improve wine grape quality, there is such a thing as not providing enough water for the vine," says Dr. Markus Keller, lead investigator of regulated deficit irrigation research supported by the Wash- ington State Wine Commission, a state agency representing all wine grape growers and wineries. Keller, a horticulturist at WSU's Irrigated Agriculture Research & Extension Center in Prosser, specializes in vine physiology, irrigation and cold hardiness and is author of The Science of Grapevines: Anatomy and Physiology. The research by Keller et al. could help wine grape growers save up to 30% of the water used to irrigate grapevines and save energy costs to pump the water without sacrificing grape yields and quality. Throughout the world, water availability is a growing problem due to a changing climate. During the 2015 drought in Washington state, water was rationed in prime irrigated acreage in the Yakima Valley, where high-value crops such as apples, grapes and hops are grown. 2 The WSU study showed that regulated deficit irrigation (hereafter referred to as deficit irrigation), while generally beneficial, can be taken to extremes and go too low. Vines receiving only 25% of crop evapotranspiration (ETc) in the study were economically unsustainable due to reduced yields and vine decline compared to other treatments in the trial. Earlier research has suggested that relatively severe deficit irrigation can achieve significant water savings compared to mod- erate deficit irrigation and can have additional effects on vine performance. 3,4 But that research raised two questions: 1) How severe is too severe? 2) Can water be saved and grape quality improved without sacrificing long-term vine productivity? The impact of increased water supply during ripening and its relationship to alleviating drought-induced berry shrinkage was examined because little research in this area has been conducted in the field. Recommendations in the "Guidelines for Integrated Production of Grapes" from the International Organization for Biological and Integrated Control declare that irrigation of vines for wine production must not be applied after véraison (or is highly restricted) to guarantee "good wine." 5 But withholding water after véraison is at odds with recom- mendations to avoid inappropriate water stress during ripen- ing. 6 Some studies have suggested that late-season irrigation may help alleviate drought-induced berry shrinkage and does not increase berry size. 7 Deficit Irrigation How low can you go? By Melissa Hansen This text was condensed from a report in the American Journal of Enology & Viticulture. A small sensor called an iButton is situated in clusters located on the interior and exte- rior to log temperatures every 10 minutes. MARKUS KELLER, WSU