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s m a r t v i t i c u lt u r e appearance of the grapevine, especially the leaves, to indicate water stress. Both of these scorecards return a numerical value between one and five, related to water stress. For red wine grape varieties, the aim is to commence water stress after fruit set to achieve the cessation of shoot growth a couple of weeks before véraison. Following véraison, water stress should be moderate so as not to impair the ripening process. The "Smart" approach to wine grape irrigation is iterative. One makes a guess at the irrigation amount to be applied based on the soil moisture measurement reading and/or the vine scorecard reading and uses this guess to establish a modified value of kc. This modified value is called kcs (or kc stress). Moisture stress is induced by reducing the value of kc in the calculations of vineyard water use and hence the amount of irrigation water to be applied. The approach is iterative in the sense that the changes in vine water status as recorded by the scorecard should track toward the desired outcome of final water stress. Let me summarize the "Smart" approach to vineyard irrigation for wine grapes: 1. Assess root distribution profiles for the vineyard prior to the commencement of the irrigation season. This can be achieved with backhoe pits made parallel to the vine row and about 12 inches from the line of the trunks. Fine root distribution can be assessed as a function of depth. Normally, the majority of the roots are within the top 2–3 feet of soil. 2. Use the Williams approach of shaded area measurement at noon to estimate seasonal values of kc for the vineyard. 3. Use average local data for potential evapotranspiration as a basis for calculating irrigation amounts. 4. Begin irrigation when soil moisture measurement indicates subsoil moisture reserves, for example greater than 2–3 feet, are mostly depleted. Typically vineyard managers begin irrigation too early in the growing season, when there is still plenty of moisture retained in the subsoil. (Depleting subsoil reserves is difficult in very deep soils; they may need little irrigation anyway.) 5. I suggest the definition of the root zone (measured from the soil surface) that contains about 60% of the root volume. When moisture stress is applied, it is this root zone depth that we need to monitor closely for soil-moisture content. SUPPORT RESEARCH 6. Moisture stress is induced by lowering the value of kc to less than the value providing for optimal water status. My suggestion for a first guess of the modified value is to make kcs say 50% of kc. 7. The irrigation interval is normally fixed, at say two to three times per week, appropriate for drip irrigation. However, the irrigation amount is varied, by using a modified kcs. Be prepared to modify this value further, depending on soil moisture content readings. With several years experience, the soil moisture readings of the root zone can be related to water stress readings on the scorecards. The soil moisture depletion graph can then be a template for future use. 8. Following several seasons of application of this technique, a relationship will be developed for the vineyard that relates soil moisture content readings in the maximum root amount depth to the scorecard value. Conclusion In a brief column like this it is not possible to go through all the details of this proposed new irrigation schedule. However, a couple of points are relevant. First, vine appearance scorecards are used to provide an indicator of grapevine & WINE INDUSTRY NEEDS THROUGH THE AMERICAN VINEYARD FOUNDATION Finding Solutions Through Research Drs. Zalom, Mills and others have completed comprehensive pesticide trials on spider mites and mite predators. Their work has provided viticulturists with insight and direction concerning the consequences of applying various spray materials on general and regional mite populations. Dr. Linda Bisson and others have helped vintners understand the yeast dynamics in high sugar musts and how to deal with "stuck" fermentations. The work has led to the development and commercialization of specialized wine yeast and her lab is currently working on yeast that produce less ethanol. For a wealth of useful viticulture and enology research and information, visit AVF.org, iv.ucdavis.edu, enologyaccess.org, or ngwi.org. P.O. Box 5779, Napa, CA., 94581 • T: (707) 252-6911 • Email info@avf.org. Visit our Web site at www.avf.org for information on funding and current research projects 80 p r acti c al w i ne ry & v i ne yard O CTO BER 20 13