Issue link: https://read.dmtmag.com/i/196125
David Copeland discusses the crush pad mechanics at Zirkle Wine Company in Prosser during a summer grape field day. Zirkle Wine is one of Washington State's newest and largest custom crush wineries. A photo by melissa hansen free WSU extension publication on nutrient sampling and recommendations for irrigated vineyards in the Pacific Northwest can be downloaded from: http://cru.cahe. wsu.edu/CEPublications/PNW622/PNW622.pdf Nutrient concentrations at veraison were stable and bloom samples far less so, she stated, adding that a downside to the veraison timing is that the results come too late to make significant changes in the current season. "But it will help you in planning your nutrition for next season." She advised growers who have traditionally sampled plant tissue at bloom time to continue for a year or two while adding the veraison timing until a baseline for nutrient status has been developed. "Do a complete nutrient analysis on your plant tissue samples every year," Davenport recommended. "A lot of what the plant needs are macronutrients like nitrogen, phosphorus, and such, but sometimes micronutrients like zinc and boron can be low, especially in high pH soils that limit their availability. If you are applying boron, it can be tricky because too much can be phytotoxic." Soil nutrient levels don't need to be analyzed as often as plant tissue. She suggests taking a soil sample every three to five years. Growers should be sure to use a laboratory that participates in proficiency testing, a voluntary quality control program that compares lab procedure and analysis against industry standards. Costs for soil and plant tissue analyses are generally less than $50 per sample and d iscounts are often given for multiple samples. Optimizing irrigation Dr. Markus Keller has spent the last three years studying optimal irrigation treatments as part of his long-term research to develop strategies to maximize production of a fully mechanized juice grape vineyard. With support from the Washington State Concord Research Council and Wyckoff Farms, the WSU viticulturist uses an eightacre Concord block planted in 2003 to conduct a variety of trials, including spacing and plant density and minimal pruning. He has studied seven different irrigation treatments on the minimally pruned vines to identify irrigation practices that would maximize long-term productivity and fruit quality, and reduce annual yield variation. "When I came to Washington State in 2001, I was a wine grape guy—I knew nothing about juice grapes," he said. "But I saw juice grape growers spending too much money in labor and water for the returns they were getting back." He began looking for ways to reduce costs while maintaining productivity and quality. In his irrigation study, control vines are subjected to full irrigation; early deficit (75% and 50% evapotranspiration) from fruit set to veraison; late deficit using full irrigation until after veraison, then reducing to 75 and 50 percent ET; and full-season deficit, irrigating at 75 and 50 percent ET during the entire fruit development period. Thus far, he's found that irrigation treatments of 75 percent ET are similar to 100 percent ET. But when 50 percent ET is applied, berries were smaller, and crop yields were reduced by 15 percent. "Applying a water deficit before veraison limited berry size and compensation for smaller berries was not possible by applying more water after veraison," he said at the field day. "If you're short at the front end, you can't apply more water later in an attempt to plump up berry size. If you want big berries, the critical time is to apply water from fruit set to veraison." Heavy watering during ripening to maintain berry size may not be as important as was previously thought, Keller added. Irrigation treatments have not affected juice composition (soluble solids, titratable acidity, pH, and color). "Irrigation treatments do influence berry size, while temperature impacts the harvest date," he said. • www.goodfruit.com Good Fruit Grower NOVEMBER 2013 31