BY MELISSA HANSEN, WASHINGTON STATE WINE

he European-held wine dilu- tion theory is so entrenched in the wine industry that many U.S. winemakers also believe it’s best not to irrigate wine grapes at Rethinking all before harvest. It’s a theory not supported by science and one that can have detrimental effects on a grower’s bottom line. Post-Veraison The combination of no pre- harvest irrigation and a prolonged fruit ripening period can have nega- tive consequences for wine grape growers, especially those in arid climates. In places like Washington Irrigation State, with scant precipitation in Electronic sensors measured the fall, withholding irrigation after changes in berry diameter veraison not only has potential for from pre-veraison to harvest yield loss but, more important, may and from water stress leave soils dry going into winter, a and re-watering. (Photo recipe for root and vine damage if credit: Washington State cold winter temperatures hit. University) Research supported by the Washington State Wine Commis- sion and the Northwest Center for Small Fruits Research has brought science into the irrigation-dilution concept to help Washington’s wine industry keep vines healthy and avoid millions of dollars in yield losses — all while maintaining wine quality. Industry officials have esti- mated that preventing 5% yield

AT A GLANCE

+ The tradition of withholding pre-harvest irrigation from vines can be damaging to vineyards. + Washington State University research proves that using drip irrigation post-veraison will not increase berry size. + The research also shows drip irrigation doesn’t dilute sugars and helps avoid berry dehydration. + As a result of the research, many Washington winemakers have changed Science disproves centuries-old tradition of their irrigation mindset. withholding pre-harvest irrigation from vines.

60 VINEYARD & WINERY MANAGEMENT | July - Aug 2016 www.vwmmedia.com loss saves around $10 million annu- those in a technical bulletin pub- ally in grower returns, based on an lished by the International Organi- average crop of four tons per acre zation of Biological and Integrated valued at $1,000 per ton grown on Control, prohibit or highly restrict 50,000 acres. irrigation after veraison under the More than a decade ago, Wash- guise of guaranteeing good quality ington State University’s Dr. Markus of the wine. Keller initiated research to bring “So pervasive is this Old World new understanding to berry water irrigation tradition that, even in the movement. He’d heard so often New World, many wineries encour- from grape growers complaining age growers to withhold irrigation about winemakers not wanting water during fruit ripening because grapes to be irrigated before har- of perceived adverse effects,” vest that he decided to look at the he said during an interview in his science behind the dilution concept. office at WSU’s Irrigated Agricul- Keller is author of “The Science of ture Research and Extension Cen- Grapevines: Anatomy and Physiol- ter in Prosser. “But the concept has ogy” and recently took on the role little scientific evidence. Even the of directing the American Society textbooks have had the berry water for Enology and Viticulture’s peer- movement theory wrong.” reviewed publications. “The tacit assumption is that irri- DRIP YES, SPRINKLER NO gation during ripening boosts berry size and dilutes the quality compo- Washington State University viticulturist Keller isn’t suggesting grow- nents of the grapes,” he stated. Dr. Markus Keller initiated research to ers use overhead sprinklers for Moreover, European laws, like better understand berry water movement. post-veraison irrigation. His experi-

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Corporate Office North Northwest West Coast Canada British Columbia 123 Castleton Street 2204 State Route 14 N 1722 SW HWY 18 Suite B 7787 Bell Road 438 Isabey Suite 270 Authorized Agent Pleasantville, NY 10570 Geneva, NY 14456-9510 McMinnville, OR 97128 Windsor, CA 95492 Montreal, Quebec H4T 1V3 Stefan Buhl Phone: Phone: (914) 769-6252 Phone: (315) 719-0480 Phone: (503) 472-6767 Phone:( 707) 838-2812 Phone: (514) 336-7117 Phone: (250) 317-4378 Fax: (914) 769-6786 Fax: (315) 719-0481 Fax: (503) 472-6768 Fax: (707) 838-3164 Fax: (514) 418-2605 [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] www.vwmmedia.com July - Aug 2016 | VINEYARD & WINERY MANAGEMENT 61 ments found that overhead sprin- observed the berry and vine xylem klers could be similar to rainfall (part of the vascular system) with during berry ripening and induce dyed water. The research showed berry cracking, although cracking that, before ripening, berries were is variety-dependent. Once a berry like balloons. The green berries is cracked, its volume can increase contracted and expanded from and sugar can rapidly be leached drought stress and re-watering. from the pulp. But after veraison, when Biondi But irrigation applied to the vine tried to make berries explode by after veraison through drip or flood forcing massive amounts of water will not increase berry size, will not through the roots via a root pres- decrease sugars and isn’t detrimen- sure chamber — so much water tal to fruit quality, he says. that leaves were dripping wet — there was no diameter change for BALLOONS, RED DYE berries with sugar concentrations above 11 °Brix. Keller’s dilution theory research, When Biondi and Zhang used which began in earnest in 2004 and red-dyed water to observe the has involved a variety of graduate vine’s xylem, they found that dye students, has turned into a contin- moved less into the berry during uum of research projects, with sur- ripening, which supports common prising and startling results. textbook wisdom that the xylem Students Marco Biondi and Yun loses functionality at veraison. But Zhang monitored berry diameter when red dye was put into the rear WSU postdoctoral research associate with electronic sensors, pressurized end of the berry to trace outflow, Yun Zhang works with Markus Keller to vines to study water movement and there was surprising water move- continue their research.

62 VINEYARD & WINERY MANAGEMENT | July - Aug 2016 www.vwmmedia.com ment from the berry to the leaves estimate yield and economic losses Joel Perez, one of Keller’s most and shoots. from extended hang time. “Grow- recent grad students, took weekly “Previously, the textbook belief ers know they’re losing tonnage berry weight and Brix measure- was that the xylem became dys- from extended ripening because ments once fruit reached 20 °Brix functional at veraison and only they can see their fruit shrivel,” on nearly 25 wine grape variet- brought water and minerals into says Keller. “But it’s hard to ask for ies for two years to quantify berry the berry up to that time, while the compensation if you don’t know weight loss due to dehydration or phloem brought the sugars in solu- how much you’re losing.” shrinkage. His study found that, tion,” Keller says. “We saw that while some didn’t lose weight, the xylem can easily move water some lost up to 45% during the out of the berry. But we’re still fig- extended hang time. The prelimi- uring out the how and why.” nary research showed that berry In explaining the why, Keller says weight loss always began before that, after sugars in the berry are visual symptoms of shrivel were unloaded from the phloem’s sugar observed. water solution, there’s a need to remove the excess water. The berry INDUSTRY ADOPTION can’t transpire enough to do the job, so the xylem pathway helps the As a result of the WSU research, berry in disposing excess water. many Washington winemakers have changed their irrigation mindset. YIELD LOSS Jim Holmes, owner of Wash- ington’s acclaimed Ciel du Cheval Keller is often asked how much Vineyards on Red Mountain near yield loss occurs when winemak- Benton City, shared that when ers want to hang fruit for extended Keller’s research was first pub- ripening to maximize flavor profiles lished, he sent copies to all of his and reach high sugars of 26 °Brix winemaker customers. “At one and above. At 23 to 25 °Brix, ber- time, I had several winemakers ries reach their sugar maximum. concerned about late season irriga- “Any further increase in sugar is a tion, but Markus Keller’s research result of sugar concentration from clearly showed there’s no problem dehydrating and shrinking berries, with drip irrigation and dilution,” not from sugar import,” he says. says Holmes. In general, berries lose 5% to His customers are told up-front 10% in weight for each increase that he irrigates up to the end of above 23 to 25 °Brix, but the the season. “In my world, there weight loss varies by cultivar. With- haven’t been any winemaker issues out quantifiable data regarding An example of Cabernet Sauvignon with our irrigation practices.” wine grape weight loss, it’s diffi- grapes shriveling from dehydration Holmes, who takes rigorous cult for wine industry personnel to before harvest. grape chemistry measurements throughout fruit ripening, notes that he hasn’t seen any change in their measurements to show dilution or decreased fruit quality effects from irrigation. ADDITIONAL READING “The vine can be shortchanged if irrigations are withheld during fruit + Ripening Grape Berries Remain Hydraulically Connected to the Shoot, ripening, especially during warm Journal of Experimental Botany (Vol. 57:2577-2587) vintages,” he says. “If you have a long hang time and no irrigation, + Sugar Demand of Ripening Grape Berries Leads to Recycling of Surplus the plants are ready to call it a day Phloem Water via the Xylem Plant, Cell & Environment (Vol. 38:1048-1059) before the fruit is picked.” + Water Economy in Grape Berries Yakima Valley appellation grape http://wine.wsu.edu/research-extension/files/2013/04/2013-VEEN-Spring- grower Dick Boushey of Boushey FINALsmaller.pdf Vineyards agrees that most wine- makers have changed their think- Pre-Harvest Irrigation Dilutes Grape Quality! Or does it? + ing to now allow drip irrigation after http://winegrapes.wsu.edu/Newsletters/vol18-1-2008.pdf veraison. He admits to discuss- ing research results often with his www.vwmmedia.com July - Aug 2016 | VINEYARD & WINERY MANAGEMENT 63 35-plus winemaker clients. “Warm vintage years, like 2014 and 2015, really reinforce the importance of watering vines enough to keep them from shutting down before grapes can be harvested.” A winemaker who only recently came around to the WSU research is Juan Muñoz-Oca, head wine- maker at Washington’s Columbia Crest Winery. Muñoz-Oca grew up in Argentina’s wine industry, where the dilution concept is still strongly believed. Keller has had many dis- cussions with Muñoz-Oca. “My upbringing in Argentina — my initial gut feeling — tells me the dilution theory should be true,” he says. “But I can’t argue against the research. It makes total sense. Keller’s research has proven to me that drip irrigation water doesn’t dilute sugars and the irrigation helps avoid berry dehydration. Winemakers some- times confuse berry dehydration with sweet fruit.” He believes the research is important because it lets everyone make more educated decisions: “Both vineyardists and winemakers have a responsibility to grow healthy vines and prepare them for winter.” Keller’s work is proof that cen- turies of tradition can be changed through science, research and per- sistence.

Melissa Hansen is research pro- gram manager for the Washington State Wine Commission (WSW), which represents every licensed winery and wine grape grower in Washington state. Guided by an appointed board, the mission of WSW is to raise positive aware- ness and demand for Washington state wine through marketing and education while supporting viticul- ture and enology research to drive industry growth. Funded almost entirely by the industry through assessments based on grape and wine sales, WSW is a state govern- ment agency, established by the legislature in 1987. To learn more, visit www.washingtonwine.org.

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