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Cabernet Sauvignon grapes grown under regulated deficit irrigation. Notice the smaller canopy and exposed fruiting zone achieved by carefully controlling irrigation from fruit set through harvest.

Cabernet Sauvignon grapes grown under regulated deficit irrigation. Notice the smaller canopy and exposed fruiting zone achieved by carefully controlling irrigation from fruit set through harvest.

The Washington State wine industry’s ability to use irrigation as a management tool is an advantage that few other premier wine regions have. While most Washington wine grape growers think of irrigation as a way to control canopy growth, it can also greatly influence berry size, fruit flavors, aromas, tannins, and can be used to stylize wines in the vineyard.

"We can use irrigation management to achieve whatever canopy size we want, from small to large," said Dr. Russell Smithyman at a Washington State Grape Society meeting. Regulated deficit irrigation, a practice used widely in eastern Washington red wine grape vineyards, reduces irrigation early in the vine’s growing season to control berry size and vegetative growth.

Smithyman, director of research at Ste. Michelle Wine Estates, Washington’s largest wine grape producer, noted that Ste. Michelle has been using regulated deficit irrigation for years. "It is a sustainable practice and has been done at Ste. Michelle for over a decade."

Timing

Timing of irrigation is critical if it is to be used to control vine growth. Smithyman explained that they apply an early season irrigation before bloom only if necessary. Some years, there is enough moisture in the soil profile that prebloom irrigation is not necessary. They use soil-moisture sensors to identify if they are reaching predetermined targets of soil moisture. These targets are developed from experience with the particular site and variety, and the wine production goals for that block. After prebloom, no irrigation is applied until shoots are three to four feet long and shoot growth is declining. In midseason, after the desired shoot length is achieved, they irrigate to replace the vine’s water use, using vine evapotranspiration to determine the irrigation amount. In late season, they go back to using soil-moisture targets to guide irrigation timing.

"At the end of July, we may have yellowing blocks already," he said.

Smithyman said they also use deficit irrigation to reduce shading around the fruiting zone. "Others have to leaf their vines [remove the leaves] to accomplish that, but we can do it by turning off water before or after veraison, and the basal leaves will drop off."

Ste. Michelle has taken its irrigation management philosophy to several vineyards like Goose Ridge Vineyards and Wallula Vineyards. In a deficit irrigation trial in a Cabernet Sauvignon block at Goose Ridge, deficit irrigation was used in place of leafing to create more exposure at the fruiting zone. No leafing was done, and the berries were still small, Smithyman said.

At Wallula Vineyards, characterized as a vigorous site with a deep soil profile, they compared standard versus regulated deficit irrigation. Again, leaves fell off the fruiting zone. "At Wallula, they didn’t irrigate a drop of water until the end of August," he said. "We’ve never taken vines that far before and gotten such good quality."

Although regulated deficit irrigation works well for red wine grape varieties, they have learned that more irrigation is necessary for white varieties to avoid stress.

In a white Riesling regulated deficit irrigation trial, they lost up to 20 percent of the crop from severe heat stress (temperatures of more than 100°F for a few days) that occurred prior to veraison. "There just wasn’t enough water in the soil profile to help it survive," Smithyman said, noting that a similar block that was better watered only lost 5 percent of the crop.

Stylizing in the vineyard

Ste. Michelle is now using regulated deficit irrigation to help stylize wine in the vineyard, creating grapes with different flavor profiles within the same block to give the winemaker more options for blending. All of their vineyard management is focused on producing grapes for a specific product, he added.

"We can give the winemaker different styles to blend together to create their masterpiece," he said. For example, at Canoe Ridge Estate Vineyard, they are growing different styles of wine at the same site, using regulated deficit irrigation and standard irrigation in the same block of Cabernet Sauvignon and Merlot. In Merlot, standard irrigation gives bigger clusters and berry size, whereas regulated deficit results in less crop and smaller berries.

The concept of tiered farming is also practiced in a red variety block grown for their new Col Solare Winery—half of the block is targeted for the high end Col Solare wines and irrigated less, while the other half is grown for higher tonnage. "We’re able to stylize within the same block," Smithyman said.

Irrigation gives Washington wine grape growers more vintage consistency and helps reduce some of the variables from year to year. Not all wine regions can use irrigation as a management tool.

"It means that we can produce a high quality vintage every year, year in and year out," he said. "And we can use irrigation to create options for winemakers."