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 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