Pacific northwestern North America is the largest wine grape production region outside of California, with over 86,000 acres spread across Washington, Oregon, and British Columbia [Bremmer and Bremmer, 2014; U.S. Department of Agriculture (USDA), 2012, 2017]. There are 55,445 acres of wine grapes in Washington, of which 99.8% lay east of the Cascade Mountains (USDA, 2017). However, there is a growing industry in the Puget Sound AVA, which is climatologically similar to most of the Oregon wine grape production areas. This AVA is one of the largest in total available area, encompassing over 4.75 million acres, but contains only 102 acres of wine grapes (USDA, 2017). From a wine marketing standpoint, it is one of the best-situated AVAs, given that it includes or neighbors the major metropolitan areas of Portland, OR; Seattle, WA; and Vancouver, BC, Canada.
The Puget Sound AVA is characterized by its diversity in climates and is the only Washington AVA located west of the Cascade Mountains. To highlight this diversity, weather (Washington State University, 2018) from extreme areas in this AVA in 2012 are described below. The year 2012 was chosen, as the grape and wine industry across the state of Washington tends to characterize that year as “average” in terms of temperature and precipitation. Rainfall in the region ranged from 14.4 to 60.13 inches (“Sequim” and “Tumwater SW” stations, respectively). The rainfall pattern is dominated by winter precipitation; low summer precipitation in some years typically results in the need for supplemental irrigation. Modified by the Pacific Ocean, the frost-free period in the AVA averages at 188 d but ranges from 143 to 245 d (same weather stations as aforementioned), making frost risk for most of the AVA a nonmajor threat.
The average heat accumulation in the area ranged from less than 1100 to just greater than 2000 growing degree days (GDD), base 50 °F (“Sequim” and “Seattle” stations, respectively); however, 2000 GDD is generally considered the minimum heat units necessary to ripen traditional wine grape varieties (Amerine and Winkler, 1944; Moyer et al., 2014). Thus, heat accumulation in the growing region is a potential production limitation in this AVA. To help mitigate the challenges posed by a cooler growing season, research on short-season/cool-tolerant varieties began in the 1970s at Washington State University’s Northwest Research and Extension Center in Mount Vernon, WA. These wine grape trials provided essential information to commercial wine grape producers on the best varieties for production in this climate. As a result of this research, white-fruited varieties such as Siegerrebe, Madeleine Angevine, and Muller-Thurgau (all V. vinifera) have already proven successful in commercial production.
A renewed interest in variety trials occurred in the early 2000s, with the focus on addressing the potential threat of phylloxera (Daktulosphaira vitifoliae), the shift in wine consumer preference to red wine (Olsen et al., 2006), and the related increase in price premiums associated with red varietals. Specifically, there was an interest in the Puget Sound AVA to produce ‘Pinot Noir’ after seeing the success of the variety in Willamette Valley, OR. However, the cool growing season of the Puget Sound AVA posed challenges in adequately and consistently ripening ‘Pinot Noir’ and controlling vine canopy development which resulted in very large vines with overshaded fruit. The lack of control over the timing of water application due to rainfall patterns in the area limited the greatest tool in canopy management: deficit irrigation (Wample and Smithyman, 2002). However, the use of rootstocks may help overcome these challenges associated with pest resistance, timing of ripening, and canopy management, thus expanding the range of areas where high quality red wine such as ‘Pinot Noir’ can be produced. The trial described herein aimed to look at the influence of rootstocks on the harvest parameters of ‘Pinot Noir 02A’. Rootstocks used in this study were selected for pest resistance, for their potential to advance fruit maturity or influence fruit composition, and/or control vine vigor (Bettiga et al., 2003; Catlin, 1991; Reynolds and Wardle, 2001; Ruhl et al., 1988; Shaffer et al., 2004), but only the effects on fruit maturity are discussed in this report.
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