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Michelle M. Moyer, Jaqueline King and Gary Moulton

The Puget Sound American Viticulture Area (AVA), located west of the Cascade Mountain Range in Washington State, is a large and uniquely situated area with diverse topography and mesoclimates. Given the young age of the AVA, little formal information exists on the appropriate rootstock–scion combination in wine grapes (Vitis vinifera) for the region. This project reports on a series of rootstock trials from 2003 to 2007, which evaluated the influence of ‘420A Millardet et de Grasset’, ‘3309 Couderc’, ‘101-14 Millardet et de Grasset’ (all Vitis hybrids), and a self-rooted control on basic harvest metrics of the wine grape scion ‘Pinot noir clone 02A’. At the warmer site in Everson, WA, rootstocks had no effect on final juice harvest metrics measured by soluble solids, titratable acidity (TA), and pH. At the cooler site in Mount Vernon, WA, the use of rootstocks did not always influence soluble solids or pH but did reduce final harvest TA, a desired effect for the region that is typified by low sugar–high TA wines. Even with a reduction in TA in some rootstock–scion combinations, overall, TA remained at the upper end or above the range typically desired for many wine styles.

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Hemant L. Gohil and Michelle M. Moyer

Sufficient heat accumulation is critical for fruit ripening in wine grape (Vitis vinifera). In 2013, a directed-heat application machine was evaluated for its ability to abridge vine phenology and improve fruit quality in commercially grown ‘Syrah’ and ‘Merlot’ in Paterson, WA. Heat was generated through the propane burning and applied to the vine via angled vents. The heat-generator was pulled by a tractor operating at 4 mph, resulting in a 2-second exposure of heat per vine. Rows were treated on a weekly to biweekly basis with transient heat treatments during: 1) bloom only, 2) véraison only, 3) both bloom and véraison, 4) from budbreak to harvest, and 5) a no-heat applied control. Data collected included the timing of phenological stages, percent fruit set, duration and level of heat exposure of the fruit and canopy, juice soluble solids, titratable acidity (TA) and pH at commercial maturity. Air temperature at the vent blower was ≈300 °F; however, by the time the air reached the canopy, air temperature was ≈130 to 150 °F. As a result, the typical increase in leaf or cluster temperature was 10 to 20 °F for 10 to 20 s. Heat application did not increase the number of berries per cluster or fruit set, did not enhance or abridge key vine phenological stages, did not increase soluble solids concentration accumulation, and did not alter juice TA or pH. Results indicate that heat application of this form does not advance vine phenology and in-field measured aspects of fruit quality in climates with large day-night temperature changes such as those in eastern Washington.

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Ian-Huei Yau, Joan R. Davenport and Michelle M. Moyer

Site selection is critical in wine grape (Vitis vinifera) production. The wine grape industry is expanding in the inland Pacific northwestern United States (IPNW) using traditional means of site evaluation including on physical examination of topography, geomorphology, soil characteristics, and analysis of long-term observations from weather stations. Through the use of modeled spatial data, we present a geographic information system (GIS) representing environmental features important for evaluating vineyard site suitability for the production of wine grapes. Elevation, slope, insolation, heat accumulation, growing season length, extreme minimum temperature and the soil parameters of drainage, available water-holding capacity (AWC), depth to restrictive layer, and pH combine to represent composite topographic, edaphic, and overall production suitability. Comparing modeled site suitability predictions with existing vineyards, we found modeled data on site properties aligned with vineyard manager perceptions of production quality in established vineyards. Although remote spatial evaluation will never replace physical site examination for addressing specific site conditions, it allows an efficient, spatially extensive, initial assessment of sites that can direct attention to potentially problematic or distinguishing environmental characteristics.