Evaluation of New Winegrape Varieties for Warm Climate Viticulture in the San Joaquin Valley
Fifty six different red and white wine grape selections are being evaluated at the Kearney Agricultural Center, in Parlier, CA. These varieties were originally selected because they originate from warm-climate Mediterranean regions, and/or were believed to have traits that would be desirable in a warm climate wine region, like the San Joaquin Valley. Most of the selections were recently released to the industry from Foundation Plant Services and had not been previously evaluated in San Joaquin Valley or California. All vines are on 1103P rootstock, trained to bilateral cordons, and most were spur pruned. Beginning in 2013, certain varieties have also been subjected to simulated mechanical pruning. In 2016, the effect of not shoot-thinning some select varieties was evaluated. Grapes were harvested according sugar accumulation, with the harvest target for white varieties at 22° Brix, and reds at 25° Brix. At harvest, yield components, rot incidence, and basic juice chemistry were determined for all 56 varieties. The first harvest was on August 3, 2016 for whites (Petit Manseng) and August 12, 2016 for the reds (Ederena, spur and mechanical pruning). Harvest dates were similar or slightly later than the historically early 2014 and 2015 seasons. Total yields were lower than previous years for almost every variety. Yields for the spur pruned, shoot-thinned standard treatment ranged from 6.54 kg/vine (Carmenere) to 32.14 kg/vine (St. Emillion). Given the repeatedly delayed ripening, poor color accumulation, and lack of adaptability to mechanical pruning, Caladoc, Corvina Veronese, and Counoise are not recommended for the SJV. Segalin, a darkly pigmented variety that looks promising, responded well when not shoot thinned in the spring, while the white varieties had a range of responses to the lack of shoot thinning. These differences in response to more minimal canopy management offer insight into how these varieties may need to be managed in a commercial setting. For the mimicked mechanical pruning selections, yields were only sometimes greater than their hand pruned counterparts, since the greater, smaller clusters also tended to exhibit worse raisining and have smaller berries that reduce yields. Red and white varieties varied widely with respect to harvest date, pH, and titratable acidity. Petit Manseng is the most acidic, which consistently measures >10g/L titratable acidity in this trial every year, but other high acid white varieties include Arinto, Falanghina, and Fiano. Clonal selections of Charbono and Teroldego were grafted in 2014 and used to make wine in 2016. Differences in rot incidence, and ripening are more predominate in the Charbono selections, whereas the Teroldego clones are more similar to one another. Among the reds, these clonal selections, Morastell, Sagrantino, and Segalin consistently produces reasonable yields under deficit irrigation while producing high levels of desirable color and flavor compounds. From the work done in previous years, the most promising varieties continue to be narrowed down and some were made into wine at Constellation Brand’s experimental winery and the UC Davis teaching winery, which provides enological information and valuable extension opportunities in the future. The final juice chemistry and finished wines will be evaluated and presented during 2017. Four new selections were grafted over into more-promising selections at the start of 2016 (Assyrtiko, Nero d’Avola, Grand Noir, and Petit Bouschet). Extensive extension and outreach efforts have been made to promote this work, including being published in trade magazines and local newspapers, giving extensions, and hosting an educational wine tasting and field day.