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530-753-3142
Viticulture – Measuring and Managing Vine Water Status Session
June 18, 2025 – 2:20 pm – 4:20 pm
Research Reports
Location: Portola Hotel, Monterey, California
Moderator:
To be announced
Speakers:
Caetano Albuquerque* | Alexander Levin | Andrew McElrone
To Shed or Not to Shed: Different Responses of Cabernet Sauvignon and Malbec Vines to Drought-Induced Leaf Shedding
Caetano Albuquerque,* Alexander Levin and Andrew McElrone
*California State University, Monterey Bay, 100 Campus Center, Seaside, CA, 9355, calbuquerque@csumb.edu
Water deficits and other factors can induce abscission of basal, older leaves on grapevine shoots. While leaf removal is a common practice to improve fruit quality and reduce disease pressure, when excessive it can lead to berry sunburn. Understanding when vines start to shed their leaves during water stress, whether wine grape varieties differ in this response, and the cause of this phenomenon, is useful for irrigation management to match production goals and variety-specific responses to improve berry quality and yield. We hypothesized that Cabernet Sauvignon and Malbec would have different thresholds for water-stress induced leaf shedding and that petiole xylem embolism would drive these responses. We measured leaf shedding and midday leaf water potentials (Yw ) of vines grafted onto 1103P grown at the UC Kearney Station. We also scanned petioles of intact plants of both varieties across a dehydration range using synchrotron-based microcomputed tomography (microCT) to directly observe xylem embolism. Leaf shedding started in the field around Yw = -1.3 MPa for both varieties and Malbec vines shed more leaves than Cabernet Sauvignon with this difference increasing with greater water stress. Malbec petioles were more susceptible to drought-induced embolism than Cabernet Sauvignon, which can be attributed to pith capacitance. The pith cells of Cabernet Sauvignon dried quickly after embolism initiation, while pith cells of Malbec petioles were full of water until severe water stress. Petiole shrinkage had a linear response to water stress for both varieties. These findings show that winegrape varieties show different vulnerabilities to drought-induced leaf shedding, embolism, and pith capacitance. Water released from drying pith cells of Cabernet Sauvignon likely contributed to more resistance to drought-induced embolism. Combined with petiole shrinkage, these data can be used to develop new technologies to track vine water stress for improved irrigation management.
Funding Support: Allocated Beamtime at the Advanced Light Source (ALS) US Department of Energy Henry Jastro Scholarship (UC Davis)
Charles Obiero* | Markus Keller
Impact of Extra Irrigation During Heatwaves on the Performance of Cabernet Sauvignon and Riesling Vines
Charles Obiero* and Markus Keller
Washington State University, 24106 N. Bunn Road, Prosser, WA 99350, Prosser, WA, 99350, charles.obiero@wsu.edu
Grapegrowers often apply extra irrigation water during heatwaves to mitigate heat stress. However, it is uncertain whether this extra irrigation water improves vine performance, and the practice also risks jeopardizing the benefits of the grower’s regulated deficit irrigation (RDI) program. We evaluated Cabernet Sauvignon and Riesling winegrapes to determine the impact of extra irrigation applied before or during predicted heatwaves on vine water status, growth, and productivity. From 2022 to 2024, field trials were conducted in a WSU drip-irrigated research vineyard near Prosser, WA. Extra irrigation water was applied for 24 hours (hr) immediately before or 4 hr daily during heatwaves. The outcomes were compared with standard RDI (control). Extra water before or during the heatwaves increased leaf water status compared with the control. However, 4 hr of extra irrigation daily during heatwaves increased plant water status more than the 24 hr of extra irrigation once before heatwaves. In both varieties and all seasons, shoot growth did not stop, especially in the 4-hr daily extra irrigation treatment. On average, extra irrigation increased berry weight by 8% compared with the control. In Cabernet Sauvignon, but not Riesling, extra irrigation increased yield by 16% and pruning weight by 20%. In both varieties, extra water did not alter fruit total soluble solids, titratable acidity, or pH compared with the control. Thus, 24 hr of extra irrigation ahead of heatwaves or 4 hr of daily extra irrigation during heatwaves lowered plant water stress but did not influence the basic fruit composition in Cabernet Sauvignon and Riesling vines compared with RDI without extra irrigation. However, shoot growth did not stop in vines that received 4 hr of daily extra irrigation during heatwaves. This might jeopardize growers’ overall goal of using RDI as a canopy management tool.
Funding Support: 1. USDA Northwest Center for Small Fruits Research 2. Washington State Grape and Wine Research Program
Pietro Previtali* | Thomas Giagou | Luis Sanchez | Nick Dokoozlian
Drip Irrigation or Vine Cooling: Which is the Best Strategy for Heatwave Mitigation in Cabernet Sauvignon?
Pietro Previtali,* Thomas Giagou, Luis Sanchez and Nick Dokoozlian
*GALLO, 600 Yosemite Blvd, Modesto, CA, 95354, Pietro.Previtali@ejgallo.com
The frequency of heat days (Tmax > 38°C) and heatwaves (>2 consecutive heat days) has increased steadily over the past decades. In California, unprecedented heat has been recorded in vintages such as 2017, 2020, 2022, and 2024. Heat extremes cause yield losses and negatively shift wine composition toward higher alcohol and lower color, mouthfeel, and aroma compounds. Increased irrigation during heatwaves mitigates heat effects on yield, fruit composition, and wine chemistry of Cabernet Sauvignon, and the intensity of this effect is dependent on irrigation timing and intensity. In 2024, we compared drip irrigation treatments with canopy cooling systems in Cabernet Sauvignon in Sonoma, CA. Six drip irrigation treatments, combining three timings (0, 1, and 2 days prior to the heatwave) and two amounts (50% and 100% more than the control), and four cooling systems, were compared to a control with standard drip irrigation and no cooling. Vine cooling treatments received the control irrigation and were automatically triggered at T > 35°C. The 2024 season was exceptionally hot, with 14 heat days and heatwaves across all summer months. Both drip irrigation and cooling reduced canopy temperature during heatwaves and improved vine water status. Lower air temperature in the fruit zone was only recorded for cooling treatments and to a different degree depending on the system used, up to 10°C. Both standard irrigation and vine cooling improved yield components and fruit composition at harvest. Greater improvements in yield (+4 kg/vine) and berry weight (+0.3 g) were observed in drip irrigation treatments. Fruit quality parameters were maximized with cooling systems, including lower sugar levels and off-flavors and improved anthocyanins and mouthfeel-related phenolics. These findings show that drip irrigation and vine cooling can be used to mitigate the effects of heatwaves and preserve yield and quality under heat extremes.
Funding Support: GALLO
Patricia Skinkis* | Grace Lilly | Abigail Sriram
Rootstock Drought Tolerance or Vigor Control? A Quandary for Cool Climate Dry-farmed Vineyards
Patricia Skinkis,* Grace Lilly and Abigail Sriram
*Oregon State University, 2750 SW Campus Way, 4017 Ag & Life Sci Bldg., Corvallis, OR, 97331, patricia.skinkis@oregonstate.edu
Pairing rootstock traits with desired winegrape growth responses is an important consideration for vineyard owners as they seek environmental and economic sustainability. While rootstocks have been used in Oregon’s Willamette Valley for 30 years, the focus had been on vigor-reducing rootstocks that lack drought tolerance. The seasonal climate has changed since that time, with warmer and drier growing seasons. Growers seek rootstocks to match climate, soils, and production goals, with the most important parameters being increased drought tolerance for no-till, no-herbicide use, suitability to restrictive soils, and balanced vine vigor to reduce vineyard inputs while achieving desired yields and quality. To address these concerns, vine growth, water stress, and fruit composition were evaluated in a mature vineyard from 2020 to 2024. The trial was established as a split-plot design with cultivar as the main plot and rootstock as the subplot. Pinot noir was grafted to 18 rootstocks and Chardonnay and Pinot gris were grafted to nine rootstocks of varying parentage. Results show that rootstocks have the greatest effect on vine vegetative growth and yield. Vines with the most vegetative vigor were on 5BB, 1103P, 420A, and 140R and had 1.5- to 3-fold higher pruning weights than vines on vigor-reducing rootstocks (101-14, 3309C, Schwarzmann, 44-53, and Riparia Gloire). Vines with larger canopies also had higher yields, while Riparia Gloire, Schwarzmann, and 44-53 had 1.4- to 2-fold lower yields than average. We hypothesized that larger vine size and fruit yield could reduce drought tolerance, but the most vigorous vines had the least plant water stress. Vines on 101-14 and Riparia Gloire had the most drought stress. However, there were differences in cultivar response by rootstock. Differences in fruit composition by harvest were primarily explained by vine vegetative vigor, with the weakest vines having the most advanced ripeness compared to the largest vines with highest yields.
Funding Support: Oregon Wine Board and Northwest Center for Small Fruit Research
Eve Laroche-Pinel | Vincenzo Cianciola | Khushwinder Singh | Gaetano Vivaldi | Luca Brillante*
Evaluating Machine Learning for Spatial-Temporal Prediction of Grapevine Water Status Using Landsat 8 Imagery
Eve Laroche-Pinel, Vincenzo Cianciola, Khushwinder Singh, Gaetano Vivaldi and Luca Brillante*
*Department of Viticulture and Enology, California State University Fresno, 2360 E Barstow Ave, Fresno, CA, 93740, lucabrillante@csufresno.edu
Climate change exacerbates drought and heat stress in vineyards, increasing the need for efficient water management. This study evaluates using Landsat 8 imagery and weather data to predict grapevine water status through a gradient boosting machine (GBM) model. Midday stem water potential (Ψstem), net assimilation (AN), and stomatal conductance (gs) were measured over two seasons in a Vitis vinifera cv. Merlot vineyard in Central California. Spatial and temporal predictive accuracy was assessed using block-out and date-out cross-validation. Machine learning accurately predicted vine water status spatially within training dates, with low normalized root mean square errors (NRMSEΨstem: 2.7%; NRMSEgs: 16.2%; and NRMSEAN: 11.2%) and high accuracy (R² > 0.8). However, forecasting for new dates is more challenging, with NRMSE reaching 17.7% for Ψstem and 72.5% for gs. Incorporating prior ground data at a single location improves model performance, reducing NRMSE to 6.8% for Ψstem (R² = 0.90), 53.4% for gs (R² = 0.74), and 25.5% for AN (R² = 0.78). These findings highlight the importance of validation methods that account for spatial-temporal dependencies in agricultural data sets. By integrating remote sensing with machine learning, this study provides a scalable approach to monitoring vine water status, enhancing decision-making in precision viticulture under climate change.
Funding Support: American Vineyard Foundation; Bronco Wine Co. Chair in Viticulture
Ashraf El-kereamy* | Alaaeldin Rezk | Lauren Hale | Maha Afifi
Boosting Soil Water Retention and Vineyard Sustainability: Effect of Biochar and Hydrogels
Ashraf El-kereamy,* Alaaeldin Rezk, Lauren Hale and Maha Afifi
*UCR, 900 University Ave., Riverside, CA, 92521, ashrafe@ucr.edu
Soil water retention is a critical factor influencing plant growth, soil management, and drought resilience. Organic matter plays a key role in soil moisture retention, with its ability to absorb up to 20 times its weight in water. Changes in temperature further impact evapotranspiration, soil infiltration, and groundwater recharge. Enhancing soil water retention is essential to mitigate the effects of drought, particularly in agricultural systems. Hydrogels, a class of polyacrylamide-based amendments, improve soil water-holding capacity and plant growth by increasing water availability. Similarly, biochar, a carbon-rich material derived from biological residues, enhances soil moisture retention due to its porosity and large surface area. While hydrogels have demonstrated effectiveness in improving soil water retention in Scarlet Royal grapes, the potential of biochar in table grape production remains underexplored. A 3-yr study examined the effects of hydrogel and biochar on the productivity and quality of two table grape varieties, Great Green (Sheegene 17) and Allison (Sheegene 20), grown in clay and sandy soils under limited water supply (60% ETc). Applying hydrogel at 260 or 520 lb/acre and biochar at 5 or 10 tons/acre mitigated yield losses and improved berry size, weight, color, and firmness, with higher application rates proving more effective, particularly in sandy soils. Additionally, treatments enhanced soil microbiome activity and improved overall soil health. Ongoing trials are assessing lower application rates. This presentation will highlight the findings and explore the feasibility and costs associated with hydrogel and biochar applications in table grape production.
Funding Support: California Table Grape Commission
