Location: Horticultural Crops Production and Genetic Improvement Research Unit
Project Number: 2072-21000-055-035-G
Project Type: Grant
Start Date: May 1, 2022
End Date: Oct 31, 2025
Objective:
1. Determine the impact of fruit removal during droughts on vine performance and long-term productivity of different wine grape varieties.
2. Evaluate the impact of extra irrigation in anticipation of heatwaves on vine performance and fruit composition of different wine grape varieties.
3. Develop recommendations for wine grape growers on vineyard best-management practices through droughts and heatwaves.
Approach:
To evaluate common but scientifically untested industry practices, we will establish field trials with two major wine grape varieties, Cabernet Sauvignon and Riesling. Trials will be conducted in a Washington State University (WSU) vineyard near Prosser. Water supply in this arid region (8” annual precipitation) is controlled via drip irrigation with water fed by snow melt in the Cascade mountains.
Objective 1: We will simulate drought due to irrigation water shutoff (e.g. due to insufficient mountain snowpack) either after fruit set or during ripening. None, half, or all the fruit will be removed at the start of each drought period. The experiment will be designed as a replicated (four blocks) split-plot with irrigation shutoff timing (and a standard RDI control) assigned to main plots and fruit removal assigned to sub-plots within neighboring blocks of each of the two varieties. The trial will be repeated three times from 2022 through 2024; if irrigation water were to be shut off at other times by the irrigation district (pitfall), we will adapt treatments accordingly. We will measure soil moisture (neutron probe and capacitance probes), vine water status (pressure chamber), gas exchange (infrared gas analyzer), canopy growth (shoot number and length, pruning weight), leaf wilting or yellowing, and (except in the 100% fruit removal treatment) yield and its components (cluster number and weight, berries per cluster, berry weight) and fruit composition (total soluble solids, titratable acidity, pH). Carryover effects on vine growth and yield formation into the next growing season will also be evaluated. Data will be analyzed using statistical methods (analysis of variance, correlation analysis) consistent with the experimental design used.
Objective 2: In another field trial using the same two varieties, we will apply extra irrigation water ahead of any forecasted heatwaves (>95°F) for comparison with standard regulated deficit irrigation (RDI) without the addition of extra water. An unlikely pitfall is that no heatwaves will occur through 2024, but treatments may be modified in Years 2 and 3 depending on results from year 1 and on the frequency and severity of heatwaves. A completely randomized design with four replicates will be used in each of the two varieties (Gohil et al. 2016). Measurements and data analysis will be done as described for Objective 1. In addition, the incidence of sunburn on the fruit clusters will be estimated and, in Cabernet Sauvignon, tannins, anthocyanins, and other phenolics (HPLC), and methoxypyrazines (MS/MS/QQQ) will be analyzed in berry samples sent to ETS Laboratories.
Objective 3: We will integrate the results from all field trials to develop evidence-based practical recommendation for growers regarding best-management practices for mitigating drought and heat stress episodes. The outcome will enhance growers’ preparedness and resilience in coping with the challenges posed by a changing climate.
