Unveiling the Spatial-Temporal Impact of Red Blotch on Grape Composition and Grapevine Physiology and Exploring Mitigation Strategies Via Cultural Practices. AVF Project # 2025-2964.
Summary of Progress:
Grapevine Red Blotch Virus (GRBV) is a disease that can slow grape ripening and reduce fruit quality, creating economic challenges for vineyard owners and winemakers. During the first year of this project, our team focused on understanding how this virus affects grape sugar levels, acidity, and vine health in real commercial vineyards, and on testing practical ways growers might reduce its impact.
Field research was conducted in commercial vineyards in Napa Valley and Paso Robles, California. We compared vines that tested positive for the virus with healthy vines using laboratory molecular testing to confirm infection status. Throughout the growing season, we measured vine water status, leaf photosynthesis, and grape chemistry. The results showed that infected vines generally produced less sugar and ripened more slowly, while differences in acidity and pH were smaller and more temporary. On average, fully infected vineyard blocks could experience approximately 1.5–2 degrees lower sugar levels at harvest, which can influence wine alcohol content and overall quality.
A key accomplishment this year was the use of advanced imaging technology, hyperspectral sensors mounted on drones and ground equipment, to map vine health and fruit composition across entire vineyard blocks. These high-resolution maps revealed that the virus does not affect all areas equally. Instead, sugar losses tend to appear in clusters or zones. This finding is important because it suggests that growers may benefit from targeted management, selective harvesting, or fruit segregation rather than treating an entire block the same way.
In addition, we established a large field trial to evaluate potential mitigation strategies using plant growth regulators, nutrient supplements, and biostimulants. Early results indicate that some treatments may influence ripening speed or sugar accumulation, although differences were modest in this first season. This work is ongoing and will be expanded in future years to better separate treatment effects from infection status and to include additional management factors such as irrigation and canopy management practices.
Overall, this year’s accomplishments include: (1) confirming measurable sugar losses associated with GRBV, (2) demonstrating that spatial mapping can reveal hidden economic risk within vineyard blocks, and (3) launching practical field trials aimed at identifying tools growers can use to reduce disease impact. Future work will continue data analysis, integrate imaging results more deeply, and repeat experiments across additional sites and seasons to strengthen recommendations for the industry.
