Grapevine Red Blotch Virus​

Grapevine Red Blotch Virus (GRBV) is one of the most complex viral challenges facing vineyards today. It affects vine physiology, delays fruit ripening, and reduces sugar accumulation, ultimately impacting grape quality and vineyard economics.​

​What is Red Blotch?

Grapevine Red Blotch Virus is a DNA virus in the Geminiviridae family that causes Grapevine Red Blotch Disease (GRBD).
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Common impacts include:

• Delayed ripening and reduced sugar accumulation in fruit
• Reduced cluster weight and potential yield loss
• Altered acid balance and phenolic development
• Visible red blotches or vein discoloration on leaves in red varieties, or chlorosis in white varieties

​Once a vine is infected, there is currently no cure, making early detection, clean plant material, and vineyard monitoring essential. 

Grapevine Red Blotch Virus (GRBV) was first recognized in Napa Valley in 2008 at the UC Davis Oakville Experimental Station, when researchers observed unusual red leaf symptoms in Cabernet Sauvignon vines that did not match known grapevine diseases.

Examples of NVG’s Work to Combat Red Blotch

Commitment
Napa Valley Grapegrowers recognizes the Red Blotch Virus as one of the most significant vineyard health challenges facing Napa Valley today. Because vineyard viruses do not respect property lines, effective mitigation depends on collaboration across neighboring vineyards and the broader growing community.
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Education
Education remains NVG’s most important role in addressing red blotch.

NVG has worked to bring the latest science directly to growers through programming and field-based learning opportunities. In 2024, NVG dedicated the entire ROOTSTOCK conference to Red Blotch, convening leading researchers and growers to discuss the current understanding of the virus, vineyard impacts, and emerging monitoring tools.

Continuing this effort, NVG hosted a grower field day in 2026 focused on collaborative management approaches and new detection technologies. NVG continues to feature red blotch research and updates through conferences, field days, and educational communications so growers remain informed as science evolves.

Advocacy
NVG also advocates for continued investment in red blotch research and solutions that support vineyard sustainability.

Executive Director Caleb Mosley serves on the Board of Directors of the California Association of Winegrape Growers (CAWG), where NVG helps elevate grower priorities and encourages continued funding for research into grapevine diseases, including red blotch.
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Through this industry collaboration, NVG works to ensure that growers remain part of the conversation shaping research priorities, policy discussions, and long-term strategies for vineyard health.

Additional Resources

University of California Agriculture and Natural Resources - UC IPM Pest Management Guidelines

Sustainable Vineyard Practices 2023
Biological and Chemical Pruning Wound Protectants and Update on Trunk Disease Management
Akif Eskalen, Department of Plant Pathology, UC Cooperative Extension 

​Sustainable Pest Management: A Roadmap for California

Sustainable Vineyard Practices 2023
Spider Mite Management: Biological and Chemical Approaches
​David Haviland, Farm Advisor, UC Cooperative Extension
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​Sustainable Vineyard Practices: Pests & Disease 2022

• Updates on vine mealybug management: mating disruption, biological control, and organic insecticides 
  Dr. Kent Daane, CE Specialist, UC Berkeley
• A regional approach to VMB management in Napa County 
  Dr. Monica Cooper, ANR Advisor (Viticulture), UCCE-Napa County
• The value of a Grape Powdery Mildew (GPM) spore trap network: how decision-makers are using spore data to manage GPM
  ​Bryan Rahn, President, Coastal Viticultural Consultants, Inc.