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.

One of the defining challenges of Red Blotch is its latency period. Vines may be infected for two to three seasons before visible symptoms appear. During this time the virus can spread within a vineyard without being detected.
Researchers and growers increasingly believe that many infected vines may remain asymptomatic for extended periods, meaning visual scouting alone cannot identify all infections.
​Because symptoms appear late in the season and may resemble other vine stresses, lab testing and systematic monitoring are often required to confirm infection.

How Red Blotch Spreads 

Infected Plant Material: 
The virus can be introduced into vineyards through infected propagation material if vines are not sourced from certified clean plant programs.
Insect Vectors:
Research has confirmed that the three-cornered alfalfa hopper (commonly referred to as Tika) can transmit the virus between vines.
​The insect feeds on vine tissues and can move the virus from infected plants to healthy vines.
The insect is often associated with vegetation surrounding vineyards, including grasses and cover crops.

Vineyard Management Strategies

​Because infected vines cannot be cured, management strategies focus on reducing spread and minimizing economic impact.
Rogueing Infected Vines:
Removing individual infected vines can be effective when infection levels are low and spread is localized.
Vineyard Removal and Replanting:
When infection levels increase within a block, growers may need to remove larger sections or entire vineyards. In some Napa Valley vineyards, hundreds of acres have been removed in recent years as part of coordinated Red Blotch management strategies. These Replanting decisions often take into account both vineyard economics and neighboring vineyard conditions.
Harvest Protocols:
Some growers have adopted pre-harvest scouting protocols to identify infected vines before harvest. Vines showing symptoms are marked so harvest crews can pick around them, preventing compromised fruit from entering the production pipeline.

The Importance of Neighborhood Collaboration

One of the most important lessons emerging from grower experience is that Red Blotch cannot be managed effectively by individual vineyards alone. The virus and its insect vector move across vineyard boundaries. As a result, management decisions in one vineyard can directly affect neighboring properties.

Growers throughout Napa Valley have begun forming neighborhood vineyard groups (such as Neighborhood Alliance for Vineyard Protection (NAViP)) that meet regularly to discuss disease management and share information. These groups provide a forum for growers and vineyard managers to:

• Share infection maps and monitoring results
• Discuss management strategies
• Coordinate vine removal timelines
• Align replanting plans
• Identify infection hotspots and coordinate responses between neighboring properties

These discussions can be difficult. Different vineyards may face different financial realities, grape contracts, or production goals. But growers consistently report that open communication helps prevent the virus from moving back and forth between adjacent blocks.
Some growers have even delayed replanting until neighboring infected blocks were removed to reduce reinfection risk.
Neighborhood collaboration has become one of the most practical and effective tools currently available for Red Blotch management.

Current Neighborhood Group Contacts

-NAViP is Chris D'Alo [email protected]
-Rutherford Central is Justin Leigon [email protected] 
​& Jake Maus [email protected]
-East Oakville is Maya Dalla Valle [email protected]
-Pritchard Hill is Cris Romero [email protected]
-West Rutherford is Enrique Herrero [email protected]

Example neighborhood map the group updates

Emerging Technology: Hyperspectral Imaging

One of the most promising areas of Red Blotch research involves hyperspectral imaging.

Hyperspectral sensors detect hundreds of wavelengths of light reflected from plant tissues. These signals can reveal biochemical changes in leaves that occur before visible symptoms appear.

Researchers are currently exploring several ways to deploy this technology:

• Drone-mounted hyperspectral cameras
• Aircraft surveys covering large vineyard regions
• Ground-based robotic or tractor systems

Recent aerial surveys have already mapped more than 15,000 acres of vineyards using hyperspectral imaging, allowing researchers to analyze infection patterns across large areas. 

In recent field tests, researchers have demonstrated that hyperspectral systems can identify infected vines with approximately 75–85 percent accuracy, even before symptoms are visible.

Key Takeaways for Napa Valley Growers

​Red Blotch remains one of the most challenging vineyard diseases facing Napa Valley today. However, grower experience and ongoing research are helping build a clearer understanding of how to manage it:
Early detection matters:
Visual scouting, lab testing, and emerging technologies can help identify infections sooner.
Management decisions are vineyard-specific:
Strategies depend on infection levels, vineyard age, economics, and neighboring vineyard conditions.
Collaboration is essential:
Communication between neighboring growers can significantly influence outcomes.
Integrated management works best:
Successful strategies combine monitoring, rogueing, vector management, and coordinated replanting.

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.

​Research & Industry Resources

Staying informed on Red Blotch requires both practical vineyard guidance and access to emerging research. The following resources connect growers with trusted information from university, industry, and scientific partners.

Practical Grower Guidance
UC Agriculture and Natural Resources / UC Davis
California-focused research and extension guidance on Red Blotch, vector management, diagnostics, and vineyard decision-making.
Cornell University Viticulture Program
Research from leading Red Blotch experts, including work on virus biology, vector transmission, and disease ecology.
Oregon State University Extension
Grower-facing guides on Red Blotch prevention, testing, monitoring, and economic decision-making.

National Research & Industry Coordination
National Grape Research Alliance
NGRA helps coordinate national grape research priorities, funding, and extension efforts across the U.S. grape and wine industry. Their site is especially useful for tracking current research priorities, supported projects, webinars, and newsletters related to vineyard health, clean plant material, pest management, and emerging technologies. NGRA notes that its collaborative approach has helped yield approximately $65 million in funded grape research.

Advanced & Technical Research
IVES Open Science
IVES is a global open-access platform for viticulture and enology research. It is best suited for growers, vineyard managers, consultants, and technical teams looking for deeper scientific information on Red Blotch, including vine physiology, wine impacts, disease detection, and emerging technologies such as hyperspectral imaging. IVES allows users to search across its open-access media, including OENO One, IVES Technical Reviews, and IVES Conference Series.

Additional Resources

ROOTSTOCK 2024: New Research on Red Blotch 
Marc Fuchs, Professor, School of Integrative Plant Science Plant Pathology and Plant-Microbe Biology Section Cornell AgriTech​ 

ROOTSTOCK 2024: Recent Advances in Red Blotch Disease Ecology Inform Management
​Monica Cooper, Director & ANR Advisor, UC Cooperative Extension, Napa County
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