The west coast wine industry is vital to the U.S. economy. Together, the states of California, Oregon, and Washington contribute over $80 billion to the market and employ nearly 500,000 people. However, grapevine viruses, like leafroll and red blotch disease, are putting west coast vineyards at risk.  

In October, a committee of experts convened by the National Academies to study grapevine viruses travelled to Washington State to advance their understanding of these viruses and identify avenues for improving their management. The trip included a visit to the Irrigated Agriculture Research and Extension Center (IAREC) in Prosser, Washington and area commercial vineyards. 

Dr. Anna Whitfield, chair of the committee and a professor of entomology and plant pathology at North Carolina State University, detailed the importance of seeing the impact of grapevine viruses in a field setting. 

“Visiting the nursery provided an opportunity to see the grapevine production system first-hand and learn about challenges that viruses pose to grapevine propagation,” Whitfield said. “We were also able to see side-by-side comparisons of healthy and virus infected vines to see the effect of virus on fruit yield and the impact on sugar content in the fruit.” 

The committee is specifically interested in understanding the current state of knowledge on leafroll and red blotch disease, two viruses causing adverse effects to commercial wineries around the world, and identifying areas for future research.  

What is Grapevine Leafroll Associated Virus Type 3?

Grapevine leafroll-associated virus 3 or GLRaV-3 is considered the most economically harmful virus impacting grapevines.  Typically spread by mealybugs and other insects, the virus is difficult to effectively control. Infected vines have a decreased lifespan and a decreased yield and fruit quality, which sets back wine production and creates monetary losses to growers. 

Grapevines are long-lived, perennial plants, so if one plant becomes infected, it can be a source of infection to other nearby vines and vineyards. Growers must be extremely careful to not spread GLRaV-3 from infected vines to other vineyards through propagation of cuttings or budwood.    

According to committee member Dr. Naidu Rayapati, there is no way to cure a vine infected with leafroll because plants do not have a way to fight the disease. 

“Plants do not have an immune system analogous to humans where vaccines can boost immunity to viral infections,” Rayapati said. “So, the only option for managing viral diseases in plants is a ‘prevention is better than cure’ strategy.” Rayapati is the director of IAREC and leads an integrated program of research, teaching, and outreach in plant virology with a strong focus on grapevine viruses in Washington state. 

What is Grapevine Red Blotch Virus?

Similar to leafroll, red blotch disease creates visible damage to grapevines. Red Blotch disease can result in grapevines having a decreased lifespan and poor fruit quality. The spread of red blotch virus (GRBV) is facilitated mainly by humans. Growers can unintentionally introduce these viruses to vineyards by using virus-infected plant material during propagation and planting. 

“Starting with clean planting materials is the first step towards reducing the spread of these viruses,” Dr. Whitfield said. 

Other modes of transmission, such as the treehopper insect, have been evaluated but additional research is needed to confirm their role in field spread of the virus. 

Impact of Viruses on Wine Production

Both leafroll and red blotch viruses reduce overall yields and alter key quality characteristics in grapes, like sugar content, that can negatively influence the quantity and quality of wine production.  

“Reduced yield has implications to growers’ income and poor quality of fruit translates into low quality wine with less favored quality attributes,” Rayapati said. “These viruses affect both growers and wineries, and ultimately tarnish the reputation of the Washington wine industry as a premium wine producing region.”    

If not controlled, both viruses will continue to spread to surrounding grapevines and result in greater losses to the industry. The committee learned that while viruses are an urgent and priority issue, they are not the only thing impacting wine production. Climate change is also threatening the long-term production and sustainability of growers and wineries.  

“The work of the committee is increasingly urgent due to the impact of changing climatic conditions on vector biology and plant physiology,” Whitfield said. 

The committee members have varied expertise and aim to take a holistic approach to this project. Together, they will review the state of grapevine viruses, identify knowledge gaps and institutional challenges, and suggest areas of research to improve management of leafroll and red blotch. The study, slated for release in 2024, is being led by the National Academies’ Board on Agriculture and Natural Resources and sponsored by the California Department of Food and Agriculture. 

“We have a greater responsibility and unique opportunity to set the stage for effectively dealing with the two viral diseases from a long-term perspective and provide the right direction for the American wine industry and its global competitiveness,” Rayapati said. 

• To learn more about this project please visit the project webpage: https://www.nationalacademies.org/our-work/assistance-to-the-california-department-of-food-and-agriculture-pierces-diseaseglassy-winged-sharp-shooter-board-on-grapevine-viruses-and-grapevine-disease-research 
  
  
• To stay updated on the project’s progression, including upcoming webinars, sign up for updates: https://www.nationalacademies.org/banr/board-on-agriculture-and-natural-resources  

• To learn more about this project please visit the project webpage: https://www.nationalacademies.org/our-work/assistance-to-the-california-department-of-food-and-agriculture-pierces-diseaseglassy-winged-sharp-shooter-board-on-grapevine-viruses-and-grapevine-disease-research 
  
  
• To stay updated on the project’s progression, including upcoming webinars, sign up for updates: https://www.nationalacademies.org/banr/board-on-agriculture-and-natural-resources