Grapevine Virus Resources

The Lodi Winegrape Commission has been actively studying the California grapevine virus situation since 2017. The Commission’s Research, Education, & Communications Committee formed two teams which have been instrumental in gathering information, creating educational materials and offering real-world, practical outreach for our winegrowing community: the Lodi Mealybug Biocontrol Research Focus Group and the Lodi Grapevine Virus Research Focus Group.

Grapevine viruses pose a severe threat to the sustainability of California viticulture. Unfortunately, there is little faith in virus prevention at any level. Growers are losing contract dollars as wineries reject grape loads due to virus-induced ripening problems. The good news is that there are virus management strategies that growers can implement right now in the short-term, which can be taught through real-world, hands-on, integrated outreach from a team of growers, extension personnel, PCAs and scientists.  With the right communication, a long-term cooperative virus strategy can save the California industry from devastating future losses. For more insight, see our blog post entitled, “Why Its Particularly Difficult to Protect Your Vineyard from Mealybugs & Viruses in California.”

Both the Mealybug Biocontrol and the Grapevine Virus Research Focus Groups were funded via grants from the American Vineyard Foundation, and the Virus Focus Group was aided by additional funds from the CDFA PD/GWSS Board for a project titled “Grapevine Virus Management in Lodi: A Collaborative Research & Integrated Outreach Effort to Help Solve a Statewide Challenge.”  Members from both Focus Groups continue to study vine mealybugs and grapevine viruses for the betterment of us all.

CANINE DETECTION OF VINE MEALYBUGS & LEAFROLL VIRUS

Can the robust olfactory senses of man’s best friend detect vine mealybugs and leafroll virus in a scalable and economically feasible way to help protect our vineyards? Yes, they can!

Canines have an extraordinary sense of smell due to the ~300 million olfactory receptors in their noses which they rely on for survival. Canine detection, already used in numerous applications for human health and safety, was recently rediscovered as an integrated pest management tool. In citrus orchards, dogs are used to locate Asian Citrus Psyllid, an insect that vectors Huanglongbing disease. Applied in viticulture, canine detection offers an opportunity for early, real-time, non-destructive field identification of pests and disease.

In 2023, the California Department of Pesticide Regulation (DPR) awarded a team led by the Lodi Winegrape Commission $428,118 for a proof-of-concept study looking at whether canines could detect our state’s most challenging vineyard pest and disease combo: leafroll 3 virus and its main vector, the invasive vine mealybug. The interdisciplinary research team included humans Stephanie Bolton, PhD (Lodi Winegrape Commission); Lisa Finke and Miguel Encinas (Canine Detection Services); Neil McRoberts, PhD (UC Davis); and Maher Al Rwahnih, PhD (Foundation Plant Services, UC Davis) as well as canines Malbec, Sauvi B, Cab and Zinny (pictured below).

Truly alarming shortfalls exist in our ability to quickly and accurately detect mealybugs and viruses, our available methods for mealybug and virus control and in our California Department of Food and Agriculture (CDFA) Grapevine Registration and Certification Program which is meant to help provide clean nursery vines for commercial vineyards. Below are some of the major challenges we face when it comes to protecting our grapevines from mealybugs and leafroll virus, in addition to the prohibitive cost of management for many farmers:

• Mealybugs and viruses continue to move through our grapevine supply chain.
• It takes up to two years before a human notices mealybugs in a vineyard. It may take much longer for leafroll virus to be noticed. Symptoms of leafroll virus are apparent in red grape varieties, but not in rootstocks or white grape varieties.
• The CDFA grapevine certification program offers a false sense of security due to the very limited – arguably, negligible – amount of virus testing it conducts. In 2023, only 0.0297% of registered nursery increase block vines (3,068 out of 10,324,963 vines) were tested by the CDFA for leafroll 3 virus. In comparison, New York State tests 25% of their registered nursery vines annually.
• Neither nurseries nor growers have access to real-time, non-destructive, affordable early detection virus testing that is accurate.

Well before we began our project, we hosted several meetings with California’s top nurseries, extension personnel, virus testing laboratories, growers, pest control advisors, consultants and leading mealybug and virus experts from across the globe. It became clear that to offer the most value to our industry, canine detection for leafroll virus should first be applied to the most popular/at risk nursery increase blocks with a focus on rootstocks and white varieties which do not show virus symptoms.

Following odor imprinting, behavior exercises and detection training with skilled Canine Handlers, three sets of trials using mealybug-infested and virus-infected vine material – indoor, outdoor and field experiments – led to statistically significant calculations for sensitivity and specificity. Sensitivity can be described as how good the dogs are at determining if a vine has vine mealybugs or leafroll 3 virus. Specificity is how good the dogs are at determining if a vine does not have vine mealybugs or leafroll 3 virus.

Anything above 90% for sensitivity and specificity is considered exceptional in the canine detection world for such a study, and detection is only expected to improve with more time and experience. Our four canines exceeded expectations, achieving average sensitivity and specificity levels between 93.4 – 99.6%! Now, we are ready to work with the winegrape industry to see how canine detection can help us all protect our vines and wines.

A very sincere thank you to the many growers and nursery professionals who took time to provide real-world advice which greatly contributed to the usefulness and accuracy of this research. Especially: Jordan Weibel and the DPR, the Lodi Winegrape Commission, Canine Detection Services, Dr. Nick Dokoozlian, Eric Pooler, Jason Saling, Dan Martinez and Martinez Orchards, Wonderful Nurseries, Nicholas Podsakoff and Sunridge Nurseries, Foundation Plant Services, Dr. Neil McRoberts’ lab, Charlie Starr, Emma Canepa, Dr. Kent Daane, Dr. Mark Sisterson, Dr. Marc Fuchs, Dr. Ying Zhai, James Brown, Sean Uchima, Dr. Bill Schneider and Dr. Bill Turechek. Our proof-of-concept canine detection project (DPR GRANT 23-PMG-R003) was funded by the California DPR with in-kind donations from nurseries, growers, scientists, industry, Foundation Plant Services, Canine Detection Services and the Lodi Winegrape Commission. The contents may not necessarily reflect the official views or policies of the State of California.

Interested growers and nurseries may contact Stephanie Bolton (209.367.4727) or Lisa Finke (lisa@canine-detection.com) to learn more.

NEW GROWER VIRUS WORKBOOKS AVAILABLE

Thanks to American Vineyard Foundation, CDFA PD/GWSS Board, and Lodi Winegrape Commission funding, members of the Lodi Grapevine Virus Research Focus Group and experts produced a 138-page book for the winegrowing community called WHAT EVERY WINEGROWER SHOULD KNOW: VIRUSES.  Full of pictures and written in grower language, the book addresses these topics and more: grapevine virus basics, nursery ordering, mealybugs, beneficial insects, virus testing, mapping your vineyard, virus spread, infected vine removal (including the USDA TAP), local case studies, and the sudden vine collapse.  Hard copy and electronic versions (with educational videos) are available.  Email Dr. Stephanie Bolton (stephanie@lodiwine.com) to get your copy.  Books will continue to be available while copies last.

To sign up for our new grapevine virus email list-serve, where you’ll be invited to all outreach events and given any important updates as they come along, send an email to Dr. Stephanie Bolton with the subject “virus email list subscribe.”

The Commission is happy to announce that Lodi is part of a CDFA BIFS project team looking at “Refinement and Implementation of an Areawide Program for Vineyard Pathogens and their Insect Vectors” and led by Dr. Kent Daane.  This project continues decades of work studying the regional management of mealybugs and leafroll virus in Lodi and the Central Coast.

OUTREACH VIDEOS

Below are recordings from the Lodi Mealybug & Virus Outreach Meeting on April 4th, 2019.  Speakers included Dr. Kent Daane (UCCE, vine mealybug expert), Dr. Marc Fuchs (Cornell Univ., grapevine virus expert), Prof. Gerhard Pietersen (South Africa, leafroll virus expert), and Dr. James Stamp (Stamp Associates, planting material expert).  There is a Q&A panel with the speakers, Chris Storm (Vino Farms, viticulturist) and Aaron Lange (LangeTwins, Vineyard Operations).  Funding for this meeting was provided by the American Vineyard Foundation, the CDFA PD/GWSS Board, the Lodi Winegrape Commission, and UCCE.  Over 250 people were in attendance and there are a lot of great take-home messages for virus management.

LEAFROLL VIRUS SPREAD VIDEO:

WESTERN SARE MEALYBUG BIOCONTROL VIDEO:

MALE MEALYBUG LOVES PHEROMONE LURE MORE THAN FEMALE MEALYBUG, VIDEO COURTESY OF DR. NATHAN MERCER (UC):

SUDDEN VINE COLLAPSE

As you are likely aware, we’ve been studying a mysterious vine collapse situation (happening mostly in San Joaquin, Stanislaus, and Coastal Counties in California thus far) since around 2010.  Patches of grapevines collapse over time – some of the growers saw 30% of a vineyard block collapse within just two years.  The vines may show stunted shoots and they usually push out some fruit before collapsing.  We have seen this collapse happen mostly on Freedom rootstock, but we now have confirmed cases on O39-16 and 101-14 and there are likely other rootstocks affected as well.  Many tests were conducted over the years by several PCAs and researchers until in 2018 a local team started uniformly collecting case studies and testing the patches in a consistent manner.  During the summer of 2019, Dr. Akif Eskalen and Dr. Maher Al Rwahnih came to Lodi to collect samples from four affected sites for high-throughput sequencing (HTS) to test for known viruses and any possible novel virus/es, and a thorough fungal analysis (partially funded by the Lodi Winegrape Commission).  Every collapsing vine tested positive for a leafroll virus and for a vitivirus. There were trunk disease pathogens isolated from each sample, but not the same ones.  We continue to collect case studies to investigate the potential role of leafroll virus and vitiviruses in the collapse disease complex. At this point, it is looking like a combination of a leafroll virus-sensitive rootstock, a leafroll virus, a vitivirus, and another stress (which could be possibly trunk pathogens, crop or water stress, etc.), leads to the collapse – which may be a form of virus-induced rootstock incompatibility.  Learn more at any CD11 LODI IPM NETWORK BREAKFAST meeting (held on the first Tuesday of every month, 8am, Burgundy Hall, Lodi Grape Festival Grounds – paused due to pandemic) or the next MEALYBUG & VIRUS OUTREACH MEETING. All are welcome. There is a significant amount of information about the Sudden Vine Collapse – including how to test for it and tips on management – included in the new virus workbook, WHAT EVERY WINEGROWER SHOULD KNOW: VIRUSES (available now by contacting stephanie@lodiwine.com).

Articles about the Sudden Vine Collapse:

  • Read our Lodi Growers Coffee Shop Blog article posted on February 24, 2020. “Sudden Vine Collapse.” By Stephanie Bolton, PhD. Reviewed by Maher Al Rwahnih, PhD, Akif Eskalen, PhD, and Charlie Starr IV, PCA.
  • Read Ted Rieger’s re-cap of the October 1, 2019 Mystery Vine Collapse Update Meeting in Lodi, hosted by the Lodi Winegrape Commission: “Sudden Vine Collapse May Be Associated with Combination of Virus Pathogens” (Wine Business Monthly).
  • Read the Chapter on the Sudden Vine Collapse in the grower virus workbook, WHAT EVERY WINEGROWER SHOULD KNOW: VIRUSES.

FURTHER READING

Here are some resources that we have found helpful as we’ve researched grapevine viruses:

If you have anything to add, please let us know! Send a link to Dr. Stephanie Bolton, stephanie@lodiwine.com.

HANDOUTS/PRESENTATIONS FROM OUTREACH EVENTS

WHAT EVERY WINEGROWER SHOULD KNOW: VIRUSES

As information became available, the Lodi Grapevine Virus Research Focus Group created draft booklets on different virus management topics.  These booklets were partially funded by the American Vineyard Foundation and the CDFA’s PD/GWSS Board.  In Spring 2020, we published these draft booklets, along with more educational material, tons of photos, and case studies, into a 138-page virus grower workbook called WHAT EVERY WINEGROWER SHOULD KNOW: VIRUSES.  Hard copies and electronic versions (flash drives) are now available for FREE to those interested – contact Dr. Stephanie Bolton for more information (stephanie@lodiwine.com).

TABLE OF CONTENTS

The Reason for This Book
Grapevine Virus Basics
– 7 Stages of Virus-Induced Grief
– Teamwork Required
– The Sneaky Cost of Viruses
– Virus Comparison Chart
Nursery Ordering 101: Viruses
– Plan Ahead for CDFA-Certified Material
– What to Do & Say to Order CDFA-Certified Material
– What is a CDFA-Certified Grapevine?
– Limitations of the CDFA Grapevine Registration & Certification Program
– Extra Testing by Growers
– How to Stay Informed & Organized
– Taking Responsibility
– Relationship Building
Mealybug Management
– The Basics
– Vine Mealybugs by the Numbers Poster
– Scouting for Vine Mealybugs
– Marking Hotspots
– Beneficial Insects
– Trapping for Vine Mealybugs
– Vineyard to Vineyard Spread
– Vine to Vine Spread
– Ants – The Other Farmer on Your Ranch
– Underground Roots
– Mealybug Resources
Virus Testing
– Why Test for Viruses?
– Before You Test for Viruses
– Red Leaf Flow Chart (for red grape varieties only)
– Which Viruses Should You Test For?
– When to Test for Viruses
– Commercial Virus Testing Laboratories
– How to Test for Viruses: A Step-by-Step Practical Guide
– How to Reduce Testing Costs
– What If You Have Viruses?
Infected Vine Removal
– Rogueing Basics
– Tips for Rogueing Infected Vines
– Pulling Out a Vineyard? Read This First (USDA TAP)
CASE STUDY: Scouting, Mapping, and Rogueing Vines
CASE STUDY: Replanting Following a Leafroll-Infected Vineyard
– Rootstock Trial
CASE STUDY: Neighborhood Communication
Sudden Vine Collapse
– The Beginning of a Collapse
– The History in Lodi
– Symptoms of a Collapsing Patch
– Getting Closer to Solving the Mystery
– The Dangerous Leafroll Virus & Vitivirus Combination
– Rootstocks & Virus Sensitivity
– Collapsing Vine Physiology
– Management Options for the Collapse
Future Research
BIFS Grant Announcement
Outreach Version of This Book
Beneficial Insect Risk Chart
Record Keeping

HELPFUL LINKS

IN THE PRESS

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