A Virus Scouting and Vine Rogueing Program in Lodi Vineyards
November 01, 2019
|Red leaf symptoms on a Cabernet Sauvignon vine in Lodi that tested positive for leafroll virus. Photo: Ted Rieger
LangeTwins Family Winery & Vineyards in Lodi has implemented a vineyard virus scouting, mapping and vine rogueing program aimed at managing leafroll and red blotch virus infections and preventing their spread. The program, used in newer plantings of red winegrape varieties (planted since about 2013) is modeled after a successful program used in South Africa where vine mealybug (Planococcus ficus) and leafroll viruses have been ongoing management issues in winegrape vineyards.
The Lodi Winegrape Commission (LWC) held a leafroll virus tailgate talk October 17 at a LangeTwins managed vineyard where virus scouting and vine rogueing takes place. Aaron Lange, vineyard operations manager at LangeTwins, provided background, presented case studies and displayed maps and data for specific vineyards where the program is used.
Lange described symptoms and problems associated with the virus of most concern, grapevine leafroll-associated virus 3 (GLRaV-3), that can turn vine canopies red in red grape varieties, reduce yields, and reduce color and anthocyanin content in fruit. He acknowledged that leafroll virus has existed a long time in Lodi and other California vineyards, but said it has become a bigger concern and problem over the past 15 years due to the introduction and spread of the vine mealybug (VMB). “We’ve never had a vector like the VMB that is so efficient at spreading leafroll and is difficult to control--that is a critical point,” he observed. He told growers, “If you don’t think you have viruses or VMBs in your vineyard, you’re not looking hard enough.”
Lange noted the virus management challenges in the Lodi region where vineyards are the dominant crop and numerous landowners and growers are involved. He explained: “We have vineyards everywhere, and managing just your own field is not enough. You have to look across the road at your neighbor and have that delicate conversation about their virus issues and management. It’s not easy, but it’s something we have to do. This has to be a community-wide effort.”
LangeTwins has trained in-house vineyard workers to recognize virus symptoms for scouting vineyards. A crew of 10 to 15 people walk vineyard blocks during the season when red leaf symptoms are most prominent—generally from about August through October. Scouting usually begins during the season of a new vineyard’s third leaf, when virus titer reaches high enough levels to show visible symptoms. Charlie Starr, a grape grower and an independent pest control advisor (PCA) who works with Lange Twins is involved in training and managing the crew. Starr said, “We train them to recognize red leaf symptoms by taking them to a field where we know the vines have viruses and symptoms and have tested positive for leafroll.” Starr believes it’s best to use the same people each year. They tend to get better over time, they are in the field regularly throughout the season, and they develop the ability to see nuanced differences in symptoms between different varieties.
Communication between crew members who inspect both sides of the vine row is helpful to better identify symptoms. Based on his experience, Starr says leafroll symptoms can be more easily seen when the leaves are backlit with sunlight. Starr said the vines should show red leaves throughout the whole vine on multiple canes before being marked. A goal is to try to eliminate the possibility of other problems such as petiole girdling or nutritional deficiencies that may show up as more spotty red leaf patterns. Symptomatic vines are marked with flagging tape tied around the vine trunk, with a different color tape used each year.
A more experienced crew member will follow-up using GPS on a portable device to record and map symptomatic vines. This person also serves as an auditor to validate the crew’s decision to mark the vine, or they can remove the flagging if they don’t agree. Once the vines are marked and mapped, field samples are taken for lab testing to confirm virus infections. To date, the crew has had a high success rate with 90 to 100 percent of flagged symptomatic vines tested being confirmed for GLRaV-3 infection.
The scouting program is used only for red varieties (white varieties do not display enough symptoms). This includes common varieties such as Cabernet Sauvignon, Pinot Noir and Zinfandel, and newer plantings of Italian varieties such as Aglianico and Teroldego. Starr said Petite Sirah is more challenging as it commonly displays red leaves due to potassium (K) deficiency.
Lange provided detailed information about a 45-acre vineyard of Cabernet Sauvignon planted on virgin ground in 2013. Virus symptom scouting began in 2016 and leafroll testing indicated 8.1 percent of the vineyard was infected. (See chart below for vine infection status by year.)
|2016||2,468 vines virus +||(8.1% of vineyard)|
|2017||334 vines virus +||(1.2% of vineyard)|
|2018||338 vines virus +||(1.2% of vineyard)|
|2019||408 vines virus +||(1.5% of vineyard)|
Lange said a goal is to maintain virus infection below 1 percent each year to maintain economic viability (based on the South African management model). Although rogueing and management provided good results in this vineyard for two years after the first year of scouting—reducing infections from 8.1% to 1.2%, Lange is concerned that the infection rate increased slightly in 2019 to 1.5%.
He suspects the initial virus infection came from infected vines in source wood from the nursery. Based on his experience, he said, “I don’t think any nursery can guarantee 100 percent clean material.” However, given the rise in symptomatic vines this year and their distribution based on mapping, Lange suspects secondary infections could be occurring.
He said, “It’s my anecdotal opinion, if vine roots are left in the ground that are infected with the virus and VMB, this can be a source to re-infect remaining vines. We need to do a better job of removing roots when rogueing vines.” Lange noted that during the second year of rogueing, the company not only removed known infected vines, but began removing one vine on both sides of each known infected vine in the row.
This is now standard practice to reduce spread, as adjacent vines may be more likely to be infected but not show symptoms.
Although VMB is managed to the extent possible using treatments with products such as Admire, It is difficult to control VMB and prevent its spread. It is known that birds can spread VMB within and between vineyards, particularly if they contact sticky honeydew in the vines produced from VMB feeding. Argentine ants are also found in Lodi vineyards that will protect VMB from predatory insects, thus, ant management is required for VMB control.
In another case study, Lange talked about a block of Aglianico planted in 2013 near an old vine Zinfandel vineyard planted by his grandfather in 1952. Symptoms and leafroll infected vines were initially seen in the new Aglianico vineyard in the rows closest to the Zinfandel vineyard, indicating an “edge-effect” of leafroll virus vectored from the Zinfandel by VMB. The Aglianico vineyard has been scouted, tested and rogued since 2016. Although old Zinfandel vineyards can continue to be productive and show few virus symptoms, they can harbor latent leafroll virus that can be vectored to clean vineyards. Lange faces a decision on whether to remove the historic Zinfandel vineyard that his family has farmed for three generations.
|Aaron Lange, vineyard operations manager for LangeTwins Winery & Vineyards, discusses a virus scouting, mapping and vine rogueing program implemented in his company's vineyards. Photo: Ted Rieger
Lange said the cost of scouting with the trained crew is about $15 to $25 per acre. Other costs include lab testing, mapping and data recording, and the cost of vine rogueing and replacement.
Generally, if more than 20 to 25 percent of the vineyard is infected, it is not considered economical to rogue, and vineyard removal may be more practical. However, other considerations include the yields and quality parameters for the grapes being produced from the remaining viable vines, and the prices received for grapes and overall income from the vineyard.
Lange pointed out that every grower’s vineyard status and financial situation is different, so rogueing and removal programs will not be possible for every grower. Nonetheless, he said, “The longer an infected vineyard stays in the ground, the longer it acts as a potential reservoir that can spread virus to nearby vineyards. In some situations, aggressive and careful vector control may be the only weapon we have against the spread of this virus.”
Lange advocated that growers contact trade associations they belong to and lobby for more funding for programs such as the U.S. Department of Agriculture’s (USDA) Tree Assistance Program (TAP) that provides some funding for specified grapevine losses. Such programs could provide financial incentives for growers to rogue virus-infected vines and remove and replant vineyards. Since it is unlikely the VMB can be adequately controlled, Lange believes research is also needed to come up with genetic solutions for virus management.
LWC Virus Outreach Activities
The LWC field day included a chance for participants to test their own virus symptom identification skills. Vines in two rows of a Cabernet Sauvignon vineyard were lab tested for GLRaV-3. After visually inspecting each vine, participants could check their answer by looking within a folded paper at each vine indicating whether it was positive (+) or negative (-) for GLRaV-3.
The LWC plans to host its third and final annual Mealybug & Virus Outreach Meeting, open to all growers, on April 9, 2020 at the Cabral Ag Center in Stockton.
The LWC has produced draft educational booklets through its Grapevine Virus Research Focus Group that include “Nursery Ordering 101: Viruses,” “Vine Mealybug Management,” and “Grapevine Virus Testing 101.” More information and copies are available by contacting LWC grower communications and sustainable winegrowing director Dr. Stephanie Bolton by e-mail at firstname.lastname@example.org