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Foundation Plant Services Institutes Annual Vine Testing After Red Blotch Finds at Russell Ranch

FPS Annual Grape Meeting Informs Industry on Red Blotch Issues
by Ted Rieger
January 10, 2018

After finding grapevine red blotch disease, caused by grapevine red blotch virus (GRBV), in five grapevines in the Russell Ranch Foundation Vineyard in 2017, UC Davis (UCD) Foundation Plant Services (FPS) has instituted a new management policy to perform annual testing for red blotch and leafroll viruses for every vine at Russell Ranch.

FPS Foundation vineyard blocks serve as the source repository for certified, virus-free and true-to-variety clean grapevine plant material distributed to nurseries under the California Department of Agriculture’s (CDFA) Grapevine Registration and Certification (R&C) Program. The Russell Ranch Vineyard was developed beginning in 2011 to meet the National Clean Plant Network’s “Protocol 2010” standards for clean plant material that exceeds the California R&C Program’s requirements, and now requires testing for 38 different grapevine viruses and diseases.

FPS first announced its 2017 red blotch test findings in a letter to its industry customers dated December 20, in addition to meeting with affected customers and posting information on its website (http://fps.ucdavis.edu).

The new management procedures, and a detailed discussion that shed further light on the red blotch finds and remediation measures, were presented at the Annual FPS Grape Advisory Committee meeting January 9 at the FPS facility in Davis by FPS diagnostic and research laboratory director Dr. Maher Al Rwahnih.

“Moving forward, all of Russell Ranch will be tested annually for grapevine red blotch virus (GRBV), and for grapevine leafroll associated virus-3 (GLRaV-3) by composite testing,” Al Rwahnih said. In addition, the vineyard will be visually inspected for virus symptoms and vectors more frequently. Under CDFA R&C Program requirements, every Foundation vine is required to be tested only once every five years for red blotch and leafroll, and the vineyard is required to be visually inspected twice a year.

Al Rwahnih said red blotch was suspected at Russell Ranch after a visual inspection in the vineyard in September 2017 showed red leaf symptoms on one Syrah vine. There were also signs of the presence of the known red blotch vector, the three-cornered alfalfa hopper (Spissistilus festinus).

Planting at the Russell Ranch Vineyard began in 2011. GRBV was formally identified in 2012 as a new virus and disease of grapevines. Since 2013, vines at Russell Ranch have been tested for GRBV at least every two years. No GRBV was found until 2017, when five vines tested positive out of 4,132 vines planted. The locations of the five GRBV-positive vines in the vineyard was scattered, with no adjacent vines testing positive, indicating a random transmission to the individual vines by the vector. The five vines were removed and destroyed.

The vines testing positive in 2017 were one each of the following varieties/clonal selections: Chardonnay 102.1, Pinot Noir 82.1, Syrah 6.1, Syrah 13.1, and Sweet Scarlet 1.1 (a table grape). Of these selections, only two have a history of distribution to commercial nurseries—Chardonnay 102.1 with two orders in 2013, and Sweet Scarlet with one order in 2014. Since FPS records show that vine material for each of these selections was distributed prior to their last negative test result, the material distributed was likely free of GRBV. FPS notified the customers of its findings and offered testing services.

FPS has also been regularly testing its older Classic Foundation Vineyard (with planted material dating to 1992) for GRBV since 2013. In 2017, one vine of Pinot Noir 47, tested positive out of 4,088 total vines planted. This was the first red blotch positive vine found in the Classic Vineyard since 2014. It has been previously reported that nine vines tested positive for GRBV in 2013 and 6 vines tested positive in 2014 in the Classic Vineyard.

Following the 2017 red blotch finds and suspected vector transmission, FPS staff conducted a survey covering a two-mile radius surrounding Russell Ranch to locate possible sources of GRBV in nearby grapevine material. The survey located grapevine material at four properties that was collected for testing: a home backyard, an elementary school, a retail home garden center, and the riparian corridor of Putah Creek. FPS lab testing showed one or more GRBV-positive vines from the first three sites listed above. The property owners were contacted, and they cooperated with removal of the infected vines. Further lab testing of the virus from the Russell Ranch positive vines compared with the outside infected vines indicated the infections came from multiple (perhaps all three) sources, and likely occurred in separate infection events.

In addition to annual testing of Foundation vineyards, Al Rwahnih listed the following steps FPS is taking to prevent red blotch infections:

--Pursue an area-wide approach with nearby growers to reduce and better manage alfalfa plantings that could host the vector.

--Further study the epidemiology of the vector.

--Increase regular visual inspections for the vector in Foundation vineyards that will be biweekly from April through June, and weekly from July through October.

--Continue and improve vector control treatments in Foundation vineyards that include systemic insecticides, and the possible use of contact insecticides and kaolin sprays.

To date, the three-cornered alfalfa hopper is the only confirmed red blotch vector, however, researchers continue to evaluate other possible “candidate” vectors. Some insects have been shown to be able to acquire GRBV after feeding on infected plant material, but their ability to transmit the virus has not yet been confirmed in lab or greenhouse studies.

Al Rwahnih summarized, “We will continue to maintain the highest standard of testing for our Foundation vineyards and keep you informed as soon as possible as new information becomes available.”

FPS director Dr. Deborah Golino said, “From a policy viewpoint, we will test every vine every year until we know more about red blotch infection risks.” Golino said if the vector and infection risk become an ongoing problem, other measures to consider would be downsizing the number of selections planted at Russell Ranch, and the possible use of screen houses to protect vines from vectors.
 

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