A year ago grape growers and wineries feared that a shortage of grapevines from commercial nurseries could impact their replanting efforts, but nurseries assured them they’d have plenty of vines to plant by now.

Red blotch virus has changed all that. The troublesome virus has become a priority issue, and the demand for vines free of the infection has caused a new setback for some nurseries trying to fill growers’ orders. “Red blotch has pushed deliveries back to 2015 and 2016 for many vines,” said Michael Monette of Sunridge Nurseries in Bakersfield, Calif. “We were already juggling vines because of leafroll virus, and now every customer demands vines free of red blotch.”

The National Clean Plant Network (NCPN) at Foundation Plant Services based at the University of California, Davis, has developed strict “Protocol 2010” standards that confirm the absence of many plant pathogens including viruses. To qualify as Protocol 2010 plant material, the vines must have been created using micro-shoot tip culture and tested for an extensive list of pathogens. This process can take several years. Vines that meet the Protocol 2010 standards are planted in the
primary NCPN foundation collection
at Russell Ranch, near Davis, Calif.

To date, however, only a limited number of plants have been available to nurseries for commercial-scale propagation. The first vines to qualify for Protocol 2010 vines were rootstocks planted in 2011. There are now more than 1,000 vines planted at Russell Ranch that are starting to produce plant material for grapevine nurseries.

Until the supply of new plant materials from the NCPN ramps up to the level they need, the nurseries will continue using their own strategies to deliver virus-free vines.

Sunridge manager Steve Maniaci said, “We have tested and found absolutely zero red blotch-positive vines in our Bakersfield certified increase blocks.”
The company won’t accept scion wood for grafting unless it’s certified, he added.

At Duarte Nursery in Hughson, Calif., one of the largest grapevine suppliers, John Duarte said, “There is a high demand for vines that are certified free
of red blotch. We are propagating and supplying vines that are red blotch tested and clean. The supply of vines is sufficient, but we have a few rootstock varieties where we cannot accept further commitments. We have many that we
can offer for spring 2014 delivery.”

Novavine in Santa Rosa, Calif., also provides red blotch-free vines. “We’re testing a lot of material,” said Novavine’s Sam Caselli. “Red blotch likes to hide,”
he said. “We’ve had to readjust. A lot of orders were affected by the new demand for vines clean of red blotch.”

About red blotch
The symptoms of red blotch disease—more formally, grapevine red blotch
associated virus (GRBaV)—were first described in 2008, and transmission by grafts was confirmed in 2012, according to Dr. Marc Fuchs of the Department of Plant Pathology at Cornell University in Geneva, N.Y., who recently shared the latest intelligence regarding red blotch virus.

The virus also was recognized in 2012, and an assay was developed to detect and confirm its presence. The first potential vector was identified in 2013. The symptoms of the virus are red blotches and spots on leaves, though a small percentage (2.5%) of infected vines don’t show any symptoms, likely because of the latency of disease onset. The red ranges from pink to crimson.

(Editor’s note: Find further description of GRBaV, numerous photos by Dr. Fuchs and others, as well as a short list of labs that can test for the virus in Wines & Vines’ April 2013 issue.)

Other viruses like leafroll also color leaves, but GRBaV displays a different pattern of red than leafroll does. “Red blotch can dramatically affect quality,” Fuchs said. Red blotch virus delays ripening. It can lead to 5° or 6° lower Brix in mature grape berries. It also affects the anthocyanins and can lead to reduced color in red grapes and their wines.

Fuchs mentioned the challenge of confirming that the phenomenon met the criteria for a disease, a problem partly because viruses won’t grow in petri dishes—only in their hosts. Nevertheless, researchers have found that GRBaV causes red blotch. Unfortunately, he noted, your eyes aren’t enough to identify the virus.

Polymerase chain reaction (PCR) assays are available to identify GRBaV. Tests can identify presence of the virus in any tissue of the vine—leaf, petiole, dormant canes or clusters—at any time of year. Because of the difficulty confusing symptoms of the virus with other viruses, he said: “Test, don’t guess.”

Fuchs said research suggests there may be two variants of the virus. Red blotch virus can be found in both red and white wine grapes, in table grapes, raisin grapes and rootstocks. As of November 2013 it had been detected in winegrowing regions in California, Oregon, Washington, British Columbia, Virginia, Pennsylvania, Maryland, New Jersey, New York and Ontario, Canada.

Red blotch virus is spread by propagation and grafting, and anecdotal evidence suggests it may spread by other means. The Virginia creeper leafhopper (Erythroneura ziczac) seems to be able to transmit red blotch virus from vine to vine in the greenhouse, but it’s not yet proven that the leafhopper is a vector in the field. Fuchs says that at this point, the best way to manage the disease is to select planting material carefully.

Grower’s concerns
Novavine’s Caselli added that after two heavy crop years, many growers are being cautious about planting anyway. He said Novavine has good availability of dormant vines for 2014. “We will sell out what we have, however.”

Duarte does not expect a shortage of vines, but the company is seeing a higher demand for certain varieties. Overall, its sales are currently about even with 2013.

Duarte noted that growers are more educated about diseases and viruses than in the past, and they request clean plant stock. “We have seen an increasing number of customers who would like to come and test our mother blocks. Duarte Nursery allows any customer to test its mother block stock or any plant material prior to grafting. This has been requested more with the concern for red blotch disease.”

Sunridge’s Maniaci said that growers ask for certified vines, but many compromise by using “tested” non-certified wood for their projects.

A viticulturist experienced in advising Northern California growers told Wines & Vines: “Most companies doing testing run a panel for red blotch plus six leafroll viruses. Since virus infections are not uniformly distributed in vines, the nurseries can do testing and still accidently propagate infected vines unless they start with absolutely clean mother blocks and keep them that way.”

Sunridge general manager Maniaci said the company has planted substantial new acreage of Protocol 2010 rootstock and Protocol 2010 varietal scion wood on virgin and isolated new property.

“Isolation is a key factor because viruses are being moved from vineyard
to vineyard more now than ever before. Nursery blocks are not immune from becoming infected, so keeping them clean requires isolation of a long distance from any and all vineyards that might have either a virus or a vector.

“Short of growing every vine in a plastic bubble, we are doing everything practical to service the industry,” Maniaci said.

He added that plantings are coming into balance with demand, “but we have been sold out for 2014 for over a year. So there will be ongoing planting through all of 2014 and 2015 until each winery is satisfied with their individual balance of supply and demand.”

Though red blotch is a growing concern, Monette said that some of the symptoms growers see might not be red blotch. “Every time they see a red leaf I get a call, but it’s been a terrible year for potassium and phosphorus deficiencies after the two big crops and lack of rain, which can cause those symptoms. This has been a huge challenge the past few years.” He said that this is particularly true of Petite Sirah, Zinfandel and Malbec.”

Monette recommends that growers perform tissue tests and apply fertilizer if needed.

A word from Washington
Inland Desert’s Kevin Judkins claims his firm is the largest grapevine nursery in Washington state, where conditions are significantly different than in California. In the first place, almost all vines in that state are own-rooted since there’s no Phylloxera present—and frequent freezes can kill the tops of vines.

Fortunately, Judkins said, “There’s no red blotch here, except for a few patches due to growers buying plant material from California.”

He added, “Washington nursery plants have been tested completely free.” He said part of the reason is that Washington State University in Prosser acquired clean material that had gone through micro-shoot tip culturing from Foundation Plant Services at UC Davis, then performed the same process before releasing vines for propagation to Inland.

Views from the east
Conditions in eastern vineyards obviously differ from those in California and the northwest. Dennis Rak of Double A Vineyards in Fredonia, N.Y., has tested source wood for red blotch and said he avoided sources that are positive. “We are also establishing new budwood blocks from the 2010 protocol material that is free of red blotch,” he said.

Rak added that supplies of nursery vines are good, but the demand is strong. He doesn’t expect shortage beyond what is normal on hot varieties.

Joseph Dressel at Davis Viticultural Research in Carrollton, Ill., said the supply of nursery stock is excellent in most varieties. He expects shortages only in a few new varieties.

Dressel anticipates increased demand for vines, especially as French hybrid vines are being replaced. The biggest demand is for Crimson Cabernet, Cabernet Doré and Zinthinanna. Growers also ask for PD-resistant varieties.

Maniaci of Sunridge may have summed up the red blotch and vine supply situation when he said: “Growers are going to have a tough time finding the absolute cleanliness they desire until the Protocol 2010 material is in full production.”