Since the late 19th century, Pierce’s disease has been a source of heartbreak and great expense for viticulturists in coastal and riparian zones across the United States. The affliction is a grapevine-killer, delivered by insects from the sharpshooter family. They feed on a plant’s vascular tissue, known as xylem, and introduce the bacterium Xylella fastidiosa. As the flow of xylem through the plant is constricted, infected vines are clogged and starved of water and nutrients. Leaves turn yellow, the grapes dehydrate and the vine eventually dies.
The affliction can deliver a devastating economic blow. In California alone, Pierce’s disease costs the wine industry more than $100 million annually. It’s also hit vineyards spanning from Florida to South Carolina and all along the Gulf Coast.
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Unsurprisingly, Pierce’s disease-resistant grape varietals have major appeal. Such is the impetus of Dr. Andrew Walker and Dr. Alan Tenscher of the University of California at Davis’s Department of Viticulture and Enology, the driving forces behind a slew of new pest and mildew-resistant cultivars. Five hybrid varietals, known as Walker varieties, were released from commercial grape nurseries in limited quantities in 2020 and made more widely available the following year.
“I’m confident that these materials will make a significant impact on the wine industry, as they exhibit strong resistance to powdery mildew and Pierce’s Disease,” says Luis Diaz-Garcia, who currently leads the grapevine breeding program at U.C. Davis. “[These varietals] also boast excellent wine quality.”
But are these new varieties all they’re cracked up to be? Early plantings in the Southeast and Texas suggest that the hype is real.
vines afflicted with pierce’s Disease. Image Courtesy of Dr. Justin Scheiner
Decades in the Making
The debut of these new varietals took more than 20 years of development in the lab of the now-retired Dr. Walker. Each variety a cross between Vitis vinifera, which encompasses popular European grape varieties, and Vitis arizonica, a grape indigenous to the U.S. Southwest that carries a gene resistant to Pierce’s disease.
Over time, Walker’s lab gradually increased the percentage of vinifera by backcrossing the most recent iteration of the hybrid with the vinifera base. This was done to help boost the appeal of the resulting grapes, as vinifera varieties are most familiar to mainstream wine drinkers.
Early studies in Texas and Georgia—led by Jim Kamas, an associate professor at Texas A&M; professor Elina Coneva at Auburn University; and Dr. Violeta Tsolova of Florida A&M University’s Center for Viticulture and Small Fruit Research—suggest the varieties are even more successful than researchers had first anticipated. Scientists in these regions were particularly interested in these varietals due to the intense pressure of Pierce’s disease in the area that suffocates most vinifera vines.
“We’ve confirmed that they are indeed disease resistant and are much higher quality than previously evident, when vinifera levels were 88%,” says Kamas. “So, we are at the dawn of a new age.”
All of the varietals—three reds and two whites—are named for derivations of the word “walk” in Spanish or Italian. Among the reds, there’s Camminare Noir, which contains 94% vinifera. It includes 50% Petite Sirah and 25% Cabernet Sauvignon, exhibiting characteristics of both. The grape is the most widely planted of all the Walker varietals, due to its concentration of color and tannins. Another red is Paseante Noir—similar to Zinfandel, it’s 97% vinifera, including 50% Zinfandel, 25% Petite Sirah and 12.5% Cabernet Sauvignon. Finally, Errante Noir, which most closely resembles Cabernet Sauvignon, is 97% vinifera with 50% Sylvaner and 12.5% each of Cabernet Sauvignon, Carignan and Chardonnay.
For the whites, there’s Ambulo Blanc, which is often compared to Sauvignon Blanc. It’s 97% vinifera, bred from 62.5% Cabernet Sauvignon, 12.5% Carignan and 12.5% Chardonnay. Finally, there’s Caminante Blanc, which boasts characteristics of Chardonnay and Sauvignon Blanc. It’s 97% vinifera, comprised of 62.5% Cabernet Sauvignon, 12.5% Chardonnay and 12.5% Carignan.
Over the past few years, Lone Star State grape growers have been gradually rooting these vines into the ground. In the Gulf Coast and North Texas regions, at least one of the five new varieties is being grown in 20 different counties, says Dr. Justin Scheiner, assistant professor and extension viticultural specialist at Texas A&M University. Between those areas and Texas Hill Country AVA, just over 20 acres of Camminare Noir have been planted, along with nearly 15 acres of Paseante Noir, around 15 acres of Errante Noir, approximately seven acres of Camminante Blanc and eight acres of Ambulo Blanc. The number of vines per acre varies from 550 to 900.
If these vines do as well as studies have suggested, it will be a game changer for the state’s wine industry—and could potentially have far-reaching implications across the country.
“Texas has around 30 [species of] sharpshooter that can convey Pierce’s, as we have so many riparian habitats and native grapevines growing everywhere,” says Brianna Crowley, an extension viticulture program specialist at Texas A&M. “So, if the new varieties can survive here and not show signs of disease, then they truly are resistant.”
Bending Branch Estate’s owner Bob Young and Melvin Mendez in Bending Branch Estate’s Crimson Cabernet Vineyard. Image Courtesy of Lauren Elizondo
Potential from Coast-to-Coast
In sharpshooter-heavy regions in Texas and the Southeast, these Walker varieties are expected to help grape growers who are working hard to grow or establish their vinicultural identities. But they’re also proving a salve in long-respected California AVAs impacted by the disease.
Around 2016, the vines at Whitehall Lane’s Oak Glen Vineyard in Napa Valley’s Oak Knoll AVA were “being decimated by Pierce’s disease,” says winemaker Jason Moulton. The issue was taking a toll on the winery’s bottom line. “There was constant replanting,” he adds. “From a business perspective, you’re throwing a lot of money at something.”
After Whitehall’s consultant viticulturist, Dr. Paul Skinner, connected the winemaker with Walker, Moulton says he was gripped by “a wine-nerd Sputnik moment, like a Space Race opportunity.” These hybrids could help to mitigate his pricey pest problem now, but also well into the future. After all, scientists expect the warming climate will further enable the problem.
In 2019, Moulton processed his first harvest of Camminare Noir and Paseante Noir, which he obtained directly from Walker’s lab three years earlier. He was impressed with the results. “During harvest, I blind-taste these daily next to our Cabernets,” says Moulton. “I see their full potential—they ripen to high Brix levels while not depreciating in structure, they accumulate sugar while reflecting the highest-bound tannin content I’ve ever measured.”
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The success of Whitehall’s Walker wines inspired grape growers in less established regions to make the switch. Seven years ago, Bending Branch Winery in the Texas Hill Country AVA was hit hard by a combination of hail, heavy rains and Pierce’s disease. Owner Dr. Bob Young lost what had been successful plantings of Tannat, Cabernet, Tempranillo, Aglianico, Malbec, Sagrantino, Charbono and Souzao. After tasting Moulton’s Camminare Noir and Paseante Noir in 2022, he decided to replant his Comfort, Texas estate vineyard solely with Walker varietals. He rooted the first 800 Camminare Noir vines in the ground last year. Another 400 are expected to arrive in 2024. “I became totally convinced when I got a few bottles from Whitehall Lane,” says Young. “I’m really optimistic.”
In East Texas—which is even more humid and more deeply affected by Pierce’s disease—the potential impact of these new varietals could be momentous. For example, on the Gulf Coast, grape growers often look to hybrids like Blanc du Bois and native grapes like Lenoir (usually referred to as Black Spanish) to build wine programs. The Walker varieties may help to improve the bottles made from these already-established vines.
“Blanc du Bois is versatile and aromatic, and you can do interesting things with it, but it’s one single variety,” says Scheiner. “Lenoir doesn’t have the mouthfeel or tannins of vinifera; it finds itself like some other hybrids.” Scheiner believes that the higher tannin content in Errante Noir may make it great for counterpart for blending with Lenoir to improve its structure. “That alone is exciting,” Scheiner adds.
Student Researchers Examine Camminare Noir Grapes. Image Courtesy of Dr. Justin Scheiner
Overcoming Hurdles
Though a growing contingent of winemakers are enthusiastic about the quality and disease-resistance of the Walker varieties, challenges persist. Paul Bonariggo of Messina Hof Winery in Bryan, Texas, has struggled with the color and ripening of the Camminare Noir he’s planted within the Gulf Coast region. This does not surprise Kamas.
“It’s a learning curve,” Kamas says. “But a great opportunity for Texas to expand its wine industry in areas that previously couldn’t grow high-quality grapes.”
To combat the color issue, Crowley decided to take advantage of Camminare Noir’s cherry undertones in an experimental rosé for Texas A&M. At this early stage, she feels this lighter style is an ideal way to demonstrate the variety’s characteristics to winemakers and grape growers. “In a nice mild ripening year, I foresee better color development,” she says. “But the fact that these show promise this early on and survived the major heat and drought that usually happens during ripening here, I think we’re off to a good start.”
Further south, in the Rio Grande Valley, a small group of growers—Bonita Flats Farm and Vineyard, Rubiano Vineyard, Rio Farms and Wright Vineyard—has collectively planted close to 5,000 of the Walker variety vines, says Art Delgado, owner of Bonita Flats. Camminare Noir has been proving especially successful in terms of color and ripening. Delgado speculates that the unique growing conditions here help. Both soil temperature and annual rainfall are higher than in other parts of the state and prevailing southeastern sea breezes throughout the year further protect vines against diseases. Delgado has also planted the two white varieties, Ambulo Blanc and Caminante Blanc, with some success and will be vinifying them and the other Walker varieties later this year.
In the Hill Country, Crowley describes both whites as having “beautiful [pH and Brix] levels.”
Another hurdle to ensuring Walker varieties success will be consumer education, since U.S. wine drinkers tend to gravitate toward buying the easily recognizable varietals that are familiar to them. Shelly Wilfong, a Dallas-based wine educator, suggests that wineries may want to focus on branding their bottles with a label that conveys a premium blend, like the ubiquitous The Prisoner, as a potential marketing strategy.
Even early adopter Moulton, who has been harvesting his Walker grapes for nearly half a decade, has questions in terms of consumer acceptance.
“Can we introduce these to our wine club? Can they be part of our annual red blend?” he asks. The winery’s club members tend to be an open-minded group, he says, familiar with the operation’s many projects. But is it enough to change hearts and minds?
“Will a small inventory go quickly, or be around for a longer period because they are unfamiliar?” Moulton wonders. “Nonetheless, its success for the industry has wide-reaching implications.”
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