Vineyard growers and many others are working hard to keep pests and diseases out of Wine Country.
At the end of the day, you uncork a bottle of your favorite wine and pour a glass: swirl, sniff, sip and smile. Yet so often we give little thought to the work it takes, and the role growers play, in creating a good glass of wine. Disease and pest control is probably the most vexing problem—and the least fun subject—when it comes to grape growing. But if farmers don’t get this part right, the damage can be significant and there would be no wine.
As they say in France, “Mais non!”
Managing pests and thinking strategically to prevent disease is the key to growing healthy grapevines. “There are a lot of challenges in farming, and this is just a tiny subset,” says Rhonda Smith, a viticulture farm advisor with the University of California Cooperative Extension (UCCE) in Sonoma County. “The North Coast has an ideal climate for growing winegrapes, but those conditions are also ideal for certain pests and diseases.”
While Mother Nature cooperates most of the time, the business of growing grapes can be risky. Case in point: the European Grapevine Moth (EGVM)—also known as Lobesia botrana—is a serious pest that can cause significant damage to the flowers and berries of grapevines. Native to the Mediterranean, the EGVM is a pest of economic importance in vineyards throughout Europe, North and West Africa, the Middle East, Southern Russia, Japan and Chile. It was found in Oakville in October 2009 and quickly became a countywide problem in Napa, according to Agricultural Commissioner Greg Clark. For one Chardonnay grower in Oakville, the pest destroyed his entire 11-acre vineyard.
The moth was subsequently found in 10 other California counties. It was first found in Sonoma County in the Kenwood area in March 2010, and a total of 59 moths were trapped in the county that year.
The damage was extensive and the threat was taken seriously in the industry. “Because it was invasive and the first time it was discovered in the United States, federal and state governments took action and convened a group of experts from around the world to make recommendations,” says Clark. The federal government provided funding to pay for trapping, which was a colossal effort. In Napa, for example, that meant setting 100 traps per square mile;12,000 traps were inspected every two weeks during growing season. “It was a significant effort that let [growers] engage in business under certain conditions required by the quarantine,” explains Clark.
In 2011, nine moths were trapped, and they came from only two sites. There were no moths trapped in Sonoma County in 2012 or 2013. “We’ve gone two years without trapping [an EGVM] in Napa County, while a single moth was trapped in 2014 in Sonoma County. Both Napa County and a small portion of Sonoma County continue to be under quarantine,” Clark says.
The Sonoma County Department of Agriculture is continuing to work with the U.S. Department of Agriculture and the California Department of Food and Agriculture to survey the county and detect moths in 2016. “If we don’t find any moths next year, our hope is we can declare it eradicated,” adds Clark. Here’s an overview of the grape infestations, by pests that are currently troubling Wine Country growers, as well as the discovery of one new disease, and what farmers are doing to combat them.
Red blotch disease
Grapevine Red Blotch-associated Virus (GRBaV) is a new grapevine virus identified by virologists at UC Davis in 2011. Initially, the symptoms were confused with grapevine leafroll disease. Red blotch disease can be a significant problem for North Coast grape growers. “The virus delays the accumulation of sugar in the fruit and causes other changes in fruit composition,” explains Smith. And what’s most troubling, the vector (often an insect that acquires the virus from diseased vines then transmits it into healthy vines) has yet to be found.
“Red blotch disease is considered new, but there’s evidence it’s been around for at least 75 years,” says Smith.
GRBaV impacts both red and white winegrape varieties within California and other states. Disease symptoms in red varieties include reddening of regions within leaf blades and red veins. In white varieties, disease symptoms include both subtle and obvious yellow regions within leaf blades. Diseased vines, especially those in cooler growing regions like the North Coast, have delayed fruit maturity.
Currently, it’s not known what factors affect the onset and severity of symptoms or the development of diseased vines, but variety, rootstock and vine age may play a role, according to a report by the UCCE.
“Growers are frustrated,” says Smith. “The increase in diseased vines they see in their vineyards is either caused by a vector that’s spreading the virus or by infected vines that came from a nursery and symptoms didn’t appear until later. Some growers are considering replanting, but at this point, there are too many unknowns when it comes to how to keep healthy vines from becoming infected.”
Clark believes red blotch started spreading when the vines were in nurseries and distributed for planting. But nurseries are taking action to prevent the disease from spreading. “It’s a big challenge for nurseries, and they’re working on it,” says Smith.
Red blotch has been a significant issue at Dutton Ranch, especially with a young 4.5-acre Chardonnay vineyard. “We grew the vineyard for five years and had to replace the whole thing,” says Steve Dutton, president of Dutton Ranch Corporation and a fifth generation farmer who operates 1,200 acres in Sonoma County with his brother, Joe. “[The grapes] would get up to 22 [Brix] in sugar and we couldn’t get them any riper.” The 2016 harvest will mark the Chardonnay vineyard’s first year of production since it was replanted.
Pierce’s disease (PD) has once again become a major problem in Napa and Sonoma counties. “It’s a complicated disease that was first reported in the 1880s,” says Smith.
PD was first described by Newton B. Pierce, California’s first professional plant pathologist, who called it Anaheim disease. The disease is endemic in Northern California, where the glassy-winged sharpshooter (GWSS) vectors it, spreading the disease to grapevines adjacent to its riparian habitats.
“PD is present in California and some winegrape varietals are more susceptible to it. It can be fatal to grapevines,” says Clark. “We’re experiencing heavy losses and high disease pressure right now. We’re not sure what’s causing it. It’s cyclical and balloons out. It may be associated with drought or there may be other vectors we’re not aware of. Growers are experiencing loss and looking for help.”
PD occurs when a bacterium is introduced into a vine as insects feed on grape leaves. Xyella fastidiosa is a bacterium that lives in the water-conducting system (the xylem) of host plants and is spread from plant-to-plant by sap-feeding insects that feed on xylem fluid. The principal breeding habitat for the glassy-winged sharpshooter is riverbank vegetation, although ornamental landscape plants may also harbor populations.
According to a report from the University of California Agriculture and Natural Resources Department, in the 1990s the glassy-winged sharpshooter became established in Southern California and became a serious threat to most California vineyards. That vector flies greater distances and occurs on a wider range of host plants than other pests.
“The glassy-winged sharpshooter continues to be a serious concern,” says Clark. “It’s a big insect and feeds on the hardier portion of the plant. We inspect all plant shipments and we’ve found GWSS on occasion.”
What’s causing current problems? “Four years of drought and milder winters have not only caused GWSS populations to increase in Southern California, but it’s also led to population increases within Napa County of native sharpshooter species and other disease spreading vectors,” explains Clark. “The agriculture commission and grapevine nurseries work hard to make sure plants are shipped clean, but Mother Nature is making it difficult. We’re vigilant and always on the lookout.”
Insecticide treatments aimed at controlling the vectors in vineyard-adjacent areas have reduced the incidence of PD by reducing the number of sharpshooters immigrating into vineyards during early spring, according to UC Pest Management Guidelines. The degree of control, however, isn’t effective for susceptible varieties, such as Chardonnay and Pinot Noir, or for vines fewer than three years old.
“PD is like a snake bite. All it takes is one bite from a vector that lives in areas such as creeks and streams,” says Dutton, who experienced damage from PD near the family’s Russian River acreage. “Sharpshooters feed on plants that are PD hosts, then fly into the vineyard in the spring and feed on the vines,” he explains. “The vine is then infected with PD and will completely collapse and die within a few years.”
To thwart vectors at his property, the Duttons now monitor for sharpshooters and spray to control. However, they also worked with Fish Friendly Farming to clear the area and replant it with native, nonhost species such as toyon and bigleaf maple. In addition, every year during harvest, they employ an etymologist to walk about half their 1,200-acre vineyard and mark any infected vines. If a vine appears infected, it’s removed and replaced. (Fish Friendly Farming is a certification program for agricultural properties managed to restore fish and wildlife habitats and improve water quality. It’s operated by the California Land Stewardship Institute, a nonprofit organization in Napa.)
A new virus
Grapevine Pinot Gris Virus (GPGV) is a grapevine virus formally recognized in 2012 by Italian researchers. It was detected in California grapevines in Napa Valley near the end of 2015. “It’s the most recent grapevine virus to grab the attention of growers and virologists,” says Smith. According to Wine Business Monthly, disease symptoms include chlorotic leaf mottling, leaf stunting and deformation, delayed vine growth, stunted canes and reductions in yields.
Virus testing was performed by Agri-Analysis, a laboratory testing service company based in Davis, that tested 96 randomly selected grapevine samples the lab already had in its possession to test for grapevine and red-blotch-associated virus, also reported by Wine Business Monthly. Seven vines tested positive for GPGV, including selections of Cabernet Sauvignon, Cabernet Franc and Chardonnay from three separate vineyards in Napa Valley.
““It’s unclear how significant it is,” says Clark. “As technology advances, they’re increasingly identifying viruses. The presence of a virus doesn’t necessarily mean that it has a phytotoxic effect on the plant. Some people say they’re seeing damage from GPGV, but I haven’t heard of any further problems at this time.”
Much is still unknown about this virus, as its detection in a grapevine doesn’t necessarily mean impactful disease symptoms are present or will occur in the future.
According to Agri-Anaylsis, the virus requires further studies. What’s more, the challenge of future research isn’t so much the development of more refined techniques to identify it, but finding dependable strategies for preventing deterioration of vineyards.
Pests and sustainable farming
How does the push for sustainable vineyards in both Napa and Sonoma counties by 2020 increase the likelihood of pest infestations that were previously wiped out?
“We already have a large number of people using sustainable practices,” says Clark. “It means being sensitive to the environment. Farming production is about making sure you address water quality issues [such as not letting sediment run into rivers and streams], incorporating integrative pest management and using the least toxic pesticides.”
John Bacigalupi, a Russian River Valley grower, is among the first to use an ozone generator—AgriOzein—to reduce pesticide use in managing vineyard pests. The AgriOzein produces ozoneated water that shatters the cell walls of pests and fungicide in vineyards, reducing standard chemical regimes when applied. (See “How Does AgriOzein Work?” below.)
Bacigalupi used the AgriOzein machine in a limited fashion last year, on 14 acres of vineyard that has low fungal pressure because of its location and low vigor of the vines. “The machine seems to work well and, as far as efficiency goes, it eliminates the cost of fungicides,” says Bacigalupi, whose vineyard was a major contributor to the Chardonnay that won the 1976 Judgment of Paris, which placed California on the global map for winemaking.
While the AgriOzein machine has no effect on red blotch or Trunk disease, it could help eliminate vine crawlers, though it has no effect once crawlers make their way into the bark. What’s more, AgriOzein also has pesticidal properties that can help reduce the population of glassy-winged sharpshooters that spread PD.
Bacigalupi sprays every seven to 10 days and, unlike applying chemical applications, he’s able to send his crew in to pick immediately afterwards. One major advantage is the inability of fungus and pests to develop resistance over time to the application. Applying Ozein is much healthier, he says, because there’s no residue. “You’re taking something as old as the earth and reapplying it,” says the second-generation grower.
A symbiosis with Mother Nature
“Pests have always been a part of agriculture and growers deal with them regularly,” says Clark. What’s more, he adds, new pests are always invading the area. “The world has gotten smaller because of our ability to travel great distances in a matter of hours.”
And while there are pesticides and treatments, perhaps the best line of defense comes when growers foster a hands-on approach to create a symbiotic relationship with Mother Nature. “Working in the vineyard is still the best way to see what’s happening,” says Clark. “A person who spends a great deal of time in the vineyard will have a better sense of what’s going on and be the first to see something unusual.”
“You have to pay attention,” Dutton agrees. “It takes effort and knowledge.”
In addition, those working in agriculture need to take great care with their farming practices and how they’re impacting the environment, Clark advises. When corporations manage vineyards in other parts of the world as well as in Napa, he says, sometimes winery equipment moves back and forth—and pests can travel with the equipment. The EGVM, for example, may have been introduced in Chile on mechanical harvesting equipment. Parts, machinery and field equipment should be thoroughly cleaned before shipment, says Clark, and, in addition to generally being unlawful, it’s stupid to pack grapevines in luggage when traveling, as that risks spreading pests, viruses and bacteria—potentially threatening an entire industry and economy.
As for staying current with what’s happening in the industry, Clark advises taking advantage of opportunities for education through trade organizations and the University of California Cooperative Extension.
While managing pests and disease is irksome, farmers still manage to produce healthy crops. Says Smith, “Farmers are passionate about their land and will address these challenges with sustainable practices to achieve a successful business, now and for future generations.”
“It takes a special person to farm,” adds Clark. “It’s a lot of hard work and uncertainty. Rain at the wrong time of year, increasing government regulations, labor costs and pests. It takes someone who’s committed to growing grapes. Some of the best wine in the world is coming out of the North Bay, and it all begins with the person growing the grapes. There’s a little magic in there.”
How does AgriOzein work?
The O3 molecule (ozone) is introduced into water, which is then applied to the grapevine with a sprayer. Being unstable, the O3 molecule breaks off and releases an intense amount of energy. It takes a lot of energy to bind O3 or create electrical energy, which is the function of AgriOzein. In vineyards, the ozone sprayer is lethal to anaerobic organisms, such as fungus, and to organisms that require oxygen, such as leafhoppers, mites and other insects. Ozone selects these organisms and, as they breathe in the O3, it shatters their cell walls. For further information, go towww.agriozein.com.
“Farming can be an unpredictable business and crop insurance provides a risk management tool to the grower,” says Fred Carvajal, vice president of insurance sales at American AgCredit.
Multiple Peril Crop Insurance (MPCI) is a federal government subsidized program, designed to cover loss of crop yields from all unavoidable types of natural causes. Winegrape crop insurance is available for purchase between November 1st and January 31st annually.
Coverage for MPCI includes coverage for any weather-related damage including frost, hail, wind, excessive heat or rain. MPCI also covers plant disease, destruction from wildlife and fire. One disease not covered, however, is phylloxera, which is caused by a tiny aphid-like insect that feeds on the roots and leaves of grapevines, stunting growth. “We don’t see a lot of that these days,” explains Carvajal.
Insurance premiums are calculated based on the county where the grapes are grown, variety of grape, acreage of the vines and the vineyard’s historical average of production (when setting up a policy, historical averages are calculated by looking at a minimum of four years or a maximum of 10 years of production). The cost of insurance is also impacted by the amount of coverage purchased. Grape growers can cover 50 to 85 percent of a vineyard’s historical yield. For example, for 2016, if you have a 10-acre Chardonnay vineyard that averages four tons per acre and want to cover 75 percent of that average, the cost would be approximately $980. If you choose to insure 50 percent of it, it would cost about $167. Insurance is by varietal; you must insure all of that particular varietal within the county, not just a portion of it.
“Crop insurance remains affordable to a majority of farmers because of the subsidy. It’s also a very effective tool in protecting the grower’s investment. For a small or large grower, the program simply works,” says Carvajal.
There are countless diseases and insects that Wine Country growers contend with these days. The Western grapeleaf skeletonizer pest, for example, was found in Calistoga on Tubbs Lane in a vineyard trap in June 2015. Scientifically known as Harrisina brillians, it looks similar to a caterpillar. This is a destructive and serious pest, according to Napa Agricultural Commissioner Greg Clark. All larvae are voracious feeders that cause extensive damage to grape leaves, including partial or complete defoliation of grapevines, he says.
Meanwhile, Trunk diseases and the vine crawler continue to be problematic.
“Trunk diseases are a collection of fungal pathogens. They infect the woody parts of grapevines, eventually killing portions of the vine,” explains Rhonda Smith, a viticulture farm advisor with UCCE in Sonoma County. “It’s a ubiquitous problem and the principal reason why vineyard blocks produce less fruit over time and eventually have to be replanted.”
Pruning vines is part of the problem. Fungi are prevalent during the rainy season and can infect pruning wounds. “Every winter, growers prune their vines, creating wounds that are susceptible to infections by fungal spores carried by wind and rain,” she says.
Trunk disease is present throughout Wine Country. Growers cover the vines with various products such as VitiSeal or B-Lock, which can be painted or sprayed on. Does it work? “None of these treatments is 100 percent effective,” says Steve Dutton, president of Dutton Ranch Corporation. At Dutton Ranch, the treatment is painted on rather than sprayed. That way, there are no issues getting a tractor out there, he says, and they treat the wound itself rather than spray the entire vine.
The grapevine crawler is a small, soft, oval, flat insect, covered with a white, mealy wax. According to UC Pest Management Guidelines, all or most stages of the vine crawler can be present year-round. “It was found in the 1990s and is a difficult pest to control and manage,” says Clark. “By the time farmers see it, it’s usually heavily infested and hard to beat it back without significant chemistry. It takes persistence.”
According to Clark, education and outreach programs can help curb problems. “We’ve had success bringing in large groups and working with them to trap, coordinate spraying and using mating disruption pheromones,” he says. “It’s also important that people understand how their own behavior can adversely impact their farming operations and agriculture as a whole.”
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