Vine Mealybug Flares Up in the Central Coast
Disease vector can hibernate in wine grape roots, requires multi-pronged approach
San Luis Obispo, Calif.—A proliferation of vine mealybug (VMB) has many grapegrowers on California's Central Coast returning to the drawing board for treatment options.
“It’s definitely increased,” Greg Miller, Central Coast field representative for insecticide manufacturer Nichino America, says of the recent outbreak. “Viruses like red blotch and leafroll are waking a lot of growers up to the severity of what mealybugs are doing.”
Viticulture farm advisor Mark Battany tells Wines & Vines that the mealybug problem is not exclusive to the Central Coast. Battany says he is not collecting data on VMB but notes, "It's been increasing througout the state for many years."
In the same order as whitefly, aphids and phylloxera, VMB is one of several mealybug species spread most commonly through equipment and bird droppings, according to Dan Rodrigues, owner of Vina Quest Vineyard Consulting and a faculty member of the Wine & Viticulture Department at California Polytechnic State University in San Luis Obispo.
“In terms of mealybugs on the Central Coast, we have ones that range from the grape mealybug, which can be found up and down California, including the San Joaquin Valley, as well as the obscure and longtail mealybug, which live in cooler regions.” But the most detrimental species of late, Rodrigues says, is the vine mealybug, which emerged 10 to 15 years ago.
“The reason it’s so devastating is that it has multiple generations per year,” he says. “The others have one or two, but vine mealybugs have four to eight, depending on where they are and how hot it is. They can multiply pretty quickly.”
VMB is more likely to proliferate in warm climates, Rodrigues says. “Everything grows on heat. Mealybugs don’t grow much in the Arctic, but they do in California and Florida because there are more food sources; their population is based on what they have available to them.”
The pest also spreads under the protection of ants, which feed off the mealybug’s sweet honeydew excretion, in a symbiotic relationship that hinders the effectiveness of beneficial insects and natural predators. Rodrigues cites footage of parasites attempting to feed on VMB until an ant removes them quickly to another part of the vine; some pest-management experts posit that VMB control is commensurate with ant control in the vineyard.
According to Miller, the spread of VMB seems to have a cumulative effect on more established vineyards, as the pest can survive winter by hibernating in a vine’s roots. The longer a vineyard has had VMB—especially untreated or minimally treated VMB—the greater its pressure. From his perspective, he sees older Santa Maria and Paso Robles vineyards struggling the most with VMB, followed by those in Monterey County.
The continuum of practices for eradicating and managing VMB varies from beneficial predators and pheromone disruptors to chemical applications and even replanting. Lino Bozzano, vice president of vineyard operations for Laetitia Vineyard & Winery and Santa Barbara Highlands Vineyard in eastern Santa Barbara County, says that whereas grape, obscure and longtail mealybug were managed on an as-needed basis with natural predators and the occasional pesticide application, VMB didn’t respond to the same treatment.
“When I came to Laetitia in 2004, (VMB) was identified in a few hot spots on the ranch,” he says, adding that some of the infected vines were coming from vine nurseries. “We took a conservative approach, meaning we only treated the problem areas, but it kept spreading. Now it’s grown to the majority of the property, but we have it under control and do very diligent trapping.”
One of the first growers to be SIP Certified—a designation by the Central Coast-based Vineyard Team, which addresses the sustainability of wine grape growers’ operations—Laetitia practices resistance management with mating disruption, pheromone technology that confuses VMB and prevents reproduction. (A recent article by the Vineyard Team studies the sustainable and organic control measures taken by Willy Cunha of Sunview Shandon and Bart Haycraft of Jackson Family Wines in Los Alamos, Calif., to manage VMB pressure.)
But Bozzano also applies pesticides when VMB doesn’t respond to less invasive treatment.
“When it comes to mealybug, we’re aggressive,” Bozzano says. “In the past couple years, it’s been associated with the vectoring of viruses, and we’ve fallen victim to that. We’ve had virus spread via mealybugs and have had to go through a series of replantings, and that’s how we’re addressing it.”
Incidentally, Bozzano doesn’t see VMB emerging with the same ferocity at the Santa Barbara Highlands Vineyard, a sister property on the eastern edge of Santa Barbara County. “We see isolated incidents there, but not at the level of what other places are dealing with. Mealybug isn’t as prevalent there because it’s hard to get it out there unless it’s actively brought in.”
When it comes to prevention, Bozzano mitigates the spread of VMB through everything from preventative maintenance to sanitation. “If we know that a block has mealybugs, we don’t work there until the end of the day,” he says. “We wash whatever’s touched it to prevent further spreading.”
As for the prevalence of VMB on the Central Coast, Bozzano is unfazed. “I’ve seen them in every vineyard I’ve worked in over the 20 years I’ve been working in vines. They’re nothing new. The best way to deal with mealybugs is to assume you have them, even if you don’t see them. And be diligent about trapping. If you’re not seeing it, you’re not looking hard enough.”
