Grapevine leafroll virus is very costly to growers, studies in major wine-grape-growing regions show.
Economists in New York, California, and New Zealand have looked at the costs of leafroll virus in recent years and all found that it significantly reduces yields, said Trent Ball, director of Yakima Valley Community College’s agricultural department and partner in Agri-Business Consultants.
“When you replant, the cost is huge.”
A New Zealand study estimated yield losses from grapevine leafroll virus as high as 40 percent in Sauvignon Blanc. Cornell University economists found that a 30 percent yield reduction resulted in a loss of $10,000 per acre over a 25-year period and that it was beneficial to replant entire vineyards when infection levels reached 25 percent of the vines. University of California researchers estimated that the state’s vine certification program for grapevine leafroll-3 virus, which is designed to ensure virus-free planting material, provides a benefit to growers of between 30 and 47 cents per vine for certified vines, totaling between $400 and $615 per acre.
Ball is working with Dr. Naidu Rayapati, Washington State University plant pathologist, to estimate the economic losses to Washington growers from grapevine leafroll virus, a project funded by a specialty crop block grant of the Washington State Department of Agriculture. A primary objective of Ball’s economic study is to determine how the disease affects growers’ pocketbooks and when it is more advantageous to rogue infected plants versus removing the entire vineyard and starting over.
The study is based on yield and quality data collected from a commercial Merlot vineyard from 2008 to 2012 by Rayapati. Preliminary numbers show annual yield losses due to the virus ranging from 12 to 28 percent, with an average loss of 18 percent and Brix reductions ranging from 4 to 8 percent.
Using operating cost numbers provided by growers and an average yield of 4.5 tons per acre valued at $1,127 per ton, Ball calculated the economic return per acre. The return did not include fixed costs such as management, land costs, depreciation, and interest. Under this scenario, a Merlot block with no leafroll virus returned $2,683 per acre; the same block with a 10 percent yield reduction returned $2,224 per acre. A yield reduction of 30 percent resulted in $1,377 per acre less return than the noninfected vines.
Ball is expanding the analysis to include the economic impact from declining quality, noting that many winery contracts set a minimum Brix and implement price penalties if grapes don’t meet minimums. Also, he’s extending his analysis to reflect the long-term life of a vineyard, while considering management tools of roguing infected vines and replanting.
“Ultimately, we want to learn when the economic impact from grapevine leafroll virus is high enough to warrant removing the entire vineyard,” he said.
Mimi Nye, vineyard manager of Ste. Michelle Wine Estates’s Canoe Ridge Estate, shared her experiences of trying to manage leafroll virus while striving to produce world-class grapes.
“I’ve been vineyard manager since Canoe Ridge Estates was planted in 1991,” she said. “Imagine my horror when we discovered grapevine leafroll virus.”
Symptoms were first noticed ten years after planting the 63-acre block of Cabernet Sauvignon near Paterson, Washington, but Nye thinks the disease was there in the beginning. “We just weren’t scouting for it.”
At first, just a few infected vines at a time were removed. Then the number jumped from 76 in 2008 to 182 rogued vines the following year. In 2011, 370 vines were removed. She began mapping locations of removed vines in 2012 and noticed disease progression followed the direction of the wind. WSU’s Rayapati found virus in a neighboring Chardonnay block located 120 feet away.
“Grape mealybug crawlers in the Chardonnay block were coming out in the spring, and wind was blowing them across to the Cab block,” Nye said. Since they began applying Platinum (thiamethoxam) to control grape mealybug and monitoring for the pest, the number of vines that need to be removed has declined significantly.
She estimated that living with leafroll virus adds about $100 per acre to production costs. Costs include insecticide sprays for grape mealybug ($25 per acre), virus testing ($25 per acre), and $50 per acre in labor costs for scouting, vine removal, and regrowing vines by layering (burying a shoot from a neighboring vine to regrow in the space of the removed vine).
Rick Hamman, viticulturist for Hogue Ranches, Prosser, likened the economic impact from leafroll virus to an expensive “grape virus tax,” a tax that cost Hogue Ranches $66,000 in 2010. He explained that 2010 was a cool year, resulting in late ripening in a Cabernet Sauvignon block. The block struggled to ripen and failed to reach minimum Brix by one degree, resulting in a loss of around $66,000. “That’s a big chunk to swallow,” he said. “It goes down slowly.”
Since 2008, Hamman has replaced 112 acres of red and white wine grapes in 11 blocks because of leafroll virus. Seven of the 11 blocks were Cabernet Sauvignon, which totaled 58 acres. Last fall, another 20 acres of Chardonnay were pulled out for replanting due to virus.
One of the removed Chardonnay blocks, planted with certified material from California, was in the ground for only three years before showing unusual symptoms that at first were thought to be nutritional. Because the entire vineyard showed uniform symptoms, Hamman believes planting material was infected. Tests were positive for grapevine leafroll virus-3 and Rupestris stem pitting.
“The block was Chardonnay Clone 37, and we really wanted that clone. But in 2010, we had a lot of trouble getting the fruit ripe,” he said, “After 2010, I knew we didn’t have a choice except to replant.” It takes three years for a new vineyard to begin showing revenue, he noted, and those three nonproducing years were the equivalent of a $119,000 loss of revenue from the 8.5-acre vineyard.
“When you replant, the cost is huge,” he said. Hamman estimated it costs more than $7,500 per acre for full vineyard removal and replacement. “These are real costs that we actually paid out, and not just this past year, but for several years.”
It’s a big decision to replant a vineyard, he says. “We take it very seriously because the cost is so huge.”
Vine removal starts with a three-person crew and a front-end loader to pull out the vines. A very large horsepower tractor must be rented to rip the ground both ways to also remove PVC irrigation pipe. A dumpster must be rented to dispose of pipe and other materials. A root-lifter implement is used to remove as much root material as possible. A burn permit is needed to burn the vine wood and wooden posts. Soil fumigation must be done before replanting. New rows must be marked and vines planted and new irrigation lines installed.
In all of this, Hamman has learned that it’s critical to scout for the disease and make sure all employees are aware of symptoms. “If you see something, get a lab analysis to learn what you have and quickly remove infected plants.”
Vineyards with leafroll virus require extra management to ensure that vines are not stressed. Also, he recommends lowering yield targets to three to four tons per acre for red varieties and four to five tons per acre for whites to improve chances of ripening. “Don’t propagate if you have any suspicions of virus, and double-check your vine source when using propagative material.”
The discussions about the economics of grapevine leafroll virus were held at the Washington Association of Wine Grape Growers annual meeting.