For years, tree fruit growers in hot climates have used overhead cooling to improve the quality of apples and protect the fruit from sunburn. With wine grapes, few have used water for sunburn protection because of concerns of adding too much moisture to what is often a very controlled irrigation regime. But two Washington State vineyardists are using water’s cooling effect to protect wine grapes from sunburn.
While each of the two growers has a different cooling set up, the end result of producing premium wine grapes is the same.
At Red Willow Vineyard, located in the foothills of Mt. Adams in western Yakima Valley, Mike Sauer keeps a small block of Nebbiolo wine grapes cool during hot summer afternoons by misting them overhead with water. Barbera grapes grown along the banks of the Columbia River at Alder Ridge Vineyards are cooled down by under-the-vine microsprinklers.
Nebbiolo, a red wine grape varietal from northern Italy, is very sensitive to sunburn, Sauer said. “The canopy of Nebbiolo grows upright and can be quite gangly. The long stems of the clusters allow them to hang exposed from the canopy and in the open.”
The thin skin of the variety, coupled with potential for sun exposure, can result in raisining and dehydration of the berries from sunburn, he explained.
“Nebbiolo is difficult to grow, with marginal and variable success,” he said. “It’s a variety that hasn’t traveled well out of its northern Italian region. Some varieties, like Nebbiolo, are real specific to the site they are grown on.”
He planted the one-acre block in 1985, and installed the cooling system over the vines in 1997. The misting system, which is plumbed into the existing drip irrigation lines, is turned on manually in the afternoons when temperatures reach 95°F and turned off in the evening as temperatures cool.
Sauer chose mister emitters instead of microsprinklers because he wanted to create a more fog-like environment and add a little humidity to the vineyard microclimate. However, he conceded that with the downhill slope of the block, the misters are more effective at cooling than adding humidity.
“The root word of Nebbiolo—‘nebbia’—means fog,” he said, noting that in Piedmont, Italy, fog enshrouds the hills and helps to ripen the late-season variety by protecting it from summer heat.
The mister system is relatively simple, he said. Drip lines are attached to the top of long stakes that are placed in every other row of the vineyard, with misters hung off the line about every fourth vine.
“On a hot day, the misters instantly cool the vineyard down 10 to 15 degrees,” Sauer noted. Last year, he ran the misters for about 15 days. “I think it does help as it has cut down on the raisining problems. But I’m not sure if this would be economical for a large block.”
He has not seen any increase in mildew or disease pressure from running the misters. And, misting trace amounts of sulfur and calcium that are contained in their well water has not impacted the clusters.
“Merlot is the only other variety that I’d be worried about for sunburn, but you can usually manage sunburn in that variety by the canopy,” Sauer said.
Another reason for choosing mister nozzles instead of microsprinklers was his concern about the effect of additional soil moisture added for the cooling.
“I was worried that if I put on too much water, it could have irrigation consequences. If there is an irrigation factor, you might grow a bigger canopy, and that has other consequences. Hopefully, the system is irrigation neutral.”
Managing the canopy of Nebbiolo is still critical, he noted. Leaf pulling must be done, but only on the shady side of the row. Most of Sauer’s vineyard rows are oriented to run east to west, a direction he believes helps to reduce sunburn.
One negative of the overhead cooling is the high-wire attraction to birds. Though birds are not yet a significant problem in the vineyard, they do roost on the wires.
When temperatures reach 95°F at Alder Ridge Vineyard and Estate, microsprinklers placed under the canopy in a three-acre block of Barbera wine grapes are manually turned on and off, according to John Farmer, Alder Ridge vineyard manager for Winemakers, LLC. Winemakers is the vineyard management arm for Corus Estates and Vineyards, owner and operator of six vineyards in the Pacific Northwest and two wineries—Zefina at the Alder Ridge location and Sawtooth Winery in Nampa, Idaho.
The 814-acre Alder Ridge Vineyard, located on the south-facing slopes of the Columbia River, is within the new Horse Heaven Hills wine appellation that was federally approved last summer. Elevation at Alder Ridge varies from 300 feet, near the banks of the river, to 1,000 feet at the top of the vineyard.
The vineyard’s proximity to the Columbia River helps moderate seasonal temperatures, Farmer explained. “It takes the top off the hot days in the summer and moderates the cold temperatures in the winter.”
Farmer noted that during hot summer days, the sprinklers begin their cooling around 3 p.m. and are turned off by 6 p.m. The sprinklers run for 15 minutes on and are off for 30 minutes before being turned back on. They chose microsprinklers over mister emitters because they were concerned that misters would wet the ground too much, adding unwanted soil moisture.
The microsprinkler nozzles use 4.5 gallons of water per hour, and are the smallest size available without having clogging problems, said Luke Ransom, who is in charge of water management at the vineyard. A separate line and system from the vine’s drip irrigation was installed for the microsprinklers, giving them greater flexibility in irrigation scheduling. This will be the third season that microsprinklers are used on their Barbera grapes.
Ransom added that last summer the sprinklers were used on fewer than ten days. The sprinklers cooled down the block, on average, by five degrees, but at times, the Barbera grapes were eight degrees cooler than the blocks without the sprinklers.
The Barbera canopy is managed to allow dappled sunlight to reach the clusters, but Farmer has found that with Barbera, canopy management alone is not enough.
“We were a little concerned about disease when we started,” Farmer said. “But there is little disease pressure here, and low humidity. Most of the moisture evaporates away.”
With Barbera—a vigorous Italian variety known for its bright red color—quality is all about color, he said. “We’re looking for quality parameters, and that means color.”
Farmer noted that sunburn, which can be a problem for the variety, negatively affects the berry color as well as the ultimate color of the wine.
Since they began cooling down the grapes, they have received positive reports from David Lake, winemaker at Columbia Winery where the grapes are destined. “David told us that he thought the undervine cooling helped the color,” Farmer said.
“I would only consider doing something like this for varieties that have color issues,” he said.
The undervine sprinklers may provide another benefit for Alder Ridge. In the future, they plan to experiment with the system in establishing a cover crop between vine rows.
Farmer and his staff are taking the beginning steps in moving the Barbera block and some other small blocks of Rhone varieties toward being organic.
As they work towards farming organically, cover crops will play a more important role. They plan to see if the microsprinkler system can provide the needed moisture to help establish a cover crop that is beyond the reach of the drip irrigation lines, a major challenge to growing cover crops in the arid climate of eastern Washington.