Wild Weather Has Northwest Growers on Toes

Hot, dry conditions conducive to lightning and fires near wine grape vineyards

by Peter Mitham
The number of growing degree-days is significantly higher than normal for this time of year, according to calculations from Washington State University.
Prosser, Wash.—Just six months ago, growers in Washington state were discussing vintage variation with respect to cool years. Today, with wildfires ripping through tinder-dry swaths of Eastern Washington and growing degree-days outpacing the long-term average, growers are wondering how grapes will fare post-véraison.

While drought conditions in many parts of the state have been of little direct concern to growers, the early accumulation of growing degree-days underscores reports that estimate the vintage at three or more weeks ahead of schedule.

Prior to April 1, the weather station at Washington State University in Prosser racked up 91 growing degree-days—four times the long-term average of 23.

The trend has continued since then, with 1,103 growing degree-days on the books versus 882 in 2014 (the benchmark for a warm year) and the long-term average of 791.

The phenomenon was spurred not only by an unusually warm, dry winter that saw some growers sending pruning crews into vineyards in early February, but blasts of temperatures above 100° F in early June and again this week.

Vines have grown wildly, but with cluster formation taking place, the question for Michelle Moyer, an assistant professor and extension viticulturist at WSU in Prosser, is the timing of véraison.

“We have no idea when véraison is, “ she told Wines & Vines this week. “If it’s super-hot like this, plant development will slow down, and it may just sit there and then start the normal development process in August again.”

On the other hand véraison might occur earlier than usual, and the vintage may come to fruition under warmer than usual conditions. This could result in fruit with relatively more sugar and less of the acid Washington wines typically exhibit.

“Right now, we really don’t know what this heat is going to do in terms of fruit ripening,” Moyer said. “It’s too early in the game to figure out.”

However, over at Sagemoor Vineyards, vineyard manager Derek Way said the season’s variable weather has impacted fruit set.

Wet weather in May delivered a season’s worth of rain to some areas in the course of a day, washing away drought concerns while driving canopy growth.

But the blast of heat that followed two weeks later put the canopy in competition with blossoms, contributing to shatter in some blocks.

“I don’t know if any amount of water would have stopped the shatter that happened,” Way said.

While new plantings and low pest and disease pressure mean the state remains on track for another record harvest, the extreme weather vineyard managers are facing is keeping them on their toes.

Veteran viticulturist Dick Boushey told an audience assembled for a panel discussion of vintage variation this February at the Washington Association of Wine Grape Growers’ annual meeting that 2011 was the industry’s trial by fire.

“If (2011) is the toughest we get here, then we can handle it,” he said.

Yet fire is also a real and present danger for growers this year, which is far drier than 2011.

Isenhower Cellars posted a dramatic image to social media of smoke billowing from a wildfire adjacent to the Wallula vineyard near the confluence of the Walla Walla and Columbia rivers.

While the flames left the vines at Wallula unscathed, any advance in the date of véraison could put grapes at risk of smoke taint from future fires. Wildfire season typically peaks in July and August, and forecasts note that dry weather has made the landscape prone to lightning strikes.

Smoke taint was last a concern in Washington in 2008, following experiences in California and British Columbia in 2003 and 2008, respectively. Many Northwest growers sense that this year could bring the issue to the fore again. This is especially true in British Columbia, where memories of the Okanagan Mountain Park fire that devastated the east side of Kelowna in 2003 and singed local wineries remain fresh.

Severe thunderstorm warnings are in place across the province for this week, threatening a landscape where the snowpack is 0% of normal (not a typo), and temperatures have surpassed 100° F to break long-standing records.

Osoyoos in the southern Okanagan Valley, one of the prime red wine grape regions in the province, saw the mercury hit 104.7° F this past weekend, while Lillooet in the emerging Fraser Canyon growing region broke a 90-year-old record for the day with a high temperature of 103.1° F.

While many records trumped more recent benchmarks set in 2006, there’s no disputing that the heat is on as the 2015 season progresses.

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