Medford, Ore.—Grapevines are known to shut down at temperatures of 85° F and above. Yet as harvest enters the homestretch for wineries across southern Oregon this week, vineyard workers have been clamoring for an early start to the day so they can shut down early.

While respite is in sight as September comes to a close, temperatures approached 100° F across the Rogue Valley AVA on Monday. This had harvest crews hitting the vines at 6 a.m. to beat the heat.

The hot weather continued through Wednesday, with mid-afternoon temperatures reaching 90° F near Kriselle Cellars, just north of Medford, and in the Applegate Valley to the west, where Mark Wisnovsky, principal of Valley View Cellars, told Wines & Vines he can’t remember such a hot harvest in more than 40 years in the business.

Wisnovsky said the environment of the Applegate Valley AVA, which lies within the larger Rogue Valley AVA, is “amazingly consistent” thanks to mountains that limit outside influences, including inflows of cooler coastal air.

“Every year is different,” he said. Wine grape growers can’t be bound by tradition when nature throws unusual circumstances their way, such as unseasonably warm weather.

“There’s always the main concern, which is the plant,” Wisnovsky said.

The first day of autumn brought cooler weather to vineyards in Eastern Washington and the Okanagan Valley of British Columbia, where Graham Pierce, winemaker at Black Hills Estate Winery, recently told Wines & Vines, “Our best case scenario is high 20°s (C) at this point.” (See “Cooler Weather Promises Photo Finish for Northwest Harvest.”) 

Mother Nature has met Pierce’s expectations, but in Southern Oregon, Wisnovsky and other growers have had to tweak standard practice to accommodate the unseasonable weather.

Water, something traditionally avoided in the run-up to harvest, has been granted to Valley View’s vines to reduce stress. While the grapes are physically mature, and flavor components have developed at lower sugar levels levels in Wisnovsky’s fruit (23° versus 25° Brix), water has helped keep the vines happy and ensure grape composition remains in balance.

It’s “just enough to make up for the loss,” he said.

Concentrated flavors
Cabernet Sauvignon, Cabernet Franc and Malbec are among the varieties still on the vine at Kriselle Cellars, where winemaker Scott Steingraber said this week’s heat has helped concentrate flavors as harvest on his 30 acres of estate vineyard enters its final two weeks.

“We like them to dehydrate a little bit to concentrate the flavors,” he said.

Water hasn’t been a concern this year, but Steingraber typically hits vines with water right after harvest to prepare them for their long winter’s nap and a fresh start in the spring.

The one fact all growers are wrestling with is the need to adapt in the face of a changing climate.

Traute Moore of South Stage Cellars in Jacksonville, Ore., said her harvest started 2.5 weeks earlier than usual this year. While 2016 has seen more precipitation than 2015, the shift in environmental conditions that have taken place since she and her husband Don Moore planted Quail Run Vineyard in the Applegate in 1989 underscore that a shifting climate is something that growers must acknowledge.

Wisnovsky believes Southern Oregon grape production may shift westward into the Applegate, an area that’s traditionally been cooler than the Rogue Valley to the east. Besides Valley View, the AVA hosts Wooldridge Creek and Serra Vineyards as well as hundreds of acres planted by California’s Braden Farms. Willamette Valley wineries such as King Estate and A to Z Wineworks draw from local fruit for some of their well-known wines.

Between 2009 and 2014, plantings across the Rogue grew from 1,985 acres to 3,226 acres, with an increase of 650 acres logged between 2013 and 2014, the most recent period for which figures are available.

During the same period, grape production has increased from 4,940 tons to 8,667 tons, or about 11% of the state’s total harvest.