Rain is normally Mother Nature’s major threat to Napa Valley grower Domenick Bianco’s wine grape harvest. It can cause clusters to rot, rendering them unfit for making wine, and creating muddy conditions in the field to impede access for harvest equipment.

But this year’s harvest was not normal harvest — not in the least.

The first threat was a historic heat wave, less than a week after crews started picking grapes at the end of August, resulting in dehydration and shriveling damage to some of the fruit. Five weeks later, on the night of October 8, wildfires erupted throughout California’s North Coast wine region. Fanned by 50 mph winds, racing flames spread death and destruction over tens of thousands of acres in Napa, as well as in Sonoma and Mendocino counties

Three days after the wildfires erupted Bianco, who heads up grower relations and viticultural practices for Hall Wines, and his co-workers at the winery, based in St. Helena, Calif., were assessing their options for dealing with the last of their grapes still on the vines — about 25 percent to 30 percent of their Cabernet Sauvignon crop.

 “With the smoke in the valley so thick you could taste it, we were concerned about smoke taint of any remaining grapes,” Bianco said at mid-October. “The lab has sent us results that show smoke taint concentrations to be very low. This is in part due to how late in the season we are, and how little the plant is doing — being that it’s ready for harvest.”

The fire literally surrounded the valley on all ridge lines, he says. “Everywhere you looked, you could see the glow of orange. Looking out my living room window in the city, I could see the hillsides engrossed in flames.

“So far, we only know of one grower who has unfortunately lost a home. We are discovering that most of our grower vineyards are actually perfectly fine. If the fire got close, a few vine rows along the edges might have been burnt, but within vineyards we are finding very little damage. What we’ve learned is that vineyards are actually very, very good fire breaks. There is no doubt that they helped slow the fires’ progression, and saved homes, and possibly lives.

“The other thing to note is that, with all the irrigation ponds throughout the valley, firefighting helicopters had ample water sources to pull from, often right next to fires. This probably saved a lot of homes, and lives too.

“I am also hearing stories about farmers jumping on their tractors to disk around peoples’ houses to save them, and vineyard developers using their dozers — putting themselves in harm’s way — to cut lines in and around homes with, no direction to do so, other than a sense of community and kindness. In many ways, the agriculture community helped protect this community, and I believe, prevented this fire from being a lot worse than it could have been — even though it was horrific.”

The starting date of Bianco’s harvest this year, which began with Sauvignon Blanc August 30, was accelerated by two weekends of unusually hot weather earlier in the month. The freak, intense heat that moved into Napa Valley and vineyards throughout California’s coastal and central valley wine grape regions started two days later, at the beginning of the Labor Day weekend. “The heat was brutal, he says. “Temperatures in St. Helena peaked at 117 degrees.”

Record-breaking high temperatures burned the skins of some of the most exposed fruit, sending sugar levels soaring as berries dehydrated, some shriveling into raisins. The amount of damage in his Napa Valley vineyards, as well as those he works with in the Sta Rita Hills AVA of Santa Barbara County and the Santa Lucia Highlands of Monterey County, varied from block to block and from one part of a cluster to another.

“If the cluster was hanging outside the protection of the canopy, berries on the outer face of the clusters might be sunburned, pink, shriveled, and generally discolored, while those on the back side of the cluster were solid and normal-looking,” Bianco says. “This was especially prevalent in our Pinot Noir grapes.”

Performance of his Napa Valley blocks of Cabernet Sauvignon and Merlot varied widely. Some on rocky soils made it through the heat in good shape. But some on the valley floor — perhaps reflecting soil conditions, rootstocks/clone, or other factors — did not. “Those that didn’t take the heat well were just outliers,” he says. “The majority of our vineyards performed very well.”

Despite lighter cluster weights and lower yields for heat-damaged fruit, losses weren’t as high as he had feared, although they still were high for Chardonnay and Pinot Noir. His yield target goals are limited to about 3½ tons to 4½ tons per acre for Cabernet Sauvignon, 4 tons for Chardonnay, and 3 tons to 3½ tons for Pinot Noir.

“Because we thin our fruit for high-quality wine production, any reduction in yield is a concern,” Bianco says. “Our Chardonnay and Pinot Noir yields this year were down about 20 percent to 30 percent, while Sauvignon Blanc is down only slightly. I expect Cabernet Sauvignon Blanc and Merlot production this year will be about average, but we will see as the season progresses.”

In anticipation of, and during the several late summer heat waves, he was irrigating vineyards regularly, applying anywhere from 8 gallons to 10 gallons per hour, depending on soil types and irrigation capacity, to help vines cope with the high temperatures. But, it wasn’t always successful. “Sometimes, with the extreme heat we had, Mother Nature takes control and you just can’t provide enough water to prevent premature dehydration of the fruit,” he says.

Immediately, after the heat, he and his crews found that most fruit had held up well. They dropped damaged crop, or picked and sorted grapes in some blocks earlier than originally planned, to prevent further losses and negative impact on wine quality. Then, with the weather cooling, they allowed grapes less affected by the heat to recuperate and mature further.

“The cooling trend was great,” Bianco says. “It allowed for hang time without forcing our hand. But the rise in sugar levels then leveled off for several weeks, before the weather turned warmer and also very dry, and ºBrix began rising again. By early October, his grapes had reached the desired level of ripeness for harvesting.

“I’ve remained concerned about the ability of the vines to recover from the shock of the early September heat, but they seem to have recovered fine. Although some clusters were damaged by the heat, our optical sorter kicked out bad grapes to minimize any loss of quality from the first picks. The feedback from the winemakers is that the quality of the grapes we’ve harvested so far has been exceptionally good.”

The unusually wet weather last winter encouraged unusually vigorous growth in his vineyards this year, Bianco says. To help control that, he adjusted nutrient applications and kept a close eye on irrigation schedules/rates to maintain his deficit irrigation program. Timing of the first irrigation was also key. To discourage more growth, he waited to irrigate until soils were nearly dry and vines were ready for water.

“It was very difficult to manage canopy growth.” he says. “It wasn’t enough to go into the vineyards one time to remove leaves and laterals, to hedge and to open up the fruit zone. We had to repeat those processes several times. Those extra passes blew up our canopy management budget.”

Even then, though, to better protect the fruit from summer heat, he was somewhat less aggressive in removing leaves and laterals than he has been in previous seasons. “It wasn’t that we had been expecting the spells of unusually hot weather in August and September. But, in the last few years we’ve been noticing that the grapes have needed a little more protection from sun and heat. We plan to continue this approach in the future.”