If Domenick Bianco and other Napa Valley wine grape growers weren’t actually singing in the rain at the end of February, chances are they were humming a different tune than a month earlier.

That’s when Bianco and two other speakers at a Napa Valley Grapegrowers press conference discussed options for managing vineyards in drought conditions this season, after the driest year on record. But, that was before a day or two of rain fell in the area in mid-February followed by five more days of rain two weeks later.

Rainfall the last week of February totaled from around 2 to 3 inches on the Napa Valley floor to 4 inches or more on the hillsides. While long-term forecasts predict continued below-normal precipitation, the wet start to March wasn’t stopping Bianco and other growers from cheering. “We were absolutely giddy,” he says.

 

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Until this month, when Bianco began working with HALL Wines, he had looked after more than 1,300 acres of wine grapes throughout most of Napa County’s appellations for Renteria Vineyard Management.

The wet February weather brought Napa Valley’s total rainfall since last Oct. 1 to about half that for the same period a year earlier, he notes. “Theoretically, we could make up some of the difference by the end of May when our rainy season usually ends,” Bianco says.

After dry weather earlier this winter allowed growers to get a jump on their dormant pruning chores, unseasonably warm temperatures in January pushed bud development off to an unusually early start. That prompted growers to hold off on pruning altogether. In some case, later pruning will delay bud-break, he notes.

By the end of February, bud break in Los Carneros AVA at the southern end of Napa County was running about three weeks ahead of normal. “Were seeing a lot of bud activity in Chardonnay and Pinot Noir on the hillsides in Carneros and in some warm valleys, like Pope Valley, where Sauvignon Blanc buds are swelling,” he says. “A lot of vines are still dormant on the Napa Valley floor, but we are seeing bud activity in Bordeaux varieties along the hillsides.”

At the end of the 2013 season, available soil moisture in his vineyards was around 20 percent of full. He expects the recent rains added to those levels, particularly in the valley floors where soils were saturated with water. However, on the benches and higher elevations much less of the rainfall was soaking into the ground, he notes.

Looking past bud break

Looking past bud break, Bianco reports some of the Renteria Vineyard Management’s properties have no frost protection. Others have wind machines and roughly a fourth are equipped with overhead sprinklers. “This year, they’ll try to use as much water as needed to protect the vines from frost,” he says. “Where the sprinklers draw from wells, the aquifers are in good shape. So, we expect no problems with frost protection in those blocks. Other locations with overhead sprinklers are supplied from reservoirs. Many of these reservoirs, which are supplied by subsurface drains, have not filled back to normal levels – some are as low as only 30 percent full. In those vineyards, they have begun trying to fill them with whatever means they can. One property in Pope Valley has a reservoir large enough to meet crop needs for two years. So, having enough water for frost protection there isn’t an issue.”

As for making the most of water resources in drought conditions, Renteria Vineyard Management crews complement the use of such technology as soil moisture sensors, ET modelling, neutron probes and pressure bombs with visual inspections to apply water as precisely as possible. “The company is incredibly progressive in conserving water,” Bianco says.

All vineyards are on drip irrigation systems with one emitter per vine, he notes. In some cases, the use of two drip tubes allows workers to irrigate individual sections, based on water needs, rather than applying water to the entire block regardless of actual soil moisture levels.

Also, crews are very diligent about walking all blocks to look for symptoms of water stress, Bianco adds. Early in the season, this can include brown or dead shoot tips and leaves angling downward. Later in the year, dehydrated clusters can indicate the need for irrigation.

This season, where water is adequate, the crews will follow customary irrigation practices. However, their approach will change in the case of limited supplies of water, Bianco says. “Where ranches are strapped for water, the vines will be irrigated to reduce any water stress from bud break through fruit set. After that, if possible, water will be applied during any heat event or whenever symptoms of dehydration are observed.”

This season, crews will hold off on shoot thinning to reduce crop load and removing any leaves to control exposure to the sun for a while, he adds. Currently, in vineyards that have very little water, crews won’t be reducing spur positions or bud counts. They’ll wait until rain season ends to adjust crop levels. If water levels continue to remain very low, they will reduce crop loads during the shoot thinning pass.

“They want to hedge their bets for later in the season” Bianco explains. “They’ll wait until the vines have received all the rain they’re likely to get before making any

crop adjustments.”

Just about all of Renteria Vineyard Management’s vineyards feature various erosion-controlling grass and legume cover crops, including specific blends for hillsides. This vegetation has responded to the February rainfall. Rainfall in November and early December spurred some limited growth. “Germination was very spotty,” Bianco says. “The cover crops that did germinate and normally would have grown 2 to 3 feet high grew no more than about 5 inches. However, since the first rains in February we’ve seen some great growth. But, it’s still very spotty.”

Should dry weather prevail this year, Bianco expects vineyards with depleted soil moisture levels to experience higher-than-usual pressure from diseases as well as insects, like leaf hoppers and mites. Water stress would result in much smaller canopies, leaving the vines more vulnerable to attack, he says.

 

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