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Dryland Central Coast vineyard challenged with another dry seasonDryland Central Coast vineyard challenged with another dry season

This season’s unseasonably warm temperatures early and the lack of rainfall have forced wine grape growers to alter management.  

Greg Northcutt

July 11, 2013

4 Min Read

“All things considered, the vines are doing pretty well,” says Levi Glenn, viticulturist for Tablas Creek Vineyard. He manages 110 acres of primarily Rhône variety grapes near Paso Robles, Calif.

One of those “things” is a second-straight year of drought – no small consideration for the organically-certified vineyard, where all but a few blocks are dry-farmed.

The vineyard gets most of its “normal” 25 to 30 inches of annual rainfall during winter and spring. This past winter was the driest on record, Glenn reports. Since last September, he’s recorded a total of just 16 inches of rain.

The few drip-irrigated areas of the vineyard are located on the more water-challenged hilltops. Elsewhere, moisture in the high-clay soils frequently can be found no deeper than about 6 inches, Glenn reports.

His 2013 season started early, prompted by unseasonably warm 80-degree temperatures, allowing crews to finish field work ahead of schedule.

Anticipating another dry year, Glenn’s crews have been doing more cluster-thinning and leaving more canopy to protect varieties prone to sunburn.

The crop load this season is about average to slightly higher, he notes.

It has been warmer-than-usual and if that continues, Glenn expects the grapes to be ripe and ready for picking around Sept. 1. “It could be a quick, non-stop harvest,” he says. “Instead of the usual 10-week harvest, we could be finished in just six or seven weeks.”

Despite a Powdery Mildew Index ranging between 70 and 100 throughout much of June, Glenn hasn’t seen any signs of the disease in his vines. “But other growers have,” he says. “So, it’s around.”

Because of the area’s low humidity levels, often in the teens, powdery mildew usually isn’t a major threat, Glenn says. Only in cool growing seasons, such as 2010, has he had to ward off mildew.

“We’ve been more proactive the last few years in treating the vineyards to prevent any problems with powdery mildew,” he says. “Usually, it’s a concern only in blocks with more north-facing exposure and little air movement.”

His powdery mildew control program includes a dormant spray of lime sulfur followed by early-season sprays of copper and micronized sulfur before transitioning to Stylet oil. Oil also helps control young leafhoppers feeding on the bottoms of leaves.

Silver bullet

To prevent a phytotoxicity interaction between sulfur and Stylet oil, he applies a biofungicide, or Kaligreen, to control powdery mildew before transitioning from sulfur to the horticultural oil. Usually one treatment is enough to protect the vines between the last sulfur application and start of the Stylet oil treatment.

The high calcium carbonate levels in his soils imparts certain unique qualities — like minerality — to the wine made from his grapes not found grapes grown on alluvial soils, Glenn notes. But his vines struggle to grow in these high-pH conditions.

“We always battle nutritional issues to produce as much shoot, leaf formation and leave area as possible so that the vines can produce grapes most efficiently,” he says.

The vineyard’s primary red varieties are Mourvèdre, Syrah, Grenache and Counoise, while the major white grapes are Roussanne, Marsanne, Grenache Blanc, Viognier and Picpoul. Tablas Creek Vineyards is one of the few in California to grow Tannat and Vermentino. Last month, Glenn and his crew planted about a half-acre of Picardan vines. That increased total worldwide acreage of this French variety by about 50 percent, he reports. “It's supposed to be a mid-ripening variety, with good acidity, that is well-suited to our hot, dry, low-fertility sites,” Glenn says.

His most widely-grown white grape – Roussanne – provides his biggest fertilizing challenge. Heat stress seems to throw Roussanne vines into a tailspin, and they turn yellow, he reports.

“We’ve called in various agronomists and held seminars trying to figure out what is going on,” he says. “But, we’re still looking for a silver bullet that will solve the problem.”

In the meantime, he’s trying to keep his soils as fertile as possible

“We’re really proactive in the Rousanne blocks,” Glenn says. “After harvest we fertilize with 2 to 5 tons of organic compost per acre. We also apply various organic fertilizers in foliar sprays. We’ll spray foliar fertilizers in conjunction with our fungicide sprays or apply the nutrients through the drip system where possible. We want to keep the vines green and happy so that they will ripen the crop effectively.”

Dealing with uneven ripening is another challenge in his Roussanne blocks. “We may have to hand-harvest a particular block three to five times before we can get them all,” Glenn says. “We tolerate all the frustration and worry this variety causes, because it ends up making such beautiful, age-worthy wines.”

High demand for water from grape growers and cities in Paso Robles has dropped water tables 50 to 100 feet recently, he adds. That has only heightened concerns about wells going dry soon.

“Farmers are planting more vineyards and municipalities want larger water allocations,” Glenn says. “Within the next 10 years water is going to be a real point of contention between them.”

If you would like to read more about California grape growing, subscribe to GrapeLine, the exclusive electronic newsletter sponsored twice a month by Chemtura: See here for sign-up. It’s free and e-mailed the second and fourth weeks of each month from March through October.

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