Paso Robles, Calif.—With nearly all of the region’s grapes off the vine, growers in the Paso Robles AVA are asking each other: “What the hell happened?”

Some vineyards were a total loss, and most yields in the region were off by 50% or more. Growers who suffered a 30% loss are considering themselves lucky in a year that at first seemed merely earlier than normal but proved instead to be dramatically light.

At a Sept. 30 grower seminar organized by the Independent Grape Growers of the Paso Robles Area (IGGPRA), Dr. Lowell Zelinski, founder of Precision Ag Consulting and the group’s vice president, delivered a presentation about how things went so wrong this year. He said he learned of one vineyard written off as a total loss in August, while some vineyard blocks normally known to produce as much as 20 tons per acre ended up yielding just 2 tons.

The losses do not appear to be limited to any particular variety, although Zelinski described Syrah as “mostly devastated,” and Cabernet Sauvignon could be much reduced as well.

Years of drought, which has exacerbated salt accumulation in the root zone, as well as a freak storm in July that dropped 3-4 inches of rain and hail in mid-June all played a role in the reduced yields. Yet even with all those factors, Zelinski said he expected some vineyards to enjoy good yields this year. Instead, the reduced yields appear to be the normal throughout the region.

Poor set leads to low yields
Zelinski attributes the low yields to unseasonably cool temperatures in May that prevented the pollen tubes in vine flowers from fully forming and thereby interfering with fertilization. The cold temperatures also caused widespread retention of flower caps that also prevented pollination.

The only vineyards that produced crops closer to normal were those in microclimates where bloom didn’t occur in May. “Those guys just by luck had their bloom in more favorable weather,” he told Wines & Vines.

The IGGPRA is comprised of more than 130 grower members who own vineyards throughout the sprawling Paso Robles AVA. Ken Bray, the group’s president and owner of a 2.5-acre Syrah vineyard west of Atascadero, Calif., said he’s heard of reduced yields from all over the appellation. “There was really nothing you could do,” he said.

In November, Bray said the IGGPRA would hold another forum about what growers can do during the winter to help ensure the problems of 2015 don’t cause any issues for the 2016 vintage.

Check for bud necrosis
While yields were a bit low in 2014, Zelinski said he thinks that had more to do with salt accumulation from the drought than problems with fruit set. The conditions that led to reduced yields could also have caused primary bud necrosis, and Zelinski said growers should test for that if they suffered losses this year. “I would suggest anyone who has an issue with yields in ’15 to have it done because it will influence your pruning decisions,” he said.

Based on any primary bud damage, growers may have to leave extra buds on the spur or prune later to mitigate potential losses.

Jason Domingos, owner of JD Farming Inc., manages nearly 1,000 acres of vineyards in San Luis Obispo County and southern Monterey County. He said he saw yields that were about 30% to 60% less than normal on all the vineyards he manages and has never experienced anything like this year.

Domingos said he owns about 200 acres and was able to achieve close to normal yields on about half of that acreage because of an Agrothermal machine he purchased earlier this year. He said he was conducting a trial on half his vineyards with the new machine but wishes he had used it on all of the acreage he owns.

The machine blows hot air on the vines, and Domingos said it appears to have helped improve conditions during set. Cabernet Sauvignon vines that were treated with the machine yielded close to normal tonnage at about 5 tons per acre, while the untreated vines produced about half of that.

Bray said after the warm winter and unsettled spring, most growers were expected to see diminished yields but nothing like what the area experienced. “There are a number of factors, not just the weather that caused this problem,” he said. “We were heading this way already, we just weren’t expecting to drop off a cliff.”

Jason Haas, general manager of Tablas Creek Vineyard in Paso Robles, has posted detailed accounts of the vintage on the winery’s blog. In his latest post, Haas described this year’s yields as “painfully low.”

Haas writes the 2015 harvest will likely be the smallest ever in yield per acre and smallest since 2001, when an untimely frost diminished potential yields and the winery had less than 45 acres in production. On the bright side, 2013 and 2014 provided excellent quality and quantity and this year matched those at least in quality. “If there’s not much of it, at least it will be of stunning quality.”