Harvest time wine grape Brix readings from heavily frosted Central Coast vineyards will look more like Joseph’s multi-colored coat than a Hart Schaffner Marx Navy blazer.

The lack of uniform maturity is the only bet veteran grape grower Dana Merrill is willing to make on the outcome of this year’s wine grape crop in the wake of a bone-chilling spring frost.

Merrill manages 6,000 acres of wine grapes on the coast under the umbrella of Mesa Verde Management in Templeton, Calif. He has been farming on the coast for 40 years and has experienced nothing like the early April frost this year. Temperatures plummeted down to as low as 24 degrees and stayed there for an extraordinary nine hours or more in some areas. It fried tender, just emerged shoots so badly there may not even be a crop worth harvesting in some vineyards.

While Merrill is certain whatever crop is harvested will not be uniform, beyond that he is waiting and watching like other growers to see how the vines compensate for the killing frost. Crop loss estimates now range from 30 percent to as much as 90 percent. The county agricultural commissioner is documenting losses in anticipation of declaring a disaster.

San Luis Obispo County UC Cooperative Extension Viticulture Farm Advisor Mark Battany is advising anxious growers anxious to sit tight before trying salvage a crop by pruning off damaged wood or doing much else.

“It is going to be awhile before people know exactly what they have. I would be leery of a definitive early assessment at this point,” said Battany. “When we start seeing flower clusters and set, we’ll have a much better feel for the crop and damage.”

Battany admits damage is “pretty significant, but we really do not have numbers to put on it,” he added.

Battany is getting calls about what growers can do to salvage a crop. The first thing he reminds them is that frost season is not over. “The danger for frost continues until late May” and growers do not want to do anything that will jeopardize what crop they will make.

Post-frost recommendations

Battany is putting together post-frost recommendations for growers.

Merrill agrees with Battany that waiting is the right decision for now.

“We are seeing some dramatic changes in the growth of the vines. Growth is coming out everywhere, except where buds used to be. We are seeing suckers coming out of cordons,” Merrill said. He does not believe there are as many secondary buds as people are counting on to replace the fruit from primary buds killed by frost. Some spurs are “totally dry” like the result of winter kill. Merrill has seen year old wood dead from the frost.

The loss of the primary buds will result in less fruit from secondary or tertiary buds. It could easily be off as much as 50 percent.

“It was damn cold. Very bizarre,” he added. “Rain storms came through and then the temperature dropped real fast, creating a super cooling effect.” Growers with frost protection impact sprinklers or small pulsating sprinklers atop the rows gained protection — if the water supply held out during the night. It did not in some cases. “If you ran out of water during the frost, the damage will actually be worse.” Wind machines were worthless because there was no inversion layer of warmer air.

All of this will result in a “completely uneven harvest” said Merrill.

He predicted wineries must be “a little more supportive” at harvest this year because they are not going to find tonnage and homogenous Brix readings.

“You are going to find everything from 29 to 18 Brix in the same vineyard. If wineries are going to demand equal quality for super premium wine, they may only get a ton or even only a half ton per acre. They are going to have to be a little more flexible than in the past,” he said. “Uniformity across all tonnage is going to be hard to achieve this year.”

The wine grape market was already active before the frost and the loss of tonnage on the Central Coast will only heat up the market. The market may be so short of grapes that wineries will take non-uniform Brix grapes for wine priced at $10 or less and try to compensate at the winery.

Wake-up for wineries

“I think a few privately held wineries are awakening to the fact that this will not be a uniform year. I don’t think some of the big corporate wineries have caught on to that fact yet, but they will eventually,” he said.

Sixty percent of Central Coast wine grapes are shipped to major wineries away from the coast.

“If this frost had hit Napa and Sonoma, there would have been a panic now. With the Central Coast being a source of ‘extra grapes’ so to speak, it has not hit the market yet,” he said.

Battany reminded growers that the biology of the grapevine is to begin forming the current season’s flower clusters during the spring of the preceding season. Therefore, extra fertilizer or irrigation this spring will not create more flower clusters for this year.

However, it is important to continue taking proper care of the vineyard, including disease control and adequate nutrition, as this will help ensure that one can maximize the full potential crop this year and will help ensure that next year’s crop will not suffer inadvertently,” Battany reports.

One positive consequence of the reduced crop load this season is that the same vines will generally compensate by producing a larger-than-average crop next season, all else being equal, he said.

As the danger of frost continues into late May for most of the area, Battany said it is very important to maintain frost protection efforts because if the newly emerged secondary and basal shoots themselves become damaged from another frost event, then the next batch of replacement shoots will generally have even less potential for producing any crop.