University of California viticulture experts say it “makes sense” to leave unsold grapes to wither on the vine when the prices offered would be less than the cost of production.

UC Cooperative Extension viticulture advisor Rhonda Smith and agriculture ombudsman Karen Giovannini say continued market fallout from the large 2018 crop is causing a dilemma for some growers.

With this year’s yields coming in average or better and with a significant unsold inventory of bulk wines, custom-crushing uncontracted grapes in 2019 may not be worth the expense, Smith and Giovannini wrote in an essay earlier this month.

“Hopefully there will be buyers as the harvest continues, but in this market, the prices offered are likely to be less than the cost of production,” they wrote. “Allowing unsold fruit to remain on the vines may seem unthinkable, yet with no income from those blocks, it makes sense. This means not dropping clusters by hand and not running a harvester in the vineyard to get the berries off.”

Clusters that decompose either on the vine or on the ground won’t likely cause a significant increase in fungal disease pressure in the next year given common vineyard management practices, even though they are colonized by fungi and act as a source of spores of grapevine pathogens, they added.

“All common grapevine fungal pathogens exist inside vineyards,” Smith and Giovannini wrote. “For example, fallen petioles, rachises that remain on the vine after mechanical harvest, pruning debris and woody tendrils that cling to trellis wires all support the growth of fungi. These fungi act as sources of inoculum that can infect wounds caused by pruning and suckering, and infect berries at bloom and other green tissue.”

Big supplies, flat demand

Growers are weighing the risks amid a market thrown into flux by plentiful supplies and flat demand. Shipments of California wines last year were up a paltry 1.5 percent after a 2017 season that saw the first statistical decline – albeit just 0.1 percent – in a long time, industry leaders have reported.

Meanwhile, growers last year crushed a record crop in excess of 4 million tons – a volume that Allied Grape Growers President Jeff Bitter has called “a new normal” absent disaster.

“If wine shipments had maintained their decades-long growth trend we’d be talking about a shortage of grapes,” Bitter said in July. Instead, “we have a supply plateau higher than our demand plateau,” he added.

Although wine inventories have slowly increased over the past several years, 2019 is the first year growers are feeling the effects of the excess supply, Smith and Giovannini wrote. Many in California are facing the dilemma of what to do with fruit that won’t be sold, they added.

The two say the fungi that colonize decaying berries include the same fungi seen growing on damaged berries before harvest, which can cause rot. Before bud break, parasite spores released from infested fruit and overwintering structures have no impact because there’s nothing to infect, they explain.

“Eliminating pruning debris will remove the inoculum formed on decomposing clusters and pieces of canes prior to bud break,” they wrote.

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