Concord growers adjust to low prices
Mechanically thinning vines can help ripen juice grape crop.
Juice grape producers in the Lake Erie region face even more challenges than their counterparts in Washington State, as they struggle with low prices as well as productivity issues, says a Cornell University viticulturist. As eastern growers adjust to lower juice prices, they are shifting to mechanical pruning and thinning as a way to reduce costs.
The grape industries of Washington and the Lake Erie region are similar, though the landscapes are very different, said Dr. Terry Bates, viticulture research associate at Cornell’s vineyard laboratory in Fredonia, New York. “Prices are as low for us as for you. The last two years’ prices have been well below the cost of production.”
Growers in the Lake Erie region struggle with vine productivity due to cooler summer weather and sometimes less than adequate solar radiation during bud initiation. Average Concord grape yields are six tons per acre compared with ten tons per acre in Washington.
To help growers be more efficient, Bates has focused his research in recent years on reducing the costs of viticulture practices without “taking a hit on producing quality.” He presented some of his research results during the annual meeting of the Washington State Grape Society.
“If you increase the number of buds, you can increase yields, but you do reach a plateau in the number of buds at some point,” he said. For the Lake Erie region, 120 buds is the magic number that will result in maximum yield without delaying harvest. The number for Washington vineyards is higher, perhaps around 150 buds, he added.
Research trials have evaluated hand, mechanical, and minimal pruning methods to reach the 120-bud number. Minimal pruning gave the desired yield, but delayed harvest with lower Brix, which is not good in New York, he noted. The difficulty with mechanical and minimal pruning during the trial was the frequent need to adjust crop load.
Some growers are using machines to prune the vineyard canopy, with hand follow-up. “But you have to be comfortable with crop adjustment and do crop estimation,” Bates said. “Adjusting the crop is a quality issue—you’ve got to ripen the fruit and get the wood to harden off.”
Data showed that if a full crop of 10 to 11 tons per acre is left on the vine, ripening is delayed. “With machine pruning, you’re right at the edge of the cliff with 120 nodes. In a good year, the crop will ripen, but in a bad year, you’ll have to thin.”
Going from a 13-ton per acre crop to a 10-ton crop works because a moderate adjustment is being made, he explained. “But it doesn’t work if you’re trying to cut the crop in half.”
Such a dramatic crop reduction results in too much damage to the canopy and not enough increase in Brix. Reducing the crop by three tons per acre will increase Brix by about one degree.
To determine how much crop adjustment is needed, growers measure berries 30 days after bloom when they are about 50 percent of their final weight. Some growers clean pick a premeasured area of the vineyard block (one percent of the vineyard), weigh the berries, and multiply the weight by two. Bates has developed a chart to serve as a guideline in helping growers determine estimated crop size and the appropriate amount to thin.
About half of the industry’s 30,000 acres were mechanically thinned in 2003, he said, although since then, not as many have needed to adjust the crop.
However, some of the larger growers use crop thinning on some portion of their vineyard every year as a management tool so they can field blend during harvest, Bates said. “Then they know where the sweet spot is and know where to get a load that will meet sugar if a processor needs one.”