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Lodi Mechanized Pruning Trials in Progress

Goal is managing vine balance to optimize yield and quality

by Jon Tourney
Recently pruned vines are trained on a high-cordon machine-pruned trellis at Gallo Liberty Vineyard in Lodi as part of a vineyard field trial to compare trellis systems and mechanization to achieve vine balance to optimize fruit quality and yield.
Lodi, Calif.—Paul Verdegaal, the University of California Cooperative Extension viticulture advisor for San Joaquin County, updated growers on two mechanized pruning field trials in progress to evaluate and compare different trellis systems for managing vine balance at Lodi Grape Day, held Feb. 4 at Hutchins Street Square.

Providing background on the experiments, Verdegaal noted that traditional vineyard management philosophies commonly tend toward one of two extremes: A California Coastal/French winemaking philosophy is that only low yields can produce high-quality grapes and wine. On the other extreme, a traditional Central Valley grower philosophy is that high yields are necessary to compensate for low grape prices and the need for mechanized operations.

As Verdegaal explained: “While overcropped vines can occur and often result in sound but average or below-average quality fruit, there is more evidence from research and field experience to indicate that high yields on properly designed and machine-adapted vineyard systems can produce quality wines. In summary, a ‘balanced vine’ can produce economic yields and high-quality fruit.”

Mechanized pruning equipment and practices have been used to some degree for more than 30 years in vineyards worldwide. Mechanical “pre-pruning” has been more commonly used to remove the bulk of pruning vegetation prior to hand pruning follow-up. Mechanically pruned, or “box hedged,” vineyards that require little or no hand follow-up have been successful in Australia and some California vineyards. Some growers have tried to adapt and retrofit existing vineyards and trellis systems to mechanical pruning, and it has sometimes been used to improve yields and economics in low-performing vineyards. However, designing and planting a vineyard specifically for mechanized operations from the ground up is the best way to optimize vine management for yield and quality.

Labor availability and costs in California are factors that increasingly favor mechanization. As new vineyards are planted and redeveloped, more growers are designing vineyards to optimize mechanized pruning, harvesting and other operations.

The Lodi Winegrape Commission has made mechanized pruning and management a focus of educational meetings and field days for its growers in recent years. At a 2012 meeting, E. & J. Gallo Winery vice president of viticulture Nick Dokoozlian noted that Gallo does box hedging in some of its highest value, premium wine vineyards. Dokoozlian said, “I don’t want to hear people say they do mechanical pruning to save money. You may do that, but the more important reason should be to improve and maintain vine balance and improve fruit quality.” Dokoozlian provided data from trials comparing hand- vs. machine-managed Merlot and Cabernet Sauvignon in the same vineyard that showed better tannin and wine quality parameters in wines produced from the machine-pruned and harvested grapes.

Trials compare trellis systems/management
The two Lodi field trials were created to compare trellis systems designed for mechanized management with standard trellis systems that can use pre-pruning with hand-pruning follow-up or all hand-pruning. Yield data for berry and cluster weights and vine yields are being collected along with data from grape berry juice analysis for Brix, pH and titratable acidity at harvest. Since the vines are still relatively young, harvest data to date is limited and results are inconclusive. In future years, wines will be produced for comparison. The trials are also expected to provide information on differences in susceptibility to diseases based on pruning and canopy management such as possible long-term effects from canker and trunk diseases.

Kautz vineyard trial
A trial was established in 2011 in a Kautz Farms vineyard in Lodi with Cabernet Sauvignon clone 337 on 039-16 rootstock with row spacing of 6 feet x 10 feet. The Kautz site is a replicated trial to compare four trellis systems:

• Standard bilateral cordon with a T-top trellis—spur pruned

• Horizontally divided canopy—quadrilateral cordon, spur pruned

• Horizontally divided canopy—cane pruned

• High-cordon machine pruned—a trellis with a single cordon trained on a cordon wire at a height of 66 inches with no foliage catch wires. The vine row is machine hedged (box hedged) with an over-the-row hedging tool with fruiting buds located within this 8- to 12-inch-wide hedge along the established cordon of each vine down the row.

Vine establishment is still in progress at this trial, but good growing conditions and crop allowed for a first harvest by hand in 2013. There were no significant differences in berry juice analyses for the four trellis treatments or in cluster weights. The cane-pruned vines showed significantly higher cluster numbers per vine and yield pounds per vine. Verdegaal observed, “We saw some differences this harvest, but not what we expect to see down the road.”

Gallo Liberty Vineyard trial
A field trial at Gallo Liberty Vineyard near Acampo was established in 2009 and is comparing two trellis types: a standard bilateral cordon (standard) and a high-cordon machine-pruned (HCMP) system with five grape varieties: Cabernet Sauvignon, Merlot, Pinot Noir, Chardonnay and Pinot Grigio. All varieties are planted on 1103 Paulsen rootstock with row spacing of 7 feet x 10 feet.

Fruit was hand harvested at this trial in 2012 and 2013. Varieties varied in their response to Standard vs. HCMP systems, and between the two harvests. The 2013 harvest showed bigger differences between the two systems for Merlot and Cabernet Sauvignon in Brix and yield levels, but the effects of the trellis systems should begin to separate with clearer differences during the next two to three harvests. As Verdegaal pointed out, “Vines being established are not put under any deficits until the fifth year, but will be more differentially provid ed inputs at this trial beginning in 2014.”

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