Mechanical pruning helps reduce labor costs without affecting winegrape quality
By Marni Katz
For California Central Coast viticulturist Gregg Hibbits, the dreary labor picture is written on the wall.
“The future is dark,” says Hibbits, general manager of Mesa Vineyard Management, a full-service vineyard management company that farms 4,000 to 6,000 acres of winegrapes each year. “Either we are not going to have enough people or the people that are available will be much more expensive.”
To help address the challenge, Hibbits is looking to mechanize vineyard operationsparticularly pruning, which is his largest labor cost.
Mesa Vineyard Management machine harvests about 75 percent of its acreage and is moving toward harvesting all of its acreage mechanically.
The next frontier in mechanization is machine pruning, Hibbits says.
“Labor is such a huge component of our vineyard [production costs], and the biggest single labor cost we have is pruning,” Hibbits says.
On the low end, he estimates the company spends about $200 to $300 per acre to prune winegrapes, and that cost has more than doubled in recent years. Per-acre labor pruning costs reach $400 to $500 for more elaborate vineyard canopies and configurations.
For more than a decade, Mesa has been mechanically prepruning—cutting spurs by machine down to a 12-inch cane. Hand crews then come in a month or two later and make the final cuts.
Machine prepruning has significantly reduced the number of workers Mesa needs to prune the vineyard and helps condense that labor-intensive hand-pruning period in January, Hibbits says.
Machines take on hand pruning
Still, it wasn’t enough. Four years ago, the company started looking at full mechanization to further cut costs and decrease its reliance on seasonal labor.
Mesa developed a side-by-side trial in a single vineyard in San Ardo, comparing full mechanical pruning—machine prepruning followed six weeks later by mechanical shoot and crop thinning—with mechanical prepruning and manual follow-up.
The trial has expanded to additional vineyards throughout several Central Coast counties, encompassing different trellis systems and varietals, including merlot, syrah and cabernet.
“We probably mechanically pruned 100 acres this past year, and the plan is to ramp that up to 300 to 400 acres this coming year,” Hibbits says. “There is a real possibility that 75 percent of the stuff we farm, especially in the warmer climates, will go to full mechanical pruning.”
A multi-staged approach
Mesa is working with Korvan Industries to adopt its mechanized pruning systems to its vineyards.
Korvan Industries was purchased two years ago by Oxbo International Corp. of Lynden, Wash., which is now marketing its vineyard mechanization system under the Korvan label.
The Korvan line features three different machine pruners—a rotary pruner designed for vertical shoot positioned trellises, one for California sprawl systems and a sickle-bar pruner for divided canopy systems.
The tool carriers cost about $50,000, and heads range from $10,000 to $25,000. But Greg Berg, a viticulturist with Oxbo, says many customers lease or rent the machines as they get their programs going.
Current mechanized pruning programs are based largely on work done at the University of Arkansas in Fayetteville during the 1980s and 1990s, Berg says. The system uses a multi-staged approach to manage the crop load through mechanical pruning, shoot thinning and crop thinning.
Blades or bars on the Korvan rig are set to preprune vines to about 200 percent of the desired estimated crop load during the dormant season.
During Stage 2—about 30 days after bloom—the crop load is re-estimated, and the vine is mechanically shoot-thinned, creating shoot lengths of about 4 to 8 inches. The crop load is reduced to 110 to 130 percent of desirable levels. The final mechanical crop thinning is performed another month or two later to reach the desired load.
The theory behind the Korvan system is to manage the crop load in stages to avoid overcropping and potential quality problems that can result from hastily done machine pruning, says Maxwell Norton, a University of California Cooperative Extension farm adviser in Merced County.
“It is very unwise to just allow the vines to load up with as much crop as you can possibly handle because you run the risk of the vine becoming overcropped, which can hurt quality and delay maturity,” says Norton, who has studied mechanical pruning for several years. “If growers do it right, they should expect yield or maturity to be similar to what it was with hand pruning. And they may see quality enhancement due to the smaller berries that result from machine pruning, including more intense flavors and more intense color in red varieties.”
Growers also may see less bunch rot or powdery mildew because the smaller berries and looser bunches are less conducive to disease, Norton says. Studies in the Lodi-Woodbridge area also showed reduced incidence of dieback diseases, which are typically spread by cuts made during hand pruning.
Borrowing from European designs
Gary Wilson of Wilson Ag in Shafter, Calif., has been working with mechanical pruning for nearly 20 years and agrees the approach not only helps manage costs but diseases as well.
Machine pruning was pioneered in Italy and Australia, where labor traditionally has been in short supply. Wilson began building his own machines shortly after hearing about innovations in those countries.
He now mechanically prunes all his own winegrape acreage in Kern County and commercially machine prunes for outside growers.
In the central San Joaquin Valley, Wilson says the mechanical pruning system typically is simpler than on the Central or North coasts.
He runs three different custom machine pruners that create a hedge-like box canopy. Except for Thompson seedless, Wilson hedge prunes all varietals.
With Thompsons, he prefers to skirt them to compensate for a lack of fruitfulness in the first buds.
Wilson Ag’s machines, which use a combination of rotary blades and sickle bars to create a box around the trellis, work best on simpler, single-wire trellis systems, he says. But machines are available that can accommodate more complicated crossarm and canopy configurations.
Wilson estimates his clients save up to 60 percent on pruning labor costs by using machines.
Berg agrees, saying he thinks growers can save 40 percent to 60 percent on their labor expenses with significant reductions in labor hours.
A few challenges to overcome
Norton says there has been a gradual increase in interest in machine pruning over the years. But two factors have largely tempered enthusiasm.
Wineries have been wary of mechanical pruning for fear it may affect fruit quality. In most cases, Norton says, fruit quality is not a problem if the crop load is managed.
Although vines may overcrop initially, Hibbits and Wilson say they do even out with time and proper management.
Many growers also are reluctant because once they convert to machine pruning, they may find it difficult to go back if it doesn’t work.
As a result, Norton recommends that interested growers seek help from a farm adviser or vineyard consultant to explore the available options.
In addition, he says growers need to communicate with their wineries before jumping into any mechanized system.
Hibbits says wineries are becoming more receptive to machine pruning, particularly as they also see the writing on the wall.
“When you are looking at lower grape prices with higher costs, something’s gotta change,” Hibbits says. “They know the direction it’s going to go.”
California State University, FresnoInfluence of training systems, pruning practices and soil types on wine quality in cabernet sauvignon:
CSUFPruning methods tried on chardonnay grapes: