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.