However, ugly becomes beautiful when it’s penciled out in a economically challenging wine grape market and shows a reduction in pruning costs of as much as 80 percent.
For Seibert, manager of Castle Farms just north of Merced, it also made the difference in sparing older Chenin Blanc and French Colombard vineyards from the bulldozer when pruning costs dropped from much as $180 per acre to $35 due to machine pruning.
Mechanical pruning is nothing new, according to Norton, Merced County University of California Cooperative Extension viticulture farm advisor, who hosted a field day recently to show results from three years of mechanical pruning trials at Castle involving Rubired, Chardonnay, Zinfandel, Chenin Blanc and French Colombard varieties.
There are vineyards in California that have been mechanically pruned for years. Italian and Australian wine grape growers have long mechanically pruned vines.
In fact, in Australia where labor is much more scarce and therefore more costly than in California, some growers do not even dormant prune, according to Maxwell. "They come in during the growing season and mechanically prune the canes hanging down. They make a V cut that starts at the cordon and extends upward and outward, leaving any upright growth,"
California grape growers have yet to be forced to go to that system, but Norton evaluated V dormant pruning along with box pruning. Boxing involves mechanically pruning the top and the sides of vines with hydraulic, tractor-mounted pruners.
Regain yield, quality
Generally, Norton has determined that the second year after switching older vineyards from hand, spur pruning to mechanically pruning there may be yield and quality reductions, but it is generally not very significant. By the third and fourth year after converting to mechanical pruning, vines have rebound to yield and quality levels equivalent to spur pruning.
Although there can be a yield increase once the vines have adapted to mechanically pruning, that is not the primary reason for going to machine pruning rather than hand pruning. It is cost savings.
"We have an adequate labor supply. It is the economics of the grape industry that is driving us into mechanical pruning," said Seibert, who has converted 300 of the 1,100 acres of vines he manages to mechanical pruning. He likely will not go much beyond that largely because winery contracts preclude it and some varieties, like Zinfandel and Grenache do not adapt well to mechanical pruning, he added.
While Norton said yield increases should not be expected, Seibert said he has logged a sharp increase in Chenin Blanc yields in an older vineyard, from an average of six tons per acre to 12 tons.
This can be attributed to a variety of things, but it is primarily due to creating a larger overall vineyards leaf area collecting sunlight and maturing fruit.
In older vineyard, Norton said vines die and these missing vines reduce the overall crop. "When you mechanically prune, you create a larger canopy earlier in the season and that can increase yields because you have more leaves harvesting sunlight," he said.
Ideally, mechanical pruning works best when it is adapted to a new vineyard, but Norton said it will work in established vineyards.
Less bunch rot
And, there are benefits beyond labor savings.
--It can reduce bunch rot dramatically because fruit is dispersed through the canopy instead of being concentrated near the cordon. Berry sizes and bunches are smaller and that minimizes bunch rot.
--With those smaller, loser bunches; powdery mildew control should be enhanced. Air circulation is better.
--These loose bunches also reduce omnivorous leafroller damage.
--And perhaps most importantly for San Joaquin Valley growers, it can reduce Eutypa and "Bot" canker infections.
"With mechanical pruning you can wait until as late as possible in the winter to prune because you don’t have to worry about availability and scheduling of hand pruners," Norton said. "This reduces the chances of infection."
Also, mechanical pruning cuts are made in smaller wood and that reduces the chances of a Eutypa infection, said Norton, who noted that mechanical pruning in Lodi-area vineyards has almost eliminated Eutypa.
The simpler the trellising system, the better — no fancy crossarms, no catch wires, said Norton. "The vine is self supporting and does not flop over…there is not that much sprawl with mechanical pruning. Any canes hanging down can be cut off with mechanical cane pruners," he said. "I think a vertical shot positioned system can be adapted if you cut close enough to the sides."
Hand pruning is virtually eliminated. "The only hand labor that is necessary is taking off anything hanging down from the cordon. The cost of that is minimal," he said. Castle estimates it costs less than $1 per acre for cleanup.
"Mechanical pruning is not pretty, but after the vines leaf out, from the road you cannot tell the difference. The only way to tell is to go into the vineyard and stick you head inside the vines," said Norton.
Norton warns that mechanically pruned vines can result in overcropping. Also, mechanically pruned vineyards may be a few days later to harvest maturity than hand-pruned vines.
However, crop size can be regulated by making the box smaller during dormant pruning or by mechanically dropping part of the crop with mechanical pruners during the season.
Mechanical pruning can only be used where vineyards are mechanically harvested. "You cannot economically hand harvested mechanically pruned vineyards," Norton said.
Seibert said he has experienced no problems with excessive wood in mechanically pruned vines. "The only problems we have seen is that the harvesters may have to go slower because there is more fruit to harvest, but that is not necessarily bad," he added.
Weaker, older vineyards may not adapt to mechanical pruning, cautioned Norton.
While there are many benefits to mechanical pruning, the reason he and other SJV farm advisors have been getting calls about it is lower grape prices and increasing production costs.
In the premium wine grape regions of the North Coast, the research effort may be focused on clonal selection. In the San Joaquin Valley, it is focused on economic survival, Norton said, and one way to do that may be switching to mechanical pruning.
"There are several cane pruners than can be adapted to mechanical pruning. Or you can make your own, which is what Castle did to mechanically prune their older vines," said Norton.
"Where you have older vineyards teetering on the edge of being bulldozed, the cost saving of mechanical pruning may be a way to leave them in for a few more years," said Norton.