The Korvan 7240 blueberry harvester was first demonstrated at the Clarksville Horticulture Experiment Station by Michigan State University’s team at the start of the research project in July 2008.
Some Michigan tart cherry growers are not waiting for the final research results to come in and are instead plunging ahead in what could be a paradigm shift in the way tart cherries are grown and harvested.
Ken Engle, a grower from Williamsburg in the Traverse City area, and Ed Oxley, a grower from Lawton in southwest Michigan, both have plantings made in a new style and have a year or less before they need to harvest them. Other Michigan growers are cooperating with researchers in a large research project and are experimenting on their own as well.
They intend to harvest using over-the-row harvesters, treating the cherry trees as if they were blueberry bushes or grapevines, both of which have been mechanically harvested for some years. Oxley has already bought a blueberry harvester he intends to use, and Engle is still contemplating.
Tart cherry harvest was mechanized more than 50 years ago. Hand harvest went out, rapidly, about the same time that the Bracero program providing Mexican labor ended in the 1960s. Growers adopted limb shakers and inclined plane catching frames, a technology that lasted a few years. Then, limb shaking was replaced by trunk shaking, which became, and still is, the mode.
It takes just a few seconds of shaking to drop a tree’s hundred or so pounds of fruit onto a sloping canvas, from which it rolls into a conveyor that takes it to a tank filled with water for transport and cooling. It takes only about half to three-quarters of a minute to shake a tree, collect the fruit, and moved the inclined double-frame system to the next tree.
But tart cherries have not been a particularly profitable crop—and some of that is related to trunk shaker harvest. It takes too long to grow a tree with a large trunk, and tree trunk injury from the shaker reduces orchard life.
In July 2008, researchers at Michigan State University organized a demonstration in which an unmodified blueberry harvester took a row of the trees into its five-foot-wide and eight-foot-tall throat, shook off the fruit with vibrating fingers, caught the fruit on its platform, and moved it by conveyor to bins on the machine. Fruit quality was good, but it was clear that not all trees were suited to the process.
Nonetheless, the demonstration inspired researchers to pursue further research, and it also inspired growers to go ahead based on what they’d seen.
A freak hailstorm in April 2010 put Ed Oxley on the path. He had a three-year-old, 50-acre planting of Montmorency tart cherries, the predominant variety, that was stripped of its leaves and branches by hail.
Oxley responded to some advice from Dr. Ron Perry, a long-time friend and the Michigan State University horticulturist who heads the over-the-row cherry harvest research project. Oxley had attended the demonstration Perry had organized.
“On 20 acres, we cut the trees down to 18 inches tall and let them sucker out,” he said. The results were short, bushy trees. “They’re looking good,” he said about the trees now. “They bushed out down low. We put trellises over some rows to try that out.”
Oxley is working with Perry and the research team on the hypothesis that even with Montmorency, in a canopy with branches established lower, tree resources are divided earlier in the life of the tree, and that can discourage overall canopy vigor and keep trees small.
Traditional systems call for removal of competing branches up to 40 to 48 inches above ground to allow room for trunk-shaking devices and catch frames. Therefore, in the traditional tree, canopy development begins much higher and encourages a taller and wider tree, Perry said.
Oxley is a grower of both wine and juice grapes. “In grapes, over-the-row technology has been with us for a long time,” he said.
Originally, his trees were planted in rows 20 feet apart and 19 feet between trees. “We added two trees between every two trees, putting them on a spacing of about six and a third feet.” This year, he bought a Korvan (Oxbo) blueberry harvester and hopes to use it next year.
“We were leaning this way even before the hailstorm,” he said. “The storm kind of pushed it.”
Oxley has grown tart cherries since 1968, so he’s been through the original transition period from hand to machine harvest. The main problem with trunk shaking, he said, is that it takes six years to bring trees into production. “I don’t know of any economist who’d think making an investment like that is a smart one,” he said.
The other issue is the life of the trees. Tart cherries can be easily damaged by heating and thawing during the winter months, especially on the sunny southwest side of the trunks, and by age 20, tart cherry orchards start showing the effects of tree loss. The decline is accelerated by trunk shaking that accumulates trunk injury and encourages tree borers, Perry added.
Ken Engle, too, has been bothered by the economics of tart cherry production. He worked with Jacob McManus, who was studying for his master’s degree in economics at Michigan State University and who, for his thesis, was investigating the economic aspects of converting tart cherry orchards to over-the-row harvest. McManus is developing a decision model for growers.
For some years, Engle has been trying to improve the profitability of tart cherries by increasing the planting density. Because trunk shakers and inclined planes take a lot of space in which to operate, the typical planting is 20 by 20 feet or even 22 by 22, he said.
In trying to achieve something different, he created a new style planting using a 42-inch tree spade that he owns and could afford to use for the purpose. He tripled the density of an existing planting, which was originally done with trees spaced 16 feet apart in 18-foot rows. Using the spade, he dug trees and planted them in the rows between existing trees.
Convinced he was onto something, he followed that up by planting 5,000 trees last year and 8,000 trees this year using a tree planter and a spacing of five feet apart in 12-foot rows—for a density of 700 trees per acre, about six times the normal density.
He planted the standard variety—Montmorency, on the standard rootstock—Mahaleb. “Rather than waiting for the right rootstocks, we went ahead,” he said. “Tart cherry trees aren’t all that large, so we don’t really need dwarfing rootstocks.”
His plan is to keep them to a tall spindle design, about 10 feet tall and narrow, with limbs about two and a half feet long. He already grows apples in the tall spindle design, and thinks the training and pruning rules for tall spindle apples will work for cherries as well. In addition, the practice of hedging tart cherries is well established and can be used to shape the trees to fit the berry harvester. “I have yet to build the harvester,” he said, “but I’ll need it in 2014.”
Tree spades have been used by other growers to move tart cherry trees; one moved an entire orchard from a site slated for development to a new area. Conceivably, that technology can be used to keep orchards productive longer by replacing lost trees.
If the Montmorency trees grow too vigorously even as he tries to keep canopy vigor under control, Engle leaves himself an alternative of using the spade to remove every other tree if they get too crowded by, say, the tenth growing season.
Engle noted that growers work hard to keep trunk damage low by lubricating the pads that clamp onto the trees and using well-trained operators. Still, the trunk shakers can crush trunk tissue, split trunks, slip bark, and invite the onset of damage by canker-causing diseases and borers.
But the chief problem is time. In his new plantings, Engle hopes to fill the space in year three or four, compared to six and seven in conventional plantings, and start harvest in the third year, instead of the sixth.
“Growers of traditional trunk-shaking orchards actually try to avoid early harvest by using gibberellic acid to knock fruit off up to year six so that they can avoid injury harvesting trees five years or less in age,” Perry said.
“Therefore, a traditional tart cherry orchard of 22 years in age at the average end of its productive life actually is harvested for only 16 or 17 years. Our over-the-row approach allows trees to be harvested without fear of significant tree trunk injury from the year three, when most first come into bearing.”
And it’s faster. Perry estimates it takes only about ten seconds to harvest a tree with over-the-row harvest.