Bringing machine harvesting to cherry orchards could launch a revolution within the industry.
A four-year, multistate research project illustrates how far-reaching the overhaul might be, tackling new tree architecture, genetics to breed new varieties and packaging to showcase the stem-free fruit—as well as developing harvesting machines.
Matt Whiting, associate professor of horticulture at Washington State University’s Prosser research center, leads a team of researchers and growers from Washington, Oregon, California and Michigan. Funded by a $3.9 million federal specialty crops grant, they’re building on years of previous work.
“We’re trying to be ahead of the curve,” says Denny Hayden, president of Hayden Farms in Pasco, Wash., a longtime proponent who added a packing operation to help build a market for the stem-free cherries central to machine harvesting. That, he says, “isn’t a marketing ploy but a way to survive in the future with less labor.”
Reaching critical mass
Reaching the machine-harvesting goal has stalled until recently, he says. “We’re just now getting the dwarfing rootstocks and systems for pedestrian orchards, and there needs to be a critical mass.”
In the project’s first year, grower partners planted test blocks using the planar upright fruiting offshoot (UFO) architecture expected to provide the best results with any harvesting machine. It also offers efficiencies for growers who opt for hand-harvesting or interim machine-assist platforms, Whiting says.
With the UFO system, “It’s really important to get a lot of uprights in the first year because they turn into the fruiting wall two years down the road,” he says.
Fruiting walls also open up trees for more efficient spray and harvest operations.
Sold on the UFO system
Growers joining the roster in the following years will incorporate early findings, accelerating the process. Harvester prototypes under development will be tested in these blocks in the final two years as trees come into production.
Mark Hanrahan, of Knight Hill Farms in Buena, Wash., is sold on the UFO system. His experience—20 acres of fifth-leaf cherries on upright vertical UFO and an older 4 acres on an abbreviated V-trellis UFO—has him convinced. “I’m not going to plant another system,” he says.
Hanrahan has earned back his investment on these trees in their fourth year.
Architecture is key, says Tim Dahle, owner of Dahle Orchards in The Dalles, Ore. The ideal orchard setup will permit either machine-harvesting of stem-free cherries or pedestrian picking of stemmed fruit.
Dahle is enthused about helping bring machine harvesting for cherries to fruition. “We have concerns about the reliability of the labor supply for hand harvest,” he says. Machines could “revolutionize the industry.”
Perfecting the machinery
Qin Zhang, director of WSU’s Center for Precision Agricultural Systems in Prosser, heads the harvester research, focusing first on problems in two existing shaking machines.
A handheld limb shaker using highfrequency vibrations “works perfectly under ideal conditions,” Zhang says. But those ideal conditions appear in at best only 10 percent of tree limbs.
That shaking frequency also is far higher than needed to achieve results on UFO trees, increasing the potential for limb damage, he says.
A larger tractor-driven shaker punches tree trunks to produce the needed force. “It works reasonably well, but it’s difficult to target the trunk,” Zhang says.
The impact can cause tree injuries that often lead to disease and ultimately replacing trees. “That’s a killer” for grower acceptance, he says.
This initial data will steer designs of a new prototype harvester for testing next year, Zhang says.
High-speed video shows fruit damage occurs mainly as cherries hit branches on their fall into the catch frame.
Positioning the catch frame directly under targeted branches should minimize damage, he says.
“With a simpler [tree] structure we can design simpler machines,” Zhang says. “More complexity means higher costs.”
Seattle area-based Picker Technologies is a project partner developing cherry prototypes of its mechanical-assist harvest platform. Randy Allard, vice president of research and development, says he anticipates integrating the company’s system with Zhang’s harvester for this year’s tests.
Ultimately Allard aims to field-sort culls, size harvested fruit before it leaves the orchard and field-pack high-value cherries into bags for immediate shipment.
“The packinghouse only has so much volume capacity” during harvest peaks, he says.
Variety selection is key
Another crucial factor to machine harvesting is variety selection. Shaking fruit off trees requires loosening the cherry from its stem—and the looser that connection, the softer the force needed.
Some cherry varieties, such as Skeena, naturally loosen as they reach maturity, while for others, including Bing, ethephon sprays can induce abscission. But not even abscission sprays will make some varieties, notably Chelan or Rainier, machine-harvestable, says Amit Dhingra, assistant professor of genomics and biotechnology at WSU in Pullman.
Dhingra is identifying which genes produce Skeena’s natural loosening and Bing’s positive response to abscission materials.
He’s narrowed the hunt by comparing cherry genes to known abscission-related genes in apples and other fruit.
His results should speed up breeding of high-quality varieties for machine harvesting, Whiting says. “Our ultimate goal is a full-season roster of varieties.”
Growers hope the breeding program reduces reliance on ethephon.
“It’s not a sustainable practice,” Hanrahan says. “It’s too weather-dependent.”
Market development also plays a part in the project.
“Clearly we need to develop markets if any of our technologies rely on [stem-free cherries],” Whiting says.
Packaging showcases stemless fruit Michigan State University researchers are working on new packaging to highlight the fruit’s different look.
Meanwhile, 60 percent of consumers in marketing panels preferred stem-free cherries when price and quality were equal, Whiting says.
Leaving stems on the tree should improve cherries’ post-harvest quality. “Stems cause a lot of damage to fruit through harvest and packing,” he says.
Hayden says he’s looking forward to building an orchard system—rootstocks, varieties, architecture and technology— that produces even better cherries more efficiently “without having to go in with [ethephon] or mangling the tree.”