Qin Zhang explains during a WSU field day how he is working to improve the mechanical cherry harvester developed by USDA researcher Donald Peterson more than a decade ago.

Qin Zhang explains during a WSU field day how he is working to improve the mechanical cherry harvester developed by USDA researcher Donald Peterson more than a decade ago.

Geraldine Warner

Washington State cherry growers Denny Hayden of Pasco and Bob Harris of Yakima began anticipating mechanical harvesting of fresh sweet cherries more than a decade ago after Dr. Don Peterson, engineer with the U.S. Department of Agriculture in ­Kearneysville, West Virginia, developed a mechanical ­harvester.

The harvester has been extensively tested in the state of Washington, but never commercially manufactured.

Machine-harvested cherries are stemless. Ethrel is applied to the cherries shortly before harvest to loosen them from the stems so that they fall easily from the tree when the trunk or limbs are shaken. Hayden and Harris have been developing a market for stemless cherries so that they’d be able to sell their fruit whenever machine harvesting became a reality.

“This wasn’t a gimmick to sell cherries,” Hayden said. “This was looking to the future, trying to survive and stay in business. We knew at some point in time it was going to happen.

“Our initial dream was we can go out and compete against anybody in any industry any time. If we can reduce the amount of labor, we can be competitive with our cherries,” he explained. “Labor is the biggest single cost in cherries.”


The biggest obstacle has been that most sweet cherry orchards aren’t designed to accommodate a harvester like Peterson’s. It works best with an angled canopy so that when the tree is shaken, the fruit can fall onto a catching surface, rather than down through the branches. Hayden reckons that only a fraction of a percent of Washington’s cherry acreage would be adaptable to machine harvesting. And since many of the cherry orchards in the ground have been planted within the last few years, they’re not likely to be replaced soon.

“This industry, five or six years ago, went through a heavy capitalization in cherries,” Hayden said, “And they’re just getting revenue back. They’re not going to reconfigure them.”

What would really help increase efficiency in the cherry industry would be a dwarfing rootstock equivalent to Malling 9 for apple, he said. Although Gisela rootstocks are smaller than traditional ones, such as Mazzard, they are not small enough, and trees on Gisela can produce small fruit, he said.

Hayden is hoping that a cherry rootstock development project led by Dr. Amy Iezzoni of Michigan State University and funded by the Specialty Crop Research Initiative will eventually generate rootstocks that can be used to create pedestrian cherry orchards where most of the work can be done from the ground.


What’s needed in the meantime, he said, is something between fully automated harvesting and hand picking. To harvest his stemless cherries, he is using a hand-held olive shaker. The tree branches are shaken individually and the fruit falls onto some kind of catching surface—Hayden has experimented with bubble pad, blankets, and lightweight metal frames.

The olive shakers are too heavy and too clumsy, but it’s the right technique, he said, because they’re adaptable to different orchard configurations. “Something that’s hand-held is going to be the immediate future in mechanizing this. We’re not going to have a completely automated harvest. We’re going to have a machine-aided harvest so we can reduce our labor inputs.”

Dr. Qin Zhang, engineer at Washington State University’s Center for Precision and Automated Agricultural Systems at Prosser, is working to address some of the problems associated with the Peterson harvester. One was that it sometimes removed clusters of cherries with stems, rather than just stemless cherries, because the force applied to the limb was too strong.

This is one aspect of a Specialty Crop Research ­Initiative-funded project led by WSU horticulturist Dr. Matt Whiting to develop a sustainable production, ­processing, and marketing system for stem-free cherries. Hayden is cooperating in the project.

Qin said the private company Picker Technologies is also involved and has built a prototype cherry harvester that he is using in his research. Once the optimal harvesting system has been designed, possibly by 2013, Picker Technologies will commercialize it.

Qin is also working on finding a better hand-held device to harvest cherries. In place of the heavy engine on the olive shaker, he’s exploring the idea of lighter-weight devices that would be hooked up with hoses to a hydraulic power unit on a self-propelled platform so workers don’t have to carry the engine.