WSU scientists perfecting mechanical harvest of cherries

PROSSER, Wash. — Rich, velvet-red, fresh sweet cherries are in high demand, and so are skilled laborers to harvest the highly perishable crop.

However, labor shortages and labor costs may soon be a thing of the past for Northwest cherry producers, if consumers will accept their fresh cherries free of stems. In a project funded by Washington State University’s International Marketing Program for Agricultural Commodities and Trade Center, scientists here are perfecting a mechanical alternative to hand-picking fresh sweet cherries.

Cherries are the most labor intensive fruit crop and one of the fastest growing fresh fruit exports in the Northwest. According to Matt Whiting, a researcher with the WSU Irrigated Agriculture Research and Extension Center in Prosser, cherry harvest costs typically account for 50 to 60 percent of annual expenses for growers.

Exactly how much money would a producer save by using a mechanical cherry harvester? Whiting and his team predict about 24 cents per pound, and that’s enough for John Deere and other large equipment manufacturers to take a look at the USDA/ WSU dual-mechanical cherry harvester for a possible future design.

“The two-unit mechanical harvester is exceeding our expectations and is performing beautifully,” said Whiting.

In WSU’s first harvest test with the relatively new “Skeena” cherry variety, cherries were “coming off great,” said doctoral student Erick Smith.

“We’re talking fresh market quality cherries,” Whiting said enthusiastically. This is an important distinction for Whiting; other fruit mechanically harvested, such as tart cherries, are destined for lower-grade processing markets. 

Pennies a pound

With approximately 30 pounds of fruit on each tree and a density of about 600 trees per acre, Whiting figures that there are about 8 tons of cherries per acre. Figuring in the estimated cost of the dual-unit harvester, the labor cost of using the harvester comes out to mere pennies a pound. The mechanical cherry harvester has the potential to reduce annual harvest labor costs by 80 to 90 percent, according Whiting and his research team.

“Including the cost of the harvester, our research estimates that the cost of labor per pound will be one to two cents,” said Whiting. Currently, the cost of harvest labor per pound varies between 18 and 25 cents.

Limitations to the widespread adoption of the mechanical harvesting system are related to orchard design. Whiting estimates that less than 5 percent of the current sweet cherry acreage is designed for machine harvest.

The research focuses on a more efficient orchard design, a more systematic pruning technique and the ability to successfully harvest an entire cherry orchard with as few as three people.

What about the stem?

Whiting’s research is investigating the potential for this stem-free harvest system from all angles   harvest efficiency, fruit quality, shelf life and consumer acceptance. He believes there are potential benefits of stemless cherries in terms of export. Cherries without stems have less pitting and bruising because stems can puncture the fruit, causing damage. This is important because “when a consumer purchases cherries, they look very closely at fruit appearance and taste texture,” said Smith.

Stemless cherries also have an increased export life because exporters and retailers do not have to worry about the inevitable discoloring and shriveling of stems on the store shelves. Whiting and Smith are investigating the role of the stem after harvest and suspect that the stem deteriorates faster than the fruit. It is also possible that some countries may view cherry stems as debris; the mechanical harvester eliminates that debris allowing more actual fruit to be shipped.

Another likely benefit of the mechanical harvester is fewer injuries and labor and industry claims associated with ladder use. “Using the mechanical harvester, the only reason a ladder is needed is to hand-pick the less than 10 percent of cherries still left on the tree after it has been mechanically harvested. We anticipate there being far fewer injuries using the harvester than using hand-pickers and ladders,” said Whiting.