Researchers work on mechanical peach harvest

Issue Date: May 23, 2018
By Bob Johnson

Research is continuing on shake-and-catch mechanical harvest systems that could significantly reduce production costs in producing canning peaches.

The University of California breeding program is yielding varieties with fruit that can hang on the tree longer, which makes for more efficient single-pass harvest.

"We are trying to make harvest more manageable, so that you can avoid having some of the fruit become too ripe as the rest of the fruit becomes ready," said Tom Gradziel, University of California, Davis peach breeder. "The northeast corner of the orchard gets less light and ripens slower, so you need hang time because uniform ripening is not possible. Longer hangers should let you have fruit that has more uniformly sized, and fewer small fruit. It also goes with uniform good color and flavor."

Gradziel has already been able to develop numerous varieties the past few years with good to superior hang time by using germplasm from a broader range of sources.

"We are getting new germplasm from both Brazil and South Africa," he said. "We are also bringing in material from almonds, originally for disease resistance, but it also looks to help hang time."

Under Gradziel's leadership, the UC breeding program already released the new Kader variety, which comes in around the same time as Carson and has a hang time of at least a week after the fruit ripens.

More recently, the program also already released the new Vilmos variety, which ripens around the same time as Andross or a little later.

"We are breeding for at least one week of hold time on the tree for once-through harvest, or later on, mechanical harvest," Gradziel said. "For mechanical harvest, we're looking at compact tree types, that is two thirds to three fourths of regular sized trees regardless of the rootstock. They are more compact because they have shorter spaces between nodes, that is shorter shoot length."

The more compact trees could reduce pruning costs, but their main benefit in mechanical harvest systems would be reducing injury as the fruit falls after shaking.

"Only around 12 percent of cling peaches are machine harvested, and the main challenge is fruit damage," said Stavros Vougioukas, UC Davis associate professor of biological and agricultural engineering. "The biggest problem is damage during the fall, but damage also happens during detachment, and from fruit-to-fruit or fruit-to-machine contact."

Vougioukas is working on a long-term project to make the mechanical shaker harvesting systems already used for almonds, walnuts, pistachios and prunes practical for more sensitive crops like pears and canning peaches, where hand harvest alone accounts for around 30 percent of the cost of production.

Previous efforts at mechanical canning peach harvesters attempted to cushion the blow with soft rods that catch the fruit before it bounces off branches and crashes to the ground.

"Why should I catch my fruit after a 10-foot fall instead of putting in something that can catch them in the canopy after a foot or two," Vougioukas said. "Early attempts at this would reduce large bruises, but increase small ones as the fruit bounced its way down."

Vougioukas' most recent models catch more of the fruit sooner by adding inflatable fingers that come out from a series of soft rods inserted into the canopy as the tree is shaken.

He is using computer simulation models, based on where the fruit is located on real trees, to predict how many of them would hit branches, or the soft rods, as a harvester shakes the tree.

"If a fruit hits a branch before it hits a soft rod, it will get damaged," Vougiokas said. "Simulation tells you how often that happens, depending on how many layers of soft rods you use."

There is a multi-state research effort, with funding from several crop groups and the U.S. Department of Agriculture, to develop the next generation mechanical shaker fit for use on relatively vulnerable fruit.

For California canning peach growers, improved efficiency is a matter of survival in the face of low-cost competition, mostly from China.

"A big part of what we're doing is making sure we don't get further harmed by foreign competition," said Chris Zanobini, executive director of the California Cling Peach Board.

The Cling Peach Board has received a $220,000 specialty crop grant to educate school officials about canned peaches, and about the rules regarding buying domestic.

The peach sector has also invigorated its outreach campaign with greater use of social media to explain the nutritional benefits of canned peaches to consumers, as well as retailers and other buyers.

"We are trying to communicate to parents that this is a great nutritious food for their children," Zanobini said. "We're not trying to throw fresh under the bus, but we promote California cling peaches as being as nutritious or more as fresh, and as having less sugar than many of the alternatives."

(Bob Johnson is a reporter in Davis. He may be contacted at

Permission for use is granted, however, credit must be made to the California Farm Bureau Federation when reprinting this item.