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A drum shaker to thin off green fruit in soft fruit orchards is being tested in Pennsylvania.

A drum shaker to thin off green fruit in soft fruit orchards is being tested in Pennsylvania.

Mechanical thinning is being studied as a way to reduce hand fruit thinning, which is one of the most labor-intensive and costly practices in stone fruit production. Growers have reported spending as much as $1,000 per acre to hand thin fresh-market peaches.

Tests of mechanical thinning of peaches in Pennsylvania show that the need for hand thinning of green fruit can be cut by half, says Dr. Tara Baugher, extension educator for Penn State University in Adams County. In addition, eliminating competition between fruit at bloom time by mechanical thinning results in larger fruit at harvest. The combination of less hand thinning and more fruit in the higher-value size range could boost grower returns by as much as $500 to $800 per acre.

Baugher is a cooperator in a national research project focusing on innovative techniques for thinning of fruit. Together with Penn State horticulturist Dr. Jim Schupp, she has been testing a string thinner called the Darwin for blossom thinning in commercial peach orchards. The Darwin is produced in Germany by Adolf Betz, who operates a company called Fruit Tec. His initial machine, used primarily to thin apples in Germany, is called the ­Darwin 300 and has a vertical spindle with plastic strings. The number 300 represents the length of the spindle in centimeters. The machine can be attached to a forklift on the front of a tractor and is best suited to training systems where the branches are on a ­single plane, such as a fruiting wall or perpendicular V.

Betz has visited Pennsylvania to see the machine being tested and, at the suggestion of a peach grower, developed a second version of the thinner with a 2.5-meter-long ­horizontal spindle that is designed to operate over the top of the trees to thin fruit on open-center-trained trees. He then went on to develop the PT 250 that can be used in either vertical or horizontal orientations. Researchers in peach-­producing regions around the country are testing the various models.

Schupp and Baugher report that in tests in Pennsylvania, between 30 and 50 percent of peach blooms were removed with a vertical string thinner and 25 to 70 percent with the horizontal prototype. Follow-up hand thinning was reduced by 29 to 60 percent by the string thinners. They found that the vertical string thinner performed best at two miles per hour, while the horizontal thinner worked best at one mph. They also found that mechanical thinning at 20 percent full bloom resulted in larger fruit than thinning at 80 percent bloom. 

Drum shaker

As part of the same innovative thinning techniques project, researchers with the Agricultural Research Service in Kearneysville, West Virginia, are developing a drum shaker that can be used to mechanically thin green fruit after frost risk is over and natural drop has occurred.

This project began two years ago when Steve Miller at Kearneysville began adapting a mechanical citrus harvester, developed by Dr. Don Peterson, as a fruit thinner. Tests in Pennsylvania orchards showed that the concept had merit, but the machine was too big for peach trees and removed too much fruit, Baugher said.

This year, tests will be conducted with a refurbished raspberry shaker, also originally designed by Peterson. In earlier tests, the two-drum shaker had damaged tree bark, so the design was changed so that it had only one drum. Baugher said the researchers hope they will have more control over the level of fruit thinning with the smaller piece of equipment. The machine has been built inexpensively using recycled equipment.

The string thinner, drum shaker, or both have been tested in 12 commercial orchards in Pennsylvania. Baugher said the devices work well together. The string thinner was used during bloom, and the drum shaker was tested at 35 days after full bloom to remove green fruit.

Kevin Bittner at Singer Farms in Appleton, New York, said his family bought a Darwin PT 250 this spring after seeing it in trials. They have more than 80 acres of peaches, but were experimenting with the machine on plums and apricots, too. Their peaches often overset, and the family spends a couple of hundred dollars per acre on hand thinning, he said. "If we can cut that by a third or half, that’s a huge savings. We’ve got to try something different. It could be a huge money saver, and it could be the wave of the future."

He estimates that the machine, which cost $12,500, will pay for itself in the first or second year. Bittner said it would also alleviate concerns about the availability of labor, should there be an immigration crackdown.

Joy Cline, production manager at Bear Mountain Orchards in Aspers, Pennsylvania, said her company also bought a PT 250 machine this spring after seeing the results of three years of trials at the orchard. They have 270 acres of peaches and nectarines, some trained to a perpendicular V, some on a quad V, and some with open-centered trees. They have been doing both blossom thinning and green fruit thinning by hand.

Cline expects to be able to reduce labor costs by 30 to 40 percent. "Anything we can do mechanically is a tremendous savings for us," she said.

She’s also interested in enhancing fruit quality by being able to do more early blossom thinning. Larger fruit should mean better returns to the orchard.

With the one thinning machine, Bear Mountain was able to cover about 60 acres during bloom this spring, focusing on the earlier, smaller varieties where there was the most potential gain. Cline said there is still much to learn about how to adjust all the variables, such as spindle RPM and tractor speed, to achieve the desired results.

Workers hand thinned the rest of the acreage and also touched up the mechanically thinned blocks—particularly the quad Vs—in parts of the trees that the machine didn’t reach.

Cline said she is interested in having one or two more machines to cover more acreage.

Baugher said a number of other growers have bought or plan to buy Darwin machines. "This is really exciting research because at most of the field days that have been held in California and here in the East, growers are interested in adopting the ­technology pretty quickly."