May 2, 2008
Mechanical Thinning Brings Larger Peaches with Less Labor

Spring was slow to arrive in Adams County, Pa., this year, but eight growers had already lined up with Penn State Extension to use machines to thin their peaches when blossoms arrived several weeks later.

That was a good indication that mechanical blossom thinning was on the right track.

One morning a year ago, a preliminary research trial was held in a commercial orchard. When everyone broke for lunch, the grower, Doug Lott, excused himself and took the thinner back to the orchard while the others ate. He had seen enough and was ready to use it in a larger block of peach trees.

The scientists who were doing the testing would take longer, collecting data during the growing season and using the post-harvest period to analyze it. But in the final analysis, they too, agreed: Mechanical thinning of peaches at blossom time produced larger peaches and cut the labor costs needed to get them.

Katy Lesser, the Ag Innovations Coordinator in Adams County, tells that story about the grower and the research last year to see how two different mechanical thinners would work on peaches.

One is a German machine called the “Darwin” that takes off blossoms. It is a vertical rotating spindle with nylon strings. The other is a rotating spiked drum invented by USDA ag engineer Don Peterson for harvesting citrus fruit. This machine has shown promise as a green-fruit-removing machine in studies conducted by Peterson’s long-time collaborator, USDA horticulturist Steve Miller.

The research in Adams County is part of the Pennsylvania Ag Innovations Initiative, which was born three years ago when a “summit” of leaders met to discuss “the future of agriculture” in this historically productive East Coast fruit belt. Many areas, including Adams County, were losing land to development. The orchards were aging, markets for processing fruit were poor and plum pox virus had recently wiped out 1,600 acres of the county’s stone fruit.

The leaders quickly agreed that agriculture was not something to be lightly tossed aside. It needed help. Three priorities were identified, one of them being the need to mechanize more aspects of fruit production and move away from hand labor where that could be done.

Right away, Penn State Extension geared up to address labor-related problems. Besides working with orchard platforms as an aid in fruit tree pruning, thinning and harvest, they began work on reducing the need for costly hand thinning.

Tara Baugher, the Adams County tree fruit educator, had worked closely on chemical thinning with Jim Schupp, the horticulturist located at the Penn State Fruit Research and Extension Center in Biglerville. After three years, they concluded that the chemicals were variable in their performance, did not take off enough fruit and didn’t consistently cut the need for hand labor for thinning.

So, when Katy Lesser reported seeing, at the Interpoma equipment show in Europe, a machine invented by a German grower to thin organic apples, the Adams County innovators asked, “Why not peaches?” What was just an idea in January 2007 was transformed into a machine in the field by May. The German manufacturer is Adolf Betz, who started a small, family-owned company named Fruit-Tec. The machine, the Darwin 300, can be seen at www.fruit-tec.com.

Baugher said the labor-saving strategy they’re working on would use a blossom thinner to remove about 70 percent of the blossoms that would need to come off. The potential crop load is easy to see at that point. Then, after the fruit is set, a grower would come back with the green fruit thinner or hand thinning or both.

“Crop load management is vital for annual crops of large, high-quality fruit that meet consumer expectations in today’s marketplace,” wrote Jim Schupp in the Ag Innovations Progress Report published in January. “Perennial fruit crops tend to set more fruit than can be matured to adequate size and quality to meet market expectations and allow for adequate flower production for the subsequent season.

“The availability and efficacy of chemical thinning programs vary by crop, orchard and season, so hand thinning is often required to adjust crop load for optimal fruit size, quality and to promote return bloom. Hand thinning, along with pruning and harvesting, is among the most labor-intensive orchard practices; consequently, it contributes significantly to fruit production costs.

“Interest in reducing dependence on manual thinning is especially strong in organic apple production and for stone fruit – crops for which chemical thinners are not registered. Interest in mechanical bloom and/or fruit thinning was renewed in 2007, as the supply of skilled workers continued to decline and labor costs increased.”

Machine thinning at blossom time has several advantages, Baugher said.

Competition for tree resources is reduced by taking off part of the excess crop early, and that affects both fruit size and return bloom. In fact, data from last year indicate that thinning at 20 percent bloom produced larger fruit than waiting for 80 percent bloom, and the researchers are looking closer this year at why that is.

Being non-chemical, machines avoid the obstacle of EPA registration for a new thinning compound.

Evaluations of mechanical peach thinners were conducted in 2007 in four Adams County commercial orchard blocks trained to either a perpendicular V or quad V system. The German string thinner was tested at 20 percent or 80 percent full bloom. The USDA spiked drum shaker was tested at 35 days after full bloom.

The results: Mechanical thinners reduced crop load by an average of 36 percent, decreased follow-up hand thinning time by 20 percent to 42 percent and increased fruit in higher market value size distributions by 35 percent. Net profits, according to Ag Innovations economist Matt Harsh, ranged from $71 to $796 per acre.

The researchers conducted detailed counts of flowers on branches with different orientations. Limbs that pointed into the tree gave up fewer blossoms, suggesting that growers will need to adjust their pruning to put the fruit where they want it.

There is now an Adams County distributor for the string thinner who assembles parts shipped from Germany (www.dbkilmer.com).

The machine can be front-mounted on a standard tractor equipped with a fork lift. The thinner is powered by hydraulics.

The rotating spindle is about 10 feet tall and has 36 plates containing as many as 648 cords. The number of plates and number of strings per plate can be adjusted, Lesser said, to adjust the aggressiveness of blossom removal and to leave “windows” as needed based on flower density. The version they used in the tests has 18 plates and 162 cords.

The rate of rotation and driving speed can be varied, and generally should be between 180 and 200 revolutions per minute and 2 miles per hour.

The strings did not fray much, Lesser said.

“There was no injury to properly trained trees.”

The Adams County researchers are pretty pleased with their efforts, so far. They’ve developed a cooperative arrangement to share and compare data with Karen Lewis at Washington State University, who is testing a string thinner purchased in January. The joint research is supported by the Washington Tree Fruit Research Commission. Growers from California were coming to Pennsylvania in late April to look at their efforts – and California grows a lot more peaches than the East Coast.

The Ag Innovations Initiative is growing and now involves an expanded multidisciplinary team, including Larry Hull, Penn State entomologist; Jim Travis, Penn State plant pathologist; and Paul Heinemann, Penn State agricultural engineer. Hull is working with Andrew Landers, Cornell University spray technology engineer, to organize a field day on precision spraying June 25 in Biglerville, Pa. Schupp, in cooperation with Sky-Bit and Carnegie Mellon scientists, just received funding to investigate sensor networks for pest management in orchards. Heinemann is a member of a writing team developing national objectives for engineering solutions for specialty crops. The group receives valuable guidance from a national specialty crops working group coordinated by USDA and industry leaders.




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