Mechanical thinning increases fruit size, reduces labor for producers


BIGLERVILLE, Pa. — Hand thinning is a necessary but costly management practice in peach and organic apple production.

Mechanical devices designed to help with thinning have been developed, but none has proven highly effective and capable of completely replacing hand thinning.

J.R. Schupp and a team of researchers from the Department of Horticulture at Pennsylvania State University, Penn State Cooperative Extension and the U.S. Department of Agriculture’s Agricultural Research Service published a study in the American Society for Horticultural Science journal HortTechnology that evaluated two mechanical thinning devices on peach and organically grown apple trees during 2005, 2006 and 2007.

First machine

The first machine was a rotating string thinner designed by H. Gessler, a German grower, to remove apple blossoms in organic orchards.

Second machine

The second machine was a vibrating direct-drive double spiked-drum shaker designed for harvesting citrus fruit.

In 2007, the spiked-drum shaker, designed by the U.S. Department of Agriculture and slightly modified for these tests, was used to thin pillar (columnar) peach trees at 52 to 55 days after full bloom.

The drum shaker was driven at two different speeds in the orchard and reduced crop load an average of 58 percent and follow-up hand thinning time by 50 percent.

Increased fruit size

The spiked-drum shaker increased fruit size by 9 percent at harvest compared with conventional hand-thinned or non-thinned control trees, a result appreciated by growers and consumers.

As consumer demand for larger-size peaches increases, fruit brokers pay premiums for peaches measuring 2.75 inches in diameter or larger.

Hand or mechanical thinning resulted in average fruit sizes within the desired size range.

Peach and apple producers can see multiple economic benefits from mechanical thinning technology.

According to the research, the “net economic impact of mechanical thinning versus hand thinning alone ranged from $175/hectare to $1,966/hectare.”

Promising technique

The researchers summarized mechanical thinning appears to be a promising technique for supplementing hand thinning in apple and peach trees.

The application of mechanical thinners offers a solution to critical components of fruit grower profitability: the premiums paid for large fruit in the fresh fruit market, growing labor costs and a potential shortage of farm labor.

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