Peach thinner may bear fruit

As consumer demand for premium fruit increases, growers are being challenged to bring consistently high-quality fruit to market. And to boost their bottom line, orchard owners are experimenting with new techniques that can increase fruit quality while reducing labor costs.

Thinning by hand, a common practice used by growers to produce larger, healthier fruit, is among the most labor-intensive orchard practices, with significant impact on fruit production overhead, and ultimately, prices paid by consumers. A Penn State research team published the results of new research on a horizontal string thinner used in peach production in a recent issue of HortTechnology. A string thinner prototype for open-center tree canopies was tested in six orchards. Remarkably, fruit size at harvest was increased by the horizontal string thinner in all but one trial.

Key Points

• New mechanical peach thinner promises savings for producers.

• Product helps create superior peaches, as growers are asked for high-quality fruit.

• Thinning by hand costs California growers $1,000 or more per acre.

Eliminates hand labor

Project leaders Tara Baugher and Jim Schupp noted that higher-quality fruit can result when “blossom thinning” is used. This thinning technique ideally removes 50% to 75% of the excess fruit early in the growing season, and is most often done by hand. But the practice is labor-intensive and can carry an enormous financial burden; a recent survey reported that Eastern peach growers commonly spend $350 to $600 per acre for hand-thinning peaches, while California peach producers spent an average of $1,000 per acre, with extremes of up to $1,500 per acre reported.

Trial evaluations

Horticultural and economic evaluations of chemical blossom thinners were conducted in 16 commercial orchard trials from 2005 to 2007. The treatments were applied at 80% full bloom and compared to hand thinning postbloom. Chemical efficacy was variable among years and blocks. Chemical thinners cut follow-up hand-thinning time in 33% of the trials and increased fruit diameter in 55% of the trials, resulting in net impacts of $14 to $983 per acre in 78% of the trials.

Similar evaluations of two mechanical thinners were conducted in four commercial peach orchard blocks in 2007. A mechanical blossom thinner designed by a German grower for thinning apple trees in organic orchards was tested on peach trees trained to either a perpendicular V or quad-V system. Thinning was conducted at 20% or 80% full bloom. A USDA spiked-drum shaker, originally designed for harvesting citrus, was included in the orchard tests at 45 days after full bloom.

Mechanical thinners reduced fruit set, decreased follow-up hand-thinning time, and increased the quantity of fruit in the 3-inch-or-greater size distribution in 100% of the trials. Net profit ranged from $71 to $796 per acre. Bloom thinning at 20% full bloom was similar to thinning at 80% full bloom. Detailed flower counts on branches with different orientations indicated that pruning may be adjusted to improve thinner performance. Upshot: Blossom thinning may speed adoption of narrow-canopy systems.


FOR “V” SYSTEMS: The horizontal prototype of a string thinner is designed to thin peach blossoms in orchards trained to open-center or vase systems.

This article published in the February, 2010 edition of CALIFORNIA FARMER.

All rights reserved. Copyright Farm Progress Cos. 2010.