ARS | Publication request: Performance of mechanical thinners for bloom or green fruit thinning in peaches

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 15, 2010
Publication Date: January 1, 2011
Citation: Miller, S.S., Baugher, T.A., Schupp, J.R., Wolford, S.D. 2011. Performance of mechanical thinners for bloom or green fruit thinning in peaches. HortScience. 46(1):43-51.

Interpretive Summary: Peach (Prunus persica L. Batsch) thinning is costly and time consuming, but a necessary practice in order to produce a crop of marketable size fruit. A number of mechanical devices and methods have been developed and evaluated to reduce the cost and time required for hand thinning peach. This report provides additional evidence that a string thinner can effectively thin peach at bloom, and a spiked drum shaker can thin at bloom or at the green fruit (pit hardening) stage. Five trials were conducted over two years in grower orchards with trees trained to a perpendicular V system. The string thinner at 60% to 80% full bloom (FB) reduced crop load (fruit/cm2 limb cross-sectional area) on scaffold limbs by 21% to 50%, compared to a hand-thinned control. At the 60% FB stage, a double spiked drum shaker reduced crop load by 27%, and in another trial, a prototype single drum shaker reduced crop load by 9%. Across all trials, the spiked drum shakers (single or double units) removed an average of 37% of the green fruit. All mechanical devices reduced the time required for follow-up hand thinning. Follow-up hand thinning costs (US$/ha) were reduced an average of 27% by mechanical thinning devices over hand-thinned control trees. Fruit size was increased over hand-thinned controls by mechanical thinning in most, but not all trials. A combined treatment of string thinner at bloom followed by a drum shaker (single or double unit) at the green fruit stage produced the greatest net economic impact in a number of the trials. The mechanical thinning devices described provide an economical and reliable alternative to hand thinning alone in peach production.

Technical Abstract: Removal of excess fruits (thinning) is one of the most time consuming and costly operations in a peach orchard. A mechanical aid to assist in peach thinning would be a significant advancement for peach growers. A cooperative study between Penn State University and the USDA-ARS, Appalachian Fruit Research Station (AFRS) examined the efficacy of two mechanical peach thinners, a rotating string thinner designed by a German fruit grower for thinning apple bloom and a spiked-drum shaker designed and built by an AFRS engineer and horticulturist to remove green fruit. Two years of field testing demonstrated that both machines could effectively reduce crop load and the time required for follow up hand thinning in high-density peach plantings. The results of these studies are valuable to peach growers and extension fruit specialists in developing future peach orchard planting designs and cost effective thinning strategies for peaches.