Obtaining Optimum Crop Size through Thinning

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Figure 1. Peach fruit thinned to a proper spacing on shoots with sufficient leafing have the potential to attain optimum size.

One of the most important horticultural practices to attain optimum yield of appropriately sized peaches is proper thinning. If this practice is conducted correctly and in a timely manner, growers should be able to attain optimum crop size (Figure 1). Since larger size fruit tend to garner the highest market price, it behooves growers to have their thinning strategy planned and executed properly.

Most Florida peach growers have learned that dormant pruning of thin or weak flower bud bearing shoots is a good first step in controlling the eventual fruit set later in the season. This can help reduce the expense of manual fruit thinning later in the season.

Developing peach fruit go through three phases of development: cell division, pit hardening, and final swell. An article entitled “Peach Tree Physiology” describes these three phases (http://www.ent.uga.edu/peach/peachhbk/pdf/physiology.pdf ). The article indicates that cell division is typically completed within 50 days after full bloom in most peach cultivars, pit hardening lasts a few days to a few weeks, and final swell takes about three weeks. This information is useful as a guide for developing a fruit thinning schedule, since it is necessary to thin fruit before the initiation of pit hardening to ensure that carbohydrates are properly partitioned to the fruit that you eventually plan to harvest, thus resulting in optimum sizing and yield. Growers should remember that many of the low chill peach cultivars grown in Florida tend to have multiple blooms and that additional thinning may be necessary.

The UF/IFAS Extension Publication HS1109 entitled, “Florida Subtropical Peaches: Production Practices” (http://edis.ifas.ufl.edu/hs348) indicates the importance of thinning peach fruit before the initiation of the pit hardening phase and suggests that growers can cut fruit to monitor development; typically occurring when fruit are about the size of a marble or a nickel. The document indicates that most cultivars will attain optimum size when the best fruit on stems with sufficient leafing are thinned to an average spacing of 6-10 inches and smaller fruit are removed.

Some growers also practice mechanical or chemical bud and/or bloom thinning. While this process can potentially increase efficiency, it also runs the risk of crop failure should a serious frost/freeze event occur. The Southeastern Peach Growers Handbook has suggestions on methods to evaluate for those interested in experimenting with bud and/or bloom thinning, but it should only be conducted on a very limited basis.


by GARY K. ENGLAND, UF/IFAS Multi-County Extension Agent – Fruit Crops