Publication 360, Fruit Production Recommendations:
Peach Calendar - Thinning Peaches

Excerpt from Publication 360, Fruit Production Recommendations 2010-11,
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Table of Contents

1. Thinning peaches
   • Factors to consider when thinning peaches
   • Other methods that have been investigated
2. Other Peach Calendar Sections
   • Dormant (in March or early April before buds swell)
   • Prebloom (half-inch green to first pink)
   • Bloom
   • Petal fall and shuck
   • Shuck split
   • Special sprays (when monitoring indicates the need during early green fruit stage to pit hardening)
   • Second generation oriental fruit moth spray
   • Special sprays (when monitoring indicates the need)
   • Third generation oriental fruit moth spray (late varieties)
   • Prepick
   • Postharvest fruit treatment
   • Fall spray (preferred time to spray for leaf curl)
3. Other Information on Peaches
   • Notes on Tender Fruit Insects & Diseases
   • Table 7-8. Products Used on Peaches
   • Table 7-11. Activity of Fungicides on Stone Fruit Diseases
   • Tender Fruit Nutrition
4. Peach Calendar PDF 119 KB
5. Chapter 7 - Tender Fruit Calendar PDF 401 KB
6. Related Links

Thinning Peaches

Peach thinning is an essential orchard management practice. Thinning is necessary to obtain good-sized, quality fruit and to reduce limb breakage, reduced fruit size and quality, loss of tree vigour, shortened orchard life and increased pest management problems.

When thinning, consider fruit load as well as fruit spacing. Optimum fruit load depends on cultivar, tree vigour, tree age and health, and orchard management practices such as tree spacing, irrigation and pruning. Peach growers tend to space the fruit 15-20 cm apart. However, distance between fruit is less critical as long as clusters are broken up and fruit is separated. Tree crop load (kg per tree or number of fruit per tree) is a more important consideration. As an example, a yield of 18-27 tonnes/ha (8-12 tons/acre) in an orchard with a tree density of 490 trees per ha (200 trees per acre) requires about 200-300 fruit per tree, if you assume an average fruit size of 4-7 fruit per kg (2-3 fruit per lb). With current emphasis on increased fruit size for better marketability and trends towards higher tree densities, fruit loads of 175-200 fruit per tree may be more ideal, at least for cultivars that normally produce large fruit.

Factors to consider when thinning peaches

Timing - Start thinning near the end of June drop (about mid-June) when it can be determined which fruits will abort and fall on their own. Thinning at early fruit development or even blossom time is more beneficial than late thinning. However, it is difficult to get a true assessment of crop load before June drop occurs. Thin cultivars that ripen early in order to obtain good fruit size. In some years, a follow-up hand thinning may be necessary.

Pruning - Pruning is an essential part of the fruit-thinning procedure. Pruning selectively removes fruit-bearing surface, as well as some of the excess crop. Normal fruit thinning must follow to avoid over-cropping.

Cultivars - Cultivar selection over the years has tended towards larger fruit. Earlier ripening cultivars have a high percentage of fruit with split pits. Some growers thin early cultivars twice; thinning lightly to remove some crop load, then a second time to selectively remove split-pit fruit. Harrow Diamond is the earliest-ripening commercial cultivar that has few split-pit fruits under normal conditions. This cultivar must be well thinned to obtain suitable size. There is little likelihood of over-thinning early cultivars when the set is heavy. Heavy-setting, hard-to-size cultivars such as Redhaven require heavier thinning than easier-to-size types like Vivid and Loring. As a rule of thumb, however, late maturing cultivars with a good, uniform set are thinned 10-13 cm apart in order to produce good-sized fruit. Thin each cultivar according to its individual requirements.

Irrigation - Irrigation is recommended to enhance fruit size, especially in long periods of dry conditions. There are two key periods to irrigate peaches; during cell division (from bloom to 30 days after bloom) and during cell expansion (approximately 2-4 weeks before harvest). Start irrigation early in the season and continue a regular schedule based on the amount of rainfall, rate of evapo-transpiration and soil holding capacity. Permanent orchard sod is very competitive and increases moisture requirements. Adjust the irrigation schedule based on additional factors such as crop load, winter injury, insect, disease or other stress factors. New technology is being developed for commercial growers to closely monitor soil moisture. Orchards without irrigation may, in some years, need a second thinning during July to attain marketable fruit size.

Thinning methods - Thinning is most commonly accomplished by hand. Large quantities of fruit can be removed quickly with physical aids such as a child's plastic bat, a rubber hose mounted on a bamboo pole or broom handle, or a plastic rake manufactured for this purpose. Follow this initial thinning with "touch-up" thinning a few days later to assure that fruit numbers per tree produce good-sized fruit for the cultivar and orchard condition. Ensure clusters are broken up and fruit separated. If the set is spotty on the tree, more fruit may be left on the heavy-set branches.

Other methods that have been investigated are:

Mechanical blossom thinning - Mechanical trunk shakers used in the past have resulted in over-thinning and had long-term negative effects on the root system of the tree. A relatively new device using nylon cords fixed to a rotating shaft mounted on a front-end loader is showing promise for blossom removal. Tractor speed, the rpm of the nylon cords, the number of cords used, tree shape and the timing during blossom can affect the number of blossoms removed. Follow-up hand thinning is necessary to ensure good fruit size. Mechanical blossom thinning helps to reduce labour costs, and results in larger average fruit size per tree and earlier ripening. This new technology may work best in high density, vertically trained spindle orchards.

Rope thinning during bloom and 4-6 weeks after bloom - Tree training systems need to be properly developed to adapt rope thinning. Moderate success has been achieved in some research and grower trials in the United States.

Chemical thinning - No chemicals are registered for thinning peaches in Ontario.

Any of the above methods must be supplemented by touch-up hand thinning.

Related Links

• Integrated Pest Management (IPM)
• Pesticide Application and Safety
• Pesticide Companies and Agents
• Search the PMRA website
• Ontario Minor Use Program
• OMAFRA Publication 505: Ontario Weeds
• OMAFRA Publication 360: Fruit Production Recommendations