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Mechanical Blossom Thinning - Dream or Reality

The tender fruit growers need to reduce labour costs in order to remain efficient and profitable. According to the OMAFRA publication "Establishment and Production Costs for Tender Fruit in Ontario 2006 Economic Report, the cost for thinning fresh market peaches contributed $500 per acre to the overall variable costs. There are 6,374 peaches and nectarines in the province (Ontario Tender Fruit Tree Survey 2009). The peach and nectarine industry could realize a savings of approximately $1.6 million if mechanical blossom thinning could reduce 50% of the crop and therefore 50% of the labour costs. Currently, all tender fruit must be hand thinned since there are no chemical thinners available in the foreseeable future.

Matt Peters driving the Darwin mechanical thinner

The success of the spring trials could not have been possible without the support of Matt Peters, M.N. Bartlett Inc. The company purchased two Darwin mechanical thinning machines this spring and cooperated with the thinning investigation and growers demonstrations. The funding was provided from Vineland Research and Innovation Centre through the Orchard and Vineyard Transition Fund and further supported by the Ontario Tender Fruit Producers' Marketing Board and the Apple Growers of Ontario.

Is it possible to mechanize fruit thinning in the orchard. There are many issues and questions that need to be answered:

• Can we get all the trees thinned in time during the bloom period? Answer - it can do about 10-15 acres per day depending upon tractor speed and orchard design.
  
• Is it cost effective? Answer - yes - payback could be in 1-2 years depending upon number of acres
  
• Is mechanical thinning effective on trees not yet pruned? Answer - yes - but not likely as good as pruned trees
  
• Will the machine thin enough? Yes - but always need to adjust tractor speed, number of strings, rpm of strings, timing of bloom
  
• Is it possible to over-thin? Answer - yes - same as above

Eight peach growers, one plum and four apple growers participated in thinning trials this spring. The results to date have been positive. Data collected at each site included; blossom counts pre-thin using the Darwin mechanical thinning machine and Control (hand thinning). Blossom counts were done shortly after using the Darwin. The desired goal was to reduce approximately 40-50% of the peach bloom.

The first trial involved mature Japanese plum trees that were tall and vigourous. 24.1% of the Early Golden bloom 25.0% of the Shiro bloom was removed. Since this was the first attempt, a few limbs were broken and not enough blossom thinning was achieved. Harrow Diamond trees at approximately 10-20% full bloom were also mechanically thinned. Trees that were un-pruned averaged 47.3% blossoms thinned and pruned trees averaged 46.3% blossoms thinned. The thinning was consistent but the un-pruned trees may still be carrying a larger crop since the Darwin might not have penetrated the inner canopy.

In another observation of standard pruned Harrow Diamond trees, the Darwin vertical thinner removed 56.8% of the blossoms from the sides and the horizontal Darwin removed 68.4% of the blossoms from the top. Most of the grower demonstrations for peach achieved the desired thinning affect of around 40-50% blossom removal.

Other replicated trials involved Dr. John Cline and Debbie Norton, from the Department of Plant Agriculture, University of Guelph using grower sites that had spindle trained trees at one site and central leader trained trees at another site. Intensive data such as fruit counts and size grading will be collected at these two sites throughout the growing season and reported later in the fall.

Many factors are involved in how many blossoms the Darwin can remove. Factors include the numbers of rows of strings, how many strings per row, the rpm of the rotation of the drum holding the strings and the tractor speed. In Europe, the tractor typical travels 8-10 kph for apple systems but 4-5 kph was the desired speed for peaches in Ontario orchards.

Future peach and other tender fruit orchards will have to develop new strategies such as the vertical shape to achieve the greatest benefit of mechanization. The orchard architectures would then allow growers to increase the number of rows per acre to increase overall orchard efficiency. Other benefits of mechanical thinning have been the increase in fruit size which affects grower profitability as well as reducing labor costs. Look for more information in newsletter updates and the Ontario Fruit and Vegetable Convention 2010.

Related links

• Darwin Mechanical Blossom Thinning Update (Tender Fruit Grape Vine newsletter, October 2009)
• Darwin Mechanical Blossom Thinning Update (Tender Fruit Grape Vine newsletter, Feruary 2011)