Fruit and blossom thinning can be used to give better control of mature fruit size and overcome biennial bearing, providing more consistent supplies to markets.
Fruit thinning trials for cling peaches commenced in 1956 at Berri Experimental Orchard, focussed on the variety Wight. This program used pruning and hand fruit thinning to establish ideal cropping levels for good peach yields and quality. These trials concluded at Berri in 1962 and were transferred to the new Loxton Research Centre.
Hand thinning fruits to achieve optimal fruit load and size proved the most reliable technique for peaches. In 1968–69, a review of cling peach growth cycles was conducted. This assisted development of a “Reference Date” technique for timing thinning of each main peach variety. The larger the fruit size at the Reference Date, the less thinning required.
A number of blossom thinning agents were trialled by Frank Gathercole through the 1960s including dinitro compounds, strong urea sprays, wetting agents and ethephon applied at early fruit set. Biennial bearing was a major problem in the main canning apricot variety, Trevatt. Bloom thinning with DNBP (dinitro butyl phenyl) proved very effective in overcoming biennial bearing in both Moorpark and Trevatt apricots (1970). A comprehensive publication (Spray Thinning Apricots, Extension Bulletin 12/72) with detailed instructions for application of thinning agents to the major apricot varieties was produced in 1972.
Peach bud drop emerged as a major problem for canning peach growers in the 1960s. A host of trials were conducted to identify the cause of this problem including summer pruning, phosphorus applications, DNC oil sprays, bud mite studies, excessive irrigation and insufficient winter chilling. While these trials did not conclusively identify the cause of peach bud drop, it was strongly suspected that it was caused by a combination of over irrigation and insufficient winter chilling. Peach bud drop has not been a problem since the mid 1960s.
Further research on timing and intensity of hand thinning of apricots (for drying) was conducted by Michael Rettke in the 1980s. This included economic analysis of dried fruit returns. Results showed there was a significant financial advantage from thinning at or within a few weeks of flowering to achieve crop load recommendations.
Even crop maturity and consistent fruit size are prerequisites for successful mechanical harvesting. Demonstration of mechanical tree shakers and fruit catchers for harvesting apricots, nectarines, plums and peaches were run in conjunction with adopters of this equipment (Simarloo) in the 1980s. However the high cost of this equipment along with the challenge of getting even fruit maturity made adoption uneconomic for most growers.
Post WW2 there were major shortages of farm labour. In 1947, the SA Department of Agriculture initiated a major industry development strategy to increase mechanisation in the state’s horticulture industries. This included a project to introduce bulk handling to the potato and apple industries. The use of bulk bins, fork lifts and other handling equipment subsequently flowed from the apple industry to the stone fruit industry in the 1950s.
All new apricot varieties nearing release from the SARDI apricot breeding program undergo evaluation of their performance in a “one pass” pick operation. This is done to assess their suitability for mechanical harvesting by various methods. The breeding program has had a focus on producing new varieties suitable for mechanisation should this be more widely adopted by the dried fruit industry.