This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

In Victorian canning peach orchards, fruit thinning had been traditionally practiced by hand. This was expensive, costing up to $3,000 per hectare, and had often been done too late to achieve maximum benefit in achieving optimum fruit yields.

Field trials conducted by Agrisearch Services Pty Ltd and reported in 2001 (FR96001) demonstrated that the blossom desiccant ammonium thiosulphate (ATS) was an effective fruit thinning agent in canning peaches, leading to larger fruit size at harvest compared to hand thinning alone. Agrisearch recommended the use of ATS (in combination with a suitable non-ionic wetting agent), as a single application, at around 70-90 per cent flowering. However uptake by the industry was not widespread, due to a fear of over thinning and a perception of unreliability. Research by Bound et al (2005) in apples indicated that multiple applications of ATS, without the addition of a wetting agent and using slightly lower dosages, could be more effective than a single application at higher rates applied late in the flowering period.

This project aimed to refine the application regime for ATS to improve reliability in efficacy and to reduce the risk of over thinning giving growers greater confidence in using this product.

A range of field studies were conducted over four seasons on commercial canning peach orchards across the Goulburn and Murray Valleys. Flowering patterns in the key canning peach cultivars, Tatura 204, Tatura 211 and Golden Queen were studied in year 1 to better understand variability within and between trees and determine if there was variability between cultivars. Field trials evaluated application frequency, timing and method in orchards with varying tree architecture over multiple seasons. Two different spraying systems were included; conventional air blast application and directed application through a Quantum mist sprayer.

ATS when applied as a split application at around 40-60 per cent flowering and again around 70 per cent flowering to full bloom, at 1 per cent v/v, in Tatura 211 and Golden Queen was shown to be consistently more effective than a single application, whilst in Tatura 204 an application rate of 1.5 per cent v/v was required to achieve effective thinning. The application of ATS through a Quantum mist sprayer generally provided better efficacy than the same rate applied through a conventional airblast sprayer. Dollar savings from reduced thinning time were considerable, but were offset somewhat by the cost of chemical and application. However if early thinning was optimised, gains in fruit size could lead to increased returns of up to $6,000/ha.

The use of ATS however formed only part of an integrated approach which was required to achieve effective crop load management. Smart pruning and chemical thinning followed by timely hand thinning resulted in maximum yields being consistently achieved. A program to improve understanding of the need for accurate product application, selection of appropriate use rates and determining when crops were at the correct stage for spraying, was recommended.

Data from this project will be used to establish a label extension for use of ATS in specific canning peach varieties using the new rates and application methods.