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Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.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?

Managing an efficient harvest in canning peaches was a difficult issue with growers struggling to harvest all fruit from individual varieties at the optimum ripeness for canning. SPC then had difficulty holding fruit prior to canning and managing maturity at this stage to maximise canning yield and minimise losses due to over ripening or rots. In recent years, the product ReTain® was registered and used to some extent to delay maturity in the field for between 5-7 days. This assisted with harvest on farm, and then managing the logistics of moving fruit from the farm, to the processor, then through the canning operation. Many farmers struggled with accurate timing for this product and if it was applied too late, would not be effective. As the cost per hectare was high, correct application timing was essential. Gibberellic acid (GA3) was also known to have an effect upon maturity development and fruit firmness and was registered for use in cherries at the time. GA3 was significantly cheaper than ReTain® and its use as an alternative to ReTain® or as a mix with ReTain® was studied overseas and was shown to be effective.

This project was conducted to:

• Determine if an easy physiological test or measurable physical characteristic could be used to better determine the optimum application timing for ReTain® to be applied in canning peaches
• Investigate options for a more cost effective treatment regime with ReTain®.

Fruit maturity development in three common canning varieties, namely Tatura 204, Tatura 215 and Golden Queen, was monitored in the three weeks leading up to harvest. Fruit was sampled every 2-4 days until commercial harvest started. Fruit sampled on each date was evaluated for external and internal colour, firmness, solids, titratable acidity and ethylene production.

Results from this work showed that ethylene production, internal flesh colour, external colour, acidity and solids did not had a large enough change, prior to 7 days before harvest, to be used as a simple indicator of application timing. Flesh firmness may have been a good indicator of the best time to apply these products as a large change in firmness was seen in two varieties around 10-14 days prior to the first commercial pick.

In three other studies, a range of ReTain® and GA3 treatments were evaluated for effectiveness in the same orchards that the maturity evaluation work was conducted. Treatments were applied at around 7-10 days before commercial harvest then assessments were done weekly for three consecutive weeks. Assessments of return bloom in the following season were also done.

A number of treatments in the product efficacy studies resulted in delayed maturity of fruit. The delays were equal to that seen with the current ReTain® registered rates, with no adverse effect upon fruit colour, size or return bloom in the following year.

Further work to confirm the correct application timing based upon changes in fruit firmness was recommended.

Possible permit applications with alternative treatments to ReTain® were being investigated.