Precision thinning of apple trees using chemical agents is essential to achieve optimal crop load with minimal labour for hand thinning. A Tasmanian researcher is now examining the main thinning products used in commercial orchards in greater depth.
Each spring, apple growers must remove excess flowers and fruitlets to improve fruit size and quality. Apple trees typically produce more flowers and fruitlets than they can sustain to marketable size. Tasmanian Institute of Agriculture tree crop physiologist Leticia Reis said thinning is a key orchard practice because it directly regulates crop load, influencing yield, fruit size, return bloom, and long-term orchard profitability.
During the last growing season, Ms Reis partnered with Montague Farms to trial precision thinning in a commercial apple orchard at Legana in northern Tasmania. The on-farm trial tested alternative thinning agents and measured their effects on input costs, labour efficiency, yield, and fruit quality.
Rodney Hogan of Montague Farms participated in the trial and attended a recent thinning workshop at R.W. Squibb and Sons Orchards in Spreyton, coordinated by Apple Pear Australia Limited (APAL), where Ms Reis presented her findings. "The more trials we do to see what's working and what isn't working, gives us the best results for our business," Mr Hogan said. "Any research we can do is a big help, as apple production is our livelihood. If we can make things easier, smarter, and cheaper, that's what we're here for."
The study found that Brevis, applied once or twice post-bloom and particularly when combined with ATS and Ethrel, achieved effective thinning while maintaining fruit quality, confirming its suitability as an alternative to Carbaryl. The results also indicated that higher Brevis rates may enhance thinning efficacy under specific orchard conditions.
For the 2025–26 season, Ms Reis will conduct another thinning trial at Montague Farms in a 10-year-old Buckeye Gala orchard. The new trial will test a product containing 1-aminocyclopropane-1-carboxylic acid (ACC), which is not yet registered for commercial use in Australia. The research will evaluate ACC at different application timings and doses, both at bloom and as a rescue thinner.
The trial will also assess Metamitron as a post-bloom thinner. While widely studied in Europe and North America, its performance under Australian conditions remains under review. "This project provides the chance to test ACC and deliver early answers to the industry on its efficacy, timing, and potential fit within crop load management. It is emerging as a candidate to replace or complement traditional thinners," Ms Reis said.
The research team will also validate two decision support tools, RIMpro and BreviSmart, by comparing their predictions with observed fruit set and crop load results. The trials form part of the Apple Production Systems (PIPS) 4 Profit project (AP22004), funded by Hort Innovation using the apple and pear research and development levy with support from the Australian Government.
Source: Tasmanian Country
