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Precision crop load management without chemicals

Research & Extension

In the lead-up to spring, University of Tasmania researcher Sally Bound updates us with the latest and very promising results from her research identifying how to use Artificial Spur Extension to manage crop load and get better production results.

What is Artificial Spur Extinction?

Artificial Spur Extinction (ASE) is a crop load management method using bud-thinning techniques to precisely define where and how much fruit is set on each limb of the tree. The aim of ASE is to promote the vigour and performance of floral spurs, stimulate spur strength and improve fruit quality and regularity of production.

Last year we reported on the preliminary results of a two-year study that was established to better understand how Artificial Spur Extinction (ASE) could be used in Gala and Fuji. In particular, we wanted to see if ASE could reduce extreme biennial bearing and reduce chemical thinning without compromising fruit yield and quality. This work was part of the PIPS Orchard Productivity Program, a strategic levy investment under the Hort Innovation Apple and Pear Fund.

The first year’s results were promising and gave us evidence to support that ASE may be a better tool for managing crop load without additional chemical thinning than current standard practices (see Are chemical thinners necessary? Australian Fruitgrower Oct/Nov 2016).

Here is the report on the second year’s results from the trial that further support the case that ASE could deliver better results and reduce costs if adopted by growers.

About the trials

We established trials in commercial orchards in Tasmania to test how the following practices compared: ASE, ASE with chemical thinning, conventional pruning and conventional pruning with chemical thinning.

All trees were pruned during winter; unbalanced limbs were removed and then remaining limbs were spaced out to six limbs per metre of tree height.  On the ASE trees, floral buds were thinned to six buds / cm2 limb cross-sectional area (LCSA) in late August just before bud break.  A full chemical thinning program, using the bloom thinners Ethrel® (ethephon) and NAA and post-bloom thinner Maxcel® (BA), was undertaken on trees tagged for chemical thinning. Following natural fruit drop, all trees were hand-thinned nine weeks after full bloom to six fruit/cm2 limb cross-sectional area (LCSA). Fruit was harvested at normal commercial harvest.



In ASE-managed trees the number of flower buds (clusters) was reduced before bud burst, resulting in fewer buds than in conventionally managed trees. Conventional trees were carrying approximately double the number of flower buds at bud break compared with the ASE-managed trees.  The other important point to note is that the number of clusters in the ASE trees was stable across the two years.

Crop Load Management without chemical thinners

Fruit set

In the first year (2015/16), a high proportion of clusters set fruit, which was the result of an unusual season with a very short and compressed flowering period. Flowering in the second season (2016/17) was spread over a longer period of about four weeks and a more conventional pattern of fruit set was observed. Chemical thinning reduced the proportion of clusters set in both Gala and Fuji.

Under conventional tree management it is not uncommon to see 30-50 per cent of spur and terminal buds fail to set fruit. Even allowing for the unusual spring in 2015, the proportion of buds setting multiple fruit was higher in ASE treatments than in the conventionally managed trees, and this effect was even more marked in the second season.

Even though the number of flower buds was reduced in the ASE-managed trees, the percentage of fruit set was higher than in conventional trees. This is explained by a high percentage of clusters setting fruit with a higher proportion of multiple fruit set in each cluster. These results are in agreement with our earlier work showing that most floral buds set fruit under ASE management, most likely due to stronger buds and less competition for resources. Chemical thinning was more effective in the second year of the study, reducing fruit numbers by approximately half across all treatments.


In Year 1 of this study, total yield was about 60 t/ha in the Gala for all treatments, with chemical thinning having no real effect. In Fuji, yield was 30 per cent higher in the ASE trees than in the conventional, and chemical thinning further reduced yield in both cultivars. In the second year, ASE produced higher yields in both cultivars.

ASE delivered superior benefits

ASE is a suitable tool for precision management of crop load without additional chemical thinning. It has marked advantages in that it is not weather dependent and it removes the negative impact that most chemical thinners have on fruit size and shape.

In addition, bud position is optimised in ASE, fruit is well spaced and light distribution into the canopy is enhanced.  With this technology growers are also able to set their trees up to carry a pre-determined crop load with reasonable accuracy, thus enabling improved management of fruit size.

A full cost:benefit analysis is still to be completed, taking into account time of pruning and bud removal, cost of spraying, hand thinning etc., but our results indicate the potential of ASE to supersede and eliminate the present requirements for chemical thinning to regulate biennial bearing and crop loading.

Although the first year of ASE implementation can be labour-intensive, in the longer term the application of ASE with its simplified hand-thinning and more even fruit maturity, combined with a move away from chemical thinning, is likely to reduce both time and cost to the grower.


Thanks go to Scott Price, manager of Calvert Brothers Rookwood orchard at Ranelagh, for use of his orchard and provision of the trial trees, and to the PIPS 1 project team of Stuart Tustin, Ben van Hooijdonk and Ken Breen (Plant & Food Research, NZ); Simon Middleton, John Wilkie and Heidi Parkes (DAF Queensland); and Dugald Close (TIA), who helped paved the way for this work with the initial study comparing ASE and conventional management.

This project is a strategic levy investment under the Hort Innovation Apple and Pear Fund. It is funded by Hort Innovation using the apple and pear levy and funds from the Australian Government.


biennial bearing chemical thinning crop loading PIPS vigour

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