Make a smart crop load management choice

In a commercial orchard in Tasmania a mix of different thinning and crop load management techniques have been put to the test, shedding light on which ones are the most cost- and time-effective to implement, and what impact they have on fruit quality and yield.

A trial conducted in this Gala orchard in Tasmania has shown that managing crop load through ASE is both cost- and time-effective and can produce high-quality fruit with good yields.

Previous articles on artificial spur extinction or ASE (Are chemical thinners necessary? and Precision crop load management without chemicals) have demonstrated that ASE is a suitable tool for precision management of crop load without the need for additional chemical thinning. But many growers want to know about the cost of implementation. 

Here we discuss the results of a larger semi-commercial-scale demonstration trial on Buckeye Gala and compare the costs of ASE and chemical thinning. The results provide further evidence to support the benefits of ASE in delivering better results, removing the need for chemical thinning without compromising fruit yield and quality, and reducing costs.

Demonstration site

The demonstration site was established at Rookwood orchard, Ranelagh, in Tasmania’s Huon Valley and involved five different regimes:

  1. Setup prune (SP) + ASE
  2. SP + ASE + chemical thinning (CT)
  3. Grower prune (GP) + ASE
  4. GP plus ASE + CT
  5. Standard (GP + CT)

As most growers tend to leave more limbs in the tree than is recommended for ASE, we included two different pruning regimes to allow us to compare these differences. The setup pruning in regimes 1 and 2 reduced the number of limbs down to a maximum of six or seven per metre of tree height, tied down upright limbs to a more horizontal position and removed spurs and small twiggy branches from the main trunk. The grower pruning in regimes 3, 4 and 5 maintained nine or 10 limbs per metre of tree height and the main trunk was left untouched. This meant that regimes 1 and 2 had less wood, allowing more light into the tree.

The chemical thinning program consisted of bloom applications of Ethrel® (ethephon) and NAA and a post-bloom tank mix application of Maxcel® and carbaryl.

Impacts on yield and fruit quality

Yield in the ASE regime was 57t/ha – slightly higher than the 53t/ha achieved in the standard chemical thinned regime. Chemical thinning reduced yield by 16t/ha in the ASE regime and 15t/ha in the grower-pruned-plus-ASE regime.

Even though yields were similar, average fruit weight was considerably reduced in the standard regime (162g) compared with the ASE regime (182g). This is a result of reducing the number of flowering sites early in the season, thus reducing competition for resources. Yield was highest in the GP + ASE regime (72t/ha) but fruit quality was reduced.

The highest-quality fruit was produced in the ASE regime – soluble solids content (SSC) of 12.1 degrees Brix, dry matter content (DMC) of 15.9 per cent and firmness of 8.96kg. The standard regime resulted in SSC of 11.3°Brix, 14.8 per cent DMC and firmness reading of 8.51kg, while the GP + ASE regime fruit had 10.9°Brix SSC, 14.5 per cent DMC and 8.38kg firmness.

When it came to hand thinning, the standard trees took 50 per cent longer to thin than the ASE due to the heavier crop load, and the GP + ASE took 22 per cent longer as there were more branches in the trees.

Hand thinning of ASE-managed trees is very simple because the spacing, position and number of clusters are already determined – all that is required is to thin the clusters to singles. Chemical thinning is very much hit and miss, with no control over where fruit are positioned on the tree, and the decision needs to be made on which clusters to retain. Even though most flower clusters set fruit, ASE-managed trees do not express late fruitlet drop as there is no excessive fruit set that invokes fruit shedding, so hand thinning to adjust crop load to the final desired numbers can be started within three to four weeks of flowering rather than waiting for fruit drop in December.


Cost comparison

To compare the costs of the different regimes, the times taken to prune, complete the ASE setup (bud removal) and hand thin were recorded and used to calculate the cost per hectare of each activity based on a labour cost of $25 per hour. The chemical thinning cost includes the cost of chemicals, labour at $25 per hour and a machinery cost of $25 per hour for the tractor/sprayer.

The first year of ASE implementation is the most labour intensive as it involves some restructuring of trees and removing buds across the entire tree. In subsequent years, pruning is reduced to the level that would normally be undertaken in the orchard and it is necessary to remove buds only on new wood, thus further reducing costs.

The cost of implementing ASE in an established orchard is similar to the cost of a standard chemical thinning program, and once the trees are set up the cost of crop load management drops. It should be noted that the cost of implementation will vary depending on the age and structure of the trees. However, there is the added benefit that trees can be set up with a pre-determined crop load with reasonable accuracy, thus enabling improved management of fruit size. In addition, bud position is optimised in ASE, fruit is well spaced and light distribution into the canopy is enhanced.

Grower perspective

Having watched the progress of the ASE studies over the past few years, Scott Price from Rookwood Orchard says he is keen to revisit spur extinction on the orchard. He suggests that most growers think chemical thinning is doing a good job and are reluctant to change a system that they perceive is doing a great job for them. However, the reality is that chemical thinning is unreliable and fruit quality is below optimum.

Chemical thinning has certainly served the industry well over the past few decades, but modern techniques such as ASE enable precision management of crop load – something that has been missing with chemical thinning. According to Scott, many growers are subconsciously doing spur extinction to a greater or lesser degree, especially on Gala, but he agrees that the use of ASE for crop load management is a new paradigm requiring a different mindset. He also points to growers in the Shepparton area such as Maurice Silverstein who have successfully implemented ASE as a crop load management tool.

Conclusions

ASE offers a new technology to precisely manage crop load. Bud numbers are set in late winter so trees are significantly thinned before flowering, with buds optimally placed and spaced. Because ASE-managed trees carry fewer but stronger flower buds than conventional trees, more resources are directed into these buds, resulting in improved fruit quality. ASE eliminates the need for chemical thinning and has the added advantages that it is not weather-dependent and removes the negative impact that most chemical thinners have on fruit size and shape.

Yes, moving away from chemical thinning for crop load management requires a change in mindset but, with its simplified hand thinning and high fruit quality, ASE will reduce both time and cost to the grower.

Dr Sally Bound (left) talks to growers about how ASE-managed trees carry fewer but stronger flower buds than conventional trees, allowing more resources to be directed into these buds, resulting in improved fruit quality.


Acknowledgements

Thanks to Scott Price, APAL Director and manager of Calvert Brothers Rookwood (now R&R Smith) orchard at Ranelagh, for use of his orchard and provision of trees.

This study 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.

By |February 21st, 2018|Pruning and training, Tasmania, Vigour, crop load and thinning|

About the Author:

Senior Research Fellow
Tasmanian Institute of Agriculture
03 6226 2958
Email Sally.