POMEWEST narrow orchard systems

WA Narrow Orchard Systems (NOS) project update:

INITIAL TREE TRAINING

(Year 1)

The Department of Primary Industries and Regional Development (DPIRD) is investigating the potential of 2D multileader narrow orchard systems in Western Australia for three Australian bred apple cultivars (‘ANABP 01’, ‘ANABP 09’, ‘ANABP 14’). This pilot trial is a part of the five-year national ‘Narrow Orchard Systems for Future Climates’ project, funded through the Hort Innovation Frontiers program.

Words Muhammad Asad Ullah and Dario Stefanelli, Research Scientists, Department of Primary Industries and Regional Development, Manjimup

THE three cultivars are being tested on three distinct training systems shown in Figure 1 (single cordon, crossover double cordon, and standard double cordon) and on three different rootstocks — semi dwarfing (Geneva® (CG) 202) and dwarfing (M26 and M9 Nic® 29) — for optimal growth, light interception, fruit quality, and yield. The trial orchard was established at the Manjimup Horticultural Research Institute at a spacing of 2 m between trees and 2.5 m between rows.

This article provides an overview of first-year tree training activities for 2D narrow-row orchard systems around establishing cordon shoots.

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FIGURE 1: Conceptual figure of three canopy training systems to be tested by DPIRD in Manjimup: single cordon (a), crossover double cordon (b) and standard double cordon (c).

Source: Zhou et al 2024

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FIGURE 2: Single cordon training tree with ~30-degree bend and emergence of lateral shoots.

Single cordon training:

After planting in September 2024, single cordon treatment trees were initially bent at about a 30-degree angle to create necessary bend in the main stem (to make it easier to lay it down as a cordon later). The initial bend ensured the terminal stem end keeps actively growing until it reaches 2 m. However, in some cases, there was some lateral shoot development before the tree achieved its desired length (2m), as shown in Figure 2. To slow down growth of these shoots and to promote terminal stem end growth, shoot growing ends were pinched off. All flowering clusters and fruitlets were removed to promote vegetative growth. It is important to remember not to bend stems more than 30 degrees from upright position as this may shift apical dominance to the lateral portion of the tree and cease terminal growth.

Another possible training strategy is to leave the stem upright after planting until it reaches desired length, then lay it as cordon to stop terminal growth and shift apical dominance to lateral nodes to promote growth of vertical leaders. However, in this case, there is a greater chance of stem snapping as a result of a sharp bend.

Double cordon training:

For double cordon training systems (standard and crossover), bare rooted trees were planted in late September and headed in early October 2024 at 60 cm above soil surface, to promote lateral shoot growth (Figure 3). Once lateral shoots developed to about 30 cm in length, 2–4 shoots (at least 1 on either side of the trunk) were selected as candidates to be trained as cordons. Remaining shoots were then removed to prevent further drainage of tree resources. Once selected shoots achieve ~1 m length, they will be bent on to the sides as cordons for standard double cordon system (Figure 3). However, for double crossover cordon system, shoots will be crossed over and bent to the opposite sides.

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FIGURE 3: Pictorial representation of year 1 tree training activities for standard double cordon 2D narrow-row orchard system.

These cordons will serve as permanent structure for vertical leaders to emerge in second year of tree growth.

Two potential strategies were explored for optimal upright growth of the cordon shoots. Shoots growing upwards at a slight angle from the trunk did not need additional attention apart from when they reached the next trellis wire (50 cm above) when they were tied with trellis ties to keep them in a relatively constant position and protect from wind and other damage (Figure 4b).

However, lateral shoot development may vary from tree to tree. Some trees may develop a more horizontal (wide angled) shoots (Figure 5a). Such shoots, if left unchecked, tend to develop feathers or sylleptic shoots. This creates more work for their removal later on and diverts energy from the main shoot, reducing their possible total growth (Figure 5b).

These shoots were trained using jute twine and a tapener tying machine (Figure 5c) to be in an upright position, ensuring apical dominance towards shoot tip end.

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FIGURE 4: Tree training strategies for double cordon system. Shoots at a slight angle to the trunk were selected to be trained as double cordon (a). Shoots with relatively narrow angle from the main trunk were trained using trellis ties (b).

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FIGURE 5: An example of wide angled shoots. Shoots without twine (a), feathered horizontal shoot (b), and shoots tied with twine and tape (c).

Decision to use either or both training strategies depend solely on individual tree condition, and it can vary from tree-to-tree or sometimes between two cordon shoots within the same tree. Trellis ties are labour efficient and cost effective compared to twine training but not suitable for early training of wide angled shoots.

Cultivar and rootstock combination is an important factor to consider in adopting a training strategy. Certain cultivars may tend to have lower plasticity due to higher lignin deposition in the shoots which would result in resistance to bending and potential breakage.

In that case, selecting shoots at a relatively wide angle early-on will help mitigate risk of shoot breakage while laying them down as cordons later. Similarly, vigorous rootstocks may reach desired shoot length for cordon earlier than dwarfing rootstocks irrespective of the cultivar type.

In addition to physiology and suitability of NOS system in the WA environment, the project team will also evaluate the economic aspects of NOS compared with traditional production systems in terms of initial investments, material and labour costs, and return on investments.


ACKNOWLEDGEMENT

‘Narrow Orchard Systems for Future Climates’ project is funded through Hort Innovation Frontiers with co-investment from Agriculture Victoria, NSW Department of Primary Industries and Regional Development, South Australian Research and Development Institute, Department of Primary Industries and Regional Development WA, University of Queensland, Pomewest, Tobias Industries, and contributions from the Australian Government.

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