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Multi-leader trees and mechanical pruning in Europe

Research & Extension

As part of APAL’s Future Orchards® program, Ulf Kerer shares a suite of the latest orchard management, tree structure and mechanisation technologies being developed and assessed in Italy for pome fruit growers.

The graft is low to allow the development of fruiting spurs even in the lower part of these twin-stem trees.

I recently spent some time in my home country looking at new orchard developments and mechanisation. Some new ideas and recent improvements in technology and science have created some interesting developments on how to modify or change traditional orchard canopies. Mechanisation itself is not the end goal; efficient and profitable orchards are the end goal. Mechanisation is a significant tool that can be used to help achieve higher yields and lower the cost of production, while the new orchard designs can achieve a higher quality fruit through consistency of light, crop load etc. The combination of new orchards systems and mechanisation is almost synergistic to profitability, with both technologies complimenting each other.

The key driver to develop these new narrow orchards systems was to design a new orchard that had a simpler structure that could maintain or increase fruit quality and yield. These new orchard designs are a technology change in themselves.

The following example describes how the goals of higher yields and improved fruit quality is achieved through a combination of efficiently using mechanisation and altering tree structure.

Multi-leader trees

On some research orchards in northern Italy there are a wide range of different multi-leader trees that are currently being assessed for their potential. The original idea behind creating multi-leader trees was to simplify cultural practices. The requirement was that the new design should at least have the same, or more production per hectare, while at the same time reducing labour requirements in the orchard. Instructing casual staff to do pruning in the orchard should arguably also be easier with the simplified design of multi-leader trees.

Six- and eight-leader trees have a slightly different structure because the stem runs along the bottom wire and the leader is grown vertically from a low horizontal cordon.

There are some trial rows planted that have a height of only 2.6 metres and are designed to allow all orchard work to be done without the help of ladders or platforms, and still achieve a yield of over 80 tonnes/hectare. Young trees can be formed into multi-leader trees without too many problems: the root system should be established enough to have adequate power to support a multi-leader tree, and the new leaders need sufficient light and room to grow. If trained correctly, light distribution in these trees should be more uniform than in slender spindles, which should also have a positive effect on fruit quality. Trials in northern Italy have shown that fruit on twin-stem trees is generally more evenly distributed than on a slender spindle. Foreground colour was also better overall on twin-stem trees.

There are some trial rows planted that have a height of only 2.6 metres and are designed to allow all orchard work to be done without the help of ladders or platforms, and still achieve a yield of over 80 tonnes/hectare. Young trees can be formed into multi-leader trees without too many problems: the root system should be established enough to have adequate power to support a multi-leader tree, and the new leaders need sufficient light and room to grow. If trained correctly, light distribution in these trees should be more uniform than in slender spindles, which should also have a positive effect on fruit quality. Trials in northern Italy have shown that fruit on twin-stem trees is generally more evenly distributed than on a slender spindle. Foreground colour was also better overall on twin-stem trees.

A modified FAMA trimmer.

The tree width is reduced to allow better light penetration and the design requires reduced row spacing to deliver the same yield per hectare. The trees generally have improved light penetration and staff who are hand-thinning fruitlets have simpler rules to follow. The next step with multi-leader trees is to establish what number of leaders is ideal for certain soil types, rootstocks and the level of mechanisation desired. The downside of multi-leader trees is that (with the exception of twin-stem trees) the tree formation has to be done in the field. Unlike slender spindle trees that are bought from the nursery and already have the right shape, multi-leader trees require a higher amount of formation in the first years.

Two-leader trees (also referrred to as twin-stem or BiBaum) are trees that are already well established around the world. It is an interesting option for growing a full canopy faster should an orchard be re-grafted. However there is a significant number of these trees now purpose-grown in Europe. When re-grafting trees it remains important to graft the two new stems relatively low. The graft is low to allow the development of fruiting spurs even in the lower part of the tree. Due to the different structure of the trees a high attention to detail is required when designing the orchard. The leaders generally require more support from the trellis than slender spindle trees in the first years. It is crucial that the posts and wire are designed to support the weight of this design.

The next step up from a two-leader tree is a four-leader tree, where the leaders of a twin axis tree are spread and a third and fourth leader are grown from the base. Six- and eight-leader trees have a slightly different structure again because the stem runs along the bottom wire and the leader is grown vertically from a low horizontal cordon.

An additional benefit is the reduction of vigour if a tree has multiple leaders. Stronger and /or more efficient rootstocks could be used and vigour can be managed through the creation of more leaders.

Last season, the multi-leader fruit wall yielded a total of 87 tons/hectare. Spacings in that orchard are 2.8 metres between rows and 2.15 metres between trees. Each of the 1,700 trees was cropped with 53kg on average.

Thinning with shading

Multi-leader trees with Alt’Carpo nets.

Alt’Carpo net was developed in France as an alternative for codling moth control. Entire rows in organic orchards are completely closed off with these nets. They were further enhanced in the research centre in San Michele and in recent years were trialled to determine whether they would be useful as an alternative thinning method. The standard white netting has been replaced by black netting directly above the trees. The thinning effect through shading was assessed if the trees were covered at varying times during flowering. However, overall the thinning effect was similar to a combined application of ATS and BA.

 

Mechanical pruning

There is a range of equipment available for mechanical pruning which varies between trimmers and machinery with rotating knives or saws. The standard trimmer used for mechanical pruning in Italy has now been modified in the San Michele research station. Two additional blades were added to the trimmer. This was done in cooperation with the company FAMA, who also builds and distributes these machines. These extra trimmers cut smaller ‘windows’ in the fruit wall to increase light penetration and to create a more open canopy. The smaller trimmers are movable and every season these extra trimmers are shifted to another position to create ‘windows’ in another location.

A fruit wall of Cripps Pink.

Depending on the type of equipment, branch size and tree structure, the tractor’s speed can be around 4-6 kph. It is important to assess the quality of the work continuously; if the cut is not a clean straight cut it could result in sharp edges that lead to injuries at harvest. Conventional plantings can be converted to fruit walls, but due to the reduction in tree depth, new developments should have reduced row spacing (e.g. 2.6 metre row spacing). Multi-leader trees seem also very suited for this orchard structure.

Research into productivity has shown some interesting results. Key to all the research was reducing labour costs, but simultaneously improving or at least maintaining yield and fruit quality. Financial analysis in Italy has shown the performance of fruit walls is at least equal to the traditional tall slender spindle.

Thinning in fruit walls also seems to be easier. This might be related to the very uniform tree structure and density. The use of drift-reducing tunnel sprayers for the application of agrichemicals has also been trialled with some excellent results. Generally speaking, the application and efficacy of agrichemicals should be favourable due to the similar structure of each tree in the orchard. The use of drift-reducing spray equipment is also currently being assessed in the research centre. The analysis of over-row sprayers that operate spraying and sucking to reduce unwanted spray drift has shown some good results. All spray that is not deposited on the tree is sucked back into the tank and then re-applied.

Time spent in winter on correcting missed branches or removing unwanted wood is on average 40-50 per cent lower compared to traditional winter pruning. The uniform shape of the trees also makes these orchards more suited for mechanical thinners (Tree Darwin, Type Bonn etc.)

Conclusion

Increasing costs and competition will increase pressure on the orchardist in the future. Mechanisation is certainly a way to remain competitive and produce good quality fruit. Mechanical pruning of orchards and the creation of fruit walls certainly has its challenges, but overall it offers a reduction in labour and a uniform orchard that will have benefits such as even light distribution, advantages in spray applications or uniform fruit quality. Multi-leader trees seem like a good solution to create a fruit wall canopy that will allow staff to work with simpler rules.

A reduction in row spacing and tree height will allow growers to create a truly ‘pedestrian’ orchard where all work can be done without ladders, but where production will still be at least as high as a ‘standard’ dwarf orchard. The concept of a fruit wall or an ‘espalier’ training system is not new but with some modifications, new knowledge/technologies and the potential of increased mechanisation it looks like an exciting prospect for the orchard of the future.

Acknowledgements

The author would like to thank Alberto Dorigoni at the Edmund Mach research centre in San Michele, Italy for his valuable contribution to this article.

This article was prepared as part of APAL’s Future Orchards® program that is funded by Horticulture Innovation Australia Ltd using the apple and pear industry levy funds from growers and funds from the Australian Government. AgFirst is a key Future Orchards partner.

About the author

Ulf Kerer is a Horticultural Consultant with AgFirst Nelson: +64 3 544 6371, +64 27 839 7888 or ulf.kerer@agfirst.co.nz.

 

Tagged:
Machinery and mechanisation Pruning and training

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