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Pruning in an established orchard (one that has filled its canopy space) is an important aspect of orchard management. In an established orchard pruning is used to
- maintain the balance between reproductive and vegetative growth (cropping and vigour)
- renew fruiting wood
- improve fruit quality
- allow adequate light interception
- improve access for spraying, thinning and harvesting
- remove dead, diseased or broken limbs.
Often pruning is an area that can cause confusion and debate amongst growers and experts. It is important to remember that there is no one correct 'recipe' for pruning a pear orchard.
Pruning techniques need to be applied on an individual basis, taking into account orchard conditions, canopy shape (training system) and variety x rootstock interaction.
Maintaining a balanced tree through pruning
Managing strong vigour
Further information
References
Maintaining a balanced tree through pruning
It is important that any pruning activity is done with the aim of maintaining a balanced tree. This is a tree whose shape allows adequate light interception and distribution within the tree and has a good balance between vegetative growth and fruit production.
For most systems, the ideal balanced tree structure is one where there is a strong base of fruiting wood above which are shorter fruiting branches that progressively get weaker towards the top of the tree. Too many large limbs and secondaries particularly in the top of the tree will cause shading and restrict cropping to the outer mantle of the tree.
There is no standard recipe for pruning trees to ensure a good balance between cropping and vigour. Each orchard will have its own particular issues with vigour and canopy shape. However there are some key steps that growers can follow on any system to ensure balanced tree growth and the best potential for fruit production.
3:1 Rule
Side branches should always obey the 3:1 rule - never reaching a thickness more than 1/3rd that of the leader. Secondary branches should also obey the 3:1 rule. Anything larger than this should be removed completely from the tree as it will cause shading and encourage vigour. Removal of large side branches may need to be carried out over a couple of seasons to avoid making too many large cuts at once.
Figure 1: This is a classic example of a branch that does not obey the 3:1 rule. The large upright coming from this branch is encouraging vigour (as noticed by the thickness of the branch) and negatively impacting on fruit bud production.
Remove upright shoots not needed for replacement
Too many upright limbs in the tree (particiularly in the top) will cause shading and result in weaker flowers, poorer fruit set and smaller fruit. This is particularly a problem where vigorous rootstocks are used. Pear trees also suffer more from shoot: fruit competition than apples which often results in poor fruit set despite sufficient blossom (this is especially evident on seedling rootstocks) (Strydom 1994). Where upright shoots are not needed for replacement, they should be removed. This includes;
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Vigorous upright 1 year old growth that is longer than 60cm (particularly water shoots in the tops of trees)
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Side branches with narrow crotch angles (<45°)
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Upright shoots in the first 10-15cm of a side-branch
Figure 2 & 3: Before pruning (left), this multi leader tree had poor light distribution through too many upright limbs in the tree. After pruning, many of the upright limbs have been removed improving light distribution.
Avoid making too many cuts.
Pruning encourages shoot growth, particularly when carried out during dormancy. Many small cuts will stimulate more shoot growth than a few large cuts.
Manage leader height
Most pear varieties tend to have a very strong central leader - sometimes this can be too strong (particularly if using vigorous rootstocks). If the leader becomes too strong it can suppress lateral development and growth as well as fruit production.
Once trees are established and have reached the desired height, it is important to manage the leader to maintain height and a balance between vigour and cropping.
The leader height can be maintained through cutting back to a fruitful side branch or a weaker lateral during dormancy. It can also be done during summer - as making cuts during this time will result in less regrowth.
If the leader remains strong, other techniques may also need to be adopted to slow down growth. These are discussed below in vigour control methods.
Figure 3 & 4: This corella tree before (left) and after (right) having the leader cut back to a weaker, but fruitful side shoot as well as upright limbs removed from the top of the tree.
Renew fruiting units - depending on cropping habit
Cropping habit can vary between cultivars and this can affect the type of pruning that is most suitable. For example, Williams tend to crop mainly on the apical bud of year old shoots (also referred to as brindles or pencil wood) and therefore yearly renewal of fruiting shoots should be taken into account (Sansavini 2002). It is useful to retain one year old shoots that are not too vigorous. Ideally these should be between 20-40cm. If there are a large number within the tree they should be thinned and spaced out to allow for good light interception.
Packhams on the other hand tend to crop mainly on spurs on limbs that are 2-3 years and older. As spurs get older fruit quality can decline so it is important to keep renewing spurs. One suggested ideal is to bear 20% each year on 1-year fruiting shoots and 80% on 2 (25-30%), 3 (30%) and 4 year (20-25%) branches (Sansavini 2002). It is still important to retain one year old shoots that can 'spur up' in later years. Existing spurs may need to be thinned out by cutting back to 2-3 buds.
'Prune pears onto the tree'
This phrase was used by Jef De Coster during his visits to Australia in 2006-2008. In order to encourage fruit set, shoots that were longer than 20cm and had a number of good fruit buds were headed back, through cutting or breaking, to atleast 6-8 buds. This is preferable for two year old wood, but can also be done on one year old wood. Generally one year old wood should never be headed, unless there are good fruit buds on the branch.
Preferably limbs should be cut back to a downward facing bud and should have a flatter orientation.
Figure 5: The top limb has been headed back to a downward facing bud. This limb had 6-8 good healthy buds.
Bend or tie down limbs where possible
Often this is best done when trees are young to encourage wider crotch angles (and flatter orientation of branches). In established trees it may also be necessary.
Bending shoots towards the horizontal reduces terminal growth of the limb and encourages flower bud formation. Shoots can either be tied down or positioned with spreaders or weights. It is best not to bend pears to an angle of any more than 45º.
Figure 6: Bending and tieing down of branches has encouraged wider crotch angles and flatter branches.
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Managing strong vigour
The major issue in Australian pear production is excessive vigour. This is largely due to the lack of available dwarfing rootstocks and the reliance on the vigorous seedling rootstock Pyrus calleryana D6 (D6). Often with such excessive vigour, pruning needs to be combined with other techniques to try and regain balance in the tree.
There are a number of suggested methods that can be used to try contain vigour, particularly in intensive systems. These methods are often used in combination with pruning and adjustment of the irrigation and nutrition program.
Breaking vs Cutting
Breaking out of limbs instead of cutting with secateurs has been identified as one way of helping to 'slow down the tree'. Breaking out limbs is only suggested where there is no desire for regrowth or replacement of that limb. The basic theory with breaking is that the tree has to spend more energy healing the wound from a break as opposed to a cut. Many of the dormant buds around the base of the branch are also taken out with breaking which reduces the development.
Breaking is mainly useful for removing vigorous one year old growth in the tree, particularly during summer or the post harvest period. It should not be considered a replacement for dormant pruning but a useful tool to help reduce vigour in trees that require it. Some growers have been using breaking in pear orchards since 2006 and have not observed any negative impact on their trees.
Figure 8: This 'Corella' branch has had a vigorous upright limb removed (top left of the picture). The break has healed well and not inhibited fruit production.
Figure 9: This 'Williams' tree had a large upright broken out in 2006. The photo was taken after harvest the following season 2007. There has been no regrowth from the break.
Risks
The physical nature of breaking limbs out of the trees could be a risk for worker injury.
Summer Pruning
With vigorous trees, it can be useful to perform many of the pruning activities (including breaking and bending) during summer and particularly the post harvest period. Removing vigorous growth at this stage results in the reduction of energy translocated from branches to the stem and roots prior to leaf fall. This energy would have been stored during dormancy and contribute to vigorous tree growth the following spring.
Girdling and Stem incisions
Girdling and stem incisions are two techniques that can reduce vigour in trees. Both involve cutting into the stem to sever the phloem and disrupt the transport of photosynthates in the tree - thus reducing vegetative growth.
There are a number of variations on trunk girdling. Generally girdling involves the removal of a strip of bark (up to 1cm wide) from around the trunk or simply cutting through the bark to the cambium layer.
Stem incisions are a more severe version of girdling and involves incisions made on alternate sides of the trunk with a saw/chainsaw to approximately one-third to a half of the trunk diameter, with no less than 30cm between cuts. The number of cuts made will depend on the vigour of the tree. Incisions can also be made into large branches in the tree to slow them down if it is not feasible to remove them.
Both girdling and stem incisions can be carried out in the spring, no less than 4-6 weeks before flowering.
Figure 10 & 11 : Examples of stem incisions in the central leader of 'Corella' (left) and on branches of an old 'Packham' multi-leader tree (right)
Risks
There are a number of risks associated with stem incisions. Drought stress as a result of the disruption to water and nutrient transport is a major risk in Australian conditions. There is also a risk of incisions being cut too deep causing stems to break under heavy fruit loads or as a result of extreme weather events.
It is important that growers understand these risks before applying either techniques. Growers may need to consider altering the irrigation and nutrition program to ensure trees remain healthy under stressful conditions.
Growers need to seek local advice before considering stem incisions or girdling. It may be useful to trial these techniques on a small number of trees, over a couple of seasons before applying to the orchard.
Rootpruning
Rootpruning is a technique that has become more commonly used in European pear production systems. There has been limited use of rootpruning in Australian orchards to date, however interest is growing.
The aim of rootpruning is to cut both fine and large roots to reduce the absorbtion of water and nutrients, whilst also changing the hormone balance - resulting in an overall reduction in shoot growth (Vercammen, Van Daele et al 2005). It is usually carried out no less than 4-6 weeks before full bloom. Too close to blossom can induce severe stress and poor fruit set.
The distance from the trunk and the depth of which to prune is dependant on the level of vigour in the tree and the root distribution - key factors that growers need to assess if considering rootpruning. It can either be carried out on one or both sides of a tree - but one sided pruning (alternating each year) is considered the least risky.
Figure 11 & 12: Rootpruning 'Williams' in Open Tatura Trellis (left). Prior to rootpruning root distribution was assessed through digging around the base of a couple of trees (right).
Risks
The risks associated with rootpruning are similar to those for stem incisions. In Australian conditions there is potential for rootpruning to cause severe drought stress in trees and issues with nutrient deficiency. Fruit quality - particularly for long term storage can also be reduced.
Growers should seek more advice on rootpruning before considering applying it in their orchards. It is also important that growers trial rootpruning on a small section of orchard over a couple of seasons to understand its effect on tree growth and fruit production and the possible changes needed to the irrigation and nutrition program.
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Further information
The following sites may be useful for growers. However they are intended as an information source only. Any specific chemical or other control recommendations may be outdated or irrelevant for Australian conditions and growers should seek local advice.
Please note: By electing to visit sites linking from this page you will be leaving the intensivepear.com website.
International Resources
Physiology of pruning
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References
Strydom, D.K. (1994). ' Training and pruning of pear trees in countries characterized by long hot summers and where dwarfing rootstocks cannot be used, or are not available'. Acta horticulturae 367: 130-151
Sansavini, S. (2002). ' Pear fruiting-branch models related to yield control and pruning'. Acta horticulturae 596: 627-633
Vercammen, J., van Daele, G. et al. (2005). “Root pruning: a Valuable Alternative to Reduce the Growth of ‘Conference’.” Acta horticulturae 671: 533-537.
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Orchard Management 
