Orchard layout depends on:
• Cultivar (upright varieties such as Reed and Lamb Hass can be planted closer than other varieties such as Hass and Shepard)
• Amount of land available and slope of the site
• Growing conditions (soil and environment)
• Machinery access (safe machinery operation e.g. tractors, cherrypickers and pruners)
• Canopy management system to be used during the life of the orchard.
Tree Spacing
Low Density Plantings
e.g. 12 x 12m; 10 x 10m and 10 x 8m (69 – 125 trees/hectare):
• Provide lower early returns per hectare
• Lower establishment costs and less pruning and tree removal costs in later years
• Results in large trees with increased harvesting costs, reduced picker safety and more difficult to spray for effective pest and disease control.
Medium Density Plantings
e.g. 8 x 7m; 9 x 6m; 10 x 5m; 7 x 7m and 8 x 5m (178 – 250 trees/hectare):
• Tree width and height will need to be controlled as crowding occurs to maintain orchard access, allow effective pest and disease control and improve light penetration.
High and Ultra-High Density Plantings
e.g. 8 x 4m; 6 x 5m and 7 x 3m (312 – 476 trees/hectare) and 6 x 3m; 3 x 3m and 2.25 x 2.25m (555 – 1975 trees/hectare):
• Provide higher early returns per hectare
• Higher establishment costs
• Tree width and height will need to be controlled or trees removed as crowding occurs
• Ultra high densities are more suitable for upright varieties such as Reed and Lamb Hass and in environmental conditions where tree vigour is less.
Row Direction
To maximise light penetration into the orchard it is recommended that trees are planted in rows running in a north-south direction. However, row direction needs to suit the slope of the site. On slopes greater than 15% rows should run up and down the slope to allow safe machinery operation. Ensure appropriate erosion control measures are in place in orchards where rows are running up and down the slope.
Planting Configuration
Trees are planted either on a square or rectangle configuration. A rectangle configuration where trees are spaced closer within the row than between the rows is favoured and allows the creation of hedgerows.
Trees can also be planted in a regular or alternate arrangement.
The regular planting arrangement is more common, particularly in hedgerow systems. However, an alternate planting arrangement may allow better light penetration into the orchard.
The objective of these pruning strategies is to establish a tree shape suited to the orchard layout and canopy management strategy to be implemented during the life of the orchard. These procedures are normally carried out for the first 12-18 months after planting. Two main strategies used are tip pruning and central leader pruning.
Tip Pruning
Procedure:
Growing tips are pinched out or cut back to stimulate the growth of side shoots. Trees may be tipped 2-4 times during the first 12-18 months depending on the growing conditions.
Shoot tip removed.
Side shoots stimulated.
Costs Involved:
Shoots tips are removed or cut back (1 minute/tree, labour @ $22/hr: based on 200 trees/ha = $74/ha).
Considerations:
Tree Shape
Tip pruning produces a bushier, more rounded tree suited to wider tree spacing. Using this method, 3-4 major branches can be established early which assists in developing a tree shape suited to a selective limb removal strategy later on.
Central Leader Pruning
Procedure:
This strategy involves the removal or cutting back of rapidly growing side branches to produce a strong central leader.
This is achieved by:
1. Removing side branches that are more than half the thickness of the central leader
2. Cutting back side branches that are more than one-third the thickness of the central leader
3. Keeping side branches that are less than one-third of the thickness of the central leader.
Trees may be pruned 2-4 times during the first 12-18 months depending on the growing conditions.
Costs Involved:
Small shoots/branches are removed or cut back (2 minutes/tree, labour @ $22/hr: based on 200 trees/ha = $146/ha).
Considerations:
In The Nursery
If this strategy is going to be adopted it is important that trees develop a strong central leader in the nursery. The main shoot should not be tipped.
Pruning Strategy
Young trees are trained to form a central leader with lateral branches along its length. This strategy develops a pyramid shaped tree better suited to a hedgerow pruning system later on. Higher planting densities can be achieved and maintained using this strategy.
Variety Planted
Central leader pruning is more suited to upright varieties such as Reed and Lamb Hass. However this strategy is being used on Hass overseas (e.g. South Africa, Chile, California and New Zealand).
Growing Environment
A single central leader may be difficult to maintain under the vigorous growing conditions of a warm subtropical climate. Developing a tree shape with 2-3 upright leaders may be more attainable.
The objective of these pruning strategies is to maintain the trees at the desired size and shape as long as possible to prevent crowding while maintaining fruit quality and yield. These strategies can commence in the second or third year after planting. Strategies include selective limb removal, selective and mechanical pruning, branch-scoring and plant growth regulator application.
Selective limb removal
Procedure:
These strategies involve removing or cutting back individual branches to maintain tree size and inter-row access and to open up canopies for improved light and spray penetration and picker access.
Lower and centre branches were removed in this four year old Hass tree.
Costs involved:
Branches are removed or cut back using pruning or chain saws (up to 5 minutes/tree, labour @ $22/hr: based on 200 trees/ha = $366/ha).
Small branches are mulched using slashing equipment (tractor and slasher @ $66/hr).
Considerations:
Selection of branches
Reduce the number of main branches to 2-4 depending on tree and row spacing.
Remove or cut back the tallest branch. In young trees, height may not be a problem however the most dominant branch can be cut back to a major lateral branch. Removing the tallest branch will also improve light penetration into the tree.
Remove or cut back branches that protrude into the inter-row space and affect orchard access.
Remove poorly positioned branches such as overlapping (create a dense canopy) and crossing over branches (branches that grow from one side of the tree to the other) to improve light penetration, prevent dieback of internal shoots and improve spray penetration and picker access.
Remove branches on the north to north-east side of the tree to improve light penetration into the tree.
Low branches are removed (skirted) to avoid fruit contact on the ground, maintain sprinkler efficiency and allow access for trunk injection for Phytophthora control. However in harsh environments that experience heat waves such as the Tristate and Dimbulah in North Queensland, it is often better to keep low branches in place to shade the root zone and help maintain mulch in place.
Where to cut branches
Branches should be cut back flush to the trunk or main lateral branch to minimise regrowth and promote rapid healing of the wound.
Pruning time
Pruning is best done immediately after harvest or during flowering. In locations where two crops are present on the tree, selective limb removal may commence in an “off” year to minimise crop losses.
To avoid excessive regrowth (due to a light crop load) cut branches in late autumn/early winter. Pruning at this time can also minimise potential sunburn damage to exposed limbs and fruit.
Sunburn protection
Any branches newly exposed to sun as a result of pruning should be protected from sunburn using white acrylic paint. The more horizontal the limbs the more susceptible they are to sunburn.
Diluting the paint with water so it can be sprayed onto the exposed branches will reduce the time taken to apply protection. Other preparations including bentonite clay and calcium carbonate sprays can also provide sunburn protection. Adding a copper fungicide treatment (e.g. copper oxychloride) may assist in controlling disease at the pruned surface.
Mechanical pruning
Procedure:
Trees are pruned to form a hedgerow using mechanical saws. For maximum light penetration into the orchard a north-south orientation is preferred and trees are pruned to a pyramid shape or a “barn” shape to a height of up to 6m. There are several variations on the pruning angle being used.
Five year old Shepard trees mechanically pruned to a “barn” shape.
Costs involved:
Mechanical pruning costs typically range from $0.90 – 1.75/tree ($175 – 350/ha based on 200 trees/ha).
Mechanical saws are used to reduce tree height and width and to maintain tree shape. Pruning contractors are available at rates of $175-230/hr.
Small branches can be mulched using slashing equipment (tractor and slasher @ $60/hr).
Considerations:
When to start pruning
Trees can be initially shaped in the year prior to the first commercial production. In young trees, shoots are lightly tip pruned mechanically.
Pruning time
Mechanical pruning is normally carried out twice a year – after harvest and during the summer.
The post-harvest pruning establishes the shape of the tree. Trees are pruned prior to flowering; at early flowering or during winter – when trees are in a non-vegetative phase. Pruning too early after harvest (during a vegetative growth phase) can encourage excessive regrowth at the time of early fruit set.
Once the tree shape has been established a light summer prune to cut back the spring growth flush can be implemented in the presence of fruit. The summer prune is made about 10-30cm outside of the post-harvest pruning face. Timing of the summer prune is important and can affect the level of flowering on the regrowth the following spring. For example: in subtropical climates pruning mid-late summer reduces the percentage of shoots to flower.
Mechanical tip pruning of the spring flush during the summer prune. Arrows show pruning cuts.
Pruning angle and shape
Trees are either pruned to form a pyramid (Christmas tree shape) with the sides pruned at an angle of 15-22º from the vertical, or to form a “barn” shape with the sides pruned at an angle of 10-15° and the tops pruned at an angle of 60°.
Tree shapes after mechanical pruning.
Five year old Hass trees mechanically pruned to a “pyramid” shape.Four year old Hass trees mechanically pruned to a “barn” shape.
Selective hand pruning
Shortening or removing bare and exposed branches may be necessary to avoid vigorous regrowth at the pruning surface.
Bare branches should be cut back to avoid this undesirable regrowth.
Regular mechanical pruning can result in a dense canopy wall at the pruning surface. Selective pruning (branch removal) to open up ‘windows’ may be required for light penetration into the tree and to improve the efficiency of spraying and harvesting.
Growing environment
Mechanical pruning is more suited to warm subtropical environments where fruit is harvested before the next flowering occurs. In climates where two crops are carried on the tree implementing a mechanical pruning strategy after harvest is difficult without removing developing fruit and exposing fruit to sunburn. Mechanical pruning (tip pruning) in late autumn has been used in South-West Western Australia on young trees up to six years. Flowers can develop below the cut surface on small branches.
Flowers developing behind the cut surface in trees tip pruned in late autumn.
Plant Growth Regulators
At the date of publication both SUNNY® (active ingredient uniconazole-P) and AuSTAR® (active ingredient paclobutrazol) were registered for use in avocado, however, check the status of the registrations before planning an application. Also note that AuSTAR® cannot be used when there is mature fruit on the tree.
Foliar application of SUNNY® (Active constituent: 50g/L uniconazole-P) at mid-bloom (when 50% of the flowers have opened) at a rate of 5-10L/1000L can be used to enhance fruit shape, increase fruit size and reduce the length of the spring growth flush. SUNNY® at a rate of 5-10L/1000L can also be applied to the regrowth following the summer prune to reduce the amount of growth and increase flowering in the spring. New growth is treated when shoots are 50-100mm in length. Note withholding period: Do not harvest fruit for 14 days after application.
Foliar application of AuSTAR® (Active constituent: 250g/L paclobutrazol) when trees are in full flower at a rate of 7L/1000L can be used to control vegetative growth. AuSTAR® can also be applied at fruit set at a rate of 5L/1000L to control fruit drop. Do not apply when mature fruit are on the tree. Note withholding period: Do not harvest fruit for three months after application.
Do not apply plant growth regulators to trees with low vigour, under stress or showing symptoms of Phytophthora root rot.
Branch scoring
Procedure:
Involves cutting a groove around the branch to sever the phloem using a knife or pruning saw. The aim is to increase flowering and fruiting on the scored branch. When successfully carried out, the wound will produce callus tissue and eventually heal, thereby restoring the normal function of the branch. Healing of the wound can occur within 2-4 months depending on the growing conditions.
Note: This technique is still experimental under Australian conditions.
Costs involved:
Branches are scored using a knife or pruning saw (2 minutes/tree, labour @ $22/hr: based on 200 trees/ha = $146/ha).
Three year old Hass tree scored in April showing increased flowering on the scored branch.
Considerations:
Selection Of branches
Rule of thumb: no more than one-third of the branches should be scored on any one tree in any one year. Either the tallest branch to reduce tree height or a centre branch to open up the canopy is selected for scoring. The score cut is usually made above lateral branches. In young trees only 1-2 branches are scored to prevent root starvation. After the fruit is harvested the branch can be removed as part of a selective limb removal management strategy.
1-2 branches are scored in young trees, this branch will be removed after harvest.This branch was scored incorrectly and no effect on flowering was observed. On the side of the branch where healing of the wound did not occur, the groove was not cut deep enough.
Timing
Branches are scored in autumn to reduce vegetative growth and increase flowering and fruit set the following spring.
Cincturing versus scoring
Cincturing involves the removal of a strip of bark about 10mm wide. Scoring involves cutting a groove no more than 2-3mm wide. The wound in scored branches can heal within 2-4 months thereby restoring the normal function of the branch. The wider cincture wound can take several months to heal and can have detrimental effects on branch health including small fruit, reduced leaf growth and even death.
Growing conditions
Growers in southern production areas (Hinterland of Mid North Coast NSW, Central Coast NSW, Tristate and South-West Western Australia) have been trialling this scoring technique to reduce vegetative growth and increase flowering and fruit set in the selected branch. However in some cases, yellowing of leaves and leaf drop has occurred resulting in sunburnt fruit. Nitrogen management may prevent this occurring.
Excessive leaf drop on the scored branch can expose fruit and branches to sunburn.
Strategies used will depend on tree size and extent of orchard crowding. Techniques include selective limb removal, selective and mechanical pruning, major limb removal, staghorning, tree thinning/removal and plant growth regulator application.
Selective Limb Removal
Procedure:
These strategies involve removing individual limbs to reduce tree height and width and to open up canopies for light penetration, improved spray penetration and cherry-picker access.
Selective limb removal in large trees. Arrows indicate where branches have been removed.
Costs Involved:
Selective limb removal costs $11-22 /tree (depending on tree size or $2200-4400/ha based on 200 trees/ha).
Branches are removed or cut back using chainsaws. Smaller branches can be mulched using slashing equipment. Larger branches can be mulched (tractor operated forestry mulching equipment can handle branches up to 25cm diameter); chipped (commercial operators available @ $235/hr) or removed from the orchard.
Considerations:
Selection of Branches
• Reduce the number of main branches to 2-4 depending on tree and row spacing.
• Remove or cut back the dominant branches to reduce tree height. Removing the tallest branch will also improve light penetration and stimulate growth inside the tree.
• Remove or cut back branches that grow into neighbouring trees and the inter-row space to maintain orchard access.
• Remove poorly positioned branches such as overlapping (create a dense canopy) and crossing over branches (branches that grow from one side of the tree to the other) to improve light penetration, prevent dieback of internal shoots and improve spray penetration and picker access.
• Selective pruning is carried out each year to maintain tree size and ensure light penetration into the tree.
Where to Cut Branches
Branches should be cut back flush to the trunk or main lateral branch to minimise regrowth and promote rapid healing of the wound.
Pruning Time
Pruning is carried out immediately after harvest or during flowering. In locations where two crops are present on the tree, selective limb removal may commence in an ‘off’ year to minimise crop losses.
To avoid excessive regrowth (due to a light crop load), cut branches in late autumn/early winter. Pruning at this time can also minimise potential sunburn damage to exposed limbs and fruit.
Sunburn Protection
Any exposed branches should be protected from sunburn using white acrylic paint. Diluting the paint with water so it can be sprayed onto the exposed branches will reduce the time taken to apply protection. Other preparations including bentonite clay and calcium carbonate sprays can also provide sunburn protection. Adding a copper fungicide treatment (e.g. copper oxychloride) may assist in controlling disease at the pruned surface.
Mechanical Pruning
Procedure:
Trees are either pruned to a pyramid or ‘barn’ shape using mechanical saws to reduce tree size, maintain orchard access and maximise light penetration in the orchard. Trees are normally pruned after harvest and again in summer.
Mechanical pruning of an orchard in practice.
Costs Involved:
After harvest pruning including dragging out, cutting up and mulching of branches: $2.75 – 8.25/tree ($550 – 1650/ha based on 200 trees/ha).
Summer pruning including mulching: $1.80 – 2.35/tree ($350 – 470/ha based on 200 trees/ha).
Mechanical saws are used to reduce tree height and width and to maintain tree shape. Pruning contractors are available at rates of $175-235/hr. Large trees can take 3-4 passes each side to bring trees back to the desired size. Mechanical saws can cut branches up to 10-15cm diameter. Summer pruning involves a light trimming to cut back the spring growth flush.
Smaller branches can be mulched using slashing equipment. Larger branches can be mulched (tractor operated forestry mulching equipment can handle branches up to 25cm diameter); chipped (commercial operators available @ $235/hr) or removed from the orchard.
Considerations:
Pruning Time
Mechanical pruning is normally carried out twice a year – after harvest and during the summer. In warmer subtropical production areas the major shaping prune occurs after harvest in autumn and winter. Pruning too soon after harvest whilst the weather is still warm can encourage excessive regrowth at the time of early fruit set and may affect fruit retention. It is better to wait till late autumn or winter when temperatures are cooler. Once the tree shape has been established, a summer prune to cut back the spring growth flush can be implemented in the presence of fruit, it must be done well before the summer flush appears. The summer prune is made about 10-30cm outside of the post-harvest pruning face. The timing of this pruning can influence the level of flowering the following spring.
In southern production areas where the harvest occurs during spring and summer, mechanical pruning after harvest will remove developing fruit (two crops are carried on the tree at these locations) and expose fruit and limbs to sunburn. Mechanical pruning may be implemented in late autumn/early winter during an ‘off’ year to minimise crop loss.
Pruning Angle and Shape
Trees are either pruned to form a pyramid (Christmas tree shape) with the sides pruned at an angle of 15-22º from the vertical or to form a ‘barn’ shape with the sides pruned at an angle of 10-15° and the tops pruned at an angle of 60°.
Tree shapes after mechanical pruning.
Large Hass trees before pruning.
Large Hass trees after mechanical pruning
Other Pruning Options
For a major reshaping of trees, alternate sides can be mechanically pruned in consecutive years so to retain one side of the tree in production.
Selective Hand Pruning
Shortening or removal of bare and exposed branches (particularly after the after the initial ‘hard’ pruning) may be necessary to avoid vigorous regrowth at the pruning surface.
Bare branches should be cut back to avoid this undesirable regrowth.
Regular mechanical pruning can also result in a dense canopy wall at the pruning surface. Selective pruning to open up ‘windows’ may be required to improve light penetration and increase the efficiency of spraying and harvesting operations.
Plant Growth Regulators
At the date of publication both SUNNY® (active ingredient uniconazole-P) and AuSTAR® (active ingredient paclobutrazol) were registered for use in avocado, however check the status of the registrations before planning an application. Also note that AuSTAR® cannot be used when there is mature fruit on the tree.
Foliar application of SUNNY® (Active constituent: 50g/L uniconazole-P) at mid-bloom (when 50% of the flowers have opened) at a rate of 5-10L/1000L can be used to enhance fruit shape, increase fruit size and reduce the length of the spring growth flush. SUNNY® at a rate of 5-10L/1000L can also be applied to the regrowth following the summer prune to reduce the amount of growth and increase flowering in the spring. New growth is treated when shoots are 50-100mm in length. In South Africa two sprays two-three weeks apart at 2-3L/1000L have been used to control this regrowth. Note withholding period: Do not harvest fruit for 14 days after application.
Foliar application of AuSTAR® (Active constituent: 250g/L paclobutrazol) when trees are in full flower at a rate of 7L/1000L can be used to control vegetative growth. AuSTAR® can also be applied at fruit set at a rate of 5L/1000L to control fruit drop. AuSTAR® cannot be applied when mature fruit are on the tree. Note withholding period: Do not harvest fruit for three months after application.
Do not apply plant growth regulators to trees with low vigour, under stress or showing symptoms of Phytophthora root rot.
Typically as orchards mature, in many regions canopy management needs to be undertaken to optimise and maintain orchard productivity. As the size of the avocado trees increase, canopy management may need to be conducted more vigorously to maintain the balance between orchard manageability and yield. This will most likely entail major limb removal. Three options have been recommended here for large avocado trees requiring major limb removal.
Option 1: Pruning One-Third of the Tree
Procedure:
Year 1: Manually prune one side of the tree after harvest. The eastern side is normally pruned first to minimise sunburn on the main branches. Regrowth on the eastern side is mechanically tip pruned during summer to encourage lateral branches. Water shoots or vigorous regrowth are removed.
Year 2: Centre limbs are removed after harvest. Water shoots or vigorous regrowth on the eastern side are cut back or removed.
In the first year the eastern side of the tree was removed. In the second year the centre branches will be removed as indicated by the red lines.
Year 3: Major limbs are cut back or removed from the other side (western side) of the tree. Water shoots or vigorous regrowth are cut back or removed.
In the third year major limbs on the western side of the tree were removed.
Costs Involved:
Costs range from $16.50 – 27.50/tree/year ($3300 – 5500/ha based on 200 trees/ha).
Branches are removed or cut back using chainsaws. Smaller branches can be mulched using slashing equipment. Larger branches can be mulched (tractor operated forestry mulching equipment can handle branches up to 25cm diameter); chipped (commercial operators available @ $230/hr) or removed from the orchard.
Considerations:
Pruning Time
Major limb removal is carried out after harvest. In those areas where trees carry fruit all year round, major limb removal can commence in an ‘off’ year to minimise crop losses.
Regrowth is mechanically tip pruned during summer to encourage lateral branches. Water shoots or vigorous regrowth are removed or cut back to lateral branches.
Sunburn Protection
Some sunburn on higher branches can be tolerated as these limbs are removed in the second or third year. However the trunk and lower branch stubs should be protected from sunburn using white acrylic paint, clay preparations or calcium carbonate sprays.
Diluting the paint with water so it can be sprayed onto the exposed branches will reduce the time taken to apply protection. Adding a copper fungicide treatment (e.g. copper oxychloride) may assist in controlling disease at the pruned surface.
Plant Growth Regulators
At the date of publication both Sunny® (active ingredient uniconazole-P) and AuSTAR® (active ingredient paclobutrazol) were registered for use in avocado, however check the status of the registrations before planning an application. Also note that AuSTAR® cannot be used when there is mature fruit on the tree.
Foliar application of SUNNY® (Active constituent: 50g/L uniconazole-P) at a rate of 5-10L/1000L to the summer and autumn growth flush can reduce shoot growth, and may increase flowering and yield on the pruned side. New growth is treated when shoots are 50-100mm in length. Note withholding period: Do not harvest fruit for 14 days after application.
Do not apply plant growth regulators to trees with low vigour, under stress or showing symptoms of Phytophthora root rot.
Option 2: Mechanical And Selective Pruning
Procedure:
Year 1: Trees are mechanically pruned on one side after harvest at an angle of 0-5° from the vertical. Branches are cut 1-1.5m from the trunk. Follow-up selective hand pruning is carried out to remove bare and exposed branches. Trees are mechanically tip pruned in summer to cut back regrowth.
Year 2: Trees are mechanically topped after harvest at an angle of 55-60° from the vertical. Tree height reduced to 4.5-5m. Regrowth on the side pruned in the first year also mechanically tip pruned at an angle of 15-22° after harvest. Trees are tip pruned on both pruned faces in summer to cut back regrowth.
Year 3 or 4: The other side of the tree is mechanically pruned after harvest at an angle of 15-22° from the vertical. Follow-up selective hand pruning is carried out to remove bare and exposed branches. Regrowth on the side pruned in the first year also mechanically tip pruned at an angle of 15-22° after harvest. Trees are tip pruned at 15-22° on both sides in summer to cut back regrowth.
Costs involved:
Costs range from $12 – 17.50/tree/year ($2400 – 3500/ha based on 200 trees/ha).
Trees are cut back using mechanical saws. Pruning contractors are available at rates of $175-235/hr. Mechanical saws can cut branches up to 10-15cm diameter. Bare branches are cut back using chainsaws. Trees are mechanically tip pruned in summer to cut back regrowth.
Smaller branches can be mulched using slashing equipment. Larger branches can be mulched (tractor operated forestry mulching equipment can handle branches up to 25cm diameter), chipped (commercial operators available @ $235/hr) or removed from the orchard.
Considerations:
Pruning Time
Pruning is carried out after harvest. In those areas where trees carry fruit all year this strategy can be done in an ‘off’ year to minimise crop losses prior to the ’on’ year’s flowering. Regrowth is tip pruned during summer to cut back the spring growth and encourage lateral branches.
Sunburn Protection
Exposed branches should be protected from sunburn using a white acrylic paint, clay preparations or calcium carbonate sprays. Diluting the paint with water so it can be sprayed onto the exposed branches will reduce the time taken to apply protection. Adding a copper fungicide treatment (e.g. copper oxychloride) may assist in controlling disease at the pruned surface.
When to Prune the Other Side
The other side of the tree can be pruned when the regrowth from the first pruning has come back into production. This can take 2-3 years depending on timing of the initial pruning and location.
Plant Growth Regulators
At the date of publication both SUNNY® (active ingredient uniconazole-P) and AuSTAR® (active ingredient paclobutrazol) were registered for use in avocado, however check the status of the registrations before planning an application. Also note that AuSTAR® cannot be used when there is mature fruit on the tree.
Foliar application of SUNNY® (Active constituent: 50g/L uniconazole-P) at a rate of 5-10L/1000L can be applied to the regrowth following the summer prune to reduce the amount of growth and increase flowering in the spring. New growth is treated when shoots are 50-100mm in length.
Do not apply plant growth regulators to trees with low vigour, under stress or showing symptoms of Phytophthora root rot.
Option 3: V-Shape Prune
Procedure:
Year 1: The eastern side of one row and the western side of the adjacent row are removed after harvest. More than 50% of the tree is removed. Minimal pruning to maintain access occurs in the next inter-row. The procedure is continued throughout the block. Regrowth on the pruned sides can be tip pruned in summer to encourage lateral branches. Water shoots or vigorous regrowth are removed.
Year 2 or 3: Regrowth on the pruned side is tip pruned in summer to encourage lateral branches. Water shoots or vigorous regrowth are removed. The other side of the tree is removed when the regrowth from the initial pruning comes into production. This can take 2-3 years depending on timing of the initial pruning and location.
Crowded orchard prior to pruning.Trees pruned after harvest.Trees six months after pruning.
Orchard access maintained in unpruned sides
Costs involved:
Costs range from $16.50 – 22.00/tree ($3300 – 4400/ha based on 200 trees/ha) this includes cutting down trees, mulching of limbs and applying sunburn protection. Chain saws are used to cut back the larger branches. Operations can be made quicker by using mechanical saws to remove the majority of branches. Mechanical pruning contractors are available at rates of $175-235/hr. Mechanical saws can cut branches up to 10-15cm diameter. Bare branches are cut back using chainsaws.
Smaller branches can be mulched using slashing equipment. Larger branches can be mulched (tractor operated forestry mulching equipment can handle branches up to 25cm in diameter), chipped (commercial operators available @ $235/hr) or removed from the orchard.
Considerations:
Timing
V-shape pruning is carried out after harvest. In those areas where trees carry fruit all year round major limb removal can be done in an ‘off’ year to minimise crop losses prior to the ’on’ year’s flowering. Regrowth can be tip pruned during summer to encourage lateral branches. Water shoots or vigorous regrowth are removed or cut back to lateral branches.
Removal of Over-Hanging Branches
These branches shade areas where regrowth is required. Reduced sunlight causes the regrowth to become elongated (‘shoots looking for light’).
Sunburn Protection
Some sunburn on higher branches can be tolerated as these limbs are removed in the second or third year. However the trunk and lower branch stubs should be protected from sunburn using a white acrylic paint, clay preparations or calcium carbonate sprays. Diluting the paint with water so it can be sprayed onto the exposed branches will reduce the time taken to apply protection. Adding a copper fungicide treatment (e.g. copper oxychloride) may assist in controlling disease at the pruned surface.
When to Prune the Other Side
The other side of the tree can be removed when the regrowth from the first pruning has come back into production. This can take 2-3 years.
Plant Growth Regulators
At the date of publication both SUNNY® (active ingredient uniconazole-P) and AuSTAR® (active ingredient paclobutrazol) were registered for use in avocado, however check the status of the registrations before planning an application. Also note that AuSTAR® cannot be used when there is mature fruit on the tree.
Foliar application of SUNNY® (Active constituent: 50g/L uniconazole-P) at a rate of 5-10L/1000L to the summer and autumn growth flush can reduce shoot growth and may increase flowering and yield on the pruned side. New growth is treated when shoots are 50-100mm in length. Note withholding period: Do not harvest fruit for 14 days after application.
Do not apply plant growth regulators to trees with low vigour, under stress or showing symptoms of Phytophthora root rot.
Effective orchard biosecurity practices are essential to reducing the threat of new pests impacting on your orchard. In 2011 and 2020, Avocados Australia and Plant Health Australia released two biosecurity planning documents critical to ensuring the protection of Australian avocado production against exotic pests. These were a revised Industry Biosecurity Plan for the Avocado Industry (V3) and the first Orchard Biosecurity Manual for the Avocado Industry (V1.0). (Links to these documents can be found under the Related Resources at the top of the page.)
What is Biosecurity?
Biosecurity is about the protection of livelihoods, lifestyles and the natural environment, which could be harmed by the introduction of new pests. Biosecurity is a national priority, implemented off-shore, at the border and on-farm. Biosecurity is essential for your business.
Australia’s geographic isolation has meant that we have relatively few of the pests that affect plant industries overseas. Freedom from these exotic pests is a vital part of the future profitability and sustainability of our plant industries. Biosecurity allows us to preserve existing trade opportunities and provide evidence to support new market negotiations.
Orchard Biosecurity Manual
The Orchard Biosecurity Manual is a practical document designed to assist you in protecting your property and the avocado industry from new and invasive pests. By implementing the recommended measures in your day-to-day operations, you will improve your own biosecurity and that of your region, while minimising produce losses and unnecessary costs. Orchard biosecurity is a set of measures designed to protect a property from the entry and spread of pests.
Orchard biosecurity is your responsibility, and that of every person visiting or working on your property.
Through the implementation of orchard biosecurity measures, growers play a key role in protecting the Australian avocado industry from exotic pests. If a new pest becomes established in your orchard, it will affect your business through increased orchard costs (for monitoring, cultural practices, additional chemical use and labour to apply them), reduced productivity (yield and/or quality reductions) or loss of markets. Early detection and immediate reporting increase the chance of effective and efficient eradication.
If you have found a suspected exotic plant pest, the following general precautions should be taken immediately to contain the pest and protect other parts of your orchard:
• Mark the location of the pest or symptoms and limit access to the area for both people and equipment.
• Wash hands, clothes and boots that have been in contact with affected plant material or soil.
• Restrict operations in the area while waiting for the identification of the suspected exotic pest.
If you see anything unusual, call the Exotic Plant Pest Hotline – 1800 084 881.
Click here to access & action the Orchard Biosecurity Manual document (3,162KB)
Click here to access the Industry Biosecurity Plan document (1,583KB)
Click here to watch Biosecurity Bite videos and learn more about Australian Biosecurity and Trade, Market Access requests, Import risk analysis, Border restrictions, Exotic plant pests, Export processes and your role in Australian Biosecurity.
Some states have a General Biosecurity Obligation, which means everyone must take reasonable steps to prevent or minimise biosecurity risks. Find out about your obligations under your state or territory’s biosecurity act:
Sooty blotch is widespread throughout the wet subtropical and coastal regions. It is a superficial blemish but reduces the market value of fruit.
Identification:
It can occur on all plant parts, especially in the shaded parts of the tree. Spores germinate readily on plant parts during warm, rainy weather to produce uneven smoky, sooty superficial blotches on the surface. Unlike sooty mould it does not need honeydew produced by insects to become established and the dark staining of sooty blotch cannot be rubbed off.
Sooty blotch gives green branches a dirty grey appearance. Sooty mould can look similar but is usually darker and thicker.
An uneven black superficial blemish develops on the skin surface. It is hard to rub off. Often the symptoms are streaked.
Treatment/prevention:
The program of copper sprays applied for anthracnose should adequately control sooty blotch, provided good spray coverage is maintained. Provide better ventilation to reduce dampness and humidity by pruning and shaping trees to keep the canopy open.
A dark, mouldy coating of ascomycete fungi living on honeydew excreted onto fruit and leaf surfaces by various sap-sucking insects such as aphids, mealy bugs, planthoppers, scale insects and whiteflies. The fungi do not feed on the plant but live on the honeydew.
General comments:
Sooty mould causes unsightly black marks that downgrade fruit in the market. The growth of the fungi is more prolific during wet, humid weather.
Identification:
A dark, dense sooty layer on leaves and fruit that, unlike sooty blotch, is easily rubbed off. The layer can get quite dense and acquire a felt-like appearance. In severe cases, leaves can become heavily covered, turn yellow and may fall off prematurely. Symptoms are often worse in trees alongside dusty roads where dust interferes with natural control of sap-sucking pests by beneficial insects.
Sooty mould on leaves. In this photograph, scale insects are responsible and can be seen feeding on the twigs.Sooty mould on fruit. Sooty mould is usually thicker and more ‘velvety’ than sooty blotch and can be rubbed off the skin easily.
Treatment/prevention:
Find out what insects are producing the honeydew and take action to control them. This does not necessarily mean applying more insecticide sprays; on the contrary, the proliferation of sap-sucking insects is often due to the overuse of insecticides that has killed off the beneficial insects. Provide better ventilation to reduce dampness and humidity by pruning and shaping trees to keep the canopy open.
Several species of fungi and bacteria, principally Fusicoccum aesculi (formerly Dothiorella aromatica), Lasiodiplodia theobromae and Colletotrichum gloeosporioides. Phomopsis perseae and Thyronectria pseudotrichia may also be involved.
General comments:
The disease is widespread throughout the high summer rainfall production regions of eastern Australia and to a lesser extent the southern areas and Western Australia. The disease is not as prevalent as anthracnose but can cause significant losses of fruit periodically. Fruit from stressed trees are more susceptible to stem-end rot. Infection occurs via spores through the broken surface of the pedicel, or the pathogen can already be present in the fruit but remain inactive unless the tree is stressed. New infections can start from spores produced on dead leaves, bark, branches and fruit that remain within the canopy.
Identification:
A brown to grey-black soft rot of the flesh develops from the stem end of the fruit. Because the rot does not develop until fruit have matured and started to soften, it is usually not discovered until the fruit is cut for eating. In the majority of cases the rot produces dark streaking of the water-conducting tissues in the flesh which starts at the stem end. Stem-end rot can be confused with vascular browning and chilling injury.
Early symptoms in Hass.
Symptoms spread down the fruit…
…and eventually produce the advanced symptoms of vascular browning.
Well-advanced symptoms in a green skin variety clearly showing vascular
browning which starts at the stem end.
External symptoms of stem-end rot on a green skin variety, a whitish mould can develop where the stem was. External symptoms are not always present. Symptoms are difficult to see on the dark skin of Hass.
Treatment/prevention:
Control is best managed by an integrated approach using the following practices:
Avoid nutritional and environmental stress, especially water stress, during fruit development as this appears to predispose fruit to the disease.
Follow the fungicide program for anthracnose.
Keep the orchard clean. Before flowering prune out deadwood and remove infected fruit, dead leaves and twigs in the canopy that serve as sources of disease inoculum.
Do not harvest during wet weather.
Do not snap pick any variety except Hass, and even with Hass do not snap pick fruit from unhealthy trees; in high rainfall or humid areas; where growth regulants (e.g. Sunny®) have been used.
If fruit is clipped, disinfect clippers regularly.
Handle fruit carefully to avoid damaging the skin and for green skin varieties, avoid losing the fruit stalk ‘button’.
Registered post-harvest fungicides may provide some control of infections initiated at the pedicel by fungal spores.
After harvest, follow fruit storage and ripening temperature protocols to minimise disease development.
The longer the period between harvesting and consumption the worse the disease, so minimise delays in the delivery chain wherever possible.
This viroid is rarely found in Australia. Any suspected symptoms should be investigated and reported to Plant Health Australia’s Exotic Plant Pest Hotline (phone 1800 084 881). The viroid is transmitted in both seed and grafting wood, by natural root grafting between trees and via pruning and cutting equipment. Trees may carry sunblotch viroid without showing symptoms; however, all infected trees usually have greatly reduced yields.
Identification
Symptoms can vary greatly, depending on the avocado variety, the environment and the strain of the viroid.
Leaves: Affected leaves may have distinctive white, yellow or pink streaks or mottles and may also be distorted.
Leaves affected by sunblotch viroid.
Twigs and branches: Twigs and branches develop sunken streaking and spotting of the bark; this is generally yellow but can be orange, white or almost colourless. Streaking is usually associated with grooving in the bark. In some instances a crocodile-skin pattern develops on the tree trunk.
Streaks on branches affected by sunblotch viroid are usually sunken and form grooves.
Fruit: Affected fruit develop sunken yellow or reddish streaks on the skin, generally extending from the stem end. Fruit may also be small and distorted. Trees with affected fruit may be free of visible leaf symptoms. Fruit symptoms may be confused with a chimera, but with the latter the discoloured part is not sunken or only slightly sunken and the discoloured streaks usually extend the whole length of the fruit.
Affected fruit develop yellow or reddish sunken streaks, generally extending from the stem end.
Whole tree: Trees may develop a prostrate growth pattern with branches sprawling along the ground. Prostrate growth habit may be confused with boron deficiency; however, boron-deficient trees will usually display other boron deficiency symptoms at the same time.
Sunblotch-affected trees can have a low scrambling growth habit.
Treatment/prevention
There is no treatment for affected trees; they must be destroyed to prevent transmission of the disease to healthy trees. Accredited viroid-free trees can be obtained from Avocado Nursery Voluntary Accreditation Scheme (ANVAS) nurseries. These trees are grown from scion wood sourced from accredited viroid-free trees of the Virus Tested Tree Registration (VTTR) program. Although sunblotch viroid is very rare in Australia, only fruit from VTTR trees may currently be exported to New Zealand. Each tree carries a label indicating compliance with the scheme. Plant viroid-free trees at least 15 m from untested trees to avoid transmission through natural root grafting. Use one set of pruning, injecting and harvesting implements for accredited viroid-free trees and another set for untested trees to avoid disease transmission through infected sap. Disinfect equipment thoroughly with a solution of 1.5% sodium hypochlorite between blocks.
• Remove poorly positioned branches such as overlapping (create a dense canopy) and crossing over branches (branches that grow from one side of the tree to the other) to improve light penetration, prevent dieback of internal shoots and improve spray penetration and picker access.
…and eventually produce the advanced symptoms of vascular browning.
