Canopy Management of High Density Subtropical Fruit Trees: Avocado, Mango and Lychee - Part 1

Abstract

Australian subtropical fruit industries Avocado and Lychee and the more tropical Mango are currently venturing into high density orchards with little experience and knowledge of canopy management methods required to manipulate trees to limit tree size whilst maintaining high production.

 This paper attempts to provide a basic understanding and starting point for growers considering high density orchards with some application to existing wide spaced orchards.  A glossary of canopy management terms is included, as this is an essential part in understanding and applying recommendations in the Avocado, Lychee and Mango canopy management calendars. Discussion and recommendations are based on observations of current subtropical canopy management methods being used in Mexico, Florida, Israel, South Africa, Thailand and Australia.

Introduction

 Historically Australian subtropical fruit industries have planted orchards at permanent wide spacing and more recently in the past 10- 15 years, planted at double spacing and practiced tree removal as trees compete for space and sunlight.  Apart from skirting bottoms of trees, trees have been allowed to grow at will.The result is very large trees that are difficult to harvest, spray and protect from wind, hail or native birds.  Also tree removal often is delayed and sometimes not done at all to the detriment of fruit production and profit.

 There is currently a worldwide trend in countries such as Florida, Israel and South Africa to plant subtropical fruit trees on permanent high density spacing and to manipulate tree growth using canopy management and pruning techniques to control tree growth patterns and tree shape and ultimately limit tree size, while still maintaining high fruit production of desired fruit size and quality.

 This paper deals collectively with ideas and grower practices currently being used and trialed in Mexico, Florida, Israel, South Africa, Thailand and Australia.  It is designed to be a starting point for growers wanting to plant high density and control tree size. Not all canopy management questions can be answered at this point in time and recommendations may not be fully understood until first-hand experience is gained by putting methods into practice.  Please refer to the glossary of terms for a better understanding of the actual pruning operations recommended.

Glossary of Canopy Management / Pruning Terms

Indiscriminate Pruning

Random growth removal by hand or mechanical hedging machines that mostly results in strong regrowth.

Selective Pruning

An accurate form of hand pruning usually back to a desired lateral or bud.  Tip pruning, heading back, skirting and flower pruning are all examples of selective pruning.

Determinate Shoots

Refers to an emerging flower that does not regrow a vegetative shoot from the end of the flower as mostly happens in Mangoes and Lychee.  Sporadic, strong, vertical determinate shoots in Avocados that carry exposed fruit prone to sunburn should be removed during the early spring prune.

Indeterminate Shoots

Avocados usually have indeterminate shoots on strong, upright flowering terminals that produce a vegetative shoot out of the end of the flower.  This indeterminate growth is the first vegetative shoot to appear in spring during or immediately after flowering.  Very strong indeterminate growth usually needs to be tip pruned in late spring.

Headback (heading)

Selective pruning and removal or partial removal of generally stronger upright growth back to old laterals or basal buds.  Excessive regular 'heading' can cause strong re-growth and water-shoots that will need tip pruning or controlled leader pruning during summer.

Tip Prune

Light selective growing point removal or pruning back of generally strong/medium upright growth back to newly developing laterals on the same branch.  Mostly done in older trees that already have developed proper tree shape.

Controlled Leader Pruning

Selective growing point removal or pruning back of generally strong terminal (top) growth in young trees 1-5 years old back to 1-3 vertical buds above newly developing laterals on the same branch.  This slows down the upwards growth and develops more lateral growth but still allows vertical buds to produce an upright leader.

Watershoots (suckers)

Refers to strong vigorous growth anywhere within the trees' framework above the graft, usually coming from dormant buds on mature branches.  Do not remove this growth completely as it has enormous fruiting potential, rather tip prune or headback to 5-8 strong laterals mid to late summer.

Topping (mechanical hedge rowing)

Refers to indiscriminate, non-selective, mostly external branch removal either by hand or usually by mechanical hedging machinery to maintained desired tree shape.  Hedging results in some strong vigorous regrowth that grows out past the uniform hedged canopy that must be carefully removed by re-hedging or selective hand tip pruning.  Mechanical  hedge rowing is labour saving but repeated over use can cause multi-branched dense regrowth that must be selectively hand thinned.

Skirting

Pruning of lower branches or 'skirt' of the tree to aid in weed control, surface mulch applications, mini sprinkler irrigation distribution and to discourage fruit of lower branches touching the ground.  Best time to do this is during early flowering during cool weather when trees are not in a strong vegetative growth phase.

A maximum height of 0.5m is recommended.  Repeated skirting by selective hand pruning can eventually result in strong, robust branches able to support fruit without touching the ground.

Stumping

Cutting back trees above graft to bare stumps usually 1-1.5m above ground.  Comfortable chain saw height is best.  Carried out to retrain old crowded feral orchards older than 12 years or to topwork to another variety.

 

                      Best times in subtropics.          Mango -           late September/October

                                                                             Avocado -        June/July/August

                                                                             Lychee -          May/June

If these times are not possible due to presence of fruit or frosts, then leave a horizontal nurse branch unpruned to equate about 20% of the tree's volume.  Immediately paint any exposed branches and stump with a good quality flat white plastic paint to stop sunburn.

Stump Regrowth Pruning

All vegetative shoots are allowed to regrow from the remaining stump.  When any strong vigorous shoots reach a height of 1-1.5m from stump, head back to laterals.  Do not allow any strong terminal growth to develop above 2-2.5m until a heavy crop is set 12 months after stumping.  Then carry out normal controlled leader pruning and tip pruning during the second summer growth period.

Access Pruning

Should not be necessary in a well canopy managed orchard.  If access alleys into trees to aid in harvesting or servicing irrigation is required, do during skirting operation at commencement of flowering when not in a vegetative growth phase.

Flower Pruning

Early flowers are selectively cut off or pinched out in cold areas to encourage reflowering and later fruit set when weather is warmer.  Timing of this operation is critical and dependant on variety and climate.

Snapping/Pinching

A form of -selective pruning using hands on young flowers or soft new growth often used on Mangoes to encourage lateral branching and tree complexity on 1-2 year old trees.

Primary Crotch and Branches

Main or first crotch of tree above ground level with main branches coming from at or near this crotch.

Secondary Crotch and Branches

Smaller branches coming from crotches above primary crotch and primary branches.

Cincturing (girdling or ringbarking)

Complete bark removal down to, but not into, hard wood.  Used in early maturing Lychee cultivars to prevent a second late summer or autumn growth flush.  The cincture is normally done in late summer/early autumn when the first growth flush after post harvest pruning has hardened and if a second growth flush is imminent.  Width of cincture is between 2-4 mm and must heal over by ideal flowering time.  Cincturing Avocado and Mango is not a standard practice anywhere to date.

New laterals

Lower developing lateral growth or side branches that are part of but below a strong and actively growing upright watershoot or main shoot or leader.

Old Laterals

Mature hardened lateral growth or side branches at the base of a previously pruned leader or any non-vigorous lateral growth within the tree framework.

Bud

In the context of canopy management in this paper refers to a bud, usually on a vertical branch, that has the potential for vegetative growth during summer.

Terminal Bud/Growth (dominant apical growing point)

The dominant end bud at the very end of a vertical branch that has the potential to produce the strongest growth.  The strong vertical growth of this bud often suppresses secondary regrowth of laterals and reduces tree complexity and fruiting potential.

Major Limb Renewal (window pruning)

This selective major limb removal operation occurs in mature bearing orchards from year 5-6 onwards in trees trained with 4-5 multi leaders from planting.  A maximum of only 15-20% of total tree volume should be removed at any one time.  Select the most dominant single upright limb or alternatively remove two smaller higher upright secondary limbs evenly spaced within tree canopy.  This should be done during early flowering during cool weather when the tree is in a non-vegetative phase.

Tying Up

Refers to tying up heavily fruiting branches mostly in Mangoes using single continuous pole mounted horizontal wire along row above trees or by wiring smaller branches back onto strong upright limbs.

Propping

Timber supports to hold up heavily fruiting lower branches to prevent fruit touching ground.  Less preferred than tying up as it restricts use of boom sprays for weed control.

Dormancy

Period during which a subtropical evergreen tree stops growing and either develops flower buds or remains idle during winter, until a trigger or stimulus occurs causing bud break and flower development and/or emergence.

Rejuvenation Pruning

Refers usually to mechanical hedging or topping or cutting back to the desired tree shape and sir of either younger 10- 12 year old feral orchards that have never been pruned or mature high density orchards that have failed to set a crop  and are in an off year.

 It is essential to carry out selective controlled leader pruning and tip pruning on strong vegetative regrowth throughout spring/summer growing period.  The best time for rejuvenation pruning is as for stumping.  If a crop must be harvested or cyclones remove fruit in mid-summer and pruning must be done during the summer growing season, consider pruning only half of each tree along the row at one time with the other half done when regrowth has hardened or do the following year at the correct time.

Tree Shape

Tree shape refers to the natural growth habit unique to every specific cultivar or variety.  It is advised to work with the natural growth habit of the tree rather than against it.  Generally the following two basic shapes can be identified in fruit varieties and a recommended guide is as follows

 

 

                                                                                                                                              

                                                     

                Narrow Pyramid                                                                        Tent

                 Avocado:                                                                                  Avocado:

                 Hass                                                                                          Fuerte

                 Pinkerton                                                                                  Shepard

                 Zutano                                                                                      Sharwil

                 Gwen                                                                                        HX48

                 Edranol                                                                                     86

                 Reed                                                                                         Green Gold

                 Wurtz

                 Lamb Hass

 

                 Mango:                                                                                      Mango:

                 Kent                                                                                          Keitt

                 Sensation                                                                                 R2E2

                 Tommy Atkins                                                                          Nam Dok Mai

                 Haden                                                                                      Heidi

                 Florigan                                                                                   Kensington

                 Zillate                                                                                      Palmer

                 Brooks                                                                                     Isas

                 Valencia Pride                                                                        Glenn

 

                 Lychee:                                                                                  Lychee:

                 Kwai May Pink (B3)                                                               Tai So

                 Chacapat (Emperor)                                                              Brewster (Floridian)

                 Fay Zee Siu                                                                          Kwai May Red (B 10)

                                                                                                              Wai Chee

                                                                                                              Kaimana

                                                                                                              Salathiel

                                                                                                             Souey Tung

                                                                                                              Bengal

 

 

 

Permanent High Density Tree Spacing

                                                                                                    Narrow Pyramid                        Tent

Low Vigor Cultivar                                                                    6x3                                               7x3

Medium Vigour Cultivar                                                           7x3                                               8x3

High Vigour Cultivar                                                                 7x4                                               8x4

Row Direction

North South orientation along row preferred for high density orchards, ideally up and down the slope if mounding to aid in water run off or across steep slopes to give min. 4-5% to max 8- 1 0% slope along rows.

 

Authored by: 
Peter Young, Birdwood Nursery May 1997
Sourced from: 
Rare Fruit Council Brisbane Branch Newsletter. December 2000-January 2001
Date sourced: 
25/01/2013