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Possibilities for multi-leader trees

Spindles planted at various spacings form

the most common training system in mod-

ern apple orchards. High Density (HD) super

spindles planted at more than 5000 trees

per hectare are extremely productive from

the very �rst years, and can yield 70 to 90

tonnes per ha by year 4 or 5. Moreover, HD is

an important requirement to achieve mod-

ern fruit walls.

The main drawbacks of traditional HD lay in

the high investment costs and in the di!cult

management, that often requires limb bend-

ing, precise crop-load control and skilled prun-

ing. It only takes a small mistake, for instance a

single year of under cropping or bad pruning,

to turn HD super spindles into uncontrollable

trees. This explains why in the last decade, the

dominant position of HD was challenged by

the double-leader training system, which was

proposed by the Mazzoni nursery in Italy. This

cultivation practice is simpli"ed using “Bibaum”

trees, which are a hybrid of the spindle and the

old palmetta. Double budding on M.9 in fact in-

duces a dwar"ng e#ect similar to budding on a

less vigorous rootstock. This is particularly use-

ful when the trees will be grown on fertile soils.

From Bibaum to multi-leader training

Once the concept of “more than one leader”

was accepted, the next question was whether

the number of leaders could be increased to get

a natural fruit wall from trees grown on fertile

soils and so encourage mechanisation.

A six-year trial of the Adige valley’s main apple

cultivars and extensive practical experience

in the rich soils of the Po Plain, con"rmed that

three-leader trees can be created on M.9 from

spindles by allowing two laterals to grow and

removing the competing branches (see Photo

1). Four-leader trees can be created from Bibaum

trees by spreading the original two leaders, two

additional leaders will arise between them (Fig-

ure 1bis). Spindle or Bibaum trees come from

the nursery with several limbs. The develop-

ment of two new leaders from scratch requires

care during the spring and summer of the "rst

two to three years to keep the leaders vertical

Alberto Dorigoni Unit Experimental Orchard and Cold Stor-

age, Fondazione Edmund Mach, Italy

alberto.dorigoni@fmach.it

Franco MicheliUnit Experimental Orchard and Cold Stor-

age, Fondazione Edmund Mach, Italy

franco.micheli@fmach.it

Bene�ts and drawbacks

Fertile soils are the most suitable for

ML trees. The major drawbacks of the sys-

tem are poor yields in the "rst years and

the need to com-plete tree formation in the orchard. Once

established, the main bene"ts arise from

simplicity in over-all management. ML trees are most suita-

ble for single-row hail nets (also against cod-

ling moth), mechani-sation of thinning and

pruning and tunnel sprayers. Increasing the number of lead-

ers can be a powerful tool to achieve a fruit

wall in fertile orchards where spindle would

be unmanageable.

26 36 64 82

22 49 59 77

9 16 21 32

0

50

100

150

200

250

1 leader 2 leaders 3 leaders 4 leaders

n. of branches (2-3m)

n. of branches (1-2m)

n. of branches (0-1m)

Nu

mb

er

of

bra

nch

es

72 44 38 43 40 39 43 38 28 38 38 23

0

10

20

30

40

50

60

70

80

branch length 0-1 m branch length 1-2 m branch length 2-3 m 1 leader

2 leaders

3 leaders

4 leaders

bra

nch

le

ng

th (

cm)

Figure 1. Branch numbers at di!erent heights in

the tree (Golden Delicious in year 5)

Fondazione Edmund Mach Fondazione Edmund Mach

Figure 2. Branch length at di!erent heights in the

tree (Golden Delicious in year 5)

EFM 2014-0218

and free of competitive shoots. However, limb

bending, which is important for spindles, is not

needed for Bibaum and Multi-Leader system

(ML) trees. It takes ML trees about �ve to six

years to achieve a fully formed canopy, one or

two more than the time required for spindles

and Bibaum trees.

The resulting tree shape changes from the coni-

cal shape of the spindle to a rectangular cuboid

of three- and four-leader trees, which look like

fruit walls” (Photo 2). For all of the cultivars tri-

alled, ML trees had many more shoots than the

spindles, particularly in the middle and upper

part (Figure 1) of the tree. The length of the scaf-

fold shoots was inversely related to the number

of leaders (Figure 2). The percentage of branches

longer than 60 cm (important because of the

length of the strings used for �ower thinning)

was reduced from 11% for spindles to 5%, 4%

and 3% for two-, three- and four-leader trees

respectively. Consequently, the average width

of the lower part of the trees was dramatically

reduced, in the case of Golden, from 144 cm for

spindles to 76 cm for four-leader trees.

Productivity and quality

Because early yield per ha is a function of tree

density, spindles and two-leader trees planted

at 2900 and 2400 trees/ha respectively were the

most productive systems in the �rst three to four

years. While spindles reach their maximum yield

around year four, the yield from three- and four-

leader trees, planted at 2200 and 1800 trees/ha

respectively, continues to increase in years �ve

and six (Table 1). The economic loss of yield in

the early years is partially compensated by the

lower investment. No di!erences were found in

fruit weight, however, through the years, there

is a greater reduction of red-coloured fruits at

the bottom of spindles than for three- and four-

leader trees (Photos 3, 4 and 5).

Photo 1. When creating three leaders, two

laterals must be grown and competing limbs

removed

Alberto Dorigoni

Photo2. Three- and four-leader

trees look like natural “fruit

walls”. Alberto Dorigoni

A four-leader tree is achieved by sprea-

ding a Bibaum.

Alberto Dorigoni

CultivarsWeak growing cul-tivars like Gala tend to dwarf too much, while Golden, Rosy Glow and Fuji are more suitable for growing as ML trees. Once the trees are fully established, the bene�ts are the sim-plicity in accessing the canopy and the overall management, from pruning through thinning and harvest-ing.

Table 1. Yield per ha in the di!erent orchard systems

Gala 2009 2010 2011 2012 2013 2009-2013

1 leader 17 24 49 59 53 201

2 leaders 13 21 41 59 38 171

3 leaders 18 14 45 49 67 192

4 leaders 12 13 39 46 67 177

Golden

1 leader 23 47 68 94 70 302

2 leaders 13 12 66 34 76 202

3 leaders 19 32 83 70 97 300

4 leaders 9 18 55 73 85 241

Fuji

1 leader 16 24 52 77 46 216

2 leaders 25 12 59 64 55 216

3 leaders 22 25 70 38 83 238

4 leaders 18 6 48 33 63 168

Pink Lady

1 leader 25 29 77 75 95 300

2 leaders 17 25 72 78 86 279

3 leaders 26 27 65 97 92 308

4 leaders 12 19 49 84 85 249

Fondazione Edmund Mach

19EFM 2014-02

Pros and cons of ML training

Increasing the number of leaders by splitting

the canopy into two-, three- or four- leader trees

results in signi�cantly weakened trees and a re-

markable change in their architecture. The only

structural wood left is that of the vertical lead-

ers, all the remaining wood is short, does not

bend and is covered in �ower buds close to the

trunk. After four years, due to the wide spacing,

ML trees can bear 40-50 kg of excellent qual-

ity apples ( see table 1). Because ML trees have

two to three times as many branches supported

by the same M.9 root system as spindles, the

trees can be headed back or branches can be

removed, they also tolerate short pruning and

mechanical hedging or topping much better

than spindles. This means that the width and

height of the trees can be easily reduced even

more by using Lorette early-summer pruning,

to achieve semi-pedestrian (2.8 m) or fully pe-

destrian (2.3 m) “vineyard-like” orchards.

The main drawbacks of ML concern poor yields

in the �rst three to four years and the need to

complete tree formation in the �eld. Given the

lack of the spindle’s central supporting trunk,

special care must be given to two-leader and

ML systems, to ensure that a strong trellis is

able to bear a crop which is uniformly distrib-

uted across the tree and to a large extent hangs

on the support wires. Research must establish

whether, in the end, the low vigour of ML trees

will result in a reduction in fruit weight.

Re-thinking tree spacing

The change in shape resulting from ML training

requires major re-think of tree spacing. Distance

can be reduced to maximise the bene�ts of

such systems, that mostly pro�ts by alleyways

of less than 3 meters and short “centripetal”

pruning. However, the in-row spacing must be

greater (1.5-1.8 m) to space the leaders about

0.5 m apart. At �rst glance, ML can be easily mis-

taken for classic super spindles planted at 7000

to 8000 trees/ha, except for the low number of

tree trunks ( see Photo 6).

New techniquesML is extremely suit-

able for use with new techniques, such as

single-row hail nets, mechanisation of

thinning, pruning and weed management,

or even minimum-drift tunnel sprayers and any mechanical harvesting aids. It is

likely that the thin canopy resulting from ML training allows the

fruits to continue to colour red for more years than the fruits on spindles. Finally,

increasing the num-ber of leaders can be

a powerful tool to achieve high-density

fruit walls in fertile orchards where super spindles would be un-

manageable.

Photo 6. ML can be easily mistaken for classic super

spindles planted at 7000 to 8000 trees/ha.

Alberto Dorigoni

Photo 3, 4 and 5: Red overcolour in the low part of the canopy of Rosy Glow, 2011. Alberto Dorigoni

EFM 2014-0220