Quote:Bending should be done to create the tree shape suitable to the specific training system.

Plum Training—The Unheaded Route

Nigel C. Cook1and Prof. Daan Strydom2

1Department of Horticultural Science
University of Stellenbosch
Matieland, South Africa

2Industry Consultant
Dutoit Group
Ceres, South Africa

Reprinted fromDeciduous Fruit Grower, January 1997, pgs. 24-25.

Recent years have seen further developments in plum training ideas and certain growers, seeking
earlier returns from investments, are moving away from the approach of heading trees at
planting.

While heading plums at planting is very effective in eliminating the problems associated with
transplant shock, it is extremely dwarfing.A significant portion of the existing growth and
therefore also part of the potential growth is removed—a loss that trees first have to overcome
before producing additional growth.

Keeping in mind crop-load guidelines, determined in terms of fruit per cm trunk circumference,
the advantages of thicker trunks in early years are clear.Thicker trunks and more trunks per
hectare mean more fruit in the critical, initial bearing years.However, this approach of obtaining
the maximum growth as early as possible is not as straightforward as it sounds.This maximum
growth must also be of the desired type, which requires the development of sufficient fruiting
units or bearing sites.The challenge to the grower is then to prevent growth resulting in
undesirable units that waste valuable growth energy, such as water shoots that would normally
have to be removed with pruning cuts.

To obtain maximum growth, it is important to start off with high quality nursery trees, which are
currently still whips in the local industry.Experience has shown that the larger the tree (the
thicker the caliper) at planting, the greater the chance of success in the first year.Ideally, a tree
should be formed in the nursery in one continuous growth flush.Sometimes there are side
branches that must inevitably be removed along with the reserves stored in this wood.Generally,
trees formed through dormant (spring) budding perform better than those established through the
more conventional summer budding procedures.Because the buds on the whip give rise to the
branches, it is important to handle these nursery trees with the utmost care from lifting to
planting to prevent damage to these lateral buds.

The trees should be planted as soon as possible after they have been lifted in the nursery, as
lifting often stimulates new root formation, especially in the warmer areas.This new root
formation promotes the sprouting of the buds and it is therefore important that new root growth
occur in the orchard.Maximal root growth is essential to overcome the transplant shock.
Temporary heeling in should be kept to a minimum and, if possible, avoided altogether.Damage
to the roots and bark caused by wind-rocking should be prevented by tying whips to the trellis
immediately after planting.

Trellising is advised for all plum plantings, given this fruit’s sensitivity to wind damage and the
Western Cape’svery windy conditions.Because so much bending is required in this system, the
current philosophy is that the trellis wires are used for fixing laterals, as opposed to a standard
three-wire system where wires are used solely for support of the leader.The use of wires is
believed to save far more in labor costs than their installation cost.

Wires are spaced 30 cm (12 inches) apart, starting 50 cm (20 inches) above the ground.Fewer
wires are needed in the upper part of the trellis because of the desired “soft top”of trees and the
top wire on the trellis is only required to keep the tree straight.In upright systems, an additional,
raised “tram line”for tying the basal shoots should be added.

This training method currently only permits the training of trees with a single trunk (central
leader), when starting with a whip.The system is suited to close in-row spacings from 1.5 m
(5 feet) to 0.75 m (2.5 feet).For most of the more spreading cultivars such as Songold and
Laetitia, a spacing of 1 m (3.2 feet) in the row is at this stage believed to be the optimum and
0.75 m (2.5 feet) for the more upright growing cultivars such as Larry Anne or even Sapphire.
The idea is to plant closer than wider, as the filling of orchard volume always comes at the price
of a delay in production.Between-row spacing of 3.5 m (11.5 feet) is the current trend for
upright (central leader) systems and 4 m to 3.5 m (13.1 to 11.5 feet) for V-shaped systems.

GROWTH MANIPULATION
In South Africa, to promote even budbreak an appropriate rest-breaking agent should be applied.
At bud swell the whip should be scored at a height of 70 cm (28 inches) with the blade of a
knife:a cut has to be made around the trunk, not too deeply, just enough to break the phloem
transport in the bark.Localized applications of Promalin, mixed into brown latex roof paint or
water at a concentration of 25%, can be made to selected buds below the scoring position at bud
swell.

Bending should be done to create the tree shape suitable to the specific training system and
prevent the development of undesirable growth.The aim is to produce a more or less pyramid-
shaped tree—a wider base with a softer top—but the exact shape differs according to the spacing
and training system.To create upright central leaders the base branches should be tied in all
directions around the trunk.However, the shoots above this base are only tied flat in the row,
using the trellis wires.In V-shaped systems, all shoots are trained flat in the row, again using the
trellis wires, although basal shoots should still be stronger than those in the upper parts of the
tree.

Shoots originating close to the new apex compete strongly with the new leader.Remove the
shoots on the upper 10 cm (4 inches) of the leader as soon as they are approximately 1.5 cm
(one-half inch) long.Shoots originating directly below the point of scoring often have a narrow
crotch angle and crotches must be widened with toothpicks or clothespins as soon as is
practically possible—when they are about 10 cm (4 inches) long.

Several shoots will tend to become dominant as growth continues.When they are about 50 cm
(20 inches) long, it is time to start bending them to slow down the rate of extension growth and
convert these strong, upright, dominant shoots into weak, horizontal shoots ideally suited to
fruiting.Bending becomes an ongoing process through the growing season as other, nonbent

shoots will in turn become vigorous and upright and have to be dealt with in the same manner.
Each tree needs to be manipulated every 2 weeks for bending to be effective.Growth should,
however, slow down considerably in January (July in northern hemisphere), coming to a halt in
March (September in northern hemisphere).

If branches are bent in a timely and judicious manner, virtually no pruning will be required after
the first summer, but it is possible that some of the laterals will have become too strong.These
strong branches no longer comply with the 3:1 ratio rule, which states that the diameter of the
leader should be at least three times that of a lateral at its point of origin.These nonconforming
laterals can be removed just before bud swell in the second growing season.Always keep in
mind that pruning has a negative influence on fruiting and therefore minimal pruning—which is
possible if bending has been executed judiciously—is critical to ensure a good crop in the second
leaf.In later years, the type and severity of pruning becomes increasingly dependent on the
bearing habits of the cultivar.Earlier maintenance pruning becomes more important in cultivars
that set fruit more readily, like Sapphire.

The timely execution of these manipulations is critical, arguably even more so with plums than
with other fruit kinds.The correct manipulation at the right time can help to avoid much of the
additional corrective work which, more often than not, is in the form of pruning to reduce growth
and production.

CROPPING
A crop in the second leaf helps contain the vigor of the trees in these systems.The norm of five
fruit per cm trunk circumference is used as a guide for thinning and crop load in the second leaf.
In subsequent years, thinning can be done according to the guidelines published inDeciduous
Fruit Growerin July 1995 (pages 260-261).

While experience has shown that production in the region of 10 t/ha is possible, we can only
speculate on subsequent production.Although production largely depends on factors such as
cultivar and tree density, it should be safe to say that 20 to 25 t/ha could be realized in the third
leaf, increasing to 40 to 45 t/ha in later years.

This training method—the unheaded route—is an option that could enable producers to reap
greater benefits from the maximum growth achieved during the first year from planting than with
the heading alternatives.