Top Working of
Mango Trees
Scientific
Name: Mangifera
indica
Family:
Anacardiacea
The
top working of mango trees in an orchard is a process which should be
considered part of normal orchard practice. Top working of inferior
backyard cultivars, such as the 'common' and even the high-quality
'Kensington Pride', which, unfortunately, can be regarded as a shy and
irregular bearer in many climatic situations, with a more desirable
scion cultivar is possible.
Improved cultivars in terms of high
and regular bearers, good quality, disease resistance, ripening time,
size, keeping and transportation quality, have been imported or
selected locally. Both the New South Wales Department of Agriculture
and the Queensland Department of Primary Industries have commenced a
mango-breeding program to develop cultivars that will perform better
than the present cultivars. This is why old cultivars should be
periodically replaced by new improved cultivars.
It is not
necessary to root out all established trees in order to replace them
with new ones by planting new trees. The author has used a range of
methods in top working his older trees with new cultivars by means of
grafting. If undertaken correctly, and if you are prepared for a lot of
initial work and aftercare, grafting can be highly successful.
Trees
are prepared for grafting by sawing the branches off in July, thus
enabling the new growth to benefit from the Spring surge. All the
branches are cut at a height of 1 to 1.5 metres above the ground,
leaving one (or about one fifth of the tree) 'feeder' branch. This
branch is chosen in such a way as not to complicate the grafting
process or to make it difficult to saw it off at a later stage without
damaging the newly-grafted branches. When the grafts on the top-worked
branches are growing, the 'feeder' branch is removed.
All cut
surfaces must be sealed with grafting mastic to prevent die-back.
Sunburn will be expected when the trunk and scaffold branches are
exposed to full sunlight. This can be prevented by painting the whole
tree with a water-based white paint. Extra protection can be provided
by placing dry grass in the crutches of the scaffold branches.
New
shoots will develop everywhere. When these shoots are approximately 15
cm long, two are selected for development per scaffold branch at a
distance of 5 to 10 cm from the sawn-off end of the old scaffold
branch. All the other shoots must be regularly removed.
As soon
as the shoots have reached a suitable thickness, they are grafted as in
normal grafting onto the rootstock. Whip grafting is the most easy and
suitable method. After the graft union is wrapped tightly with PVC
tape, the graft should also be wrapped up tightly with this tape.
About
three months after grafting, it will be noticed that the eye is
starting to swell under the tape. When this eye presses against the
tape, a small opening is made with a razor blade so that the eye can
grow out. This should not be done too early. Usually only one eye will
sprout, but if more begin to swell, they are treated in the same
manner. The wrapping tape is removed gradually, after the sprout has
grown out properly from the scion and the leaves are already green.
Unsuccessful
grafts are removed and regrafted. The 'feeder' branch is removed as
soon as the new grafts have formed a canopy. Young trees that are being
top-worked can have the desired scion grafted directly onto the branches.
The
author has observed a very successful method of top-working used in
Thailand, which eliminated the need for initial sawing off of branches.
At a convenient height on the branch to be topworked, two vertical and
parallel cuts are made through the bark, wide and long enough to accept
the cut edge of the scion. This rectangular piece of bark is removed
and a thick piece of scion wood taken from the current season's growth
and up to 20 cm in length is selected. This is trimmed in the form of a
long wedge (as in whip grafting) and is inserted in the rectangular
patch. The scion is tied tightly in place with PVC tape and then
completely enclosed with clear plastic such as 'gladwrap'. The clear
plastic is removed after 3-4 weeks, but edges should be sealed with a
grafting wax.
The author observed Tong Dum mango trees being
reworked to Nam Dok Mai. Trees in the orchard had been planted at a 5 x
5 metre spacing and scions attached eight weeks before harvest. As soon
as the fruit were harvested, the branches above the scions were cut.
One 'feeder' branch was left and sawed off after the grafts had
established. Only one season's fruit was lost using this technique.
In
another section of the orchard, alternate trees were top-worked using
this method, but, without the use of a 'feeder' branch. Unworked trees
provided shade and protection from wind. Top-worked trees made good
growth and within twelve months the other trees were top-worked.
Successful
grafts grow quickly, but initially the graft union is weak and the
shoots can break off easily. These shoots can be protected by fastening
them to a pole inserted into the ground next to the shoot.
Vigorous
shoots should be pruned so that they branch. This will prevent the
trees from developing sparsely with long shoots that bend under their
own weight.
About six months after grafting, the best and
strongest shoots are selected and the weaker ones removed or corrected
by pruning. Four new branches are selected for future development into
the main scaffolding.
Top-worked trees need at least a year of
special care. Even after that, a watchful eye should be kept on them
until the canopy of the new shoots has fully formed. All PVC tape
should be removed, since even the smallest remaining strip can pinch
the vigorously-growing branches and cause them to break off. The grass
with which the old scaffold branches was protected usually
disintegrates on the tree and needs no further attention, except
possibly in combating ants, which promote the spreading of aphids and
scale. After about a year, the new tree should be pruned to a vase
shape to ensure maximum light which is necessary for good fruit set.
Top-worked
trees will come into bearing within two to three years, which makes it
worthwhile to remove all outdated and poorly-producing cultivars and
replace them with superior cultivars.
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