TOP WORKING OF MANGO TREES
SCIENTIFIC NAME: Mangifera indica
FAMILY: Anacardiaceae
The topworking of mango trees in an orchard is a process which should be considered part of normal orchard practice. Topworking 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 topworking 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 topworked can have the desired scion grafted directly onto the branches.
The author has observed a very successful method of topworking 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 topworked using this method, but, without the use of a 'feeder' branch. Unworked trees provided shade and protection from wind. Topworked trees made good growth and within twelve months the other trees were topworked.
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.
Topworked 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.
Topworked 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.
DATE: May 1989
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