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Mango Growing in Kenya by Juergen Griesbach Training Materials Coordinator


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Propagation


Mangos are propagated either vegetatively or by seed. Seedlings are grown sometimes to produce new cultivars but mainly for use as rootstocks or to reproduce known polyembryonic cultivars. Mono-embryonic types, however, require vegetative propagation to retain all of the desired characteristics. It is also known that trees grafted on selected rootstocks remain smaller than the rootstock, and bear better and earlier.

The selection of suitable rootstock is as important as the selection of the scion cultivar. It has a strong influence on the growth, yield, fruit maturity and soil adaptability, among other things. In Kenya, the uniform seeds of the polyembryonic cultivars Sabre, Peach and Dodo are routinely used successfully. Seeds must be taken from ripe fruits and should be as fresh as possible at the time of planting. Before planting, the hard woody endocarp should be removed to examine the seed for disease or any damage caused by the mango weevil (Sternochetus). Freshly sown seeds should be protected from high temperatures and dessication by providing shade. Once seedlings emerge the shade is removed to harden the plants and produce a sturdy stem for grafting.

Once the seeds have germinated, the seedlings are carefully lifted and culled. This may be about one month after planting when they have reached the 3-5-red-leaf-stage. After transplanting the seedlings into containers not smaller than 18 x 35 cm they remain there until they are of pencil thickness at about 20 cm above soil level. There are many techniques used to graft mango seedlings, but the most common methods are side-graft, side veneer and wedge- and whip-graft. A mango tree must never be transplanted while it is flushing or when the leaves are still tender; the best time to transplant is after the second flush has hardened.

The top-working of fruit trees is a normal orchard practice and is necessary to replace old cultivars/seedlings with improved selections which are developed from time to time. Top-worked trees will start bearing within 2–3 years, i.e. much earlier than a newly planted tree. Furthermore, the survival of newly planted trees is not always guaranteed (drought, fire, animals, etc.).


Establishment


Mango is successfully grown on a wide range of soils. The trees do well in sandy soils at the coastline as well as on loam, black cotton and even murram soils at other elevations. The essential prerequisites for good development of the trees are deep soils (at least 3 m), appropriate rainfall (500–1000 mm), good drainage, suitable altitude (0–1200 m) and preferably a pH value of between 5.5 and 7.5. The tree itself is not difficult to grow and, once well established, is relatively tolerant of drought, occasional flooding and poor soil condition. Irrigation in the first years after planting promotes flushing (and suppresses flowering), so that tree size increases quickly. Irrigation also widens the scope for intercropping, for example, with papaya, banana, pineapple or vegetables, during the establishment phase. When the trees are big enough to produce a substantial crop, irrigation is stopped, or at least interrupted long enough to impose quiescence leading to flower initiation.

Among the various climatic factors, temperature, rainfall and humidity have a greater bearing on mango production than irrigation and soils. Furthermore, the production of high quality mango fruit does not depend so much on elevation but on the range of temperatures available. The two important considerations for mango cultivation are a dry period at the time of flowering—in Kenya mainly during the months of August to October—and sufficient heat during the time of fruit ripening. For optimum growth and productivity, 20–26°C is believed to be ideal. Temperatures exceeding 40°C may, especially in hot/dry areas, lead to sunburn of fruits and stunting of tree growth. Although not very impressive, mango trees of selected cultivars like Sabre and Peach have been observed at elevations of up to about 1900 m. However, for more successful crops areas below 1200 m should be considered.

The amount of rainfall in a given locality is not as important as its intensity and distribution. Rainfall of 500–1000 mm at the right time of the year is sufficient for successful cultivation. However, the mango cannot do well in areas which experience frequent rains or very high humidity during the flowering period. Such conditions are not conducive to good fruit set and they increase the incidence of serious diseases like powdery mildew and anthracnose. Anthracnose can be a major problem as the same organism occurs on avocado, coffee and papaya. Powdery mildew is quite common when low temperatures accompany high humidity (see Appendix 2).

Since the mango is a long-lived perennial, the planting distance usually depends to a large extent on the vigour of the cultivar/rootstock and on the environment. Most orchards (either solely mango or a few trees on small farms) are planted too densely and trees are forced to grow upright and tall. Overcrowding results in the production of fewer fruits which are apt to be poorly coloured and infected with diseases. Tall trees also present a harvesting problem and create difficulties during spraying and pruning. Normally, grafted trees are spaced at 8 x 10 m or 10 x 12 m, though at the coast seedlings require 12 x 14 m. Intercrops of short-lived fruit trees such as papaya or annual crops could be used for better utilization of land in widely spaced young plantations.


Maintenance


Mango plants should develop into strong well-shaped trees within the first 4 years and do not require pruning unless there are excessive branches or the shape is unusual. Depending on the cultivar and growth pattern selective pruning of branches may be required to encourage growth of lateral branches and to ensure development of good tree architecture for future fruit bearing. Any branches on the trunk lower than one metre from the ground should be cut. In later years, pruning is done mainly to remove diseased and/or dry branches or those touching the ground or crowding others. Grafted trees tend to flower from the first year, and the formation of fruit on year-old mango trees is nothing exceptional. Flowering at this early stage and especially early bearing weakens young trees and often damages them severely. Therefore early flowering has to be avoided by removing the inflorescences; only from the third or fourth year should trees be allowed to bear fruits.

A general criterion regarding mango nutrition is that care must be taken not to over-fertilize thereby promoting vegetative vigour at the expense of flowering and fruit set. This is particularly true for nitrogen application since trees are subject to fertilizer burn. Correct fertilizer requirements can only be determined by means of leaf and soil analyses taken in different agroclimatic regions. With trees in fruit, proper timing is critical and it is recommended that fertilizer be applied just after harvesting, during the rains. In general, a tree at full bearing age (7 years and older) needs about 1.5 to 2.5 kg of Calcium Ammonium Nitrate (CAN) (26%); 2.25 kg superphosphate and 0.75–1.5 kg potassium chloride per year, or the equivalent inputs from manure or compost for small-scale farmers. These quantities can be supplied either at one time or may be split into two doses administered with a two-month interval between them.

Orchards should be kept clean, especially under the canopy of the trees where the fertilizer is spread uniformly in a circular belt around the drip line. This is the zone where the most absorption roots are located.

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