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Mango Growing in Kenya by Juergen Griesbach Training Materials Coordinator


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Mango Seed Weevil


The weevil, Sternochetus mangiferae (F), is a common pest in Kenya and can be found in all local mango-growing areas. It is spread mainly by transportation of infested fruits since the weevil develops within the mango seed and can therefore be transported easily from one locality to another unnoticed. The mango weevil does not usually damage the fruit and consequently is not a serious pest as far as local consumption of the fruit is concerned. However, this pest hinders the development of a fresh fruit export market because the leading import countries in the Middle East and other places maintain strict quarantine regulations.

Infestation symptoms are most obvious within the seed where the weevil largely completes its life cycle. Here all stages of the insect development—larvae, pupae and adults—can be found. Externally the affected fruits appear normal, but very often are rotting from inside.

The female usually lays her eggs over a period of 5–6 weeks on fruits before these are half-grown. The hatching period is 3–5 days. The young larvae penetrate the fruit and eat their way to the seed where they feed and develop into adult weevils. These emerge from the stone by tunnelling outwards through the flesh and skin of the fruit, leaving an unsightly patch where rotting soon sets in. Once the weevils have left the fruit they search for a hiding place such as beneath loose bark of trees or in waste material under the trees where they spend the time of the year that is unfavourable for them.

To date, chemical control measures against this pest have not proved economical. However, implementing the following three steps will definitely reduce the weevil population in the orchard.


Sanitation of orchard and yard

The biggest source of infestation is dropped fruits or seeds lying around in which weevils can survive up to about 300 days. Therefore, regular removal and destruction of waste material up to the end of the harvesting period is very important and effective.

Treatment of trunk and branches

The most suitable stage for control is during the emergence and oviposition of the adult weevil. The first step to suppress the weevil population is implemented at the beginning of the mango flowering season by using preferably long-lasting contact insecticides such as Azinphos, Endosulfan, Malathion and Fenthion. It is important to thoroughly wet (by spraying) the bark of the trunk and scaffold branches or brush the insecticide mixed with a suitable carrier on to the bark.


Fruit treatment


After fruit set, carry out spray treatments mainly focussed on single fruits using Carbosulfan, Malathion, Azinphos etc. mixed with a spreader/sticker liquid. Repeat applications at intervals of 2–3 weeks and combine this with the control of anthracnose.

The mango is usually attacked by three to four key pests which require annual control measures. However, there are a number of occasional pests which may become troublesome only in localized areas or because of the occurrence of unusual circumstances. These pests include mites, thrips, scales, cecid fly and mealybugs.


Powdery Mildew


The disease powdery mildew, caused by the fungus Oidium mangiferae, is a serious problem in all mango-growing areas in Kenya. Infections can result in complete crop loss and defoliation of trees. The disease favours cool and cloudy weather but also occurs in warm and humid climatic conditions. It attacks leaves, buds, flowers and young fruits. Infected tissues are covered with a whitish, powdery growth of the fungus. Mature spores are easily blown away by wind and produce a fresh infection, or they may remain dormant during the unfavourable season awaiting optimum germination conditions in the next season. Spraying 3–5 times at 10–14 day intervals from the onset of flowering until fruit set can control powdery mildew. Several chemicals are recommended and have been used to control the disease. These include Benomyl, Pyrazophos, Triadimefon, Bupirimate, Triforine and sulphur, all mixed with a spreader/sticker.

Cultivars treated for powdery mildew in this way show remarkable increases in fruit set ranging from about 40% to more than 500%. The input costs of the spray applied per tree are justified as they are recovered fully by increased returns.

Finally, as already mentioned, all mango cultivars are susceptible to powdery mildew infestation to some extent. The range of resistance (with Sensation being the most resistant) could be: Sensation, Chino, van Dyke, Tommy Atkins, Sabine, Kent, Keitt, Gesine, Batawi, Apple, Ngowe, Haden, Maya.

Description of Mango Cultivars

Alphonso


Also known as Appus, Badami, Gundu and Khader. This cultivar originated in Maharashtra State (India).

The fruits are orange-yellow in colour, medium-sized and oval/oblique in shape. They average 11.6 cm in length, 9.3 cm in width, and weigh 300–450 g (mean: 390 g). The skin is thin and smooth. The flesh is firm to soft, low in fibre, yellow, sweet, has a pleasant taste and is of good eating quality. The seed is mono-embryonic in a large, woody stone. The fruit matures in early to mid-season.



The tree is moderately large and vigorous with a broadly rounded dense canopy. It tends to have irregular bearing, but otherwise yields are medium to heavy.



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