Mango: Pests, Diseases & Disorders

Mango is one of the finest fruits of the world with a great market value. India is the leading producer of mango fruits but I sometimes mango industry is highly endangered in India because : of certain insect pests, diseases and physiological disorders. Because of these maladies this is a great loss to the nation in itself. This booklet deals elaborately with all the entomological, pathological and physiological problems of mango, along with their suitable control measures. Care has been taken to make the language simple and interesting.

I. Introduction

Mango is the most ancient among the tropical fruits and is believed to have originated in the Indo-Burma region. 1t is in cultivation for more than 4000 years. It is the most popular and choicest fruits of India and occupies a prominent place among the best fruits of the world. It is a good source of sugar, vitamin A and C, calcium and phosphorus. Mango fruit is considered to be an esteemed item of diet through the ages and the tree has been a subject of great veneration. This was not due to any blind faith or sentiment but because of the economic importance of the fruit. The mango tree is a part and parcel of Indian heritage and culture.

Besides giving shade against the scorching sun, it provides valuable timber, fuel and fodder. Fruit.. are put to multifarious uses right from the first stage of development to maturity and ripening stage. No oilier fruit can be put to so many diversified uses in the form of processed product as the mango. Therefore, it is aptly acknowledged as the king of fruits in India.

The mango is the third largest tropical fruit after banana and citrus in terms of acreage and production of the world. However, in India, it is the major fruit crop. It is greatly relished for its succulence, exotic flavour and delicious taste. It enjoys the same popularity in the tropics as apple in the temperate region. India is the largest producer of choice table varieties of mango in the world. More than 1000 Mango varieties are under cultivation in India, each differing in shape, size and taste.

Although, India has been traditionally the major producer of mango in the world, yet it occupies only fourth position in the world export market of mango, Philippines being the first. We have got two excellent mango varieties with high export quality. These varieties are Dashehari, grown in north and Alphonso in south India. Still, we lag far behind in the world export market because our mango production is beset with several problems; such as insect pests, diseases and physiological disorders being major ones. These  constraint, not only reduce our total production but also badly hamper the fruit quality. Therefore, to obtain higher mango production, utmost attention must be given to solve these problems. Some important insect pests, diseases and physiological disorders of mango along with their possible control measures are discussed here.

II. Insect Pests

Several parts of mango plant, including the fruit, are attacked by a variety of pests, when some of these assume a virulent form, there may be even a complete crop failure. Among the various pests, those of particular importance are the hopper, mealy bug and termites.

A. Mango leaf hopper (Amritodus atkinsom)

This is also known as Aam ka chenpa, pharka, Iassi, thala, tela, etc. in different parts of India. This pest is prevalent during the flowering season, when it multiplies in large number and proves devastating to the crops. Due to recurrent annual damage by hopper some orchards fail altogether to blossom. The damage is caused by both adult hoppers and their nymphs which suck the sap of new shoots, buds and flowers resulting in drying of the entire inflorescence and even small fruits. Nymphs cause more damage than the adults. They also secrete a gelatinous substance called honey dew which interferes with the respiration process of leaves. The heavy infestation of pest usually occurs periodically after every three or four years and that is why the pest is known as the periodic insect pest attack starts from end of March arid continues till the end of June. The old trees arc more intensively damaged than the newly planted ones.

Control

1.The plants should be planted at a proper distance and old orchard should be open to maximum sunlight by giving proper pruning to the trees.

2. The pest can be satisfactorily controlled by spraying DDT @ 2.5 g in 1 litre water on the infested trees during February and March with the help of a suitable power sprayer which can spray upto 7.5 to 9 metres. Spraying with 0.05% Malathion i.e. (500 mg in 1 litre water) (50% Malathion plus 50% Chlordane) or Endosulfan 35 EC or Carbaryl 50% W.P. is also effective against this insect

B. Mango mealy bug (Drosicha mangiferae)

The mango mealy bug is responsible for devastating the crop during its serious incidence. It is not as widespread as mango hopper. It is easy to recognize by its large flattish and plump females, which are covered with a white meal.

The pest is found all along the Indo-Gangetic plains. It also attacks a wide variety of other trees including jackfruit, fig, guava, papaya, citrus, pomegranate, litchi etc. The damage is caused by the nymphs of both sexes and female adult which suck the sap from : the twigs, fruits and flowers. As a result, flowers dry up and only few fruits are set. The fruit bearing twigs become so weak that even with the slightest jerk, either by a bird or wind, the fruits will fall down. They secrete honey dew which attracts fungus due to which black spots may be seen on twigs and shoots. The attack is much more serious during the spring when the twigs or shoots are richly supplied with cell sap. The attack persists from November to April- May and by that time the insect changes into adult.

Control

1. Raking the soil around the base of the infested tree so that egg masses are exposed to the sun and are killed by the heat during May-June.

2. Application of sticky band around the tree trunk so as to check the nymphs from crawling up the trees (4 parts castor oil plus 5 parts resin) 1/2 to 1 m above the ground level during the second week of December. It remains effective for a period of two weeks after which it should be replaced with a new preparation.

3. Methyl parathion 2% or 5% Aldrin dust may be spread in the soil around the tree trunk in 1 m diameter and also on the trunk up to the height of 1 meter.

4. To kill the nymphs which are on the tree, anyone of the following insecticides may be sprayed ,in a tree after mixing in 15-20 litres of water.

a.    Phosphamidon 100 EC -6 ml

b.    Malathion 50 EC -50 ml

c.    Endosulfan 35 EC -20 ml

d.    Formothion 25 EC -30 ml

C. Mango stone weevil (Sternochetus mangiferae)

This is quite a peculiar pest which makes a tunnel inside the ripe fruit, thus destroying it. The adult of this insect is short. thick- set weevil, dark brown in colour. The weevils remain active for a very long period in a bark either in the natural crevice or in a hole prepared by it. The adults have been found throughout the years on the trees. They are also found in the soils of mango orchard. They lay tiny white eggs on mango flowers or young fruits or under the rind of the ripening fruits. The incision made by the insect for laying the eggs heals, and the outward appearance of the fruit seems to be sound though the insect is seen in the fruit

Control

1. Proper disposal of mango stones and fallen fruits should be done. General cleanliness and destruction of weevils on the bark during August should be undertaken.

2. The infested bark should be washed with kerosene emulsion.

3. It has been discovered that the insect inside the seed stone gets killed by dipping the fruits in hot water at 50'C for ; two hours.

D. Bark eating caterpillars (lnderbela quadrinotata and I. tetranois)

Fruit trees are damaged to a considerable extent by the bark eating caterpillars, which attack trees of all ages, particularly the older ones, lowering their vitality. When severely infested, the entire branch or tree may die.

The pest attack is characterized by the presence of long-winding, thick, blackish or brownish ribbon like masses composed of small chips of wood and excreta. The caterpillar bores into the bark of the trees and remains in the tunnel. By continuously devouring the tissues, il tunnels through the stem and branches. The injury weakens 'the stem, resulting in drying of branches and finally of the tree Itself.

Control

1. The main feature which should be fully exploited for its control is that its presence can be easily Spoiled out even from the distance due to the prominent web it makes. Hence, the rational approach is to clean the web and fumigate the hole with an ordinary fumigant like carbon disulfide, chlorosal or even petrol by putting in the hole with help of cotton.

2. The caterpillars  can be killed by inserting an iron spike into the tunnels.

3. This insect has also been successfully controlled by injecting ethylene glycol and kerosene oil in the ratio of 1:3 into the tunnel by means of syringe and then sealing the opening of tunnel with mud.

4. As a preventive measure spraying of the attacked trunk and branches with 0.25% D D T emulsion or 0.1 % Parathion emulsion, is effective.

E. Fruit flies

The fruit flies of vegetables are important pests of mango. A ': high percentage of ripe mangoes in important mango growing areas is rendered unfit for consumption by the maggots of these fruit flies. They cause dark punctures in the fruits for oviposition from June to August. Later, a brownish rotten patch makes its appearance on the surface of the attacked mango fruits with the characteristic oozing of fluid after the maggots have eaten the pulp. The fruits ultimately drops when the maggot comes out and enters the soil for pupation.

Control

1. Collection and disposal of fallen infested fruits and the infested soil should be removed. Undersized fruits left on the tree should be picked and destroyed. If the trees are few in number, bagging the fruit with cloth or paper bags can be resorted.

2. For the destruction of adult flies assembling under the leaves of fruit trees during night, application of suitable spray namely dilution of eight times of diesel oil emulsion (diesel oil 4.5 litres, soft soap 0.45 kg and water 4.5 litres) is recommended.

3. Heavy application of dust and sprays of Pyrethrum or DDT or BHC etc on the tree considerably reduces the infestation of adult flies.

4. The flies can also be controlled by bait sprays Carbaryl (0.2%) plus protein hydrolysate or molasses (0.1%) beginning at egg laying stage.

F. Mango stem borer (Bactocera rufomaculate)

It is a very serious pest of mango. It attacks the main trunk and branches resulting in their complete drying. The borer is the grub of a large, stout, long homed beetle. The insect is found throughout India.

External symptoms of attack are not always clear. It takes place either at ground level or at roots. The infested trunk or branches become hollow and break down very easily.

Control

1. The infested branches should be cut and the grubs inside be killed.

2. The adult beetle should be destroyed with kerosene-oil, petrol, crude oil, naphthalene or tar and water, which should be injected into these tunnels by means of a syringe and the holes are plugged by means of a syringe and the holes are plugged with cotton wool soaked with carbon disulfide and chloroform and the holes should be closed with clay.

3. It can also be controlled by one or two sprays of Carbaryl (0.2%) or Nuvacron (0.04%) during the emergence period of vegetative flush.

G. Termites

Termites are not the primary agents responsible for any damage to the mango trees. They generally find access to the trees when they are in weaker conditions due to some other causes.

The principal food of the termites is fibrous material (cellulose). The worker termites feed on root", shoots and trunks of the mango tree which sometimes dries up if the roots are severely damaged. The earthen galeries form  a safe passage, which go on destroying the bark and tissue within these galleries.

Control

1. For the control of termites, dusting with 5% BHC or 5% Aldrin or 6% Heptachlor dust at 22-27 kg/hectare in soil around infested plants is carried out

2. Orchards should be kept clean and free of all refuse or unwanted vegetation. All the dead and decaying wood, whether on the tree or on the ground should be regularly removed. Liberal application of finely ground mahua cake followed by irrigation helps to drive away the termites.

H. Red ants

These are widely prevalent in mango growing areas allover the world. They cause damage to the mango trees indirectly, that is, they render the new leaves useless for photosynthesis as they are molded together in the form of a nest by a silken substance excreted by the larvae. Also these nests serve as distribution centres for various kinds of scales and mealy bugs both living and dead, on which they feed.

Control

1. The red ants can be effectively controlled by destroying the nests or by putting in lead arsenate in the nests @ 1/2 teaspoonfull.

2. The affected trees can be sprayed with Endrin (0.02%) or Dieldrin (0.03%) to keep these ants in check.

IV. Diseases

Mango is affected by a number of diseases. These may be incited by fungi, bacteria, flowering parasitic plants, etc. Some of them are responsible for serious losses while others are of minor importance. The intensity varies in different regions where mango is grown and depends on the climatic conditions. Though mango is a hardy tree, several diseases have been recorded particularly those affecting the flowers and fruits. Besides the damage to the fruits on the tree, rotting of fruits in transit and storage is also common. Important diseases are described below along with the measures to prevent or control them.

A. Anthracnose

Causal organisms: Glomerella cingulata, Colletotrichum gloeosporiodies, Gloeosporium mangiferae.

Anthracnose of mango is prevalent in many countries where mango is cultivated. In India, it is one of the limiting factors in mango production in Bihar, Punjab, Maharashtra and Kerala. It occurs in other states also but the damage caused is less. Its incidence is influenced to a large extent by the climatic conditions. High humidity, frequent rains and a temperature of 24-32.C at the time when the young shoots or flowers or fruits are produced, are very favourable for its large scale infection and damage. Hence, the intensity of the disease is more on the west coast.

The disease appears on young leaves, stem, inflorescence and fruits. Leaves show oval or irregular greyish ,brown spots which may coalesce to cover larger area of the leaves. Consequently, the development of the affected leaves is hampered and they dry and shed off. On young stem, grey brown spots develop. These enlarge and cause girdling and drying of affected area. Often, black necrotic I areas develop on the twigs from the tip downwards causing a dieback.

In humid weather, minute black dots develop in the floral organs. The infected flower parts ultimately drop resulting in partial or complete deblossoming. When the incidence is light a few fruits may set. The tender fruits may themselves be attacked. These turn black and fall off. Maturing fruits are also infected. Black, round or irregular, sometimes shrunken spots are formed on the skin or bark tear stains may develop. As the fruits ripen, these may extend over the whole surface accompanied by the softening and rotting of the fruits.

All the varieties of mango are not equally susceptible to this disease. In Kerala, the damage in Neelum is heavy. Many other varieties and seedling trees whose fruits ripen at the outbreak of monsoon (in May -June) are also infected.

Control

1. The fungus survives on dead and dried twigs, therefore,  they should be pruned/cut and burnt as soon as possible.

2. The disease can be controlled by spraying Bordeaux I mixture (3:3:50) Blitox or Phytolan (0.3%), Bavistin or Benlate (0.1 %), thrice a year (i.e. in February, April and September).

3. Affected full grown fruits should be dipped in hot water (51.C) for 15 minutes before storage.

B. Powdery mildew

Causal organism: Odium mangiferae

Powdery mildew is a common disease of mango and is prevalent in many countries. In India, it is common in U.P, Maharashtra, Andhra Pradcsh, Mysore and Madras.

The disease usually occurs during December to March, but at elevation of 620 m to 1,240 m above sea level, it may persist for longer period. At lower elevations i.e. in plains, the infection is confined to the inflorescences.

A white superficial powdery mass of fungus growth covers the leaves, the stalks of the panicles, the flowers and tender fruits. The powdery mass consists mainly of fungal spores. The mildew affects the flowers before fertilization and the fruits in their earliest stages. The affected flowers and fruits drop prematurely, reducing the crop considerably or preventing the fruit set. Rain and mist accompanied by cool nights during the flowering period, favours the development of the disease. At higher altitudes, the infection extends to the young leaves and twigs which are covered by the white powdery fungal growth. Shedding of infected leaves may also occur.

Control

1. The most effective method of control is by dusting finely powdered sulfur on the flowering branches. More than one round of dusting will be necessary. The first round should be given before flower opening. This will be followed by two or more rounds at fortnightly interval.

2. It can also be controlled by the application of Kemthane (0.1%) or Bavistin (0.1%) or Benlate «0.1%). The spray should be given before the flowering, as a preventive

measure.

3. Along with mildew, hopper insects are also found to infect the panicles in many parts of India. In order to control hopper and mildew together, a formulation containing 5% DDT and 50% sulfur, sold under the name of Gueserol 405.50 has been used with great success in many orchards of Tamil Nadu, Andhra Pradesh and Maharashtra.

C. Sooty mould

Causal organism: Caponodium spp.

This disease is of common occurrence in India and Israel. Actually, sooty mould in itself is not a disease. The mango trees with the infestation of scales or hoppers leave honey like exudates on leaves, on which the moulds causing blackening develop. Dry, black encrustation contains innumerable fungal spores, which arrest the photosynthetic process in the leaves resulting in leaf shedding and weak trees.

Control

Spraying of orchards with Nuvacron @ 1.5 ml/one litre of water or Metasystox @ 1 mI/ litre of water or Phosphomidon @ 1 ml/4 litres of water, control hopper and scale insects population during January-April which ultimately prevents sooty mould infection followed by sprays with Blitox @ 3g/1itrc of water.

D. Pink disease

Causal organisms: Botryobasidium salmonicolor, Pellicularia salmonicolor, Corticium salmonicolor.

Pink disease affecting the branches or trees is destructive in few states like Andhra Pradesh, Madras and Kerala. Humid condition favours the spread of infection. It mainly occurs from May 10 November. Portions of the bark die off and separate in flakes from the wood. This may occur on one side of the branch or all around. The disease appears as pinkish powdery coating on the stem. The pink colour represents profuse spore production by the fungus. The pathogen invades the cortical tissues and interferes with the transport of the nutrients. Shoots and branches of the affected trees wilt and dry up and the leaves shed away.

Control

1. The disease can be checked by cutting away the infected branches and protecting the cut-wounds with Bordeaux paste (copper sulphate: lime: water in the proportion of 1:2:16-20).

2. Another formulation useful in treatment of the disease is a paste made up of one part of finely powdered copper sulphate, two parts of freshly slaked lime and three parts of boiled linseed oil. The two powders are mixed first and then the oil. The resulting paste sticks well and is not easily washed off by rains. Timely use of this fungicide will protect the branches from the attacks.

E. Bacterial canker

Causal organisms: Pseudomonas mangiferae

This disease is also called bacterial leaf spot disease. The earliest symptom is the formation of small dark green water soaked spots which finally assume the shape of a raised black spot. These areas on the fruits develop longitudinal cracks and gum starts oozing out from the splits. Seriously affected fruits drop down and the yield is reduced since affected fruits are unattractive and unmarketable.

This disease is widely prevalent and the infection increases with recurrent rainy weather. However, all the varieties are not affected equally. The varieties Neelum and Banglora are more commonly affected. This is rarely encountered in Dashehari. The varieties Alphonso and Bombay green are reported to be quite resistant. In rainy weathers the incidence is not noticed.

Control

1. Although no satisfactory control measures are available as yet, Bordeaux mixture (4:4:50) may be applied at fortnightly interval from the first appearance of the disease on the leaves.

2. Recently, two sprays of Streptocycline (200 ppm) have been found to be helpful in reducing the incidence of this disease.

3. Field sanitation and seedling certification as preventive measures and seedling branches and fruits are reported to  minimize the infestation of this disease.

V. Plant Parasites

These plant parasites can be divided into two groups, namely, (I) phanerogamic parasites and (2) epiphytes.

I. Phanerorgamic parasites

Flowering plants belonging to the family Loranlhaceae parasitise mango in India and other countries.

These parasites grow on the branches of the trees, especially  in neglected orchards or on trees planted in roads and avenues. Viscum is attached to the host at one point from which &.several shoots originate , bearing leaves, flowers and fruits. In Loranthus, the stem creeps along the stem of the host and is attached by peg-like growth al several places. It forms a much more bushy growth. At the point of attachment, haustoria (food sucking organs) penetrate into the tissues of the host for the absorption of food materials.

The damage caused will depend upon the intensity of the infestation. Though the parasites have green leaves, a large amount of nutrients is removed from the host resulting in the cessation of growth of the affected branches. The branches may lose their foliage I and dry up. Reduction of the crop and progressive deterioration of the trees result.

Control

1. Satisfactory method of control consists of cutting away the affected branches below the point of attachment of the parasites, or the complete removal of the parasite along with the suckers. Periodic inspection of the trees and removal or parasite at early stages will result in better control.

2. Spraying or injection of some chemicals like copper sulphate, 2,4-D (2,4-dichlorophenoxy acetic acid) etc, can also be tried.

2. Epiphytes

In regions receiving 200 cm or more of annual rainfall, numerous flowering plants, ferns, mosses and lichens grow on the stem of the mango. The higher the rainfall, the more of such growths occur. Lichens may be seen on the leaves also. They use mango as a support only and do not draw any nourishment from it. Though they do not cause any material damage to the growth, they are likely to harbour other parasitic organisms and harmful insects. Therefore, they are disliked by the farmers.

Control

Their growth can be arrested by brushing the trunk. A lime wash may serve the purpose. Attempts to remove them by some chemical treatment will not be economical.

VI. Physiological Disorders

Physiological disorders of mango are largely responsible for the low productivity of mango in India. Horticulturists have yet not been successful to find out a suitable treatment for a few of them. Below are discussed some important physiological disorders of mango along with their possible control measures.

A. Mango malformation

This disorder was first noticed in the Indian sub-continent towards the end of the last century. Now it is known to occur in the Middle East, Africa, Israel, Central America, Egypt, Mexico and the U.S.A. It is of very serious nature and brings down the productivity of mango to a considerable extent. During the last two decades or so it has assumed an alarming magnitude particularly in North India. It is of wide occurrence in Punjab, Delhi and U.P. Its incidence is also noticed to some extent in Bihar, West Bengal and Orissa.

The intensity of this disorder varies from year to year and variety to variety, the highest being in the varieties of 'Chausa' and 'Bombay Green', that is up to 90 per cent. The only variety known to be free from floral malformation is Bhadauran which, on the other hand, is very inferior in fruit size and fruit quality.

Mango malformation is of two types, viz (i) vegetative malformation and (ii) floral or inflorescence malformation.

The vegetative malformation is more common on the nursery seedlings and younger plants. The shoot gives the appearance of "witches broom". This stage is also known as bunchy top. In the case of floral malformation, abnormal development of inflorescence takes place. There is partial or complete suppression  of flowers by the formation of small leaves or rudiments and the complete inflorescence looks like "witches broom", Studies conducted at the Division of Horticulture, IARI, new Delhi since 1966 have revealed that the floral malformation of mango is broadly of three types i.e. light, medium and heavy, The heavy type of infestation is most damaging because of its failure to set any fruit Such panicles are characterized by a condensed mass of flower buds which are largely male. These panicles show the suppression of apical dominance and have a tendency to hang on the tree around the year. In the light and medium type of malformation, flowers of both sexes are present in the panicle and some fruit set can also be seen, though it is rare. In such cases, it is not uncommon to find a part of the panicle normal whereas the other portions are malformed.

The complexity of the disorder is attributed to a set of factors including pathological, viral, nutritional and physiological aspects. During the 'sixties, the association of fungus (Fusarium monoliniformae) with malformation was reported. Later, emphasis on the role of mite (Aceria mangiferae) as a carrier was laid. Contradictory results were also reported on the transmission of this disease through grafting techniques. It was also felt by some scientists that the tendency of malformation was due to the feeding injury caused by mites but the elimination of insects and miles with insecticides and ascaricides could not bring the satisfactory resuIts.

Many workers attributed the cause to be viral in nature too. Although nutritional deficiency was related with malformation, a remedial measure could not be ascertained. Biochemical status between healthy and malformed panicles have been reported to be at different levels. Malformed panicles exhibit high level of carbohydrate and nitrogen (C/N ratio), liquids and phenolics, amino acids, nucleic acids and proteins, and enzymes. Malformed panicles are also characterized by a relatively high level of gibberellins and cytokinin like substance in different cultivars of mango. A number of scientists have believed hormonal imbalance as the cause of malformation. The release of certain compounds like mangiferin and malformin have been reported to playa major role in mango malformation. These compounds are in higher concentration in Fusarium infected plants and are presently supposed to be the cause of mango malformation.

Control

The problem has been under investigation for a long time and definite measures remain to be evolved to eradicate the malady  effectively. However, the following measures may reduce the disease incidence considerably.

I. In areas with less than 5-10 % infection, diseased plants, trees or plant parts should be destroyed.

2. Certification of plants used for propagation by nurseries ! be made compulsory i.e. farmers should purchase only certified plants.

3. Broad spectrum pesticides should be used. Encouraging results have been obtained with Benomyl and Aphiden.

4. Diseased tissues be pruned (removal of malformed terminals along with the basal 15-20 cm apparently healthy portion).

5. The most effective control measure is the spray of 200 ppm of NAA (naphthalene acetic acid) in the month of October followed by deblossoming at bud burst stage can bring down the malady to a great extent.

6. The soil and water management in the orchards should be carried out properly and timely.

B. Irregular bearing in mango

This is one of the most burning problem of mango cultivation as it renders mango cultivation less remunerative to growers. A year of good crop may follow one or more years of poor crop or no crop at all. It has been reported that in Maharashtra there is one good crop in three years and in Bihar one in six years. However, there is no hard and fast rule about this erratic bearing trend in mango.

Nevertheless, cultivars like Totapari 'Red small', Neelam, Bangalora and Rataul do not show acute tendency of biennial or irregular bearing but these varieties are grown only in southern India and do not have superior fruit quality like that of north Indian varieties.  The bearing rhythm sets even from its early stages of fruiting and become apparent at the age of 10- I 2 years. This indicates that biennial bearing habit is of genetic nature. Some varieties like Langra, Bombay and Dashehari have a stronger tendency which is very difficult to control while others like Himsagar and Safadar Pasand are less alternate bearing. These varieties bear fruits every year except a few branches which bear later.

In case of irregular bearing varieties of mango, when laden with fruits, they do not produce new shoots. Even if after harvesting new shoots are produced, they are negligible in number and do not flower in the coming year. In the months of March-April of the following year new shoots are produced which flower only in the next year and, as such, biennial bearing occurs.      

The problem of biennial bearing has been studied in great depth by a number of workers during the last four decades. Several aspects like climatological factors, age and size of shoots, C/N (carbohydrate/nitrogen) ratio and hormonal balance have been studied. The importance of shoot growth was emphasized by many workers and the new flushes gave rise to reproductive ones, only after attaining the physiological maturity of 8-10 months. Seasonal changes in the j level of carbohydrate and nitrogen in the shoots formed another criterion. However, any relationship between flower bud initiation and nitrogen content could not be obtained. Nutritional deficiency i was also suggested as one of the cause. Indirect evidence from various experiments indicated the role of flower inducing hormone in mango. Flowering in mango has been tried externally by the application of auxins, anti-auxins, gibberellins and growth retardants.

The distinct difference in the bearing behaviour of the regular and biennial bearing varieties leaves hardly any doubt that the problem is an inherent one and the lasting solution can only be obtained through genetic engineering.

Control

The biennial bearing problem has been a major bottleneck in the expansion of mango industry in India. The growers have to split the profits of an 'on' year into two in order to lake care of the off year. Also, because of glut in the 'on' year, the price offered to the orchardist is less remunerative. During an 'off year or an year of low production, the consumer too has to pay an exorbitant price for the fruit. Therefore, this problem has posed a major challenge to the horticultural scientists during the last seven decades. Consequently a number of remedial measures have been proposed.

1. Proper upkeep and maintenance of the orchards i.e. a proper cultural schedule is of paramount importance for maintaining fruit trees in healthy and disease free conditions, and thereby obtaining better plant performance.

2. Shoots should be deblossomed in the 'on' year. These shoots will put forth panicle in the 'off year and a good crop may be harvested.

3. Flowering in 'off year can also be induced by smudging. Smudging in mango is carried out by building slow fires, emitting smoke under mango tree. Similarly, application of Ethrel can also induce flowering.

4. Recently, some scientists have recommended the grafting of Dashchari or Tolapuri on 'off season flowering varieties like "Royal Special". This induces flowering in these varieties in off season.

5. The safest way to overcome or avoid the losses of biennial bearing in mango is to cultivate regular bearing varieties like Amrapali, Mallika, Manjirn, etc. These varieties have been released recently and are prolific bearer, have good fruit quality and fit for high density orcharding, i.e. (larger number of trees can be accommodated per unit area).

C. Black tip or mango

This malady is widely prevalent in Punjab, V.P., Bihar and West Bengal. It causes considerable economic set back to the mango growers. Among the commercial cultivars, Dashchari is the most susceptible to this disorder, while Lucknow Safeda is the least.

Fruits are affected at the marble stage with a characteristic yellowing of tissues at the distal end. Gradually the colour intensifies into brown and finally black. At this stage, further development is retarded and the black spot at the tip gradually extends towards the upper part of the fruit. Such fruits prematurely drop off and become  unmarketable.

As regards factors responsible for this malady, it is a general observation that orchards located in the vicinity of the brick kilns are more severely affected by the black tip. Majority of the reports indicate that fumes of the brick kilns are the causal factors. An inverse relation between the incidence and the distance of orchard from the brick kilns has been found. The direction and velocity of the wind also playa significant role in determining the intensity of the malady. For instance, orchards situated on the eastern side of the kilns arc more vulnerable to the disorder.

Possibly, gases like carbon dioxide, sulphur dioxide and acctylene which constitute the brick kiln fume are responsible. Affected fruits are also deficient in boron. The disorder can be avoided by allowing brick kiln only at a distance of 1.6 km or 1 mile in the cast and west, and 0.8 km in the north and south of the orchard, taking into consideration the usual wind direction during the fruiting season. The chimney height should also be increased to at least 15-18 m to minimize the damaging effects of the smoke in the orchard.

2. Soil application of 500 g Borax or 1% Borax i.e. (10 g in 1 litre water) spray, at the time of fruit set reduces the 1. j : incidence considerably.

3. Varieties less prone to the disorder should be preferred. '

D. Internal necrosis of mango

This disorder is quite distinct from that of black tip in mango. During the initial stages, water-soaked brownish areas on the fruits are evident, which gradually coalesce to form dark brown patches on the external surface. At this stage exudation of gummy substance can also be seen. The lower part of the affected fruit turns brown, sometimes black with corky and leathery skin. At times, external symptoms on fruits are not visible and such fruits are characterized with necrotic seeds and cracks. These fruits are normally not retained by the trees for a longer period and drop off before attaining the  physiological maturity.

Control

This disorder can be corrected by soil or foliar application of boron. For soil application, Borax @ 500 g per tree should be incorporated at the time of October fertilization. Foliar application of 1 % borax is recommended at the time of fruit set (pea size stage) followed by two more sprays at 10-15 days interval which will minimize the disorder to a great extent.

F. Leaf scorch in mango

The characteristic symptom is akin to that of potash deficiency i.e. scorching of old leaves at the tips or margins. This condition is quite common during the winter months when the entire old foliage in some regions appear to be affected by these symptoms. The leaves fall down and consequently, the tree vigour and yield is reduced.

Studies conducted on this disorder have shown that it is caused by an excess of chloride ions which render potash unavailable. This disorder is more common in saline soils or where brackish water is available for irrigation or where muriate of potash is used as a fertilizer to meet the potash requirement of the plants.

Control

1. This disorder can be checked effectively by collecting and burning the fallen leaves, and using potassium sulphate instead of muriate of potash.

2. Acute condition can be cured by 4-5 foliar applications of potassium sulphate on newly emerged flushes at fortnightly intervals.

G. Spongy tissue

This is also called internal break down or soft centre. generally occurring in the fruits of Alphonso variety of mango. In Alphonso. it is observed to all extent of as high as 30 per cent. Other varieties arc quite free from this disorder. This disorder has adversely affected the cultivation of mango in Maharashtra where' Alphonso' is prominently grown.

Apparently normal and attractive fruits, on cutting, show spongy developments in the flesh. The break down portion (tissues) is characterized by its pale yellow colour, soft and spongy, with or without off-flavour. In extreme cases, the whole fleshy portion becomes too soft resembling bacterial rot. About 25 to 39% of mangoes (Alphonso) from different areas show this disorder.

Control

Only Control is to harvest the crop at 3/4th maturity when the incidence is quite low. At full maturity the incidence of the disorder increases.

H. Fruit drop in mango

Fruit drop in mango is a continuous process amounting to about 99%, at various stages of growth. Of the commercial varieties, Langra is more prone to the disorders, while Dashehari the least In mango, only about 0.1 % of tile perfect flowers develop fruits to maturity. The extent of fruit drop in mango varies from variety to variety and region to region.

Fruit drop in mango can be classified into three distinct phases.

i. Pin head drop

ii. Post setting drop

iii. May drop

Fruits dropping in the month of May when they attain considerable size decides the crop at harvest. Fruit drop is a complex problem involving several factors. Within the panicle, sex ratio, condition of the pistil and extent of pollination govern the fruit set in mango. Retention in most of the cultivars is generally low, although some cultivars are characterized by high sex ratio.

Besides the varietal variations, eastern and western sides of the tree appear to be more conducive for fruit retention. The drop during the day time is almost double than in the night

A good deal of fruit drop is attributed to disintegration of embryos and ovular abnormalities. Other factors like climatic conditions, disturbed water relations lack of nutrition, competition among fruits and pests and diseases, contribute to fruit drop, Further, hormones and their activities in the seeds play an important role in deciding the retention of fruits.

Control

1. The extent of fruit drop in mango can be significantly reduced by regular irrigations during fruit development  period.

2. Orchards should be protected from desiccating winds by planting wind breaks.

3. Timely and effective control measures against major pests and diseases should be adopted.

4. Growth regulators like NAA (naplhalene acetic acid) and 2,4-D (2,4 Dichlororphenoxy acetic acid) in varying concentration depending upon the variety and time of application can be sprayed. The optimum concentration lies between 10 and 15 ppm during the month of April-May.

VII. Conclusion

Mango is the most popular fruit in India. It is highly nutritious and delicious fruit. Economically, a farmer can fetch al Ieast 25 to 30 thousand rupees per year from one hectare mango' plantation. Apart from this, mango fruit or fruit products are the chief agricultural commodities India exports every year and thereby earns a lot of foreign currency.

But, recently mango orchards are facing decline which is adversely affecting their yield and productivity. Consequently farmers are getting disinclined to raising mango crops. Although a number of factors are responsible for mango decline, yet insect pests, diseases and physiological disorders play more devastating role. In this booklet these problems have been discussed in detail along with possible control measures which will certainly help farmers in timely overcoming these maladies and getting satisfactory remunerative l prices from mango cultivation.