Mangoes in India . . . . .
Mango suffers from several diseases at all stages of its life. All the parts of the plant, namely, trunk, branch, twig, leaf, petiole, flower and fruit are attacked by a number of pathogens including fungi, bacteria and algae. They cause several kinds of rot, die back, anthracnose, scab, necrosis, blotch, spots, mildew, etc. Some of these diseases like powdery mildew are of great economic importance as they cause heavy losses in mango production. Major diseases of mango and their control measures are discussed below.
a) Powdery mildew (Oidium mangiferae Berthet) : Powdery mildew is one of the most serious diseases of mango affecting almost all the varieties, It occurs up to latitude of 40o North and South of the equator. It may persist for longer period at an elevation of 600-1200 meters, in many African countries, south of the Sahara, the middle East, Southern Asia and America : from the Southern United States to Peru and Brazil.
The disease is reported to cause approximately 20 per cent crop loss in Maharashtra state alone. Sometimes, as high as 70-80 per cent crop loss has been recorded on individual plant basis.
The characteristic symptom of the disease is the white superficial powdery fungal growth on leaves, stalks of panicles, flowers and young fruits. The affected flowers and fruits drop pre-maturely reducing the crop load considerably or might even preven the fruit set. Rains or mists accompanied by cooler nights during flowering are congenial for the disease spread. The fungus parasitizes young tissues of all parts of the inflorescence, leaves and fruits.
Control : Following three sprays of fungicides at 15 days interval recommended for effective control of the disease :
- Wettable sulphur 0.2 per cent (2 g Sulfex / lit. water).
- Tridemorph 0.1 per cent ( 1 ml Calixin / lit. water).
- Dinocap 0.1 per cent (1 ml / g Karathane / lit. water).
b) Anthracnose (Colletotrichum state of Glomerella cingulata Ston, Spaull and Schrenk) : The anthracnose disease is of widespread occurrence. The disease causes serious losses to young shoots, flowers and fruits under favourable climatic conditions of high humidity, frequent rains and a temperature of 24-32oC. It is also affects fruits during storage. The disease produces leaf spot, blossom blight, withertip, twig blight and fruit rot symptoms. Tender shoots and foliage are easily affected which ultimately cause ‘die back’ of young branches. Older twigs may also be infected through wounds which in severe cases may be fatal.
Depending on the prevailing weather conditions blossom blight may vary in severity from slight to a heavy infection of the panicles. Black spots develop on panicles as well as on fruits. Severe infection destroys the entire inflorescence resulting in no setting of fruits. Young infected fruits develop black spots, shrivel and drop off. Fruits infected at mature stage carry the fungus into storage and cause considerable loss during storage, transit and marketing. The fungus perpetuates on twigs and leaves of mango or other hosts. Varietal differences in susceptibility have been noted in India. In Kerala, maximum damage was observed on Neelum, whereas variety Edward was reported to be resistant. Since the fungus has a long saprophytic survival ability on dead twigs, the diseased twigs should be pruned and burnt along with fallen leaves for reducing the inoculum potential.
Control: Trees may be sprayed twice with Bavistin (0.1%) at 15 days interval during flowering to control blossom infection. Spraying of copper fungicides (0.3%) is recommended for the control of foliar infection.
c) Die back (Botryodiplodia theobromae Pat.) : Die back is one of the serious diseases of mango. The disease is prevalent in Rajasthan, Delhi, Tamil Nadu, Punjab, Haryana, Orissa, Gujrat, Maharashtra and Uttar Pradesh. The disease on the tree may be noticed at any time of the year but it is most conspicuous during Oct.-Nov. The disease is characterized by drying of twigs and branches followed by complete defoliation, which gives the tree an appearance of scorching by fire. The onset of die back becomes evident by discolouration and darkening of the bark. The dark area advances and young green twigs start withering first at the base and then extending outwards along the veins of leaf edges. The affected leaf turns brown and its margins roll upwards. At this stage, the twig or branch dies, shrivels and falls. This may be accompanied by exudation of gum. In old branches, brown streaking of vascular tissue is seen on splitting it longitudinally. The areas of cambium and phloem show brown discolouration and yellow gum like substance is found in some of the cells.
Control : (i) Prune the diseased twigs and spray with copper oxychloride (0.3%) on infected trees. Pruning should be done in such a way that the twigs are removed 2-3 inches below the affected portion. (ii) In small plants, pruning of twigs is followed by pasting of copper oxychloride.
d) Phoma blight (Phoma glomerata (Cords) Woll. Hochapf)
Phoma blight, a new disease of mango, was first reported at Central Mango Research Station, Lucknow. The disease was later detected in mango growing belt around Lucknow region. It is now gaining economic importance.
The symptoms of the disease are noticeable only on old leaves. Initially, the lesions are angular, minute, irregular, yellow to light brown, scattered over leaf lamina. As the lesions enlarge, their colour changes from brown to cinnamon and they become almost irregular. Fully developed spots are characterized by dark margins and dull grey necrotic centres. In case of severe infection such spots coalesce forming patches measuring 3.5-13 cm in size, resulting in complete withering and defoliation of infected leaves.
Control : The disease could be kept under control by spray of copper oxychloride (0.3%) just after the appearance of the disease and subsequent sprays at 20 day intervals.
e) Bacterial canker (Xanthomonas campestris pv. mangiferaeindicae) : Canker disease of mango, caused by a bacterium, is prevalent in Andhra Pradesh, Maharashtra, Karnataka, Kerala, Tamil Nadu, U.P., Bihar, Delhi, Haryana, Madhya Pradesh and probably in several other mango growing areas. Besides being pathogenic on several varieties of mango, the organism is capable of infecting wild mango, cashew nut and weeds as well. The disease causes fruit drop (10-70%), yield loss (10-85%) and storage rot (5-100%). Many commercial cultivars of mango including Langra, Dashehari, Amrapali, Mallika, and Totapuri are susceptible to this disease.
The disease is found on leaves, petioles, twigs, branches and fruits, initially producing water-soaked lesions and later turning into typical cankers. The disease first appears as minute water-soaked irregular lesions on any part of leaf or leaf lamina. The lesions are light yellow in colour but with age, enlarge and turn dark brown to black. They become angular, cankerous and raised, and are surrounded by chlorotic halos. Several lesions coalesce to form irregular necrotic cankerous patches. In severe infections the leaves turn yellow and drop off. Cankerous lesions appear on petioles, twigs and young fruits. The water soaked lesions also develop on fruits which later turn dark brown to black. They often burst open, releasing a highly contagious gummy ooze containg bacterial cells. The fresh lesions on branches and twigs are water soaked which later become raised and dark brown in colour with longitudinal cracks but without any ooze.
- Seedling certification, inspection and orchard sanitation.
- Three sprays of streptocycline (100 ppm) or Agrimycin-100 (100 ppm) after first visual symptom at 10-days intervals.
- Monthly sprays of Bavistin (1000 ppm) or copper oxychloride (3000 ppm) were also found effective.
f) Red rust ( Cephaleuros virescens Kunze) : Red rust disease, caused by an alga, has been observed in mango growing areas. The algal attack causes reduction in photosynthetic activity and defoliation of leaves thereby lowering vitality of the host plant.
The disease can easily be recognized by the rusty red spots mainly on leaves and sometimes on petioles and bark of young twigs and is epiphytic in nature. The spots are greenish grey in colour and velvety in texture. Later, they turn reddish brown. The circular and slightly elevated spots sometimes coalesce to form larger and irregular spots.
The disease is more common in closely planted orchards. Fruiting bodies of the alga are formed in humid atmosphere. The zoospores formed by the sporangia initiate fresh infections. Stem entry is achieved by way of cracks. The affected areas crack and scale off. In severe infection the bark becomes thickened, twigs get enlarged but remain stunted and the foliage becomes sparse and finally dries up.
g) Sooty mould (Meliola mangiferae) : The disease is common in the orchards where mealy bug, scale insect and hopper are not controlled efficiently. The disease in the field is recognis by the presence of a black velvety coating, i.e., sooty mould on the leaf surface. In severe cases the trees turn completely black due to the presence of mould over the entire surface of twigs and leaves. The severity of infection depends on the honey dew secretion by the above said insects. Honey dew secretions from insects sticks to the leaf surface and provide necessary medium for fungal growth. The fungus is essentially saprophytic and is non-pathogenic because it does not derive nutrients from the host tissues. Although no direct damage is caused by the fungus, the photosynthetic activity of the leaf is adversely affected due to blockage of stomata.
- Pruning of affected branches and their prompt destruction prevents the spread of the disease.
- Spraying of 2 per cent starch is found effective.
- It could also be controlled by spray of Nottasul + Metacin + gumacasea (0.2% + 0.1% + 0.3%).
B. Postharvest Diseases : The mango fruit is susceptible tomany postharvest diseases caused by anthracnose (C. gloeosporioides) and stem end rot (L. theobromae) during storage under ambient condtions or even at low temperature. Aspergillus rot is another postharvest disease of mango.
Control : Preharvest sprays of fungicides could control the diseases caused by latents infection of these fungi. Postharvest dip treatment of fruits with fungicides could also control the diseases during storage. The following treatments are suggested.
(i) Three sprays of carbendazim (0.1%) orthiophante-methyl (0.1%) at 15 days interval should be done in such a way that the last spray falls 15 days prior to harvest.
(ii) Postharvest dip treatment of fruits in carbendazim (0.1%) in hot water at 52+1oC for 15 minutes.
More than 492 species of insects, 17 species of mites and 26 species of nematodes have been reported to be infesting mango trees, about 45 per cent of which have been reported from India. Almost a dozen of them have been found damaging the crop to a considerable extent causing severe losses and, therefore, may be termed as major pests of mango. These are hopper, mealy bug, inflorescence midge, fruitfly, scale insect, shoot borer, leaf webber and stone weevil. Of these, insects infesting the crop during flowering and fruiting periods cause more severe damage. The insects other than those indicated above are considered as less injurious to mango crop and are placed in the category of minor pests. A brief description of the biology and control of major pests of mango is given below.
a) Hopper : Of all the mango pests, hopper is considered as the most serious and widespread pest throughout the country. Idioscopus clypealis Lethierry, Idioscopus nitidulus (Walker)and Amritodus atkinsoniLethierry are the most common and destructive species of hoppers which cause heavy damage to mango crop. Large number of nymphs and adult insects puncture and suck the sap of tender parts, thereby reducing the vigour of the plants. Heavy puncturing and continuos draining of the sap cause curling and drying of the infested tissue. They also damage the crop by secreting a sweet sticky substance which encourages the development of the fungus Maliola mangiferae, commonly known as sooty mould which affects adversely the photosynthetic activities of the leaves. A low population of hoppers has been recorded in mango orchards throughout the year but it shoots up during February-April and June-August. Shade and high humidity conditions are favourable for their multiplication. Such conditions usually prevail in old, neglected and closely planted orchards.
The female hoppers lay 100-200 eggs on mid rib of tender leaves, buds and inflorescence. In summers the total life cycle occupies 2-3 weeks.
a) Chemical : Three sprays of 0.15 per cent Carbaryl or 0.04 per cent Monocrotophos or 0.05 per cent Phosphomidon or 0.05 per cent Methyl Parathion have been found very useful in controlling the pest population. First spray should be given at the early stage of panicle formation. The second spray at full length stage of panicles but before full bloom and the third spray after the fruits are set and have attained pea stage are recommended.
b) Biological : Biological control agents such as the predators Mallada boninensis and Chrysopa lacciperda, the egg parasite Polynema sp. and a preparation of the fungus Beauveria bassiana are the important useful bioagents to control this pest.
c) Integrated Pest Management (IPM)
The continuous use of pesticides though control the pests but pose some other serious problems like killing of pollinators and natural enemies, development of resistance to insecticides and residues which are on fruits hazardous to human population. Besides, the high cost of pesticides, labour and maintenance of equipments are other limiting factors in pest control. Integrated pest management is gaining momentum to take care of these problems. To manage mango hopper pest, avoid dense planting and keep the orchard clean by regular ploughing and removal of weeds. Pruning of overcrowding and over lapping branches should be done in the month of December. Chemical spray is to be minimized necessary. Neem products may be included in the management schedule of the pest. The use of insect growth regulator Buprofezin (0.0125 %) is also suggested as one of the sprays.
Mealy bug : It is another major pest of mango in India and is widely distributed all along the Indo-gangetic plain. Drosicha mangiferae Green is the most common mealy bug and causes severe damage to mango crop throughout the country. Nymphs and adults suck the plant sap and reduce the vigour of the plant. Excessive and continuous draining of plant sap causes wilting and finally drying of infested tissue. They also secrete honey dew, a sticky substance, which encourages the development of a fungus Maliola mangiferae, termed as sooty mould.
The adult male is winged and small, female is bigger and wingless. The female, after copulation, crawl down the tree in the month of April-May and enter in the cracks in the soil for laying eggs in large numbers encased in white egg sacs. The eggs lie in diapause state in the soil till the return of the favourable conditions in the month of November – December. Just after hatching, the minute newly hatched pink to brown coloured nymphs crawl up the tree. After climbing up the tree they start sucking the sap of tender plant parts. They are considered more important because they infest the crop during the flowering season and if the control measures are not taken timely , the crop may be destroyed completely.
(i) Mechanical : Polythene (400 gauge) bands of 25 cm width fastened around the tree trunk have been found effective barrier to stop the ascent of nymphs to the trees. The band should be fastened well in advance before the hatching of eggs, i.e., around November – December.
(ii) Chemical : Application of 250 g per tree of Methyl Parathion dust 2 per cent or Aldrin dust 10 per cent in the soil around the trunk kills the newly hatched nymphs which come in contact with the chemical.
Spraying of 0.05 per cent Monocrotophos or 0.2 per cent Carbaryl or 0.05 per cent Methyl Parathion have been found useful in controlling early instar nymphs of the mealy bug.
(iii) Biological : Menochilus sexmaculatus, Rodolia fumida and Sumnius renardi are important predators in controlling the nymphs. The entomogenous fungus Beauveria bassiana is found to be an effective bioagent in controlling the nymphs of the mealy bug.
(iv) Integrated Pest Management (IPM) : The IPM schedule of mealy bug is very important and useful if timely operations are done. Flooding of orchards with water in the month of October kills the eggs. Ploughing the orchards in the month of November exposes the eggs to sun’s heat. In the middle of December, 400 gauge alkathene sheet of 25 cm width may be fastened to the tree trunk besides raking the soil around the tree trunk and mixing of 2 per cent Methyl Parathion dust. The dust may also be sprinkled below the atkathene band on the tree. The congregated nymphs below the band may be killed by any of the suggested insecticides. The above IPM schedule holds promise to control the mealy bug but spraying of neem product and the spores of the fungus Beauveria bassiana will further ensure the reduction of the pest population.
Inflorescence midge : The mango inflorescence midge, Erosomyia indica Grover Diptera : cecidomyiidae) is another major pest of mango. Recently, this pest has become very serious in certain pockets of Uttar Pradesh causing serious damage to mango crop by attacking both the inflorescence and the small fruits. The adult midge are harmless minute flies which are short lived and die within 24 hours of emergence after copulation and oviposition. The flies lay eggs singly on floral parts like tender inflorescence axis, newly set fruit or tender leaves encircling the inflorescence. The eggs hatch within 2-3 days. Upon hatching, the minute maggots penetrate the tender parts on which the eggs have been laid and feed on them. The floral parts finally dry up and are shed. The larval period varies from 7-10 days. The mature larvae drop down into the soil for pupation. The pupal period varies from 5-7 days. There are 3-4 overlapping generations of the pest spread over the period from January-March. Thereafter, as the weather conditions turn unfavourable, the mature larvae undergo diapause in the soil instead of pupating. They break diapause on the arrival of favourable conditions in following January.
The midge infests and damages the crop in three different stages. The first attack is at the floral bud burst stage. The eggs are laid on newly emerging inflorescence, the larvae tunnel the axis and thus destroy the inflorescence completely. The mature larvae make small exit holes in the axis of the inflorescence and slip down into the soil for pupation. The second attack of the midge takes place at fruit set. The eggs are laid on the newly set fruits and the young maggots bore into these tender fruits, which slowly turn yellow and finally drop. The third attack is on tender new leaves encircling the inflorescence. The most damaging one is the first attack in which the entire inflorescence is destroyed even before flowering and fruiting. The inflorescence shows stunted growth and its axis bends at the entrance point of the larvae. It finally dries up before flowering and fruit setting.
- As the larvae pupate in the soil, ploughing of the orchards expose pupating as well as diapausing larvae to sun’s heat which kills them.
- Soil application of Methyl Parathion also kills pupating as well as diapausing larvae in the soil. The insecticide in the soil should be applied after monitoring larval population on white sheet below the tree.
- Spraying of 0.05 per cent Fenetrothion or 0.045 per cent Dimethoate or 0.04 per cent Diazinon at the bud burst stage of the inflorescence has been found effective in controlling the pest population.
In addition to the inflorescence midge, Erosomyia indica, two other gall-midges Dasineura amramanjarae Grover and Procystiphora mangiferae Felt have been found damaging the mango inflorescence. They infest and damage the floral buds of the inflorescence. The mature larvae of D. amramanjarae are red, whereas those of P. mangiferae are orange in colour. The larvae of the former species pupate in buds itself. The infested buds of D. amramanjarae have red coloured petals and hence can be identified easily. The infested buds of P. mangiferae swell and look bigger than normal buds. The control measures used for E. indica were also found effective against these midges.
Fruitfly : The oriental fruitfly is one of the most serious pests of mango in the country which has created problem in the export of fresh fruits. Daccus dorsalis, D. zonatus and D. correctus are the most common fruitflies which cause serious damage to mature mango fruits. The adult flies are dark brown in colour and measure 7 mm in length and 4 mm across the wings. The females have tapering abdomen which ends in an ovipositor. The female punctures the outer wall of the mature fruits with the help of its pointed ovipositor and insert eggs in small clusters inside the mesocarp of mature fruits. After hatching, the larva feeds on the pulp of fruit which appears normal from outside, but drops down finally. The mature maggots fall down into the soil for pupation. The emergence of fruitfly starts from April onwards and the maximum population is recorded during May-July which coincides with fruit maturity. The population declines slowly from August to September after which it is non-existent up to March.
(i) Chemical : The adult fruitflies can be controlled by bait sprays of carbaryl (0.2%) + protein hydrolysate (0.1%) or molasses starting at pre-oviposition stage (first week of April), repeated once after 21 days. Another method to control these flies is to hang traps containing a 100 ml water emulsion of methyl euginol (0.1%) + Malathion (0.1%) during fruiting (April to June). About 10 such traps are sufficient for one hectare of orchard.
(ii) Integrated pest management (IPM)
Collection and proper disposal of the infested and dropped fruits.
- Ploughing the orchards and exposing the diapausing pupae to sun’s heat. Releasing of parasite and predator during December to February are helpful in reducing the pest population.
- Monitoring and destruction of emerging adult with methyl euginol traps.
- Early harvesting of mature fruits.
- Selective and need based bait spray.
- Hot water treatment or vapour heat treatment (VHT) of fruits before storage and ripening for killing the larvae.
Scale insects : Scale insects were not considered serious pest on mango in any part of the country till recently, but of late, they have assumed the status of serious pest in certain parts of the country. Pulvinaria polygonata, Aspidiatus destructor, Ceroplastis sp. and Rastococus sp. are some of the most common scale insects infesting mango crop. The nymphs and adult scales suck the sap of the leaves and other tender parts and reduce the vigour of the plants. They also secrete honeydew which encourages the development of sooty mould on leaves and other tender parts of the mango plant. In case of severe scale infestation, growth and fruit bearing capacity of the tree is affected adversely. Among the above scale insects, P. polygonata is posing a serious threat to mango industry of western Uttar Pradesh.
Control : Pruning of the heavily infested plant parts and their immediate destruction followed by two sprays of Monocrotophos (0.04 %) or Diazinon (0.04 %) or Dimethoate (0.06 %) at an interval of 20 days have been found very effective in controlling the scale population.
f) Shoot borer (Chlumetia transversa) : This pest is found all over the country. Larvae of this moth bore into the young shoot resulting in dropping of leaves and wilting of shoots. Larvae also bore into the inflorescence stalk. The adult moths are shining grey in colour and measure about 17.5 mm with expanded wings. Hind wings are light in colour. Female moths lay eggs on tender leaves. After hatching, young larvae enter the midrib of leaves and then enter into young shoots through the growing points by tunnelling downwards. The full grown larva is dark pink in colour with dirty spots and measures about 22 mm in length. There are four overlapping generations of the pest in a year and it overwinters in pupal stage.
Control : The attacked shoots may be clipped off and destroyed. Spraying of Carbaryl (0.2%) or Quinalphos (0.05%) or Monocrotophos (0.04%) at fortnightly intervals from the commencement of new flush gives effective control of the pest. A total of 2-3 sprays may be done depending on the intensity of infestation.
Bark-eating caterpillar (Ludarbella quadrinotata) : This pest is found damaging a variety of plants including a number of fruit trees, forest trees and ornamentals all over India. The old, shady and neglected orchards are more prone to attack by this pest. Larvae of this moth feed on the bark and weaken the tree. The moth is light grey in colour with dark brown dots and measures about 35-40 mm with expanded wings. A single female lays about 300-400 eggs in batches on the bark. The full grown caterpillar is dirty brown in colour and is about 35-45 mm in length. The caterpillar spins brown silken web on the tree which consists of their excreta and wood particles. Larvae also make shelter tunnels inside the stem in which they rest. Larvae actually feed from April to December. There is only one generation in a year.
Control : Remove the webs from tree trunks and put emulsion of Monocrotophos (0.05%) or DDVP (0.05%) in each hole and plug them with mud.
Stem borer (Batocera rufomaculata)
Stem borer is widely distributed in India and attacks a variety of fruit trees including mango. Damage is caused by the grub of this beetle as it feeds inside the stems boring upward resulting in drying of branches and in severe cases attained stem also dies. Adult beetles, 35-50 mm in size, are stout and greyish brown in colour with dark brown and black spots. Eggs are laid either in the slits of tree trunk or in the cavities in main branches and stems covered with a viscous fluid. Full grown grubs are cream coloured with dark brown head and 90 x 20 mm in size. Pupation takes place within the stem. Beetle emerges in July-August. There is only one generation of the pest in a year.
Control : The pest can be effectively controlled by following the recommendations given for the control of bark eating caterpillar.
Shoot gall psylla (Apsylla cistellata) : It is a very serious pest of mango in many parts of India, particularly in Terai region of U.P., north Bihar and West Bengal. This pest creates green conical galls in leaf axis. The activity of the pest starts from August. The galls dry out after emergence of psyllid adults in March. The females lay eggs in the midribs as well as in lateral axis of new leaves. Nymphs emerge from eggs during August-September and crawl to the adjacent buds to suck cell sap. As a result of feeding, the buds develop into hard conical green galls. The galls are usually seen during September-October. Consequently, there is no fruit set.
Eggs are white while nymphs are flat and of pale yellow in colour. Adults are 3-4 mm long with black head and thorax and light brown abdomen. Female lays approx. 150 eggs during March-April and nymphs pass the winter inside the galls. There is only one generation of the pest in a year.
Control : The galls with nymphs inside should be collected and destroyed to prevent carryover of the pest. The pest can effectively be controlled by spraying Monocrotophos (0.05%) or Dimethoate (0.06%) or Quinalphos (0.05 %) at 2 week intervals starting from the middle of August. The use of same chemical for every spray should be avoided.
j) Leaf webber (Orthaga euadrusalis): The pest is attaining serious proportions. Its infestation starts from the month of April and goes up to December. Eggs are laid singly or in clusters within silken webbings on leaves. Upon hatching, the caterpillars feed on leaf surface by scrapping. Later, they make web of tender shoots and leaves together and feed within. Generally, 1-9 larvae are found in a single web. Pupation takes place inside the webs in silken cocoons. However, the last generation (December-January) pupates in the soil. The adult moths are medium sized and sombre coloured. Fully grown caterpillar measures 2.5 to 3 cm. They are brownish in colour with brown spots and whitish striation on the dorsal surface. The pupae diapause for about five to six months. The infestation is severe in shady conditions. Old orchards with lesser space between tree canopy have more infestation than open orchards.
Control : Pruning of infested shoots and their burning in the month of April to July is found effective. Raking of the soil around the base of the trees in January, after the last generation has pupated, helps in checking the pest population. Three sprays starting from the last week of July at 15 days interval with Carbaryl (0.2%) or Monocrotophos (0.05%)) or Quinalphos (0.05%) have been found effective in controlling the pest.
Stone weevil (Sternochetus mangiferae) : This insect is widely distributed in tropics. It is a common pest of mango in southern India. Another species, S. frigidus,of the pest is found in Assam and Bengal. Sweeter varieties such as Alphonso, Bangalora, Neelum, etc. are more prone to attack by this pest.
Female lays eggs on the epicarp of partially developed fruits or under the rind of ripening fruits. Newly emerged grubs bore through the pulp, feed on seed coat and later cause damage to cotyledons. Pupation takes place inside the seed. Discolouration of the pulp adjacent to the affected portion has been observed.
Eggs are minute and white in colour. Adult weevils are 5 to 8 mm long, stout and dark brown in colour. Life-cycle is completed in 40 to 50 days during June-July. Adults hibernate until the next fruiting season. There is only one generation in a year.
- Destroying the affected fruits and exposing the hibernating weevils by digging the soil
- Spraying the trees with Fenthion (0.01%)
a) Mango malformation : Malformation is widely prevalent in northern India, particularly in the states of Punjab, Delhi and western U.P. where more than 50 per cent of the trees suffer from this malady. The malformed panicles remain unproductive and are characterised by a compact mass of male flowers, greenish in colour and stunted in growth. The main and secondary rachis are thick and short and bear flowers with relatively larger bracts, sepals and petals as compared to normal flowers. The malformed panicles remain intact on the trees for a considerable period. Though research efforto made hitherts have not been able to ascertain its etiology, the complexity of the disorder is attributed cultural practices, nutritional, to many factors like, mites, fungal, viral, etc. hormonal imbalance. The exact cause and control of the malady is yet to be established. However, some remedial measures are recommended as follows :
- Pruning of shoots bearing malformed panicles
- Deblossoming of early emerged / infested panicles.
c) Fruit drop : Despite high fruit set initially, the ultimate retention is quite low in mango. The intensity of fruit drop, varies from variety to variety. Among the commercially grown varieties, Langra is more susceptible to drop while Dashehari is the least. The fruit drop is more or less a continuous process and can be classified into three groups : (i) Pinhead drop, (ii) Post-setting drop and (iii) May-month drop. The fruit drop in first two groups are insignificant compared to the third group which affects the final yield significantly and needs more attention. Embryo abortion, climatic factors, disturbed water relation, lack of nutrition, disease, pest and hormonal imbalances are the major factors that lead to fruit drop. The foliar application of Alary (B-nine) @ 100 ppm or NAA 20 ppm at pea stage of fruit was found effective in controlling fruit drop in mango.
d) Black tip : Black tip is a serious disorder, particularly in the cultivar Dashehari. The affected fruits become unmarketable and reduce the yield to a considerable extent. The damage to the fruit gets initiated right at marble stage with a characteristic yellowing of tissues at distal end. Gradually, the colour intensifies into brown and finally black. At this stage, further growth and development of the fruit is retarded and black ring at the tip extends towards the upper part of the fruit. Black tip disorder has generally been detected in orchards located in the vicinity of brick kilns. It has been reported that the gases like carbon monoxide, sulphur dioxide and ethylene constituting the fumes of brick kiln are known to damage growing tip of fruits and give rise to the symptoms of black tip. Apart from these factors, irrigation, condition of the tree and management practices also play important role in deciding the severity of the disorder.
Planting of mango orchards in North-South direction and 5 to 6 km away from the brick kilns may reduce incidence of black tip to a greater extent.
The incidence of black tip can also be minimised by the spray of borax (1%) or other alkaline solutions like caustic (0.8%) or washing (0.5%) soda. The first spray of borax should be done positively at pea stage followed by two more sprays at 15 days interval.
e) Clustering disorder in mango (‘Jhumka’) : A fruiting disorder, locallly known as ‘Jhumka’, is characterised by the development of fruitlets in clusters at the tip of the panicles. Such fruits do not grow beyond pea or marble stage and drop down after a month or so of fruit set. These fruits do not contain seeds when they are cut open. The disorder seems to be due to lack of pollination / fertilization which may be attributed to many reasons. Among them, absence of sufficient population of pollinators in the orchards is the major reason. Surveys conducted in the mango belt of Lucknow revealed that the more problem is area in Malihabad and Dashehari is the most affected cultivar. The other reasons causing the disorder are old and overcrowding of trees, indiscriminate spraying against pests and diseases, use of synthetic pyrethroids for spraying, monoculture of Dashehari, and bad weather during flowering. Some of the remedial measures are suggested below :
- Insecticides should not be sprayed at full bloom to avoid killing of pollinators.
- Pests and diseases should be controlled in time by spraying the recommended pesticides only.
- Introduction of beehives in the orchards during flowering season for increasing the number of pollinators.
- The practice of monoculture of a particular variety may be avoided. In case of Dashehari, 5-6 per cent of other varieties should be planted in new plantations. In old orchards, where monoculture of a particular variety like Dashehari is followed, a few branches may be top worked with pollinizing varieties.
- Pruning of old trees may be done to open the canopy.
- Spraying of 300 ppm NAA may be done during October-November.