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.
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 favorable 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, wither tip, 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. 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.
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 recognized 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.
Control: 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 spraying of Nottasul + Metacin + gumacasea (0.2% + 0.1% + 0.3%).
Postharvest Diseases: The mango fruit is susceptible to many postharvest diseases caused by anthracnose (C. gloeosporioides) and stem end rot (L. theobromae) during storage under ambient conditions or even at low temperature. Aspergillus rot is another postharvest disease of mango.
Control: Pre-harvest sprays of fungicides could control the diseases caused by latent infection of these fungi. Postharvest dip treatment of fruits with fungicides could also control the diseases during storage.
The following treatments are suggested:
- 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.
- 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. 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, fruit fly, 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.
Of all the mango pests, hopper is considered as the most serious and widespread pest. Idioscopus clypealis Lethierry,Idioscopus nitidulus (Walker) and Amritodus atkinsoni Lethierry 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 vigor of the plants. Heavy puncturing and continuous 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. Shade and high humidity conditions are favorable 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.
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. Spraying of Nimbicidine (0.2 %) is effective at initial stage of hoppers management. Chemical spray is to be minimized whenever necessary. The use of insect growth regulator Buprofezin (0.0125 %) is also suggested as one of the sprays.
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 bio-agents to control this pest.
(iii) 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, labor 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 on a regular basis. Nymph predators Mallada boninensis and Chrysopa lacciperda and egg parasite Polynema sp., Gonatocerus sp. and Tetrastichus sp. are found effective in nature against the hoppers. A fungus, Verticillium lacanihas also been found effective against this pest but under moderate climate.
Mealy bug: (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 vigor 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 favorable conditions in the month of November – December. Just after hatching, the minute newly hatched pink to brown colored 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.
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.
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.
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 bio-agent 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 the 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 the spores of the fungus Beauveria bassiana will further ensure the reduction of the pest population.
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. Bactrocera dorsalis, B. zonatus and B. correctus are the most common fruitflies which cause serious damage to mature mango fruits. The adult flies are dark brown in color 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 the 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 March onwards and the maximum population is recorded during April-May which coincides with fruit maturity. The population declines slowly from June to July after which it is non-existent up to March.
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 May). 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 vapor heat treatment (VHT) of fruits before storage and ripening for killing the larvae.
Scale insects are considered serious pest on mango 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 vigor 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.
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.
Shoot borer (Chlumetia transversa) :
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 color and measure about 17.5 mm with expanded wings. Hind wings are light in color. 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 tunneling downwards. The full grown larva is dark pink in color 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.
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.
Stem borer (Batocera rufomaculata):
Stem borer 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 grayish brown in color 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 colored 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.
The pest can be effectively controlled by following the recommendations given for the control of bark eating caterpillar.
Stone weevil (Sternochetus mangiferae):
This insect is widely distributed in the tropics. 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. Discoloration of the pulp adjacent to the affected portion has been observed. Eggs are minute and white in color. Adult weevils are 5 to 8 mm long, stout and dark brown in color. Life-cycle is completed in 40 to 50 days. 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%)
The malformed panicles remain unproductive and are characterized by a compact mass of male flowers, greenish in color 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 efforts made 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.
The term biennial, alternate or irregular bearing generally signifies the tendency of mango trees to bear a heavy crop in one year (On year) and very little or no crop in the succeeding year (Off year). Most of the commercial varieties in thePhilippines biennial bearers. When a tree produces heavy crop in one season, it gets exhausted nutritionally and is unable to put forth new flush thereby failing to yield in the following season. The problem has been attributed to the causes like genetical, physiological, environmental and nutritional factors. For overcoming biennial bearing, deblossoming is recommended to reduce the crop load in the “On year” such that it is balanced in the “Off year”. Proper maintenance of orchard by way of effectively controlling pests and diseases and regular cultural operations may also result in better performance of the tree every year. Soil application of Paclobutrazol (PP333) or @ 4 – 5 g per tree in the month of September resulted in early flowering with higher fruit set and yield. It may be applied every year for regular fruiting, particularly in young trees. The time of application may vary according to fruit bud differentiation.
Despite high fruit set initially, the ultimate retention is quite low in mango. The intensity of fruit drop, varies from variety to variety. 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) March-month drop. Fruit drop in the 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.
Clustering disorder in mango:
A fruiting disorder is characterized 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. The other reasons causing the disorder are old and overcrowding of trees, indiscriminate spraying against pests and diseases, use of synthetic pyrethroids for spraying, 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.
- Pruning of old trees may be done to open the canopy.
- Spraying of 300 ppm NAA may be done
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