Spongy Tissue
It is the development of white corky tissue in the fruit mesocarp in maturing and ripening fruits. This is non-edible sour patch and slightly desiccated in nature. Symptoms of spongy tissue are not apparent externally at the time of harvesting and the affected tissues are visible only when cut open. In severe cases, the epicarp turns brown black forming a flat depression outside. The spongy tissue could be separated from surrounding flesh with ease. Mostly fruits of Alphonso suffer from this malady to the extent of 55 per cent. Damage varies with fruit weight, picking time, place of harvesting, orchard conditions and season. Fruits exposed to sunlight suffer more, when temperature is also high the fruits under shade are also affected. Reproduction of disorder has been claimed subjecting the fruit to sun exposure, infrared rays and incubation at high temperatures above 400C at post-harvest stages.
Sod culture should be practised in Alphonso orchard. Minimize post-harvest fruit losses through creating infrastructure and employing scientific management in post- harvest handling and storage of fruits and standardizing cost-effective processing technologies. Early picking in Alphonso mango escapes the disorder to some extent but the quality of ripe fruits is poor. Higher percentage of spongy tissue in larger fruits than smaller ones has been observed. Varying degree of damage in fruits of the same tree or at different places in the same cultivar may be observed due to differences in plant environments. Post-harvest dipping of CaCl2 (1-2%) increases Ca content and has been reported to reduce spongy tissue in ripe Alphonso fruits.
Malformation
Malformation is a very serious disorder of mango in subtropics and sometimes causing up to 90 per cent crop loss, varying from place to place, cultivar to cultivar, year to year in the same cultivar, depending on tree age and other climatic factors. None of the commercial cultivars grown in subtropics of the world are resistant to this malady. However, great variability in severity of the disorder occurs among cultivars at the same location. The causes and control of this disorder/disease are still the subject of investigation.
Several causes have been suggested for malformation which include mites, nutritional problem, physiological or hormonal imbalance and viruses. Many treatments have been suggested for its control including removal of affected shoots, deblossoming at bud stage (1.0 cm long) alone or in combination with spraying of 200ppm NAA during fruit-bud differentiation. Since, safe and effective chemical control measures have not been identified, the only viable control option is annual pruning of shoots after harvesting.
Black Tip
This disorder is mainly prevalent in the vicinity of brick kilns or areas having higher concentrations of industrial gasses like sulphur dioxide and carbon monooxide. The earliest noticeable symptom of black tip is etiolation (yellowing) of distal end of fruits leaving mesocarp and seed unaffected. Etiolated area, which gradually spreads and turns nearly black and covers the tip completely. Smoke emanated from the brick kiln located in vicinity of 1.6 km is the causal factor for this malady. Spraying of Borax (1 per cent) or caustic soda (0.8 per cent) can control this disorder.
Leaf Scorch
This disorders show characteristic symptoms of potassium deficiency, i.e. scorching at the tip and margin of old leaves. The affected leaves fall down and affect the health and vigour of tree adversely. Excess of chloride ion appears to make potassium unavailable to tree and thus this disorder is more prevalent under saline soil/water-logged conditions. Potassium sulphate should be used as potassium fertilizer and use of muriate of potash should be avoided under such situations. Potassium sulphate (5 per cent) as foliar on newly-emerged leaves is effective in controlling this disorder.
PEST AND DISEASE MANAGEMENT
Efficient management of insect pests and diseases is important because they affect essentially every phase of growth and development. Out of 260 species of insects and mites, 87 are fruit feeders, 127 foliage feeders, 36 inflorescence feeders, 33 damage buds and 25 feed on branches and trunk. Most of the insect pests and diseases require annual control measures. Fortunately, except fungal and bacterial diseases, attack of other pathogens like virus, viroid, phytoplasma on mango is not common. Control measures are available for most of the major diseases. If some of the insect pests, like mango mealy bug, stem-borer and shoot-gall maker, are controlled continuously for couple of years, can be eradicated for a long period of time. However, fruit flies, seed weevils, shoot-borer, mango hoppers etc. are required to control every year. Some of
Approaches and Strategies for Precision Farming in Mango
the diseases and pests such as anthracnose, powdery mildew, mango hoppers, midges etc. cause severe damage and are present throughout the mango-growing areas of the world (1). Therefore, future of mango insect pests and disease control has a great promise with the development of IPM technology in view of a large number of insect pests and diseases attacking mango trees throughout the year. A large number of chemicals are recommended to control them. It may be difficult to produce mango crop in the absence of some of these control measures.
Of the mango pests, hoppers, fruitfly, mealy bug and stone weevils are considered as major constraints in mango production (6). Many of the major insects and pests have developed resistance due to rapid change in agro-ecosystem, advancement in orchard management practices and indiscriminate use of pesticides. This has led orchardist to use high dose of toxic insecticides, thereby causing imbalance in population dynamics of pollinators and other useful fauna and incorporating high toxic residues in fruits. Therefore, it is necessary to bring out modern concepts of IPM for important mango pests.
Mango hopper (Idioscopus clypealis, I. nitidulus and Amritodus atkinsoni): In general, this is a serious pest and starts attacking during flowering season.
Nymphs damage more than adults by sucking sap from tender shoots and panicles. The attacked panicles wither away resulting in no fruit set. Furthermore, sooty mould fungi develops on leaves and panicles due to honeydew secreted by hoppers. Over- crowding and neglect of orchard results in more severe infestation by hoppers. Thus proper canopy management is important in high-density plantations. Spraying of monocrotophos (0.054 per cent), quinalphos (0.05 per cent), carbaryl (0.15 per cent), dimethoate (0.06 per cent) and chlorpyriphos (0.04 per cent) are effective at panicle emergence and fruit set stages to control this pest.
However, this pest has developed resistance to some of these pesticides and therefore, needs further investigation on its control measures through IPM. The efforts on biological control of insect pests have given some encouraging results but large- scale field testing may lead to conclusive results.
Mealy bug (Drosicha mangiferae): Its nymphs emerge in December-January and
climb the tree by crawling and suck juice from young shoots, panicles and flower pedicels. Adults lay eggs under soil clods up to a depth of 5-15cm around tree trunk during May. Destroying eggs and pupae through ploughing is a very effective control measure. Fastening of polyethylene strip 400 gauge thick, 25 cm wide around tree trunk (30- 45cm above the ground level) in December to check nymphs from climbing the tree is
one of the most effective methods. Raking of soil around the trunk and mixing with neem cake or application of chlorpyriphos dust (2 per cent) or methyl parathion dust @ 200-250 g/tree around tree trunk is effective to control mealy bug. Application of
Beauvaria bassiana near tree trunk before emergence of first instar of nymphs has
been found effective (6).
Infloresence midge (Erosomyia indica): The pest attacks on pre-flowering shoots
and inflorescence buds, axis of inflorescence, panicles, newly-formed fruits and post- flowering shoot buds. The adult female lays eggs in between leaves and buds. The newly-hatched larvae penetrate the tissues and form small blister like galls. The larvae feed within galls and at the time of pupation come out with swift jump and pupate in the soil. Black spots of varying sizes are normal features of their infestation. It is also observed that at the site of infestation, inflorescence gets bent at an angle. The larvae also enter inside the small ovary of the fruit and develop inside. The attacked fruits turn pale, become deformed, stop growing and finally drop. The exit holes are usually observed in infested fruits.
It is controlled by need-based foliar spraying of 0.05 per cent fenitrothion or 0.45 per cent diazinon after monitoring the adult population in Febraury. Summer ploughing of orchard has been found useful in reducing the midge population as the diapausing midge larvae are exposed to sun, hot wind, etc. and are killed.
Stem-borer (Batocera rufomaculata): The pest makes tunnel through the main trunk
and branches can be identified by dry hard balls of excreta on affected parts. The borer may be controlled by clearing tunnels with hard wire, pouring kerosene oil or petrol or quinalphos (0.05 per cent) and plugged with mud.
Shoot gall psylla (Apsylla cistellata): It is prevalent in tarai region. Its nymph enters
the axillary and terminal buds turning them into hard conical galls through their secretion. It lays egg in rows of two on underside of the leaf of new flush along the midrib in March-April. The nymphs on emergence, 5-6 months after egg laying enter axillary and terminal buds. Spraying of Monocrotophos (0.05 per cent) during September is effective to control this pest.
Fruit fly (Bactocera dorsalis): Fruit flies are spread widely throughout the world.
Other species are confined to specific regions, they continue to be major problem, particularly to the export fruit producing areas. The pest makes the fruits rot by laying its eggs in clusters, just before the ripening, under the peel of fruits. Hanging of trap (methyl eugionl 0.1 per cent + 0.01 per cent malathion ) during April - June check fruit
Approaches and Strategies for Precision Farming in Mango
fly effectively. Ten traps/ha of orchard give satisfactory control. Fruit fly can be controlled by spraying of bait (0.2 per cent carbaryl + 0.1 per cent protein hydrolysate or molasses) at preoviposition stage. Vapour heat treatment (VHT) at 52oC temperature is
recommended for exporting fruits to foreign markets.
Stone weevil (Sternochetus mangiferae): Stone weevil has been a major deterrent
to mango export. Grubs damage both the pulp and cotyledons mostly of sweet cultivars. The grubs developed from the eggs laid in partially developed fruits, travel through the pulp and enter the seed. After pupation in the seeds the adults come out piercing through the stone and pulp. The pest can be effectively controlled by destroying the adults in the bark crevices and holes during August. For effective control , spraying of trees with fenitrothion (0.01 per cent) during oviposition period is recommended.
Anthracnose (Colletotrichurn gloeosporioides): Anthracnose is one of the most
important diseases of mango in almost all mango-producing areas, as it attacks leaves, flowering panicles and fruits. Yields are drastically reduced when the inflorescence is attacked. Blackish spots on shoots, leaves, panicles and fruits are caused by this pathogen. Its severity is more during rainy season, because of hot and humid atmosphere when fruits are in the last stage of maturity. This disease also expresses itself during storage of fruits. The disease produce die-back symptoms on young shoots. The fungus survives on dried twigs, hence these should be removed from trees and destroyed. Diseased leaves, twigs and fruit lying on floor of the orchards must be removed. Spraying of Blitox (0.3 per cent), Bavistin (0.1 per cent) and Phytolan (0.3 per cent) can control this disease.
Powdery mildew (Oidium mangiferae): The disease is more prevalent during panicle
development and fruit setting period under environmental conditions of high humidity accompanied by cloudy weather. Affected flowers and fruitlets show the appearance of greyish-white powdery growth and the panicles ultimately turn black and die out rapidly. For effective control measures wettable sulphur (0.2 per cent), Karathane (0.1 per cent), Bavistin (0.1 per cent)and Bayleton (0.05 per cent) can be used. Three sprays of these fungicides at 15 days interval starting from fourth week of February may be required.
Mango bacterial canker disease (Xanthomonas campestris pv. mangiferaeindicae): Small dark green water-soaked spots on leaves and fruits which
finally assume the shape of raised dark brown to black lesions are its symptoms. Fruits become unattractive and unmarketable because affected parts of fruits show longitudinal crack and oozing of bacterial exudate and leading to fruit drop. StreptocycIine (100-
200pprn), Agrimycin-100 (100pprn) and copper oxychloride (0.3%) are reported effective against bacterial canker.
Sooty-mould: The disease is common where honey dew or sugary substances secreting
insects, viz. mangohoppers, scales, coccid and mealy bugs are found. These insects must be controlled for controlling the mould. Spraying of wettable sulpher + methyl parathion + gum Accacia (0.2 per cent + 0.10 per cent + 0.3 per cent) in Indian oil formulation No. I and 2 at 15 days interval has proved to be quite effective.