The major diseases are discused below :
Powdery Mildew (Oidium mangiferae Berthet)
Dropping of unfertilized infected flowers and immature fruits cause heavy loss by mildew pathogen (32). In India, the loss varies from 22.35 to 90.41 per cent ( 24). The
1Principal Scientist and Head, Division of Crop Protection, Central Institute for Subtropical Horticulture, Lucknow 227 107, India
11
Precision Farming in Horticulture
Table 1. List of major diseases which affect mango production
Disease Causal pathogens Parasitic diseases Fungal
Powdery mildew Oidium mangiferae Berthet
Anthracnose Colletotrichum gloeosporioides Penz., Glomerella cingulata (Ston.) Spauld and Schrenk.
Die-back Lasioldiplodia theobromae (Pat.) Griff.& Maubl. (Botryodiplodia theobromae Pat.)
Phoma blight Phoma glomerata (Corda) Woll. & Hochapf. Gummosis Lasioldiplodia theobromae (Pat.) Griff. & Maubl. Leaf spot Phoma sorghina (Sacc.) Boerema Doren & Vankest Angular leaf spot Planotrichella mangiferae Prakash and Mishra
Mango malformation Fusarium subglutinans, F. moniliformae var. subglutinans) Sclerotium rot Sclerotium rolfsii Sacc.
Bacterial
Bacterial canker Xanthomonas campestris pv. mangiferaeindicae (Patel), Moniz & Kulkarni) Robbs, Ribiero & Kimura
Non-parasitic diseases
Sooty mould/sooty Meliola mangiferae Earle, Capnodium mangiferae Cke. blotch & Brown, Microxyphium columnatum Bat, Cif & Nasc.,
Leptoxyphium fumago (Woronichin) Srivastava
Algal and lichen
Red rust and lichen Cephaleuros virescens Kunze., Strigula elegans (Fee.) Mull. Arg.
disease can be noticed on inflorescence, stalk of inflorescence, leaves and young fruits. Mildew pathogen attacks flowers resulting in white superficial powdery growth of the fungus on inflorescence which causes its shedding. The sepals are relatively more susceptible than petals. The affected flowers fail to open and may fall prematurely. Dropping of unfertilised infected flowers leads to serious crop loss (Fig. 1).
Integrated Approach in Management of Mango Diseases
Young fruits are covered entirely by white mildew growth. When it grows, epidermis of the infected fruits cracks and corky tissues are formed. Purplish brown blotchy areas appear on skin of older fruits with cracking. Dropping of immature fruits leads to serious crop loss (Fig. 2).
It is frequently noticed on young leaves, when their colour changes from brown to light green. Young leaves are attacked on both the sides as small irregular greyish patches, but on the underside the symptoms are generally more conspicuous. Often, these patches coalesce and occupy larger areas turning into purplish brown in colour. At a later stage, patches become darker in colour. The pathogen is frequently restricted to the area of the central and lateral veins. Such leaves often twist, curl and get distorted.
Recently, it has been observed that distortion of leaves is more common in plains, while in foothill areas, it shows ashy brown patches with white powdery growth on leaf surface.
Perpetuation: Mildew is found
throughout the year on leaves, mostly under shade. The mildew pathogen persists on infected leaves of the previous year’s flush,
which are retained on plants in succeeding year. During flowering (January-March), conducive environmental conditions activate dormant mycelium already persisting in necrotic tissue of previous year’s infected leaves. Abundant conidia are produced and blown over to new flushes or young flowers, which in turn provide sufficient spore load for initiating the disease (18 and 23).
Epidemiology: Prakash et al. (18) advocated that high wind velocity (3-4 days) with
maximum temperature (15-300C) and relative humidity (23-84%) are conducive for
the rapid spread of mildew pathogen.
Fig. 1. Powdery mildew on flowers
Management: Removal of diseased leaves and malformed panicles and fruits reduce
the load of primary inoculum and improve the control achieved by spraying of fungicides. As the inflorescence infection causes serious harm, 3 sprays of fungicides during flowering season are recommended at 15-20 days interval. The first spray of wettable sulphur (0.2%) is done when panicles are 3-4” in size, second spray of dinocap (0.1%) after 15-20 days of first spray and third spray of tridemorph (0.1%) after fruit setting. All sprays with wettable sulphur had no adverse effect on mildew, fruit setting and yield of mango. Bioagent (Actinomycetes) gives some encouraging results (2 and 3). Anthracnose [Colletotrichum gloeosporioides Penz.=Glomerella cingulata (Stons) Spauld & Schrenk]
Losses due to anthracnose are estimated to be as high as 2-39% (16 and 25). Young plantation of mango. Bombay Green and germplasm of East Indian cultivars were completely wiped out in tarai and Lucknow regions of Uttar Pradesh due to severe wither tip. Anthracnose pathogen causes various manifestations, viz. blossom blight, twig blight, foliar blight, staining, russetting, tear staining and shoulder browning. On leaves, symptoms appear as oval or irregular vinaceous brown to deep brown spots of various sizes scattered all over the leaf surface. Under damp conditions, the fungus grows rapidly forming elongated brown necrotic areas measuring 20-25 mm in diameter. Young leaves are more prone to
attack than the older ones.
Petioles, when affected, turn grey or black, the leaves droop down, slowly dry up and ultimately fall-off, leaving a black scar on twigs. Disease produces elongated black necrotic areas on twigs. The tip of very young branches starts drying from tip downwards showing characteristic symptoms of wither tip (Fig. 3).
On blossom, the earliest symptoms are production of blackish brown specks on peduncle and flowers. Small black spots appear on panicles and open flowers, which gradually enlarge and coalesce to cause drying up of flowers (22). On fruit, initially the spots are round but later coalesce to form large irregular
Integrated Approach in Management of Mango Diseases
surface. The spots have large deep cracks and the fungus penetrates deep into the fruit causing extensive rotting (Fig. 4).
Association of anthracnose pathogen with gall midge infested leaves, twigs and inflorescence is often noticed in most of the places in India. Injuries caused by the insect on tissues, activate the pathogen, resulting in heavy incidence of the disease. After the larvae are left for pupation in the soil, the injuries caused by them develops into spot and subsequently attacked by the pathogen and produces into “Shot hole” symptom, the most destructive phase of the disease.
Perpetuation: The pathogen survives on
fallen leaves, blighted peduncle, dead stem, and diseased twigs attached to trees. The pathogen produces spores under favourable conditions and these serve as foci of infection for the succeeding bloom. However under tropical conditions, fresh supplies of spores are being continuously made throughout the year. About 70 per cent spores of the fungus, produced in acervuli on twigs are viable. On diseased leaves, the fungus remains viable for 14 months (16).
Epidemiology: The optimum temperature for infection of pathogen is around 250C.
The injury caused by the pathogen is dependent on humidity, rain, misty condition or heavy dews at the time of blossoming. Continuous wet weather during flowering causes serious blossom blight. Relative humdity above 95% for 12 hr is essential for infection and development of C. gloeosporioides on mango fruits. Infection progresses faster in wounded tissues as well as in ripe fruits.
Management: The management strategies recommended to control anthracnose include
cultural practices and tree management, varietal selection and use of protective and curative fungicides. Remove gall midge infested foliage (twig, leaf and panicles) and fruits from the orchard. Combined sprays of insecticide and fungicide are essential to combat both anthracnose and gall midge. Bagging of individual fruits with brown paper/ newspaper bags enhances the shelf-life, minimize the sunscald and develops attractive
colour without foliage attack. Mustard oil treated fruits have more shelf-life and less fungal invasion (25).
Blossom infection can be controlled effectively by 2 sprays of carbendazim (0.1%) or copper oxychloride (0.3%). The major strategies in controlling post-harvest anthracnose are scheduled pre-harvest sprays with thiophanate methyl or carbendazim (0.1%) in the field to reduce the latent infection and treatment of fruits with hot water alone or hot water with fungicides after harvesting to eradicate the leftover latent infection. Hot-water treatment at 520C for 30 minutes gave good control of anthracnose. However,
duration of hot-water treatment could be reduced to 15 minutes by supplementing with fungicides, viz. carbendazim or thiophanate methyl @ 0.1 per cent (19).
Die-back [Lasiodiplodia theobromae (Pat.) Griffon & Mouble, syn.
Botryodiplodia theobromae Pat.]
About 30-40 per cent roadside trees are found infected, but it goes much more even up to 96.5 per cent in seedling cultivars(32). It is characterized by drying back of twigs from top downwards particularly in the older trees followed by drying of leaves which gives an appearance of fire scorch. Dark patches are usually seen on young
Integrated Approach in Management of Mango Diseases
green twigs (Fig. 5). When the dark lesions increase in size, dying of young twigs begins. The upper leaves lose their green colour and gradually dry (Fig. 6). Internal browning in wood tissue is observed when its slit open along with the long axis. Cracks appear on branches and exude before they die out (13,14 and 26). When graft union of nursery plants are affected, these usually die. It has also been noticed that the infection occurs at nodes at variable distances below growing point and the part of twigs on both the sides of infection die (32).
Perpetuation: The organism is a wound parasite and capable of causing great damage
under favourable conditions. The pathogen penetrates the host through epidermal wounds and lenticels. Artificial inoculation experiments have shown that establishment of the fungus requires at least 48 hr at 27-300 C and RH of 80-85 per cent. The fungus
remains in vascular tissues until tissues die. Diseased twigs bearing fruiting bodies are the main source of perpetuation and survival of the pathogen. Use of infected bud stick is largely responsible for carry over of the pathogen from one season to the next and for spreading to new areas. Within orchards, the most important means of spread are inoculum already present and contaminated garden tools. The former accounts for the increase in disease severity and the latter contributes to the survival and spread of the pathogen within an area and from season to season. Trees damaged by gummosis, insects, sun scorch, tangle foot, stress, injury and mineral deficiencies favour disease development (10).
Epidemiology: High summer temperature predisposes the mango plants to the attack
of pathogen through reducing the vitality of plants. Disease development is favoured by rains, relative humidity (approximately 80%) and maximum and minimum temperatures of 31.5 and 25.9oC. The growth of germ tube of single celled spores was best at 30oC.
On exposure to higher temperature (54oC) for 10 minutes, loose spores lost their viability.
The mango beetle (Batocera rufomaculata) aggravates the disease incidence (12 and 26).
Management: Scion wood selected for propagation should be free from infection,
while multiplying the planting material. Pruning (3” below the infection site) followed by spraying of copper oxychloride (0.3%) is most effective method to control it. Pasting of cowdung at cut ends is very effective (2).
Phoma Blight [Phoma glomerata (Corda) Woll. & Hochapf]
lesions are minute, irregular, angular, yellow to light brown, scattered all over the leaf lamina. As the lesions enlarge, their colour changes from brown to cinnamon, and these become irregular in shape. Fully developed spots are characterized by dark margin and dull grey necrotic centres. In severe cases, the spots coalesce to form big patches, which result in withering and defoliation of infected leaves (Fig. 7). Such plants can be identified easily from a distance (27 and 31).
Management: Spraying of benomyl (0.2%) or
copper oxychloride (0.3%) have been found effective against this disease (32).
Gummosis [Lasiodiplodia theobromae (Pat.) Grifton and Mauble, syn. Botryodiplodia theobromae Pat., perfect stage Physalospora rhodina].
The disease is characterized by the presence of profuse oozing of gum on the surface of affected wood, bark of trunk and also on larger branches but more common on cracked branches. In severe cases, droplets of gum trickle down on stem and the bark turns dark brown with longitudinal cracks. Bark rots completely and tree dries up because of cracking, rotting and girdling effects (32).
Management
The affected bark/portion should be removed, cleaned and covered with cowdung or copper oxychloride paste. Application of copper sulphate (500 g/tree, depending upon the age of the tree) in soil around the tree trunk is advocated. Application of fresh cowdung around trunk or cut portion is also advocated (2).
Leaf Spot [Phoma sorghina (Sacc.) Boerema. Doren. & Vankest]
This leaf spot disease caused by Phoma sorghina has been reported on mango from Lucknow, India (20). Disease manifests itself in the form of small, irregular, oval to roughly circular water-soaked spots on young leaves, measuring mere pinhead to 2.5 mm in size. Lesions are brown, later differentiated into brown margin with straw colour. Yellow halo around the brown margin is also observed. The infected leaves become brown and ultimately dry. Lesions near the midrib are elongated and more conspicuous. In severe cases, the spots coalesce to form large spots measuring up to 14 mm. Symptoms
Integrated Approach in Management of Mango Diseases
produced by this fungus are very much much similar to those of anthracnose and these may sometimes be confused. In this case, spots are smaller and there is no cracking in the centre as found in anthracnose (10 and 32).
Management
Control measures are the same as reported for phoma blight disease. Angular Leaf Spot (Plenotrichella mangiferae Prakash & Misra)
Initially spots are minute, irregular and brown in colour. In due course, they enlarge and turn darker in colour. Spots are distinctively visible on both the surfaces of leaves and are irregularly scattered on the entire leaf surface more towards midrib. The spots are mostly angular in shape and are generally restricted by the midrib or side veins. As the spots turn older, the central area becomes grey to almost white, with distinct dark brown margin, which is characteristic symptom of the disease. Spots vary in size (3-11 mm x 2-8 mm) (Fig. 8). Number of black pycnidial bodies are distinctly visible in grey area on the old spots (17).
Spot epiphyllous, irregularly circular, olivaceous, with black dots, measuring 3-11 mm x 2-8 mm of diameter. Mycelium superficial, hyphae septate, not constricted, abundant, ramified, having arborescent disposition, olivaceous-maroon, having cells of 7.0-14.5 x 2.0-2.5 µm covering the pycniostromata. Absence of septa and hyphopodia. Pycniostromata superficial, membranous, isolated, orbicular, scutellar, dimidiated, meandriform, astomous, of irregular dehiscence at maturity, 320- 490 µm of diameter., 15-24 µm of height, maroon, glabrous; edges thin, clear maroon, film-like, up to 85 µm of extension; lower wall indistinct.
Conidiophores not observed. Hymenium superior and hence inverted. Pycnidiospores fusoid, continuous, sessile straight or curved with 9.0-1.5 x 1-2.0 µm.
Management : The disease is controlled by spraying of Carbendazim (0.1%) at 20
days’ interval before emergence of symptoms (17). Malformation (Fusarium subglutinans)
Malformation, also known as bunchy top, is a serious threat in mango-growing Fig. 8. Angular leaf spot
areas of the world. In recent years, the extent of this malady has taken such a high magnitude that the mango industry is badly threatened in India, particularly in northern mango belt. In spite of a lapse of hundred years since the disease was first reported and a good number of papers published on mango malformation (MM), the etiology of the disease still remains obscure. The complex nature of the malady is obvious by the diverse claims made by different workers from different countries about its cause(s) ranging from physiological, viral, fungal, acarological
to nutritional (12 and 18).
Mango malformation is of two types – vegetative and floral. Vegeative malformation is pronounced in young seedlings. The afected seedlings develop excessie vegetative growth. The internodes are of limited growth and short. These form bunches of various sizes, which are often produced on tips of seedlings giving buncy top appearance. Such formations are also found on bigh plants but are relatively less (Fig. 9).
Floral malformation is characerizied by the reduction in length of primary axis and secondary branches of the panicle, which make the flowers, appear in clusters. The flower buds
are transformed into vegetative buds and a larger number of small leaves and stems, which are characterized by appreciably reduced internodes, give a witch’s broom-like appearance (Fig. 10).
Management: Definite control
measures for mango malformation can be advocated. However, following measures may reduce the
incidence of malformations. It is advisable to avoid scion stick from trees bearing malformed inflorescence for propagation. Indexing of healthy mango trees be done to serve as material for propagation. Only certified samplings should be used for propagation.
Fig. 9. Vegetative malformation
Integrated Approach in Management of Mango Diseases
As soon as the disease symptom is noticed, the affected terminals should be pruned along with the basal 15-20 cm apparently healthy portion and burnt. Healthy orchards located in disease-prone pockets should be sprayed with fungicides/insecticides as a prophylactic measure to avoid further recurrence of the disease. Spraying of 200 ppm NAA in the first week of October is advocated followed by deblossoming at bud-burst stage. Early flowers should be deblossomed.
Sclerotium Rot (Sclerotium rolfsii Sacc.) About 18 per cent mango seedlings died of stem rot and many of the seeds (stones) rotted before or in the course of germination (28 and 30). The disease is characterized by the presence of mycelial weft on the base of the stem at the ground level. Beneath the mycelial growth, a dark brown spot may develop which gradually encircles the base of the stem. At this stage, the succulent top droops and bends towards the ground, tissues lose turgidity and seedlings die within a week. When the disease is at peak, the fungus may be seen encircling stem up to the height of 2" or even more above the ground level. The disease also causes severe rotting of seeds during or before germination. Numerous sclerotia develop on cotyledons of rotted seeds (Fig. 11).
Perpetuation: The sclerotia remain viable for more than a year under drought conditions
while in moist conditions persist longer or indefinitely, especially if susceptible hosts are present. The fungus passes over adverse conditions by means of sclerotial bodies. The sclerotia kept in dry conditions remained alive for more than a year.
Management: Infected soil should be thoroughly surface burnt before the seed beds
are prepared. Diseased mango and weeds should be removed and burn. Excessive use of water and close planting should be avoided as the organism is moisture-loving. Seed beds should be prepared with sufficient drainage arrangement. Planting of susceptible hosts should be avoided. Two minutes dipping of stones in Agallol/Brassicol/ Captan/Thiram/ Carbendazin (0.1%) and subsequent soil drenching at 10-15 days interval reduce the intensity of the disease (28).
Fig. 11. Sclerotium rot on young seedlings
Bacterial Canker Disease (Xanthomonas campestris pv. mangiferaeindicae Patel, Moniz & Kulkarni) Robbs, Ribiero & Kimura
The promising mango industry in northern India is threatened by bacterial canker disease. During early sixties, the disease was considered as a minor, but now it is posing a great threat to the commercial cultivars (Dashehari, Mallika and Amrapali) as well as seedling cultivars grown in the country. Canker incidence was noticed first time in polyembryonic cultivars of mango. Its widespread and severity posed much losses of mango fruits. Recurrence, intensity and spread of the disease have also been observed gradually extending in new areas (15,18 and 20).
Bacterial canker caused by Xanthomonas campestris pv. mangiferaeindicae became serious in Uttar Pradesh mainly in Lucknow as early as 1978 and thus has been commonly present in most of the states. The disease is quite widespread in mango- growing regions of the world (15,18 and 21). The losses are as high as 100% in certain