Powdery mildew is a fungal disease that affects a wide range of plants. Powdery mildew diseases are caused by many different species of fungi in the order Erysiphales. Powdery mildew is one of the easier plant diseases to identify, as its symptoms are quite distinctive. Infected plants display white powdery spots on the leaves and stems. The lower leaves are the most affected, but the mildew can appear on any above-ground part of the plant. As the disease progresses, the spots get larger and denser as large numbers of asexual spores are formed, and the mildew may spread up and down the length of the plant.
Although infection occurs both on foliage and blossom but loss due to powdery mildew is mainly as a result of blossom infection. Hence, spraying of fungicides during flowering stage is utmost essential. In India, incidence of powdery mildew has assumed such a devastating proportion that the disease has become the single limiting factor in expansion of the mango crop cultivation. Dropping of unfertilized infected flowers and immature fruits leads to serious losses.
Wefts of whitish grey mycelium appear initially on the inflorescence (flowers and flower buds) (Plate 1h). Later, the fungus spreads to tender fruits, leaves and shoots. The entire surface is covered with a powdery substance consisting of millions of spores, called condia which are borne in chains. Mildew pathogen attacks mango flowers, resulting in their shedding. The sepals are particularly more susceptible than the petals. The affected flowers fail to open and may fall prematurely.
Young fruits are entirely covered by the mildew (Plate Ii). When the fruit grows, its epidermis in the infected area cracks and corky tissues are formed, Purplish brown blotchy areas appear on the skin of fruits. Such fruits drop prematurely and some may remain on the tree until they reach up to pea size.
Since the description of the perfect stage of the pathogen has not been given, the conidial stage is known as Oidium mangiferae Barthet.
The pathogen is not reported on hosts other than mango (Prakash and Srivastava, 1987). Datar (1985), Munshi et al. (1988) and Gupta (1989) studied the perpetuation of 0. mangiferae on leaves and malformed inflorescence. Studies conducted at Lucknow revealed that mildew pathogen persists on infected leaves of the previous year's flush which are retained on the plant in the succeeding year. Abundant conidia are produced and blown over to the new flushes and provide sufficient spore load for initiating the disease. Fresh infection of mildew on young leaves in the first week of December (when flowers are not present) further confirms that the fungus perpetuates in asexual form on leaves of mango (Prakash and Raoof, 1985a). In recent studies Misra and Prakash (1995) found severe foliar powdery mildew of mango in foot hill areas of Pinjore and Dehradun during off season i.e. September which may also serve as important area where powdery mildew survives during offseason
Cultural: Effective eradication of inoculum would contribute greatly in lowering the level of infection and would improve the control achieved by spraying fungicides (Prakash and Misra, 1992, 1993; Prakash and Raoof, 1994). The loss could be reduced by 50-75 per cent if branches are shaken after each shower.
Chemical: Chemical control is the most widely adopted measure for management of mango powdery mildew.
A large number of fungicides have been tried for the control of powdery mildew of mango. Sulphur dust, wettable sulphur, dinocap, tridemorph, and carbendazim are quite effective in controlling mango powdery mildew besides several newer fungicides viz. triadimefon, thiophanate-methyl, bitertanol, hexaconazole, flusilazole, fenarimol, cyproconazole, penconazole etc. (Anonymous, 1986-96). Prakash and Raoof(1985a) tested a spray schedule at 3 stages (emergence ofpanicies, opening of flowers, and fruit set).
Spraying of Bavistin (0.1 %) at 20 days interval was found quite effective in reducing the disease (Prakash and Raoof, 1982, 1994). Sharma (1992) also found it effective at 15 days interval in H.P. Three sprays of either Microsul (0.2%) or Bavistin (0.1 %) were found most effective in controlling this disease (Prakash and Raoof, 1982, 1985c). Brooks (1991) reported excellent control of mango powdery mildew by Punch (flusilazole + carbendazim) The phytotoxic problem with sulphur dust during hot weather conditions is reported in the dry tropics (petersonet ai., 1991). All the wettable sulphur fungicides tested significantly controlled the disease without any phytotoxic effect. Use of wettable sulphur reduces the cost on fungicides application (Prakash and Misra, 1986a). In some regions, both mildew and hopper occur together. In such case a combined treatment of fungicides and insecticides has also been recommended (Pal and Prakash, 1984).
Resistant varieties: Differences in cultivars susceptible to mildew are widely recognized by various workers (Palti et aI., 1974, Gupta, 1976; Prakash and Misra, 1986b; Prakash and Raoof 1994; Datar, 1983) but none of the cvs. has been found immune or potentially suitable for incorporating in the breeding programme.
Symptoms
Wefts of whitish grey mycelium appear initially on the inflorescence (flowers and flower buds) (Plate 1h). Later, the fungus spreads to tender fruits, leaves and shoots. The entire surface is covered with a powdery substance consisting of millions of spores, called condia which are borne in chains. Mildew pathogen attacks mango flowers, resulting in their shedding. The sepals are particularly more susceptible than the petals. The affected flowers fail to open and may fall prematurely.
Young fruits are entirely covered by the mildew (Plate Ii). When the fruit grows, its epidermis in the infected area cracks and corky tissues are formed, Purplish brown blotchy areas appear on the skin of fruits. Such fruits drop prematurely and some may remain on the tree until they reach up to pea size.
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| Powdery Mildew on Mango Flowers |
Infection is frequently noticed on young leaves also, when their color changes from brown to light green. Young leaves are attacked on both the sides but mostly on their underside as small irregular greyish patches (Plate 1g). Often, these patches coalesce and occupy larger area turning into purplish brown in color. Under favorable environmental conditions, the invaded areas are covered with a luxuriant whitish growth, consisting of mycelial mat and conidia. Recently Misra and Prakash (1995) observed that while distortion of leaves is more common in plains, in the foot hill areas leaves generally showed ashy brown patches with white powdery growth on their surface.
Causal pathogen(Infectious Agent)
Since the description of the perfect stage of the pathogen has not been given, the conidial stage is known as Oidium mangiferae Barthet.
Epidemiology
The pathogen is not reported on hosts other than mango (Prakash and Srivastava, 1987). Datar (1985), Munshi et al. (1988) and Gupta (1989) studied the perpetuation of 0. mangiferae on leaves and malformed inflorescence. Studies conducted at Lucknow revealed that mildew pathogen persists on infected leaves of the previous year's flush which are retained on the plant in the succeeding year. Abundant conidia are produced and blown over to the new flushes and provide sufficient spore load for initiating the disease. Fresh infection of mildew on young leaves in the first week of December (when flowers are not present) further confirms that the fungus perpetuates in asexual form on leaves of mango (Prakash and Raoof, 1985a). In recent studies Misra and Prakash (1995) found severe foliar powdery mildew of mango in foot hill areas of Pinjore and Dehradun during off season i.e. September which may also serve as important area where powdery mildew survives during offseason
Gupta (1989) reported that dry weather favours the development of disease. Misra and Prakash (1988) stated that predominance of susceptible cultivar 'Dashehri', high wind velocity for 3-4 days with maximum temperature around 30°C, minimum temperature around 15°C and minimum and maximum relative humidity of23.4-25.5 per cent and 73.3 - 83.9 per cent respectively are conducive for the rapid spread of mildew pathogen in Kakori and Malihabad mango belt. Gupta (1988) reported that conidia of mildew are mainly liberated from 12.00 to 16.00h. In South Africa, Schoeman et al.(1995) trapped greatest number of conidia between 11.00 and 16.00h. In South Africa Joubert (199 I) observed first symptom of powdery mildew in beginning of August. Full bloom and fruit set to pea size stages were most susceptible. Lonsdale and Kotze (1991 b) also found July-August critical for powdery mildew in S. Africa
Management
Cultural: Effective eradication of inoculum would contribute greatly in lowering the level of infection and would improve the control achieved by spraying fungicides (Prakash and Misra, 1992, 1993; Prakash and Raoof, 1994). The loss could be reduced by 50-75 per cent if branches are shaken after each shower.
Chemical: Chemical control is the most widely adopted measure for management of mango powdery mildew.
A large number of fungicides have been tried for the control of powdery mildew of mango. Sulphur dust, wettable sulphur, dinocap, tridemorph, and carbendazim are quite effective in controlling mango powdery mildew besides several newer fungicides viz. triadimefon, thiophanate-methyl, bitertanol, hexaconazole, flusilazole, fenarimol, cyproconazole, penconazole etc. (Anonymous, 1986-96). Prakash and Raoof(1985a) tested a spray schedule at 3 stages (emergence ofpanicies, opening of flowers, and fruit set).
Spraying of Bavistin (0.1 %) at 20 days interval was found quite effective in reducing the disease (Prakash and Raoof, 1982, 1994). Sharma (1992) also found it effective at 15 days interval in H.P. Three sprays of either Microsul (0.2%) or Bavistin (0.1 %) were found most effective in controlling this disease (Prakash and Raoof, 1982, 1985c). Brooks (1991) reported excellent control of mango powdery mildew by Punch (flusilazole + carbendazim) The phytotoxic problem with sulphur dust during hot weather conditions is reported in the dry tropics (petersonet ai., 1991). All the wettable sulphur fungicides tested significantly controlled the disease without any phytotoxic effect. Use of wettable sulphur reduces the cost on fungicides application (Prakash and Misra, 1986a). In some regions, both mildew and hopper occur together. In such case a combined treatment of fungicides and insecticides has also been recommended (Pal and Prakash, 1984).
Resistant varieties: Differences in cultivars susceptible to mildew are widely recognized by various workers (Palti et aI., 1974, Gupta, 1976; Prakash and Misra, 1986b; Prakash and Raoof 1994; Datar, 1983) but none of the cvs. has been found immune or potentially suitable for incorporating in the breeding programme.
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