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The following points highlight the four major diseases of foxtail millet with its management. The diseases are: 1. Blast 2. Rust 3. Smut 4. Downy Mildew.
Foxtail Millet: Disease # 1. Blast:
Blast caused by Pyricularia setariae was reported from Tamil Nadu in 1919, though Nishikado recorded this disease in Japan during 1917. Since then the disease is known to occur every year during rainy season causing considerable grain losses in many states of India.
In its severe form the disease can lead up to 30-40 per cent loss in the grain yield. The isolate from Setaria readily infects finger millet, pearl millet, wheat and Dactyloctaenium aegyptium.
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Plants up to 40 days old are highly susceptible to blast. On leaves symptoms develop as small pin head water soaked yellowish dot that turns circular or oval shaped within 2-3 days with greyish centre surrounded by dark brown margin.
The small and scattered spots measure 2 to 5 mm in diameter. The spots coalesce and in severe form the leaves wither and dry up. When the node is affected, it turns black and breaks at the nodal junction.
The factors that influence disease severity are susceptible variety, availability of inoculum to initiate the disease, excessive application of nitrogen fertilizers, cloudy and drizzling weather or dew resulting in continuous leaf wetness for more than 10 h, night temperature between 15 to 24°C and relative humidity above 90 per cent.
Management of Blast:
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When initial blast spots are seen immediate spraying with fungicides like Carbendazim 50 WP at the rate 1 g/litre or Ediphenphos 50 EC at the rate 1g/Litre of water or combination product of Carbendazim + Mancozeb at the rate 1 g/litre water has to be resorted to intercept further development of the disease.
Top dressing of nitrogen has to be taken up after the fungicidal spray. Singh (1976) found the varieties SR 118, SR 102, ISc 709, 701, 703, 710, 201, JNSc 33, 56, RS 179 and ST 5307 as resistant to blast.
Foxtail Millet: Disease # 2. Rust:
Rust caused by the fungus Uromyces setariae italica was first recorded by Yoshino from Japan. It is very common on Setaria and has also been reported in Europe, Asia and Africa.
In India, it is known to be prevalent in Maharashtra, Madhya Pradesh, Tamil Nadu, Karnataka, Andhra Pradesh, Bihar and wherever this crop is grown but was of little economic importance. During certain years it becomes Epiphytotic and causes extensive losses in yield.
The disease affects the crop at all the stages, however, the damage is more when infection occurs before flowering. Numerous minute brown uredosori appear on both the sides of the leaf.
Though they are often arranged in linear rows, in heavily infected leaves they cover almost the entire leaf blade. They can also be seen on the leaf sheath, culms and stem. If infection is severe premature drying of leaves and poor grain set are observed.
The telia, which are larger than the uredia, are formed on the leaf blade, leaf sheath and stem. The teliospores are single celled, pedicellate, oblong, globose, yellowish brown, with smooth, thick walls, which are much thicker at the apex than at the base. The fungus can perpetuate in its uredial stage, with the collateral hosts possibly playing a part in its perpetuation.
Low temperature and high relative humidity are favourable for severity of the disease. During December and January months, if environmental conditions are favourable then rust appears within 20 to 25 days after sowing and the intensity increases as the plant grows older.
Management of Rust:
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Removal of collateral hosts and sprays of Mancozeb at the rate 2.5 g/ litre of water, immediately after the initiation of symptoms are some of the measures, which can reduce the severity of this disease.
Foxtail Millet: Disease # 3. Smut:
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Smut caused by Ustilago crameri is common in India, China, Europe and Manchuria. In India, it is prevalent in Karnataka, Andhra Pradesh, Tamil Nadu and Maharashtra causing heavy crop loss.
The grain loss caused by the disease varies from 8-50 per cent of the grain yield. Sundararaman (1921) reported 75 per cent infection in grains of Setaria. Fischer (1953) reported that inhalation of spores during threshing may cause Asthma among labourers.
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Low temperature and high relative humidity are favourable for rapid development and spread of the disease. The fungus affects most of the grains in an ear producing sori in the flowers and basal parts of the palea but sometimes terminal portion of the spike may escape.
The sori are pale greyish in colour and measure up to 2-4 mm in diameter. When the crop matures, the sori rupture and produce dark powdery mass of spores. The spores are dark brown and angular or round in shape and smooth walled measuring 7-10p in diameter.
The fungus is externally seed borne. Soil borne infection has also been observed. Wang (1943) recorded that the dikaryotic hyphae penetrated the tissues of two day old seedlings by mechanical pressure.
Management of Smut:
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This seed borne disease can be controlled by steeping seeds in 2 per cent copper sulphate solution or 0.5 per cent formalin for about 30 minutes. Seed treatment with Carbendazim at the rate 2 g/kg seed is also effective.
Foxtail Millet: Disease # 4. Downy Mildew:
Downy mildew (Sclerospora graminicola) is known to occur in India, China, Japan, Russia, Manchuria and the South-Eastern countries of Europe and America. In India it is prevalent in Maharashtra, Tamil Nadu, Karnataka, Andhra Pradesh, Bihar and Kashmir. In certain years it has caused losses up to 50 per cent in the foxtail millet crop.
The first symptom of the disease is chlorosis of the seedling leaves. The terminal spindle fails to unroll, becomes chlorortic which later turns brown and gets shredded. In the early stage of development, a whitish bloom of sporangiophores and sporangia of fungus are prominent on the surface of leaves in humid conditions.
When the infection is mild, the plant may develop ears, but the floral parts are proliferated into green leafy structures showing ‘green ear’ symptom. The entire parts of a spikelet including glumes, lemmae, paleae, stamens and pistils are converted into green leafy structures of variable size.
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While the fungus usually invades the entire ear, sometimes only a portion of the ear is involved, the remainder producing normal grains. When the infection is secondary, occurring late in the season, only chlorotic patches are seen on the upper leaf surface, with the downy fungus growth on the corresponding lower surface.
The fungus is an obligate parasite. The primary infection is mainly soil or seed borne oospores. The intensity of infection is influenced by the temperature and moisture content of the soil. The optimum soil temperature for infection is 20-21°C, the minimum temperature is 12-13°C and the maximum temperature is 30°C.
Intensity of infection is also influenced by time of sowing. The intensity will be high in the early sown crop than late sown crop. High relative humidity and high soil moisture content favour rapid development of the disease.
Management of Downy Mildew:
Collection and removal of infected plant debris helps in reducing the inoculum in the field. Since, the disease is partly seed borne, seed treatment with Ridomil MZ 72 WP at the rate 3 g/kg of seed helps in eliminating seed borne infection and protects the young seedlings from infection by the seed borne inoculum.
