The following points highlight the seven major diseases of finger millet with its management. The diseases are: 1. Blast 2. Seedling Blight 3. Wilt or Foot Rot 4. Cercospora Leaf Spot 5. Downy Mildew or Green Ear Disease 6. Smut 7. Damping-Off.
Finger Millet: Disease # 1. Blast:
Of the several fungal diseases that affect finger millet crop, blast disease caused by Pyricularia grisea is by far the most important disease. The disease was reported for the first time in India, from Tanjore delta of Tamil Nadu by McRae (1920).
Since then, the disease is known to occur almost every year during rainy season in all major ragi growing areas and is perceived as is one of the major disease causing recurring yield losses in all the states of India.
The extent of damage depends on the severity and time of onset of disease. The average loss due to finger millet blast has been reported to be around 28% and has been reported as high as 80-90% in endemic areas. Finger millet blast disease is by far the most devastating, causing over 50% yield loss.
According to McRae (1922) the grain loss due to blast could be over 56 per cent, while, Venkatarayan (1947) reported more than 80 per cent yield loss in Mysore. Sunil and Anilkumar (2004a) reported 3-35% loss in 1000-grain mass in head blast-affected ear heads in Bangalore.
The plant is susceptible to the disease during all stages of its growth, from seedling to grain formation stage. Young seedlings are affected both in the nursery and in the field. The lesions are generally of spindle shaped, however lesions of different sizes may also be observed. In the beginning the spots have yellowish margin and grayish centre.
Later, the centres become whitish grey and disintegrate. Under humid conditions, olive-grey fungal overgrowth can be seen at the centre of the lesions. The fungal growth comprises of conidiophores and conidia. In the beginning the lesions are isolated and afterwards they may soon coalesce. The distal portion of the leaves beyond the lesions may hang and drop off.
In older plants, the disease appears on leaf blades with typical spindle shaped spots. Under congenial conditions, such spots enlarge, coalesce and form bigger lesions. The lesions are like those on the seedlings and are about 0.3-0.5 cm in breadth and 1-2 cm in length. The apices of the infected leaves beyond the lesions hang down and sometimes break.
Stem infection causes blackening of the nodal region, penetrating into the tissues. Maximum damage is caused by neck infection. The neck region turns black and shrinks. Olive grey fungal growth is also seen on the affected area. During severe infection the ears hang down from the stalk and sometimes may also break away.
In later stages of crop occurrence of finger blast is observed. The infection on fingers usually begins from the apical portions and extends towards the base. Generally the infected ears become chaffy and only a few shrivelled grains may be found. The affected portions of the earhead turn black. The extent of loss in grain yield depends upon the time of infection.
The pathogen harbours in glumes, straw as well as on some graminaceous weeds. The seeds have also been found to carry the pathogen in the pericarp and endosperm. The climatic conditions having a temperature of 25 to 30°C, more than 90 per cent humidity and cloudy days with intermittent rainfall, are congenial for rapid development and spread of the disease.
Continuous rains at the time of heading may lead to heavy losses to the crop. It has also been observed that the incidence of blast disease increases with the increased doses of nitrogen.
Management of Blast:
Since, the primary infection comes from seed-borne inoculum, treating seeds with Tricyclazole (8g/kg seed) followed by sprays of two plant extracts of notchi and Prosopohis sp. have been found effective.
During later stages of the crop two sprays of Ediphenphos or Kitazin or propiconazole (0.1%) or Carbendazim or tricyclazole (0.05%), first at the time of ear emergence and second after 10 days or an initial spray of 0.05% Carbendazim or tricyclazole followed by a spray of Mancozeb (0.2%) 10 days later are effective.
In all India evaluation of plant products under AICSMIP, Vijayaneem and Econeem were found to be effective in many centers. Two sprays of Saaf (0.2%) first at 50 per cent flowering and again 10 days later were also found effective in reducing the blast and increasing the yield.
In addition to the chemical control, use of resistant varieties/genotypes like; VL 149, GPU 26, GPU 28, GPU 45, CO 13, GE Nos. 510 (E2-2-1), 568 (E2-7-1), 669 (IE1012; Africa), 496 (316; IND-MP), 532 (E2-3-2), 942 (IE 453), 965 (PE367; IND-UP), 1014 (V 117; IND-KAR), 1029 (TAH 409; IND-KAR), 1044 (HR 309-4; IND-KAR), 1126 (IE 24), 1328 (P 226; Africa) 1409 (P249; Africa), GE 632, GE 637, GE 669, GE 674, GE 676, GE 705, GE 718, GE 728, 2400, 4913, 4914, 4915, 4929, 4966, 5102, 5126 and 5148, IE 287, IE 976 and IC 43335 coupled with Carbendazim seed treatment at the rate 2g/kg is also effective.
Seed treatment with Trichoderma harzianum (TH) and one spray of Pseudomonas fluorescens at the time of flowering and second spray 10 days later can also control all three blast diseases. However, in organically grown finger millet, two sprays of P. fluorescens copyright 0.3% (first spray at 50% flowering followed by second spray 10 days later) are recommended for the control of neck and finger blasts.
Patro (2008) also reported that seed treatment with P. fluorescens at the rate 0.6% followed by two sprays of same, first at 50% flowering followed by second spray 10 days later ,was found to be the best for the management of blast disease. Allitin (0.1%), a synthetic product of garlic oil and neem oil were also found effective against blast pathogen P. grisea, under in vitro conditions.
Finger Millet: Disease # 2. Seedling Blight:
Seedling blight or leaf blight of finger millet caused by Drechslera nodulosum is next only to blast in terms of severity and distribution. The disease was first noticed by Butler (1918) causing foot rot, seedling blight or leaf blight of finger millet in different parts of India. In India, the disease is known to occur in Madhya Pradesh, Andhra Pradesh, Maharashtra, Uttar Pradesh, Bihar, Tamil Nadu and Karnataka.
The disease affects all the parts of plant like root, base of the plant, culms, leaf sheath, leaf blade, neck of the panicle and fingers. When infected seeds are may not germinate at all due to pre-emergence seed rot. In case such seeds germinate, post-emergence rot is very commonly seen.
The characteristics symptom on leaf lamina is appearance of brown to dark brown spots. These spots are generally oval in shape and measure 8-10 mm in length and 1-1.5 mm in breadth. Later, these spots coalesce to give the blightning appearance of leaf, especially towards tip which would ultimately be killed prematurely.
The disease also affects culm especially at nodal joints. Symptoms are also seen on leaf sheath, especially in older plants, where, in the centre of the lesion the woolly growth of the fungus may be observed under high humid conditions. The area at the juncture of leaf sheath and leaf blade is usually affected resulting in dark brownish discolouration.
Under favourable conditions, foot rot symptom is also seen. In neck infection dark tan lesions are seen initially, which may enlarge and extend up and down. In severe conditions, the neck may break and hang on to the plant. The pathogen may attack ear head, fingers as well as grains. The affected grains may not develop fully and shrivel, resulting in heavy crop losses.
The pathogen survives in soil for over 18 months and the spores on grains are reported to be viable for a year. According to McRae (1932) the optimum temperature for infection is 30-32°C, however disease can occur between 10°C and 37°C. High humidity and intermittent rains during the period of ear emergence and before grain formation causes heavy ear infection and reduction in yield.
Management of Seedling Blight:
Grewal and Pal (1965) reported that as the disease is primarily seed borne, seed treatment with Agrosan G.N. can give complete control of pre-emergence damping off seedling blight. Secondary infection can be reduced by spraying of Mancozeb at the rate 0.2 per cent control the disease.
According to Ahmed and Sullia (1973) fairly low concentrations fungicides folithion and morestan and a rhizome extract of canna inhibited germination of H. nodulosum pathogen of seedling blight and leaf spot of ragi. Allitin (0.1%), a synthetic product of garlic oil and neem oil were also found effective against H. nodulosum, the brown spot pathogen under in vitro conditions.
Finger Millet: Disease # 3. Wilt or Foot Rot:
Coleman (1920) was first in India to record the occurrence of wilt or foot rot caused by Sclerotium rolfsii from the then princely state of Mysore. Since then, disease is known to be prevalent in all regions wherever the crop is cultivated. Up to 50 per cent loss due to this disease has been recorded.
The disease appears randomly in the field. The infected plants become pale, chlorotic and stunted. The infection occurs just above the ground in collar region. The basal portion initially appears water soaked which later turns brown and subsequently dark brown with concomitant shrinking of the stem in the affected portion.
Profuse cottony mycelial growth of the pathogen can easily be seen in this area. Soon small roundish white velvety grains like sclerotial bodies start appearing in the fungal matrix which grow and later turn brown. Meanwhile the leaves loose their luster, droop and dry. Ultimately the plant dries up prematurely.
The fungus is mainly soil borne and has a very wide host range, thus survives in almost all soils. However, sandy loam soils and low soil moisture levels favour disease incidence. The disease incidence is more during warm and dry months.
Management of Wilt or Foot Rot:
It is not economical to control the disease through chemicals. However, Lucy Channamma (1980) reported that Vitavax at the rate 10 kg/ha incorporated into the soil being effective in controlling this disease.
The ideal way of managing disease would be cultural methods like deep ploughing before sowing, crop rotation with non-graminaceous crops and maintaining optimum soil conditions etc. Recently, Prakash and Ravishankar, (2007b) reported that genotypes GPU 28, RAU 8, L – 49 – 1, MR 6, OEB 82, PR 202 and OEB 10 are highly resistant to foot rot disease.
Finger Millet: Disease # 4. Cercospora Leaf Spot:
Cercospora leaf spot of finger millet (caused by Cercospora eleusine) is a serious disease in mid and high hills, where rainfall is high and mean daily temperature does not exceed 20°C. The disease has been found to occur in Nepal and Uttarakhand hills.
In Uttarakhand the disease occur from 850 m to >1900 m altitude. The disease if occurs immediately after heading, can reduce up to 40 per cent of the yield. However, there will be no loss in yield when the disease incidence is around 25 per cent.
The disease occurs most severely in the month of June in the early sown crop. Infection generally starts from the older leaves and then spreads to the young leaves.
Thus progressive infection from older to younger leaves can be observed in the standing crop. Initial symptoms appear as reddish brown speaks with yellow halo and are easily confused with those of Helminthosporiose. Later, several such specks coalesce to form large lesions with any yellow hallow.
In some cases the lesions enlarge to assume eye shaped spot measuring up to 15x3mm. Such leaves give burnt appearance. At the time of crop maturity severely infected leaves turn completely necrotic, shrivel and dry. At this stage the plants look completely blighted. Such symptoms can also be seen on the stem, leaf sheath and fingers.
Management of Cercospora Leaf Spot:
Several chemicals and biocontrol agents had been tested to for reducing the severity of cercospora leaf spot disease for many years but no convincing treatment has yet been found effective. However, field sanitation and spraying of Carbendazim at the rate 0.05% has been reported to reduce infection to some extent.
Development of varieties with inbuilt genetic resistance is the best means of combating disease problem in any crop where proper chemical management is lacking. Breeding for cercospora leaf spot disease resistance in ragi assumes greater importance in this context. Each year scores of germplasm entries are screened at Ranichauri, under natural disease pressure in field conditions.
Nearly 840 entries have been screened during 1994-1999 under different nurseries, viz., advanced varietal trial – early duration, advanced varietal trial – medium duration (AVT-II), advanced varietal trial – late duration (AVT-XII), initial varietal trial (IVT) and national screening nursery (NSN).
Out of the material screened under AVT-I, II and III no entry was ever found to be resistant while only VL 337 showed resistant reaction under SVT and NSN trials, respectively.
Finger Millet: Disease # 5. Downy Mildew or Green Ear Disease:
Downy mildew or green ear disease of ragi caused by Sclerophthora macrospora was reported for the first time in India by Venkatarayan (1946) from old Mysore state. It appeared in a severe form in the same state in 1948. Since then, it is known to occur in Tamil Nadu and other states in India. The disease has also been recorded on maize and E. indica from Indiana in the United States.
The downy mildew affected plants are generally stunted with shortened internodes and profuse tillering. The plant assumes a bunchy and bushy appearance. Often, pale yellow translucent spots are seen on leaves of affected plants. The white cottony growth, characteristics of many downy mildews, is generally not seen in the downy mildew of finger millet.
As a result, the asexual phase quite often goes unnoticed and the disease could be identified after the formation of ears. Partial or whole ear including lemma, palea and glumes change into leafy structures. The proliferation takes place first in the basal spikelets and afterwards others get affected. Finally the whole ear gives a bush-like appearance displaying typical ‘green ear’ symptom.
Temperature ranging from 25 to 30°C is highly favourable for disease development. During night, when the temperature is around 22-25°C, many sporangia are produced which release zoospore. Raghavendra and Safeeulla (1973) reported the pathogen being both internally and externally seed borne. The pathogen has been reported on E. indica, maize, wheta, oat, Eragrostis pectinacea and Digitaria marginata.
Management of Downy Mildew or Green Ear Disease:
As the pathogen is easily carried in fragments of proliferated parts mixed with seed, and such seeds after germination gives systemically infected seedlings like many other downy mildews, seed treatment with organomercurial compounds or Apron 35 SD at the rate 2.5-3.0 g/kg, would control systemic infection.
However, providing good drainage in the low lands, proper crop rotation methods, rouging of infected plants and elimination of wild grasses and related hosts will reduce the disease incidence.
Finger Millet: Disease # 6. Smut:
Kulkarni (1922) recorded this disease from Malkapur in 1918 in the then princely state of Kolhapur, described the pathogen and identified it as Ustilago Eleusine. Later, Mundkur and Thirumalachar (1946) transferred it to the genus Melanopsichium and named it as M. eleusinis. The disease has also been noticed at Mysore, Madhya Pradesh, Maharashtra and Karnataka.
The disease generally manifests itself few days after flowering. The smutted grains can be seen scattered randomly in the ear head. The affected ovaries get converted into greenish gall like bodies which are several times bigger in size than the normal grains.
In the initial stages, greenish swollen grains 2-3 mm in diameter are evident which project beyond the glumes. Later the infected grains become swollen and can reach a diameter of about 16 mm. The greenish outer tunica of the sorus gradually turns pinkish-green and finally turns to dirty black on drying.
Some times the affected grains are single or grouped in patches of varying sizes and are frequently confined to one side or towards the base or apex of the head and show signs of rupturing at several places. Spores are formed in the cavities found in the sori, mixed with a gelatinous matrix but later the mass becomes pulvurent.
The pathogen is neither systemic nor externally seed borne. Floral infection is by airborne spores.
Management of Smut:
Since, the disease is more common in late sown summer crop; early sowing in the month of January can avoid the disease. At present there is no chemical control measure in recommendation, but in vitro studies have shown that systemic compounds like Aliette and Vitavax could inhibit fungus growth.
Finger Millet: Disease # 7. Damping-Off:
The damping off disease of finger millet was reported from Annamalai in Tamil Nadu, India. It appears in ill-drained nurseries and fields, especially during rainy seasons.
The disease is characterized by yellowish brown discolouration of the hypocotyls region at the ground level. Later on, such discolouration extends to stems as well as roots. The infected patch in the nursery turns yellowish to dark brown and finally seedlings collapses. Such seedlings when pulled gently get broken at the collar region.
Management of Damping-Off:
In case of transplanted crop, seedlings can be protected by growing on raised seed beds. Light irrigation coupled with soil drenching with fungicides like; copper oxychloride, Captan, Thiram or Metalaxyl can reduce the disease incidence.
Apart from above mentioned diseases there are following minor diseases of finger millet which are of lesser economic importance at present:
1. Bacterial leaf spot: Xanthomonas eleusinae
2. Bacterial blight: Xanthomonas coracanae
3. Leaf stripe: Pseudomonas eleusinae
4. Ragi mottle streak: Ragi mottle Streak Virus
5. Ragi severe mosaic: Sugarcane Mosaic Virus
6. Ragi streak: Eleusine strain of maize streak virus
7. Nematode parasites: Heterodera spp., Rotylenchulus reniformis
8. Phanerogamic root parasites: Striga asiatica Kuntze and Striga densiflora Benth.
Many of the seed associated fungi are known to produce toxic metabolites, which ultimately result in seed deteoration during storage. Reported fourty three fungal species belonging to 21 genera associated with the seeds collected from the various places.
Among these, Aspergillus flavus, A. niger, A. fumigatus, Fusarium oxysporum, F. Miniliforme, Alternaria alternata, Curvularia lunata, Drechslera holodes, Trichothecium roseum, Stachybotrys atra, Rhizoctonia solani, Colletotrichum capsici and different species of Penicillium dominated the population.