Rice is considered to be one of the important crops among cereals. Historically, rice was cultivated l0000 years ago in the river valleys of South and Southeast Asia and it served as the most important food for the people. Although Asia is the main place of rice cultivation it is also grown in other parts of the world. The production of this crop is hampered by various factors such as biotic and a-biotic. Among the biotic factors, disease and pest are most important ones. The present topic will give an idea on the important diseases in rice and its common management practices in Manipur.
Blast Disease of Rice
The fungus attacks the crop at all stages of crop growth. Symptoms appear on leaves, nodes, rachis, and glumes. On the leaves, the lesions appear as small bluish green flecks, which enlarge under moist weather to form the characteristic spindle shaped spots with grey centre and dark brown margin (Leaf blast). The spots coalesce as the disease progresses and large areas of the leaves dry up and wither. Spots also appear on sheath. Severely infected nursery and field appear as burnt. Black lesions appear on nodes girdling them. The affected nodes may break up and all the plant parts above the infected nodes may die (nodal blast). During flower emergence, the fungus attacks the peduncle and the lesion turns to brownish-black which is referred to as rotten neck / neck rot / panicle blast (neck blast). In early neck infection, grain filling does not occur while in late infection, partial grain filling occurs. Small brown to black spots may also be observed on glumes of the heavily infected panicles. The pathogen causes yield losses ranging from 30-61 per cent depending upon the stages of infection.
• Remove and destroy the weed hosts in the field bunds and channels.
• Treat the seeds with Captan or Thiram or Carbendazim or Tricyclazole at 2 g/kg. or Pseudomonas fluorescens @ 10g/kg of seed.
Spray the nursery with carbendazim 500mg/L or tricyclazole 300mg/L.
• Spray the main field with Edifenphos 500 ml or Carbendazim 500 g or Tricyclazole 500 g or Iprobenphos (IBP) 500 ml /ha.
Brown spot of rice
The fungus attacks the crop from seedling to milky stage in main field. Symptoms appear as minute spots on the coleoptile, leaf blade, leaf sheath, and glume, being most prominent on the leaf blade and glumes. The spots become cylindrical or oval, dark brown with yellow halo later becoming circular. Several spots coalesce and the leaf dries up. The seedlings die and affected nurseries can be often recognised from a distance by scorched appearance. Dark brown or black spots also appear on glumes leading to grain discoloration. It causes failure of seed germination, seedling mortality and reduces the grain quality and weight.
• Field sanitation-removal of collateral hosts and infected debris from the field.
• Use of slow release nitrogenous fertilizers is advisable.
• Use disease free seeds.
• Treat the seeds with Thiram or Captan at 4 g/kg. Spray the nursery with Edifenphos 40 ml.
• Spray the crop in the main field with Edifenphos 500 ml or Mancozeb 2 kg/ha when grade reaches. If needed repeat after 15 days.
Sheath blight of rice
The fungus affects the crop from tillering to heading stage. Initial symptoms are noticed on leaf sheaths near water level. On the leaf sheath oval or elliptical or irregular greenish grey spots are formed. As the spots enlarge, the centre becomes greyish white with an irregular blackish brown or purple brown border. Lesions on the upper parts of plants extend rapidly coalesing with each other to cover entire tillers from the water line to the flag leaf. The presence of several large lesions on a leaf sheath usually causes death of the whole leaf, and in severe cases all the leaves of a plant may be blighted. The infection extends to the inner sheaths resulting in death of the entire plant. Older plants are highly susceptible. Plants heavily infected in the early heading and grain filling growth stages produce poorly filled grain, especially in the lower part of the panicle.
· Apply organic amendments viz., neem cake @ 150Kg/ha or FYM 12.5 tons/ha. Avoid flow of irrigation water from infected fields to healthy fields.
· Deep ploughing in summer and burning of stubbles.
· Spray Carbendazim 500 g/ha .
· Soil application of P.fluorescens @ of 2.5 kg/ha after 30 days of transplanting (product should be mixed with 50 kg of FYM/Sand and applied).
· Foliar spray P.fluorescens at 0.2% at boot leaf stage and 10 days later.
Stem rot of rice
Small black lesions are formed on the outer leaf sheath and they enlarge and reach the inner leaf sheath also. The affected tissues rot and abundant small black sclerotia are seen in the rotting tissues. The culm collapses and plants lodge. The sclerotia are carried in stubbles after harvest.
• Deep ploughing in summer and burning stubbles to eliminate sclerotia.
• Use of balanced application of fertilizer.
• Avoid flow of irrigation water from infected to healthy fields.
• Draining irrigation water and letting soil to dry.
It is to be said that whereever crops grow the diseases and insect pest will follow. The same thing is applied to rice cultivation also. Totally we cannot eradicate the diseases, instead try to minimise the losses from the diseases. In this case, the first and foremost step is the selection of the seed from the known source recommended by the Government. Follow scientific methods of cultivation from planting of the seed to harvesting. During the crop growth, monitor continuously by visiting to the rice field, any abnormalities found in the plants, immediately report to the concerned experts. In this way, we not only increase the rice production, but also income of the farmers.
The writer is Assistant Prof., Department of Plant Pathology, College of Agriculture
Central Agricultural University, Imphal
Mail: [email protected]