Kheto K Achumi, Kavi Sumi and E Lireni Kikon
Rice (Oryza sativa L.) serves as the main source of nutrition for millions of people worldwide. It is grown globally over an area of about 160 million hectares with a total production of 500 million metric ton and a productivity of 4.6 metric ton per hectare. India is one of the largest producers of rice with area, production and productivity of 45.5 mha, 125MT and 4.1 ton per hectare, respectively. There are various biotic as well as abiotic factors that affect the rice production. Among them, following are some of the important rice diseases and their management:
1. RICE BLAST (Pyricularia oryzae Cav.):
It is the most destructive and wide spread disease in both upland and lowland (severe in upland rice) causing considerable yield losses upto 70-80%.
Symptoms: Lesions are produced on all parts of the shoot. They are elliptical or spindle-shaped. The lesions may enlarge and coalesce to kill the entire leaves. The disease infects the leaf, collar, nodes and the panicle. Neck infection in the early stage of the crop growth leads to breaking of panicle and formation of chaffy grains which results in maximum yield losses. Dew deposit in the leaf for more than 10 hours and high Nitrogen application are conducive for the disease development.
Affecting stages: Seedling to late tillering.
Disease cycle: Seed and infected straw.
Management:
Keep the field clean and free of weeds.
Avoid heavy application of nitrogen.
Burn and destroy diseased plant debris and stubbles.
Flood the field atleast 4-5 inches to cover the soil.
Seed treatment and soaking of seedling roots in the solutions of Trichoderma harzianum and Azospirillium @5g/ltr of water before transplanting reduces the incidence of blast.
Use of resistant/tolerant varieties such as Megha Rice-1 and 2, Bhalum – 1 and 2, IR 64 etc.
Foliar sprays of fungicides like Dithane M-45@ 2g/litre of water is recommended for blast and brown spot.
Spray Hexaconazole 5% SC (Product name-Contaf) @250ml/acre in 150-200 L of water.
2. BROWN SPOT (Helminthosporium oryzae Breda de Hann.)
It is a serious rice disease of jhum fields. The disease has been reportedly observed specially in potash deficient soils. It is a serious disease in upland rice with an expected loss upto 10-58% in seedling stage and 90% in vegetative stage.
Symptoms: Typical symptom is the development of innumerable, dark, brown, elliptical spots on the leaves, stems and glumes. Most spots have a light yellow halo around their margins. In severe cases these spots may coalesce and cover the entire leaf. Inflorescence in a mature plant becomes distorted. The grains fail to form. In case of early and severe infection the head may fail to emerge from the sheath and perish without developing fully. The kernels of infected spikelets become shriveled and discolored. Entire leaf may become brown and dry out in heavy infection. Water stress, low soil fertility and high humidity (>90%) hasten disease development.
Affecting stage: Seedling to milky stage.
Disease cycle: Soil and seed.
Management:
Keep the field clean and free of weeds.
Use disease free seeds.
Collection and destruction of stubbles.
Hot water treatment at 53⁰C -54⁰C for 10-12 minutes before sowing to kill seed infected pathogen and also to protect the seed at the time of sowing.
Spraying of Papaya solution prepared from 2kgs fresh papaya leaves in 3-4 litres of water soaked overnight and filtered and added with 50-60litres of water and 250ml soap solution is effective.
Seed treatment with Thiram or Dithane M-45 @ 2g/kg seed helps to reduce seed borne infection.
Foliar spray(spraying on leaves) at incidence of disease with Dithane M-45 @2g/ltr of water or Hinosan @ 1ml/ltr of water is recommended.
3. FALSE SMUT (Ustilaginoidea virens)
Symptoms:
Infection results in one or more kernels on mature heads of plants being replaced by globose, yellowish-green, velvety smut balls. When smut balls burst open, powdery dark green spores are released. The symptoms produced by U. virens are visible after flowering only, when the fungus transforms individual grains of the panicle into a yellowish smut ball, which changes to yellowish orange, green, olive green and finally to greenish black coloured smut balls. Rain and cloudy days during the period from flowering to maturity are favourable condition for the disease.
Affecting stage: Flowering to maturity.
Management:
Cultivation practices including specific crop rotation, furrow irrigation and conservation tillage are effective in minimizing the false smut disease index.
Variety Pankaj escapes false smut because it matures late.
Application of fungicide Simeconazole under submerged condition at 3 weeks before rice heading is effective.
Combination of fungicide Trifloxystrobin 25%+tebuconazole 50% (Product name- Nativo) is highly effective against the disease.
Fungicides like Copper oxychloride 50 WP (0.3%) (Product name – Blitox) and Propiconazole 25 EC (0.1%) (Product name- Tilt) are also effective against the disease.
4. BACTERIAL LEAF BLIGHT (Xanthomonas oryzae pv. oryzae)
Symptoms:
Two symptoms are exhibited; Leaf blight and Wilt or Kresek. Leaf blight phase of BB has characteristic yellow lesions with wavy margins on leaf blades.
Leaf blight starts as water-soaked and yellowish stripes at the leaf tips and blades. White & coalesce. Infected plants yield fewer and lighter grains. Kresek is the most destructive manifestation of the disease, where in the leaves of the entire plant turn pale yellow and wilt during the seedling to the early tillering stage, resulting in a partial or total crop failure.
Leaves wilt, roll up, and turn grayish green.
Plants that are able to survive are stunted and yellowish.
Favourable conditions:
Incessant rains, strong wind and warm temperature favors the disease. Bacterial ooze from infected leaves has been observed in warm and humid climates, which contributes to the spread of this disease. High nitrogen fertilizer, close spacing, potassium and phosphorus deficiencies are also known to favors the disease.
Affecting stage: Tillering to heading stage.
Management:
Removal of weed hosts grasses, especially Leersia sp., Leptocloa chinensis, Cyperus rotundus etc., rice straws, and volunteer seedlings.
Seed treatment with Streptocycline and also spraying of the crop with a mixture of copper fungicides (Bordeaux mixture).
A foliar spray of cow dung extract (20 g/l) was reported to suppress bacterial blight development in the state of Kerala.
Chlorination of the field water with stable bleaching powder has also been reported to effectively reduced disease severity.
5. RICE TUNGRO (Rice tungro bacilliform virus & Rice tungro spherical virus)
Symptoms:
Leaf discoloration (Leaves turns yellow) begins from leaf tip and extends down to the blade or the lower leaf portion. There is stunted growth, reduces tillering and root growth and flowering is delayed. Panicles are small mostly sterile or partially filled grains.
Although tungro symptoms can be confused with nitrogen or zinc deficiencies and other disorders, presence of tungro can be confirmed by some serological tools to detect tungro viruses. These are latex agglutination test, enzyme-linked immunosorbent assay (ELISA), and rapid immune filter paper assay (RIPA). The presence of the vector green leaf hoppers, Nephotettix spp. is indicative of the disease.
Affecting stage: All growth stages especially vegetative stage.
Management:
Once a rice plant is infected by tungro, it cannot be cured. Preventive measures are more effective for the control of tungro than direct disease control measures.
Seed treatment with Furadan 75% WP @ 1.5 g/100 kg seed and also spraying @ 33 kg/ha.
Field sanitation, removal of weed hosts of the virus and vectors.
Spray Phosphomidan 500 ml (2 ml/litre) or Neem oil 3% to control the vector in the main field 15 and 30 days after transplanting.
Spray Thiamethoxam 25 WDG 100g/acre or Imidacloprid 17.8 SL 50-70ml/acre at 15 and 30 days after transplanting of paddy.
Set up light traps to monitor the vector population.
Plough infected stubbles immediately after harvest to reduce inoculum sources and destroy the eggs and breeding sites of green leaf hopper.
Conclusion:
Change in cultivation practices of Rice like practicing intensive agricultural practices to enhance yield causes the crop to suffer from a number of biotic constraints such as diseases and pests. In order to feed the ever-growing global population, it is necessary to manage the diseases to avoid losses. So, it is most important to address these emerging issues urgently by integrated disease management practices. Use of biological control agents and their products is an eco-friendly approach. At last, chemical pesticides should be the last option and not a priority.
(The writers are PhD Scholar, Department of plant pathology NU: SAS, Medziphema campus
