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Mode of spread and survival:
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Presence of the virus sources.
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Presence of the vector.
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Age and susceptibility of host plants.
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Synchronization of the three above factors.
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All growth stages of rice plant specifically the vegetative stage.
Identification of pathogen:
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Tungro virus disease is transmitted by leafhoppers, wherein the most efficient vector is the green leafhopper,Nephotettix virescens (Distant). The disease complex is associated with rice tungro baciliform virus (RTBV) and rice tungro spherical virus (RTSV). RTBV cannot be transmitted by leafhoppers unless RTSV is present.
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Insects could acquire the virus from any part of the infected plant. After acquiring the virus, the vector can immediately transmit to the plants.
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RTBV particles are rod-shaped and 100-300 nm in length and 30-35 nm in width. It contains DNA of 8.3 kb. RTSV particles are isometric and 30 nm in diameter. It has a polyadenylated single-stranded RNA of about 12 kb.
Mode of spread and survival:
- The pathogen survives in soil and in the infected stubbles and on collateral hosts Leersia spp., Plantago najor, Paspalum dictum, and Cyanodon dactylon.
- The pathogen spreads through irrigation water and also through rain storms.
Management:
Trap methods:
- Light traps are to be set up to attract and control the leaf hopper vectors as well as to monitor the population.
- Install light trap @ one/ha .
- Install yellow sticky trap @ 12/ha .
- In the early morning, the population of leafhopper alighting near the light trap should be killed by spraying/dusting the insecticides. This should be practiced every day.
Cultural methods:
- Planting of resistant varieties against tungro virus disease is the most economical means of managing the disease.
- Grow disease tolerant cultivars like MTU 9992, 1002, 1003, 1005, Suraksha, Vikramarya, Bharani, IR 36, IET 2508, RP 4-14, IET 1444, IR50 and Co45.
- Among the cultural management practices, adjusting the date of planting is recommended..
- Likewise, observing a fallow period of at least a month to eliminate hosts and viruses and vectors of the disease.
- In epidemic areas follow rotation with pulses or oil seeds.
- Apply neem cake @ 12.5 kg/20 cent nursery as basal dose.
- Summer deep ploughing and burning of stubbles.
- Eradicate of other tungro hosts are also advisable.
- Destruction of weed hosts on bunds.
Chemical Methods:
- Leaf yellowing can be minimized by spraying 2 % urea mixed with Mancozeb at 2.5 gm/lit..
- Instead of urea foliar fertilizer like multi-K (potassium nitrate) can be sprayed at 1 per cent which impart disease resistance because of high potassium content.
- Green leaf hoppers as vectors are to be controlled effectively in time by spraying.
- Vegetation on the bunds should also be sprayed with the insecticides. Maintain 2.5 cm of water in the nursery and broadcast anyone of the following in 20 cents Carbofuran 3 G 3.5 kg (or) Phorate 10 G 1.0 kg (or) Quinalphos 5 G 2.0 kg.
- In nursery when virus infection is low, apply Carbofuran granules @ 1 kg/ha to control vector population.
- During pre-tillering to mid-tillering when one affected hill/m is observed start application of Carbofuran granules @ 3.5kg/ha to control insect vector.
Spray Two rounds of any one of the following insecticides:
- Thiamethoxam 25 WDG 40g/acre (or).
- Imidacloprid 17.8 SL 40ml/acre at 15 and 30 days after transplanting.
- The vegetation on the bunds should also be sprayed with the insecticides.
Source of Information:
- AICRIP rice, TNAU, Coimbatore Rice diseases- online resource, IRRI, Phillippines.
Acknowledgements:
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