Welcome to Official Portal of Agriculture Department, Sikkim!

  • Change Font Size:
  • -A
  • |
  • A
  • |
  • +A
  • ||
  • Change Theme:
 
logo user
emblem userSign In
Home About Us Contact Us

More Menu

Disease Management

Diseases

The common diseases of rice crop, their symptom, disease cycle, epidemiology and management measures are given here under.

1. Blast (Pyricularia grisea)



Symptoms

This disease affects all the aerial parts of the plants like leaf, culm neck and grains.
Spindle-shaped spots with dark brown margin and grey centre leaves.
Several spots coalesce and lead to big irregular spots.
Nodal infection causes the neck to break and panicle hangs down.
If neck is infected the grain development gets affected.
Disease cycle

The pathogen is seed-borne.
It also persists in infected plant debris and collateral weed hosts.
The primary infection is due to weed hosts which harbor the pathogen.
The secondary infection is mainly due to wind-borne conidia.
Epidemiology
It occurs during June to September.

Temperature of 20oC during night and day temperature of 30oC are pre-disposing factors.
Cloudy weather.
High relative humidity above 90 per cent.
Management

Field sanitation and burning of straw and stubbles in the field.
Seed treatment with Pseudomonas flourescents @ 6 g/kg of seed.
Dry seed treatment with Pseudomonas fluorescents talc formulation @ 10 g/kg.
Stagnate water to a depth of 2.5 cm over an area of 25 sq. m. in the nursery. Sprinkle 2.5 kg of Pseudomonas
fluorescents (talc) and mix with stagnated water. Soak the root system of seedlings for 30 min. and transplant.

Spray three times Pseudomonas fluorescens talc formulation @ 0.5 per cent from 45 days after transplanting at 10 days intervals.
Early sowing after rain.
Use of tolerant varieties.
Use of Blitox-50 @ 0.3 per cent.
Regular monitoring, collection and destruction of egg, larvae, pupae and adults of different insects.
Installation of pheromone trap @ 16-20 traps/ha in a triangular pattern at 60 m distance for trapping the adult male of yellow stem borer.

Release of Trichogramma japonicum or T. chilonis @ 50,000 per hectare at weekly interval for 7-8 times starting  from 30 days after transplanting.
At the beginning of Gundhi bug infestation, a few first batch population of Gundhi bug should be collected and
 after preparing the aqueous extract from them it should be sprayed in the field to repel subsequent population.
One spray of Beauveria bassiana @ 7 g/l at the boot leaf stage to reduce Gundhi bug population.
Traps should be installed @ 30 traps/ha starting from panicle initiation stage to harvest of the crop to manage
rodents.
Use of tulsi (Ocimum spp.) leaves extract which is prepared by boiling 25 gm of leaves in one litre of water.
Use of bael (Aegle marmelos) leaves extract @ 2.5 per cent.
2. Brown spot (Helminthosporiun oryzae)


Symptoms

The disease occurs in both nursery and main field.
On seedlings it appears as minute, small, circular, brown lesions which may girdle
the coleoptile and cause distortion of the primary and secondary leaves.
On the leaves of older plants, the fungus produces circular to oval lesions that have
a light brown to grey center surrounded by a reddish brown margin.
Under severe infection the spots coalesce and cause killing of large areas of affected leaf.
The spots also appear on glumes and grains causing black discoloration on the grains.
Disease cycle

Primary infection through infected seed and collateral hosts.
Wind-borne conidia initiate the secondary infection.
Epidemiology
It occurs during June to September.
The temperature of 25 to 35oC and relative humidity of above 90 per cent favours the disease.
Management

Hot water treatment of seed at 53-54oC for 10-12 minutes.
Provision of field drainage.
Sanitation and crop rotation.
Spray Bordeaux mixture 0.1 per cent or COC 0.25 per cent at regular intervals reduces the disease.
3. Sheath rot (Sarocladium oryzae)


Symptoms

Spots with brown margin and grey centre.
Discolouration in leaf sheath.
Lesions enlarge and often coalesce and may cover the entire leaf sheath.
Severe infection causes entire or parts of young panicles to remain within the sheath.
Brown or partially brown not filled or partially filled grain is also associated with infection of the panicle.
The young panicles are generally affected leading to an increase in the number of chaffy, discoloured, and shrivelled grains and reduction in the weight and number of healthy grains.
A whitish powdery growth may be found inside the affected sheaths.
Epidemiology
It occurs during August to November.
Dense crop growth.
High relative humidity.
Temperature from 18 to 20oC from heading to maturity.
Rice (Oryza sativa L.)
Management

Seed treatment with Pseudomonas fluorescens @ 10 g/kg seeds.
Pseudomonas fluorescens @ 500-750 g/acre or 250 ml/ha as foliar spray.
Application of neem oil @ 3 per cent or NSKE 5 per cent.
Spray Ipomea leaf powder extract @ 25 kg/ha (first spray should be done at boot leaf stage and second spray 15 days later).
4. Sheath blight (Rhizoctonia solani)


Symptoms

Early symptoms include oval sheath spots (lesions) at or just above the water line, often at the junction of the leaf and sheath.
Early lesions are pale green to off-white with a narrow purple-brown or brown border, usually 2" or less wide and 1-2" long on most varieties.
Lesions may join as the disease moves up the plant. Both sheaths and leaves are commonly attacked and killed as the disease grows upward.
Disease cycle
Sclerotia are the main source of infection and they survive in the soil for several
months.
Epidemiology
It occurs during July to August.

Humid and warm temperatures.
Close planting.
Management

Burning of previous crop residue.
Crop rotation with oil seeds and pulses.
Application of neem cake @ 150 kg/ha as basal dose.
Spray neem oil 3 per cent and NSKE 5 per cent.
Foliar spray of P. fluorescens @ 0.2 per cent at boot leaf stage and 10 days later.
Soil application of P. fluorescens @ 2.5 kg/ha mixed with 50 kg FYM after 30 days of transplanting.
5. Stem rot (Sclerotium oryzae)


Symptoms

It appears as blackish irregular lesions on the outer leaf sheath near the waterline after mid-tillering stage.
The fungus penetrates the inner leaf sheath and stem. These become discoloured; black or dark brown and shrivel.
At maturity the weakened stem breaks, plants lodge and numerous small black round sclerotia develop in the dead tissues.
Disease cycle

Sclerotia of the fungus survive in soil and stubble serves as the primary and secondary source of infection.
If conidia are produced they also play a role in the spread of the disease.
Epidemiology
It occurs during July to August.
It is a weak pathogen and will be active only under certain favourable conditions, like physiological imbalance,
infestation of stem borer and leaf hopper and lodging of plants.

Management

Use of disease-free seeds.
Destruction of straw and stubbles.
Avoiding water stagnation for prolonged period.
6. False smut (Ustilaginoidea virens)


Symptoms

Grain will get transformed into smut balls with green, velvety appearance.
Infection usually occurs during the reproductive or ripening stages.
It infects only few grains and leaving others healthy.
Disease cycle

Ascospores produced from the sclerotia are the primary source of infection.
Air-borne chlamydospores are the secondary source of infection.
Epidemiology
It occurs during August to September.

Moderate rainfall with intermittent drizzle during flowering.
High relative humidity (92 per cent).
Low temperature of 20oC.
Management

Destruction of straw and stubbles.
Avoiding field activities when the leaves are wet.
Use of disease-free seeds.
Spray Blitox 0.3 per cent at boot leaf stage and 50 per cent at flowering stage.
Spray fresh cow dung extract @ 20 per cent at the initial appearance of the disease and repetition of the spray at fortnightly intervals.
Spray neem oil 3 per cent and NSKE 5 per cent.
7. Bacterial leaf blight (BLB) (Xanthomonas oryzae pv. oryzae)


Symptoms

Nursery: The leaves turn yellow and become wilted during seedling to early tillering stage called Kresek symptom.
BLB is characteristic of yellow lesions with wavy margins on leaf blades that may extend to the sheath.
Pale amber colour bacterial ooze will appear on the affected portion.
If the infection occurs during panicle initiation and during subsequent stages grain development gets affected.
Disease cycle

The disease is primarily seed-borne and initial infection is from the seed.
The pathogen also survives in soil, plant debris or on volunteer plants and wild or collateral hosts.

Rice (Oryza sativa L.)

This bacterium is disseminated through wind-borne rain and irrigation water.
Epidemiology
It occurs during July to August.
Temperature of 20oC- 22oC favours this disease.
Rainy weather and dull windy days.
Shade and close planting also favours the disease.
Management

Use of disease-free seeds.
Hot water treatment of seed at 52-54oC for 10 minutes.
Use of tolerant varieties.
Growing nurseries preferably in isolated upland conditions.
Avoiding flow of water from one field to the other.
Clipping of leaves should be avoided.
Drain the field except during flowering stage.
Removal and destruction of previous crop residue, volunteer plants and stubbles.
Spray Blitox @ 0.3 per cent 35 day after and 45 day after planting.
Spray neem oil 3 per cent and NSKE 5 per cent.
8. Leaf streak (Xanthomonas oryzae pv. oryzicola)

Symptoms

It occurs during July to August.
Initially small, dark-green and water-soaked streaks of varying length on leaf from tillering to booting stage.
Later the streaks turn to yellowish grey to transparent.
Numerous yellow beads of bacterial ooze can be seen on streaks.
Management

Removal and destruction of previous crop residue, volunteer plants and stubbles.
Use of resistant varieties.
Hot-water treatment of seeds @ 52oC for 30 min.
Drain the field except during flowering stage.
Clipping of leaves should be avoided.
Maintaining optimum plant spacing.
Spray neem oil 3 per cent and NSKE 5 per cent.
9. Tungro virus (Rice Tungro Virus)
Symptoms

Stunting and yellow or orange discolouration of leaves.
Discoloration begins from leaf tip and extends down to the blade or the lower leaf portion.
Infected plants have reduced number of tillers and may show rust coloured spots on leaves.
This disease also produces mottling, stripping and interveinal chlorosis on leaves.
Panicle emergence also gets affected and sometimes the plants produce sterile or partially filled grains.
Disease cycle

It is transmitted by several species of green leaf hopper (Nephotettix spp.) in non-persistent manner.