Diseases Of Rice

1. Blast

Causal organism : Magnoporthe grisea

Symptoms:The fungus infects leaf, leaf sheath, culm, node and neck of the panicle. On leaves, the spots are typically spindle shaped (Eye shaped) with dark brown margin and grey center (Leaf blast). Spots are sometimes encircled by yellow halo. Several spots coalesce resulting in bigger lesions, leading to drying of foliage.

Node infection(Node blast) :On nodes, necrotic black lesions are observed which cause weakening and breaking of nodes.

Neck infection (Neck blast) :The neck region of affected panicle becomes black, brittle, necrotic and breaks. Grains become chaffy or partially filled.

Favorable Conditions : Intermittent drizzles, cloudy weather, more of rainy days, longer duration of dew high relative humidity (93-99 percent);Low night temperature (between 15-20˚C or less than 26˚C);Availability of collateral hosts and excess dose of nitrogen.

2.Brown leaf spot ((Sesame leaf spot)

Causal organism : Helminthsporium oryzae (Drechslera oryzae)

Symptoms: Symptoms of the disease appear on leaves, leaf sheath,glumes and grains.

On leaves, the spots are rectangular or oval resembling a sesame seed.They are uniformly brown or reddish brown with discrete margin; Spots have a halo. On the surface of glumes and grains, brown lesions are observed leading to grain discoloration.

Favorable Conditions : Temperature of 25-30˚C with relative humidity above 80 per cent are highly favorable; Excess of nitrogen aggravates the disease severity.

3. Sheath rot

Causal organism : Sarocladium oryzae

Stage of infection: Boot leaf stage

Symptoms:Upper most leaf sheath enclosing the ear head exhibits dark brown or black, circular to irregular patches. The panicle does not emerge fully from the flag leaf. The glumes are discolored. White powdery growth of mycelium is seen inside the leaf sheath and also on the panicle. Grains get discolored. Young panicles may not emerge from infected sheaths.

Favorable Conditions : Closer planting ;High doses of nitrogen; High humidity and temperature around 25-30˚C; Injuries made by leaf folder,brown plant hopper and mites increase infection

4. Sheath blight Causal organism : Rhizoctonia solani

Stage of infection: Tillering stage

Symptoms: Lesions are formed on the leaf sheath near water level. The lesions become oval or ellipsoid and greyish green. As the disease progresses lesions enlarge and their centers turn greyish white with brown margin. Under favorable conditions lesions are formed on upper leaf sheath and on leaf blades resulting in leaf blight. Infection may extend to culm leading to rot. Inside the culm and on the leaf sheath,large number of small spherical, brown sclerotia are formed.

Favorable Conditions : High relative humidity (96-97 per cent), high temperature (30-32˚C);Closer planting;Heavy doses of nitrogenous fertilizers

5. Stem rot

Causal organism : Sclerotium oryzae

Symptoms: The fungus affects leaf sheath during later stages of crop growth near water level. Dark brown to black lesions are formed on the outer leaf sheath. The affected tissues rot and abundant small, spherical,black sclerotia are seen in the rotting tissue and visible to naked eye as dots. The culm collapses and plants lodge. If the diseased tiller is opened, profuse mycelial growth and large number of sclerotia can be seen.

Favorable Conditions : Infestation of leaf hoppers and stem borer ;High doses of nitrogenous fertilizers.

6. False smut (Lakshmi Disease)

Causal organism : Ustilaginoidea virens

Symptoms: Few grains in the ear head exhibit the symptoms. Affected grains get converted into green velvety mass that are much bigger than the normal grains. Spore balls are visible between glumes, and the glumes are not affected. Rainfall and cloudy weather during flowering and maturity favors the disease development.The fungus produce schlamydospores which later develop to sclerotia. Severe outbreak of this disease is recorded in recent years.

7. Oodubathi disease

Causal organism : Ephelis oryzae

Symptoms: The panicle emerges as a slender, dirty grey, cylindrical,spike since the spikelets are cemented by the fungal mycelium. Nograins are formed on affected ear head.

8. Grain discolouration

Causal organism : Helminthosporium, Curvularia , Alternaria Fusarium

Symptoms:The grains are discolored red, yellow, orange, pink or black, depending upon the organism involved and the degree of infection. The infection may be external or internal leading to discoloration of glumes, kernels or both. Dark brown or black spots appear on grains. Under humid conditions, the fungal growth may be prominently seen on grains 

9. Bacterial leaf blight

Causal organism : Xanthomonas oryzae pv oryzae

Symptoms: Blighting of seedling occurs in nursery.In main field,“Kresek’ phase i.e. death of seedling is usually observed one or two weeks after transplanting. Symptoms are chiefly confined to leaves.Initial infection is seen as water-soaked lesion at the tip of leaf. Infection proceeds along the leaf margin in an irregular wavy manner. The affected portion turns straw colored and the central leaf blade remains green for some time. Finally the entire leaf gets blighted. Bacterial ooze can be seen on the infected leaf surface, which dries up forming encrustation. Bacterial ooze can be observed from the cut end of the infected leaf when immersed in clear water.

Favorable Conditions : Clipping of tip of the seedling at the time of trans planting; Heavy rain, heavy dew, flooding, deep irrigation water;Severe wind and temperature of 25-30 C; Application of excessive nitrogen, especially late top dressing

VIRAL AND PHYTOPLASMAL DISEASES

10. Rice Tungro Disease (RTD)

Causal organism : Rice tungro virus

Symptoms: Infection occurs in nursery and main field. The chief symptoms are stunted growth of plant, reduced tillering, discoloration of leaves in various shades of yellow to orange. The discombobulation starts from the tip and proceeds downwards. Older leaves exhibit rusty spots or dots of different sizes. The ear heads are small and grains are ill filled. The virus is transmitted by green leaf hoppers

11. Rice Yellow Dwarf Disease

Causal organism : Candidatus Phytoplasma

Symptoms: Plants become pale green, chlorotic and stunted. Large number of thin and pale tillers with yellowish green leaves are seen.There is excessive tillering . Affected plant looks like a clump of grass.Infected plants remain sterile. The disease in transmitted by Green leaf hoppers Disease management

Prophylactic measures as seed treatments

Dry seed treatment

Thiram or captan or carboxin or carbendazim at 2 g/kg of seeds.Treat the seeds at least 24 hours prior to soaking for sprouting. The treated seeds can be stored for 30 days without any loss in viability.

Wet seed treatment

Carbendazim or Tricyclozole at 2 g/lit of water for 1 kg of seed.Soak the seeds in the solution for 2 h Drain the solution, sprout the seeds and sow in the nursery bed. This wet seed treatment gives protection to the seedlings up to 40 days from seedling disease such as blast and this method is better than dry seed treatment or Treat the seeds with talcbased formulation of P. fluorescens (Pf1) @ 10g/kg of seed and soak in 1 lit of water overnight. Decant the excess water and allow to sprout the seeds for 24 h and then sow.

Seedling dip with Pseudomonas fluorescens

Stagnate water to a depth of 2.5cm over an area of 25m2in the main field.Sprinkle 2.5 kg of the talc based formulation of Pseudomonas fluorescens( Pf1) and mix with stagnated water. The seedlings pulled out from the nursery are to be soaked for 30 min. in the stagnated water and then transplanted. Bio control agents are compatible with bio fertilizers Bio fertilizers and bio control agents can be mixed together for seedsoaking

Fungicides and biocontrol agents are incompatible

i.) Nursery Diseases

1.Blast:Spray any one of the following: (for 20 cents): Carbendazim50WP @ 1g/l or Tricyclozole 75 WP @ 1g/l or Metominostrobin 20 SC@ 1ml/l or Azoxystrobin 25 SC @ 1 ml/l

2.Brown spot

Spray ( for 20 cents) Metominostrobin @ 1ml /lit of water

3.Rice Tungro Disease (RTD)

To control Vector- hoppers

Apply Carbofuran 3G @ 3.5kg at 10 DAS or

Spray 2 rounds (10 and 20 DAS) with any one of the following

insecticides for 20 cents area

Thiamethoxam 25 WDG 8g or Imidacloprid 17.8 SL 8ml

ii.) Main Field

Blast

Cultural method

Remove collateral weed hosts from bunds and channels

Use only disease free seedlings

Avoid excess nitrogen

Apply N in three split doses (50% basal, 25% in tillering phase and 25% N in panicle initiation stage)

Use resistant variety CO 47.

Chemical

Spray after observing initial infection of the disease,

Carbendazim 50WP @ 500g/ha (or)

Tricyclozole 75 WP @ 500g/ha (or)

Metominostrobin 20 SC @ 500ml/ha (or)

Azoxystrobin 25 SC @ 500 ml/ha

Biological control

Seed Treatment with TNAU Pf 1liquid formulation @ 10 ml/kg of seeds

Seedling root dipping with TNAU Pf 1liquid formulation (500 ml for

one hectare seedlings)

Soil application with TNAU Pf 1liquid formulation (500ml/ha)

Foliar spray with TNAU Pf 1liquid formulation @ 5ml/lit

2.Brown spot

Spray Metominostrobin @ 500ml/ha

3.Sheath rot

Cultural

Apply Gypsum @ 500 kg/ha at two equal splits once basally and another at active tillering stage.

Botanicals

Neem oil 3%Ipomoea leaf powder extract (25 kg/ha)

Prosopis leaf powder extract (25 kg/ha). First spray at boot leaf stage and second 15 days later

Chemical

Spray any one of the following:

Carbendazim @ 500g/ha

Metominostrobin @ 500 ml/ha

Hexaconazole 75% WG @ 100 mg/ lit 1st spray at the time of disease appearance and 2nd spray 15 days later

Biological control

Seed Treatment with TNAU Pf 1liquid formulation @ 10 ml/kg ofseeds

Seedling root dipping with TNAU Pf 1 liquid formulation (500 ml for one hectare seedlings)

Soil application with TNAU Pf 1 liquid formulation (500ml/ha)

Foliar spray with TNAU Pf 1liquid formulation @ 5ml/lit

4.Sheath blight

Cultural

Apply Neem cake at 150 kg/ha

Botanical

Foliar spray with Neem oil at 3% (15 lit /ha) starting from disease appearance

Chemical

Carbendazim 50 WP @ 500g/ha

Azoxystrobin @ 500ml/ha

Hexaconazole 75% WG @ 100mg/ lit 1st spray at the time of disease appearance and 2nd spray 15 days later

Biological control

Seed Treatment with TNAU Pf 1liquid formulation @ 10 ml/kg of seeds

Seedling root dipping with TNAU Pf 1 liquid formulation (500 ml for one hectare seedlings)

Soil application with TNAU Pf 1liquid formulation (500ml/ha)

Foliar spray with TNAU Pf 1liquid formulation @ 5ml/lit

5.False smut

Two sprayings of Propiconazole 25 EC @ 500ml/ha (or) Copperhydroxide 77 WP @ 1.25 kg/ha at boot leaf and 50% flowering

6.Rice grain discoloration

Chemical Spray :Carbendazim + Thiram + Mancozeb (1:1:1) 0.2% at 50% flowering stage.

7.Bacterial blight

Two sprays of Copper hydroxide 77 WP@1.25 kg/ha 30 DAP & 45 DAP

Botanical / others

Spray fresh cow dung extract 20% twice (starting from initial appearance of the disease and another at fortnightly interval)

Neem oil 60 EC 3% (or) NSKE 5% is recommended for the control of sheath rot, sheath blight, grain discoloration and bacterial blight

For viral and Phytoplasma diseases

Cultural method

Plough the stubbles as soon as the crop is harvested to prevent the survival of yellow dwarf pathogen during off-season.

Physical methods

Light traps are to be set up to attract and control the leaf hopper vectors as well as to monitor the population.In the early morning, the population of leaf hopper alighting near the light trap should be killed by spraying/dusting the insecticides. This should be practiced every day.

Spray Two rounds of any one of the following insecticides

Thiamethoxam 25 WDG 100g/ha Imidacloprid 17.8 SL 100ml/ha at 15 and 30 days after transplanting. The vegetation on the bunds should also be sprayed with the insecticides.