1) It is caused by Pyricularia oryzae.
2) Boat or eye-shaped spots with grey or dark brown margin appear on the leaf and leaf sheath.
3) The central portion of the young spot becomes pale-green or dull-greyish-green and appears water-soaked but in older spots, the central portions turn grey or straw-colored in severe conditions. spots may coalesce to form large bitted spots.
4) Spots may coalesce to form large bitted spots. At the time of panicle emergence
5) The stem below the earhead gets an infection and turns into brown to black spots which may cover the entire stem and stop the translocation of food.
6)The grains remain empty.
7) Application of a heavy dose of nitrogen, high atmospheric relative humidity (86-98.), and night temperature around 20°C for a few hours are conducive for the disease
The following measures should be adopted for effective control of the disease
(1) Treat the seed with Tricyclazole 75 WP @ 2 g/kg or Carbendazim 50 WP @ 1 g/kg
(2) Spray the following chemicals after observing the initial symptoms of blast in field Carbendazim 50WP @ 500g/ha or Tricyclozole 75 WP @ 500g/ha or Metominostrobin 20 SC @ 500ml/ha or Azoxystrobin 25 SC @ 500 ml/ha
(3) Grow field tolerant varieties like IR-36, IR-64, Jaya, and Ratna, BPT-5204, CO-47
2) Brown Spot of Rice;
1) The disease is caused by Cochliobolus miyabeanus (Helminthosporium oryzae).
2) The pathogen infects the coleoptile of the seedling and causes blighting.
3) On the leaves, circular or oval, dark brown to purplish-brown spots are found. In severe conditions, these lesions may coalesce and cover the entire leal.
4) The disease symptoms also appear on grains where black spots appear on glumes.
5) The kernels of infected spikelets become shriveled and discolored.
The following steps may be taken to control the disease:
(1) Treat the seed with organomercurials, such as Ceresan, Agrosan G.N., Thiram at the rate of 2.5 g/kg of seed.
(2) Add muriate of potash to correct the potash deficiency in the soil, because the severity of disease increases in deficient soils. Apply balanced NPK fertilizers.
(3) Give three to four sprays with Metominostrobin @ 500ml/ha or Zineb or Dithane M-45 @of 0.25 % at an interval of 10-12 days just before the appearance of initial symptoms of the disease.
(4) Varieties like Rasi, Raksha, Bala, Krishna, Sabarmati, and IR-24 have been found to be moderately resistant to the disease.
3) Stem Rot of Rice;
1) It is caused by Sclerotium oryzae.
2) Primary symptoms of the disease appear after transplanting as small, black irregular lesions at the water line on leaf sheath 3) Fungus gradually enters the stem and develops a large number of black, smooth, shining sclerotia in the stem. Such infected stem rots and falls.
4) The spikelets remain chaffy or partially filled
5) The sclerotia of the pathogen remain viable even in adverse conditions for a long time and germinate during the rainy season causing primary infection.
6) Sclerotia are disseminated through irrigation water from field to field and incite fresh infection on healthy plants.
It is advisable to follow the control schedule as given below: (1) Destroy the infected stubbles by burning and/or deep ploughing.
(2) Avoid standing water in the field for a longer period. Drain the standing water from time to time. This would help in reducing the infection.
(3) Metominostrobin @ 500 ml/ha or Hexaconazole 75% WG @ 100 mg/ lit 1st spray at the time of disease appearance and 2nd spray 15 days later
4) Rice False Smut;
1) It is caused by Ustilaginoidea virens.
2) The symptoms of the disease become visible only after flowering when the infected kernel is transformed into a large velvety, yellow to orange pulverulent mass changing to olive green in color, more than twice in diameter than the normal grains.
3) Infected grains are covered with powdery spore mass which gets disseminated by wind and reaches healthy flowers and causes infection.
4) The disease appears only on a few grains in an ear.
5) In severe conditions, more grains can be affected.
6) Severe disease incidence occurs in the year of heavy rainfall
7) The use of a heavy dose of nitrogen also enhances the disease incidence.
The following control measures are recommended:
(1) Use certified seed from a reliable source.
(2) Collect the diseased grains and destroy them as soon as possible This will check the secondary spread of the disease and will also help in reducing the inoculum for next year.
(3) To control false smut apply the twice spray of the chemical like Propiconazole 25 EC @ 500ml/ha (or) Copper hydroxide 77 WP @ 1.25 kg/ha at boot leaf and 50% flowering stages
5) Sheath Blight of Rice;
1) The disease is caused by Rhizoctonia solani
2) The symptoms of the disease appear on leaf and leaf sheath as 2-3 centimeter long green shore lesions, turning to straw color and surrounded by bluish-grey narrow bands.
3)The lesions increase in size and girdle the stem.
d) Hemispherical spherical greyish-black sclerotia are formed on the lesions which the field with a slight jerk.
4) In severe infection, sclerotia form even grain. In diseased ears, grains remain unfilled.
5) The fungus has a wide host range and may attack rice. Its sclerotia also survive in the soil for a long and serve as a source of primary inoculum
6) Once the infection is established, it spreads through contact between diseased and healthy plants.
7) Close transplanting and application of a heavy dose of nitrogenous fertilizer favor the disease development.
8) Heavy incidence of the disease has been reported from Haryana, Punjab central Uttar Pradesh
1) Crop rotation collection and burning of infected plants and use of a balanced dose of nitrogen etc., minimize the disease losses.
2) Spraying of Hexaconazole 75% WG @ 100mg/ lit at the time of disease initiation stage and another spray should be done 15 days later (or) Spraying of infected plants with fungicides, such as Benomyl or Iprodione or Some of the antibiotics, such as Validamycin and Polyoxin is found effective against the disease
6) Sheath Rot and Grain Discoloration of Rice;
1) A fungal complex of microorganisms, viz. Drechslera Oryzae, Sarocladium oryzae, Alternaria padwickii, Curvularia spp., Epicoccum sp., Fusarium moniliforme, etc. are responsible for the grain discoloration.
2)The occurrence of this disease is more prone in rice crops that are affected by stem-borer, rice tungro disease, and various other biotic and abiotic stresses.