BROWN SPOT IN RICE – casual organism, favourable conditions, symptoms and management methods

S. Sakthivel and S. Balamurugan
S. Sakthivel and S. Balamurugan

It is the one of the major fungal diseases in rice in which it is caused by Bipolarisoryzae. This diseases mainly attacks the crop from seedling stage to milky stage. Brown spot is otherwise called as sesame leaf spot or Helminthosporiose. Brown spot causes both quality and quantity losses.

On average, the disease causes 7% yield loss across all lowland rice production in South and Southeast Asia. Severely infected field can have as high as 50% yield loss. Heavily infected seeds cause seedling blight and lead to 10−58% seedling mortality. It also affects the quality and the number of grains per panicle, and reduces the weight of the kernel. Brown spot is consider as the main factor in contributing “Bengal famine”, in India.

Favourable condition for the spread of this diseases:

The disease can develop in areas with high relative humidity (89−100%) and the temperature between 16 and 36°C. It is common in nutrient-deficient soil, or in soils that accumulate toxic substances.  This type of fungi is able to survive for more than 3 years in the seed . This type of fungus survive in the collateral host like Leersiahexandra and Echinochloacolonum. It spreads mainly through air.

Some of the main causes for the attack of  brown spot in the field:

  • Usage of Infected seed will gives rise to grow of infected seedlings.

  • Infected rice debris

  • Unwanted weeds that grown in the field.

Brown spot can occur at all crop stages, but the infection is most critical during maximum tillering up to the ripening stages of the crop.


  • Infected seedlings have small, circular, yellow brown or brown lesions that may girdle the coleoptile and distort primary and secondary leaves.

  • During the initialization of tillering stage lesions are being observed as small, circular, and dark purble or dark brown colour.

  • Fully developed lesions are circular to oval with a light brown to gray center. It is surrounded by a reddish brown margin caused by the toxin produced by the fungi.

  • The name of the toxin produced by the fungi is Helminthosporium (Hc Toxin).

  • Infected part will be change into blackish brown discolouration

  • In case of susceptible varieties, lesions are 7−15 mm long which can cause leaves to wilt, and in case of the resistant varieties little pin head lesions are found.

  • Spikelets can also be infected. Infection of florets leads to incomplete or disrupted grain filling and a reduction in grain quality. It also affect the grain also and make the it as chaffy grain. In certain rice varieties, brown spot lesions can be mistaken for blast lesions. To confirm, check if spots are circular, brownish, and have a gray center surrounded by a reddish margin.



  • Apply required fertilizers for soils that are low in silicon, apply calcium silicate slag before planting.

  • Nutrient in the soil should be enriched.

  • Use slow release nitrogenous fertilizer.

  • Spray in the nursery (40 ml / 8 cents ) and main field with Metominostrobin 160g/ha.

  • And spray edifenphos 250 ml, Mancozeb 1.2 kg, Aureofungin 0.005% in the main field crop.

  • Usage of resistant varieties like ADT 44, PY 4 , CORH 1, CO 44, TPS, CAUVERY, BHAVANI may reduce the level of losses.                

  • Before sowing the seeds, the seeds should be treated by using fungicides like carbendazim, thirum, captan, propiconazole, azoxystrobin, trifloxystrobin @3 g per kg of seeds. Or

  • Treat the seeds with hot water (52−55°C) for 13 minutes before planting, to control primary infection at the initial of seedling stage. To get more effectiveness, pre-soak the seeds in cold water for 8 hrs.     

Author Details

S. Sakthivel. IV Year, B.sc., (Agriculture).

Assistant Professor (Department of Entomology),

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