Brown spot is caused by the fungus Cochliobolus miyabeanus.  Also called Helminthosporium leaf spot, it is one of the most prevalent rice diseases in Louisiana.When C . miyabeanus  attacks the rice plants at emergence,the resulting seedling blight causes sparse or inadequate stands and weakened plants.Leaf spots are present on young rice,but the disease is more prevalent as the plants approach maturity and the leaves begin to senesce.Yield losses from leaf infection or leaf spots probably are not serious.Brown spot is an indicator of unfavorable growing conditions,including insuffcient nitrogen,inability of the plants to use nitrogen because of rice water weevil injury,root rot or other unfavorable soil conditions.

 Leaf spots are found throughout the season.On  young leaves,the spots are smaller than those on older leaves.The spots may vary in size and shape from minute dark spots to large oval to circular spots .The smaller spots are dark brown to reddish-brown. The larger spots have a dark brown margin and a light reddish-brown or gray center with a gold halo.The spots on the leaf sheath and hulls are similar to those on the leaves.The pathogen also attacks the coleoptiles,branches of the panicle,glumes and grains.The fungus causes brown,circular to oval spots on the coleoptile leaves of the seedlings.Damage from brown spot can be reduced by maintaining good rice growing conditions through proper fertilization, crop rotation, land leveling, proper soil preparation and water management. Seed protectant fungicides reduce the severity of seedling blight caused by this seed borne fungus. In addition, some rice varieties are less susceptible than others. Damage from brown spot can be reduced by maintaining good rice growing conditions through proper fertilization, crop rotation, land leveling, proper soil preparation and water management. Seed protectant fungicides reduce the severity of seedling blight caused by this seed borne fungus. In addition, some rice varieties are less susceptible than others.

Blight or brown spots:

Symptoms:

This disease has been recorded all over the country. Initially small dots or circular eye-shaped or oval spots appear in light colour on the leaves. These spots coalesce and result in linear spots brown in colour. Later on the withering and the yellowing of leaves occur. The seed setting is affected and causes sterility, shrivelling and shows rotting and poor germination.

Perpetuation:

The diseased seeds plant debris and soils help the fungus to survive, while air and irrigation water helps fungus in transmitting from the diseased to healthy plants.

Control:

1) The use of resistant varieties or disease-free seed in healthy soils;

2) Sanitation and crop rotation;

3) Hot water seed treatment at 54C for 10 minutes or with seed dressing fungicides;

4) Collection and destruction of stubble and spraying with copper fungicides at right time and;

5) Application of suitable foliar fungicides to help minimize further dissemination of the disease.