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1. The disease causes blighting of seedlings in the nursery and leaf spotting on the leaves and leaf sheaths in the field.
2. The spots are round to oval and dark brown; in severe cases they may coalesce to form large patches. The disease occurs mostly in deficient and poor soils and commonly referred to as poor man's disease.
3. Infection is also seen on glumes, neck of the panicle and grains as brown discolouration. This disease is more common in Meghalaya and Tripura, particularly in boro season .
4. The disease is caused by Helminthosporium oryzae (Bipolaris oryzae). The fungus produces conidiophores, which are long, septate and bear conidia singly in a sympodial manner.
5. The conidia are brown, 8-10 celled, slightly curved with a bulge in the middle and tapering towards end.
The fungus over winters mainly in infected plant parts and seeds.
6. Diseased seeds give rise to the seedling blight and secondary infection is by conidia formed on the seedlings, which become wind borne.
The control measures of Brown spot disease:
1. As the disease is seed borne, seed treatment with Thiram @ 2 g/kg seeds gives effective control
2. Application of nitrogen in three split doses and correction of soil deficiency like potash, manganese and zinc are helpful
3. Correction of soil acidity by liming help in reducing the disease.
4. Use ofHYVs resistant to the disease
5. Spraying 0.1 % Hinosan 50 EC or 0.2% Dithane M-45 (75 WP) mixed with 0.1 % Sandovit helps to control the disease