- The disease is seen during all stages of the crop growth but it is more frequent in the nursery and flowering stages.Symptoms are noticed generally on leaves, nodes, panicles and grains, and rarely on leaf sheath.
- Symptoms on leaf known as leaf blast appear as minute brown specks at first,which enlarge to form spindle shaped lesions with pointed ends in susceptible cultivars.
- The centre of the spot is grey or white with brown or reddish brown margin and with conspicuous yellow halo around the spots.
- Fully developed lesions are 1 to1.5 cm 0.3 to 0.5 cm in size.However, in resistant cultivars only minute brown pinheads are noticed. Heavily infected leaves soon become blighted and die.
- Severe infection in the nursery stage causes death of seedlings and is known as Nursery blast.
- Badly affected nurseries can be recognized from a distance by their brownish, scorched appearance.
- When infection occurs on nodes it rot leading to death of the parts above the node.This is the node blast phase of the disease.
- The most destructive phase of the disease is when the pathogen infects panicles.neck blast, The symptom is characterized by the appearance of black or grayish brown lesions at the base of the panicle(neck).
- If the symptoms occur at the time of panicle emergence, entire grains of the panicle turn chaffy.The attack at later stages,causes partly filled grains.Brown to black spots is also sometimes seen on the infected glumes.
In nursery mark 10 sq.m area. Select 100 leaves at random and look for the typical disease symptoms.
During planting to pre tillering randomly select 4 one sq.m area.Select 100 leaves at random from each of the selected areas.Calculate the % of leaves infected.At mid tillering stage select 4 one sq.m area.Select 100 leaves at random from each of the selected areas.Calculate the % of leaves infected.During panicle initiation stage to booting, select 25 leaves at random from each square and observe the leaf area damaged and work out the % leaf area damaged. Categorize the infection using 0-5 scale.During flowering and after, for leaf infection, follow the procedure given under panicle initiation to booting. For neck infection randomly select 100 ear heads, 25 each from one sq.m plots marked. Calculate the % of neck infection