Disease:Rice Blast

Pyricularia grisea Anamorph Magnaporthe grisea - Teleomorph

Blast is considered the most serious disease because of its devastating nature, widespread distribution and existence of several physiological races of the causal organism.Maximum losses due to blast occur when seedlings or plants are killed at tillering stage or when panicles are infected. The time of infection, part of the plant infected, variety of plant, environmental factors, etc. influence disease severity and eventually yield loss.

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  • Disease 9
  • Disease 10
  • Disease 11
  • Disease 12
  • Disease 13
  • Disease 14
  • Disease 15
  • Disease 16
  • Disease 17
  • Disease 18
  • Disease 19
  • Disease 20
  • Disease 21
  • Disease 22
  • Disease 23
  • Disease 24
  • Disease 25

Symptoms

  • 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.

Procedure for Observation

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

ETL

  • Nursery: 5 % disease severity Planting to pre tillering: 5% Mid tillering stage : 10 % diseases severity Panicle initiation and booting : 10 % leaf area damage Flowering and after : 5% leaf area damage or 1% neck infection.

    • Control Measures

  • Management of the disease depends on the use of resistant varieties, pathogen free seed, seed treatment with fungicides, judicious use of fertilizers and destruction of collateral host and clean cultivation.
  • High yielding rice varieties with resistance/tolerance to blast can be chosen for cultivation. Eg. Short duration varieties Kanchana, Kairali and Onam. Medium duration varieties Asha, Anashwara Ranjini, Long duration varieties Laksmi, Deepthi.
  • Apply rice hull ash @ 100 g per meter square in the nursery.
  • Seeds should be collected from disease free area and treated with fungicides such as thiram (Thiride), carbendazim (Bavistin), carboxin (Vitavax) or tricyclazole (Beam) at the rate of 2g/kg seed. The seeds are to be soaked in the fungicidal solution for 16 hours just before sowing. Soaking seeds in water at 52 0C for 10 minutes is also effective.
  • The collateral weed hosts on the bunds of paddy fields should be destroyed.
  • The nursery can be protected by spraying with carbendazim 25g for 8 cent nursery.
  • The foliar or secondary infection can be managed by spraying the main field with fungicides such as Zineb (Dithane Z 78,Zineb 75,Hexathene 75 WP) @ 2 kg /Ha; Ipropenphos (Kitazine-P48 EC-@ 500ml/Ha); Thiophanate (Topsin 50 WP,Cercobin 50 WP) @ 500g/Ha; Carpropamid (Protega 27.8 EC @500 ml/Ha; Arcado 27.8 EC@ 500ml/Ha) or Isoprothiolane (Fugione 40 EC @750 ml/Ha) or mancozeb (2 kg/ha).or Aureofungin sol 60 g /ha. One foliar fungicide spray at heading can safeguard rice crop against neck blast.
  • In highly disease prone areas application of nitrogen fertilizers has to be regulated. Early planting and restricted nitrogen fertilizer application help in avoiding serious blast epidemics.
  • Bio control agent Pseudomonas fluorescens can be applied as seed treatment (10g culture/kg seed); root dip (dip roots of seedlings before transplanting in solution of P fluorescence @ 20 g/lit for 30 minutes) soil incorporation ( @ 2 to 2.5 kg/ha one week after transplanting or 30 t0 40 days after sowing for the direct sown crops) or as foliar spray (at 45 days crop growth @ 20g/L of spray fluid). For soil incorporation, mix 2.5 kg of P fluorescens with 50 kg dry cow dung or sand and broadcast in the field. Dewater the field before application of the culture. Root dip and foliar application of PGPR mix II @ 20g/lit is also beneficial.