Rice Disease by Jagmohan sir
Rice blast Disease:
In southern states, blast incidence is primarily associated with dry periods and cooler nights that are
prevalent during November - February.Depending on the site of symptom rice blast is referred as leaf
blast, collar blast, node blast, neck or panicle blast. Amongst which, neck blast is the most destructive
phase of the disease.
Causal organism: : Magnaporthe grisea
Period of occurrence: All stages of crop growth (seedling to maturity)
Extent of yield loss: 70-80% under extreme cases 100%
Alternate hosts: Grasses (Panicum repens, Digitaria marginata, Brachiaria mutica, Leersia
hexandra and Dinebra retroflexa)
Favorable conditions for the pathogen:
➢ Low night temperature (22 to 28°C)
➢ High relative humidity (> 95%)
➢ New deposit
➢ Extended leaf wetness period (>10 hrs)
➢ Cloudy and drizzling weather
➢ Soil fertility (High N)
➢ Degree of host susceptibility
➢ Straw of the previously infected crop heaped nearby
Mode of transmission/dissemination: Wind, Seed
Sources of inoculum: Seed, Grasses
Symptoms:
Leaf blast - Elliptical spots with more or less pointed ends resembling a spindle. Initially appear as
small grayish dots of pin-head size that finally enlarge into a spindle shaped spot with brown margin
and gray centre. Usually, the disease starts from lower to upper leaves. Finally leads to the death and
drying up of the plant.
Collar blast - Death of the entire leaf blade.
Node blast - Black patches appear on the infected nodes and all parts above the infected node die
similar to the damage done by rats.
Panicle blast or Neck blast - Improper grain filling, poor milling recovery and also chaffy ear heads
similar to the damage of white ears by stem borer.
Preventive measures:
➢ Use of resistant varieties like Gauthami, IR-36, IR-64, Parijatha, Rasi, Sasyashree, Salivahana,Simhapuri, Srinivas, Tikkana
➢ Burn previously blast affected straw and stubbles
➢ Use of disease free seeds
➢ Use of balanced rates of nutrition based on soil test- split applications of nitrogen (Excessive N
use can promote excessive luxuriant crop growth which increases the relative humidity and leaf
wetness of the crop canopy. This can lead to increased infection).
Biological control:
➢ Seed treatment with Pseudomonas fluorescence (10g / 1 of water) for 30 min.
➢ Seedling root dip treatment with Pseudomonas fluorescence (4g / 1 of water) for 20 min.
➢ Foliar spray of Pseudomonas fluorescence (4g / 1 of water) at 20-25 days after transplanting.
Control measures:
Cultural practices -
➢ Delay topdressing of N fertilizers when infection seen.
➢ Remove collateral weed hosts from bunds and channels.
➢ Use only disease free seedlings.
➢ Avoid excess nitrogen.
➢ Apply N in three split doses, 50% basal, 25% in tillering phase and 25%N in panicle initiation
stage.Use resistant variety
ii) Chemical control -
Seed treatment:
Seed dress with either Tricyclazole 75 WP or Carbendazim 50 WP @ 2 g per kg of seed. (For
seed treatment, measured quantity of fungicide is thoroughly mixed with water. Seeds are then soaked
in the fungicide solution for 12 hours. The soaked seeds are then put in a cloth bag and incubated for 2
to 3 days for proper germination. The fungicide treated sprouted seeds are then broadcasted in the
nursery bed) (Video-seed treatment against blast).
Brown spot of Rice:
Brown spot is a fungal disease that can infect both seedlings and mature plants. This disease is more
severe in areas of poor management.The disease is caused by (Helminthosporium oryzae).The
pathogen infects the coleoptiles of the seeding and causes blighting.On the leaves, circular or oval, dark
brown to purplish-brown spots are found.In severe conditions, these lesions may coalesce and cover the
entire leaf.The disease symptoms also appear on grains where black spot appear on glumes.The kernels
of infected spikelets become shriveled and discolored.
Local name: Kandu Chukke Roga
Causal organism: Helminthosporium oryzae , Cochilobolus miyabeanus.
Period of occurrence: Seedling to maturity
Extent of yield loss: 50-90% in extreme cases
Favorable conditions for the pathogen
➢ Temperature of 25-30°C
➢ Relative humidity (>90%)
➢ Heavy and late north-east monsoon
➢ Cloudy days
➢ High doses of N
Mode of transmission/ dissemination: wind
Sources of inoculum: Seed, Collateral hosts, Rice straw or Stubble
Symptoms:
On seedlings - Small, slightly elongated or circular brown lesions are observed on coleoptiles and
black discoloration of the roots cause distorted seedlings.
On leaves - Spots appear as circular to oval reddish brown lesions often surrounded by a yellow or
gold halo.
On glumes - Black or brown spots appear and in severe cases the greater portion of the glume may be
covered by these spots causing black discoloration. This reduces the market value.
Preventive measures:
➢ Use of resistant varieties - Rasi, IR 36, Jagannath.
➢ Proper crop nutrition
➢ Avoid water stress
➢ Clean cultivation
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