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Integrated Disease Management of Rice

P.RAJA
R.SARAVANAN

COLLEGE OF HORTICULTURE AND FORESTRY
CENTRAL AGRICULTURAL UNIVERSITY
PASIGHAT
EAST SIANG DISTRICT, ARUNACHAL PRADESH

 

              Integrated Disease Management of Rice (Oryza sativa)

Blast

Pyricularia oryzae


Symptoms 

  • The fungus attacks rice at all stages from seedlings in nursery to heading in main field. 
  • The typical symptoms appear on leaves, leaf sheath, rachis, nodes and even the glumes are also attacked. 
  • On the leaves, the lesions start as small water soaked bluish green flecks, soon enlarge and form characteristic spindle shaped spots with grey.

Centre and dark brown margin.

  • The spots join together as the disease progresses and large areas of the leaves dry up and wither. Similar spots are also formed on the sheath.
  • Severely infected nursery and field show a burnt appearance.
  • In infected nodes, irregular black areas encircle the nodes can be noticed.
  • The affected nodes may break up and all the plant parts above the infected nodes may die.
  • At the flower emergence, the fungus attacks the peduncle which is engirdled and the lesion turns to brownish-black.
  • This stage of infection is commonly referred to as rotten neck/neck rot/neck blast/panicle blast.
  • In early neck infection, grain filling does not occur and the panicle remains erect like a dead heart caused by a stem borer. In the late infection, partial grain filling occurs. Small brown to black spots also may be observed on glumes of the heavily infected panicles. Generally, the yield losses caused by the pathogen ranges from 30-61 per cent depending upon the stages of infection.
Favourable Conditions
Application of excessive doses of nitrogenous fertilizers, intermittent drizzles, cloudy weather, high relative humidity (93-99 per cent), low night temperature (between 15-20°C), more number of rainy days, longer duration of dew, cloudy weather, slow wind movement and availability of collateral hosts.

Management
  • Grow resistant varieties like IR20.
  • Avoid cultivation of highly susceptible varieties IR50.
  • Remove and destroy the weed hosts in the field bunds and channels.
  • Treat the seeds with Captan or Thiram or Carbendazim or Carboxin or Tricyclazole at 2 g/kg.
  • Seed treatment with biocontrol agent Trichoderma viride@ 4g/kg or Pseudomonas fluorescens @ 10g/kg of seed.
  • Avoid close spacing of seedlings in the main field. Spray the nursery with Carbendazim 25 g or Edifenphos 25 ml for 8 cent nursery.
  • Spray the main field with Edifenphos 250 ml or Iprobenphos 500 ml or Carbendazim 250 g or Tricyclazole 400 g or Thiophanate Methyl 500 g or Pyroquilon 500 g/ha.


Brown Spot or Sesame leaf spot
Helminthosporium oryzae


Symptoms

  • The fungus attacks the crop from seedling in nursery to milk stage in main field.
  • Symptoms appear as lesions (spots) on the coleoptile, leaf blade, leaf sheath, and glume, being most prominent on the leaf blade and glumes.
  • The disease appears first as minute brown dots, later becoming cylindrical or oval to circular.
  • The several spots coalesce and the leaf dries up.
  • The seedlings die and affected nurseries can be often recognised from a distance by their brownish scorched appearance.
  • Dark brown or black spots also appear on glumes which contain large number of conidiophores and conidia of the fungus.
  • It causes failure of seed germination, seedling mortality and reduces the grain quality and weight.

Favourable Conditions

Temperature of 25-30°C with relative humidity above 80 per cent are highly favourable. Excess of nitrogen aggravates the disease incidence.

Management

  • Field sanitation-removal of collateral hosts and infected debris in the field.
  • Crop rotation, adjustment of planting time and proper fertilization are suggested. Use of slow release nitrogenous fertilizers is advisable.
  • Use disease free seeds. Treat the seeds with Thiram or Captan at 4 g/kg.
  • Spray the nursery with Edifenphos 40 ml or Mancozeb 80 g or Captafol 40 g for 8 cents nursery.
  • Spray the crop in the main field with Edifenphos 500 ml or Mancozeb 1 kg or Captafol 625 g/ha.

Narrow brown leaf spot
Cercospora janseana
(Sexual stage : Sphaerulina oryzina)
Symptoms

  • The fungus produces short, linear brown spots mostly on leaves and also on sheaths, pedicels and glumes. 
  • The spots appear in large numbers during later stages of crop growth.
Management

Spray Carbendazim 250 g or Mancozeb 1 kg/ha.

Sheath rot
Sarocladium oryzae
Symptoms

  • Initial symptoms are noticed only on the upper most leaf sheath enclosing young panicles. 
  • The flag leaf sheath show oblong or irregular greyish brown spots.
  • They enlarge and develop grey centre and brown margins covering major portions of the leaf sheath.
  • The young panicles may remain within the sheath or emerge partially.
  • The panicles rot and abundant whitish powdery fungal growth is formed inside the leaf sheath.

Favourable Conditions
Closer planting, high doses of nitrogen, high humidity and temperature around 25-30ºC. Injuries made by leaf folder, brown plant hopper and mites increase infection.

Management

  • Apply recommended doses of fertilizers.
  • Adopt optimum spacing.
  • Spray Carbendazim 250g or Edifenphos 1 lit or mancozeb 1 kg or Chlorothalonil 1 kg/ha at boot leaf stage and 15 days later.
  • Soil application of gypsum in 2 equal splits (500 kg/ha) reduce the sheath rot incidence.

Sheath blight
Rhizoctonia solani
Symptoms 

  • The fungus affects the crop from tillering to heading stage.
  • Initial symptoms are noticed on leaf sheaths near water level. 
  • On the leaf sheath oval or elliptical or irregular greenish grey spots are formed. As the spots enlarge, the centre becomes greyish white with an irregular blackish brown or purple brown border. 
  • Lesions on the upper parts of plants extend rapidly coalescing with each other to cover entire tillers from the water line to the flag leaf.
  • The presence of several large lesions on a leaf sheath usually causes death of the whole leaf, and in severe cases all the leaves of a plant may be blighted in this way.
  • The infection extends to the inner sheaths resulting in death of the entire plant. Older plants are highly susceptible. Five to six week old leaf sheaths are highly susceptible.
  • Plants heavily infected in the early heading and grain filling growth stages produce poorly filled grain, especially in the lower part of the panicle.

Favourable Conditions
High relative humidity (96-97 per cent), high temperature (30-32oC), closer planting and heavy doses of nitrogenous fertilizers.
Management

  • Avoid excess doses of fertilizers.
  • Adopt optimum spacing.
  • Eliminate weed hosts.
  • Apply organic amendments.
  • Avoid flow of irrigation water from infected fields to healthy fields.
  • Deep ploughing in summer and burning of stubbles.
  • Spray Carbendazim 250 g or Chlorothalonil 1 kg or Edifenphos 1 lit/ha. Seed treatment with Pseudomonas fluorescens @ of 10g/kg of seed followed by seedling dip @ of 2.5 kg or products/ha dissolved in 100 litres and dipping for 30 minutes.
  • Soil application of P.fluorescens @ of 2.5 kg/ha after 30 days of transplanting (This product should be mixed with 50 kg of FYM/Sand and then applied).


Grain discolouration
Many fungi
Symptoms

  • The grains may be infected by various organisms before or after harvesting causing discolouration. The infection may be external or internal causing discoloration of the glumes or kernels or both.
  • Dark brown or black spots appear on the grains.
  • The discolouration may be red, yellow, orange, pink or black, depending upon the organism involved and the degree of infection.
  • This disease is responsible for quantitative and qualitative losses of grains.

Favourable Conditions
High humidity and cloudy weather during heading stage.

Management

  • Pre and post-harvest measures should be taken into account for prevention of grain discolouration.
  • Spray the crop at bootleaf stage with Mancozeb 1 kg or Iprobenphos 500 ml or Carbendazim 250 g/ha.
  • Store the grains with 13.5-14% moisture content.

False smut
Ustilaginoidea virens
Symptoms 

  • The fungus transforms individual grains into greenish spore balls of velvetty appearance. 
  • Due to the development of the fructification of the pathogen, the ovaries are transformed into large velvety green masses. Usually only a few spikelets in a panicle are affected.
  • Pathogen Chlamydospores are formed on the spore balls, they are spherical to elliptical, waxy and olivaceous.

Favourable conditions
Rainfall and cloudy weather during the flowering and maturity periods are favourable.


Udbatta disease 
Ephelis oryzae
Symptoms

  • The symptoms are evident at the time of panicle emergence.
  • The infected panicle inside the sheath is matted together by the mycelium.
  • The entire ear head is converted into a straight compact cylindrical dark spike like structure.
  • The spikelets are cemented to the central rachis and the size is remarkeably reduced.
  • No grain is formed.
  • The entire spike is covered by greyish stroma and convex pycnidia are immersed in the stroma.

Management

    Hot water seed treatment at 45°C for 10 min. effectively controls the disease. Removal of collateral hosts like Isachne elegans, Eragrostis tenuifolia and Cynadon dactylon.


Stackburn disease
Trichoconis padwickii
Symptoms

  • Leaves and ripening grains are affected. In the leaves, circular to oval spots with dark brown margins are formed.
  • The central portion of the spot turns to light brown or almost white and has numerous minute dots.
  • On the glumes reddish brown or pale brown spots appear.
  • The kernels may shrivel and become brittle when severe spotting occurs.

Management

    Treat the seeds with Thiram or Captan or Mancozeb at 2g/kg. Hot water treatment at 54ºC for 15 minutes is also effective. Burn the stubbles and straw in the field.


Bunt or Kernel Smut or black smut

Tilletia barclayana

 Minute black pustules or streaks are produced in the grains which burst open at the time of ripening. The grains may be partially or entirely replaced by the fungal spores. The sorus pushes the glumes apart exposing the black mass of spores. Only a few flowers are infected in an inflorescence. The fungus survives as chlamydospores for one or more years under normal condition and 3 years in stored grains.


Stem rot
Sclerotium oryzae
Symptoms

 

  • Small black lesions are formed on the outer leaf sheath and they enlarge and reach the inner leaf sheath also.
  • The affected tissues rot and abundant sclerotia are seen in the rotting tissues.
  • The culm collapses and plants lodge. If the diseased tiller is opened, profuse mycelial growth and large number of sclerotia can be seen.
  • The sclerotia may be seen in the stubbles after harvest.


Favourable Conditions

    Infestation of leaf hoppers and stem borer and high doses of nitrogenous fertilizers. 

Management
Use of recommended doses of fertilizer. Deep ploughing in summer and burning of stubbles. Avoid flow of irrigation water from infected fields to healthy fields.

Foot rot or Bakanae disease
Fusarium moniliforme
Symptoms

  • The infected seedlings in nursery are lean and lanky, much taller than healthy seedlings and die after some time.
  • In the main field, the affected plants have tall lanky tillers and have longer internodes and aerial adventitious roots from the nodes above ground level.
  • The root system is fibrous and bushy.
  • The plants are killed before earhead formation or they produce only sterile spikelets. When the culm is split open white mycelial growth can be seen.

Pathogen

  • Fungus produces both macro and micro conidia. Micro conidia are hyaline, single celled and oval in shape.
  • Macro conidia are slightly sickle shaped, narrow at both ends and two to five celled.
  • The fungus produces phytotoxin called fusaric acid, which is non-host specific.


Mode of Spread and Survival
The fungus is externally seed-borne.
Management
Treat the seeds with Thiram or Captan or Carbendazim at 2 g/kg.

Bacterial leaf blight
Xanthomonas oryzae p.v. oryzae
Symptoms

  • The disease is usually noticed at the time of heading but in severe cases occur earlier also.
  • Seedlings in the nursery show circular,yellow spots in the margin, later enlarge, coalesce and cause drying of foliage.
  • “Kresek” symptom is seen in seedlings, 1-2 weeks after transplanting. The bacterium enters through the cut wounds in the leaf tips, becomes systemic and cause death of entire seedling.
  • In grown up plants water soaked, translucent lesions appear usually near the leaf margin. The lesions enlarge both in length and width with a wavy margin and turn straw yellow within a few days, covering the entire leaf.
  • As the disease progresses, the lesions cover the entire leaf blade which may turn white or straw coloured.
  • Lesions may also be seen on leaf sheaths in susceptible varieties. Milky or opaque dew drops containing bacterial masses are formed on young lesions in the early morning.
  • They dry up on the surface leaving a white encrustation.
  • The affected grains have discoloured spots surrounded by water soaked areas.
  • If the cut end of leaf is dipped in water, bacterial ooze makes the water turbid.


Favourable Conditions

Clipping of tip of the seedling at the time of transplanting, heavy rain, heavy dew, flooding, deep irrigation water, severe wind, temperature of 25-30ºC and application of excessive nitrogen, especially late top dressing.

Management

 

  • Burn the stubbles. Use optimum dose of fertilizers.
  • Avoid clipping of tip of seedling at the time of transplanting.
  • Avoid flooded conditions. Remove weed hosts.
  • Spray Streptomycin sulphate and tetracycline combination 300 g + Copper oxychloride 1.25 g/ha.


Bacterial leaf streak
Xanthomonas campestris p.v. oryzicola
Symptoms

 

  • Fine translucent streaks are formed on the veins and the lesions enlarge lengthwise and infect larger veins and turn brown.
  • On the surface of the lesions, bacteria ooze out and form small yellow band-like exudates under humid conditions. In severe cases the leaves may dry up.

 

Management
Similar to bacterial leaf blight.

Rice tungro disease
Rice tungro virus
Symptoms

 

  • Infection occurs both in the nursery and in the main field.
  • Plants are markedly stunted. Leaves show yellow to orange discoloration and interveinal chlorosis.
  • Yellow discoloration is commonly seen in “Japonica” varieties, while “Indica” varieties show orange discoloration.
  • Young leaves are often mottled with pale green to whitish interveinal stripes.
  • The plants may be killed if infected early.
  • Tillering is reduced with poor root system.
  • The infected plants have few spikelets and panicles are small with discoloured grains.
  • Tungro infected plants can be chemically identified by
  • lodine Test: Ten cm long leaf tip is cut in the early morning before 6 A.M. and dipped in a solution containing 2 g lodine and 6 g Potassium lodide in 100 ml of water for 30 minutes. Tungro infected leaves show dark blue streaks.


Mode of Spread and Survival
Transmitted by leaf hopper.
Management

  • Summer deep ploughing and burning of stubbles.
  • Destroy weed hosts of the virus and vectors.
  • Control the vectors in the nursery by application of carbofuran 170 g/cent, 10 days after sowing.
  • Spray Phosphamidan 500 ml or Fenthion 500 ml or Monocrotophos 1 lit/ha or Neem oil 3 per cent in the main field 15 and 30 days after transplanting to control leaf hoppers.


Grassy stunt
Virus

The infected plants are markedly stunted and have excessive tillering and has an erect growth habit. The leaves become short, narrow, pale green or pale yellow and have numerous small dark brown spots. On older leaves these spots spreading give a bronze colour to the plants. The plants may produce a few small panicles which bear dark brown and unfilled grains.
Mode of Spread and Survival
The virus is transmitted in a persistent manner by the brown plant hopper, Nilaparvata lugens. It has a latent period of 5 to 28 days in the vector.

Rice dwarf Virus
Symptoms

  • The virus infected plants show marked stunted growth with chlorotic or whitish specks on the leaves.
  • The size of specks varies often and form interrupted streaks along the veins and distal part of infected leaves show diffuse yellowing.
  • The number of tillers may be reduced with retarded growth.
  • The diseased plants may survive until harvest time, remaining more or less green.
  •  Plants which are infected at early stage produce no ear heads, if produced, may have small unfilled grains.

Favourable Conditions

High population of Nephotettix cincticeps, Recllia dorsalis and N. nigropictus. The presence of gramineous weeds like Echinochloa crusgalli, Glyceria acutifolia and Panicum miliaceaaum.
Mode of Spread and Survival
The virus is found to survive in the gramineous weeds. The virus is transmitted through the egg masses of leafhoppers from one generation to another (Trans ovarial transmission).

Management 

Destroy the weed host which harbors the virus and the vectors. Spray Phosphamidon or Fenthinon 500 ml or Monocrotophos 1 lit/ha.


Ragged stunt Virus
Symptoms

Formation of ragged leaves with irregularly edged portions, stunting of plants, vein swelling, delay in flowering, and production of nodal branches and incomplete emergence of panicles are the main diagnostic symptoms.
Mode of Spread and Survival
The virus is transmitted in a persistent manner by the brown planthopper, Nilaparvata lugens but not through seed. It has a latent period of 3 to 35 days in the vector.


Rice yellow dwarf
Mycoplasma Like Organism (MLO)
Symptoms

  • The infected plants are stunted and have yellowish green to whitish green leaves.
  • There is excessive tillering and leaves became soft and droop slightly. Plants are usually sterile but some may produce small panicles with unfilled grains.
  • If plants are infected early they usually die before maturity, and even if they do survive no panicles are produced or only a small number with no grains.
Mode of Spread and Survival
The MLO is transmitted by Nephotettix virescens and N. nigropictus with a latent period of 25-30 days. It survives on several grass weeds.
Management
Deep ploughing during summer and burning of stubbles. The management practices followed for Rice Tungro disease need to be adopted for this disease also.