Rice

Disease Management

Detailed Study of Diseases

Blast

Classification

Casual Organism:Pyricularia Oryzae Cavara
Order:Deuteromycetes
Family:Moniliaceae

Occurrence

Earliest known plant disease Also known as rotten neck or rice fever. Reported from 80 rice-growing countries. First recorded in China (1637). Later from Japan (1704), From Italy (1828), from USA (1876), from India (1918). Expected grain loss : 70 to 80%

Disease Cycle

• In tropics, air borne conidia are present all round the year, because of the availability of collateral host grasses such as Setaria intermecia, Digitaria marginata, Panicum repens and Leersia hexandra.
• Some of these grasses may be acting as primary source of inoculum.
• The infection may be sometimes through infected seed and infected plant debris.
• The conidia produced on the leaves of nursery seedlings become wind-borne and cause secondary spread of the disease.

Epidemiology

• Day temperature (30°C), night temperature (20°C) and day light (14 hours) found to predispose the plants to infection.
• Relative humidity (92%) and free water required for conidial germination and infection.
• Spores do not germinate in direct sun light
• Cloudy overcast weather, dew drops encourage blast spread
• Conidia exhibit nocturnal pattern of diurnal periodicity with peak concentration of spore dispersal occurring around 4AM favored by night temperature (25 - 27°C) and relative humidity (86 -98%)
• Conidia could remain viable under snow to over winter period and 4 - 6 months after harvest.

Nature and Symptoms of Damage

• Disease can infect paddy at all growth stages and all aerial parts of plant (Leaf, neck and node).
• Among the three leaf and neck infections are more severe.
• Small specks originate on leaves - subsequently enlarge into spindle shaped Spots(0.5 to 1.5cm length, 0.3 to 0.5cm width) with ashy center.
• Several spots coalesce -> big irregular patches

Control Measures

• Use seed from a disease - free crop
• Destruction of wild collateral hosts
• Timely removal of weed hosts
• Destruction of infected plants
• Avoid excess N - fertilizer application
• Use of tolerant varieties (Penna, Pinakini, Tikkana, Sreeranga, Simphapuri, Palghuna, Swarnamukhi, Swathi, Prabhat, IR - 64, Jaya, IR - 36, MTU 9992, MTU 1005, MTU 7414)
• Burning of straw and stubbles after harvest

Chemical Control

• Seed treatment at 2.5 gm/kg seed with Capton or Carbendazim or Thiram or Triclyclazole.
• Spraying of Triclyclazole at 0.6 gm/liter of water or Edifenphos at 1 ml/lit of water or Carbendazim at 1.0 gm/lit.
• 3 to 4 sprays each at nursery, Tillering stage and panicle emergence stage may be required for complete control.

Nursery stage

• Light Infestation - Spray carbendazim or Edifenphos @ 0.1 %.

Pre-Tillering to Mid-Tillering

• Light at 2 to 5 % disease severities - Apply Ediphenphos, Carbendazim or 1 BP 48 @ 0.1 %. Delay top dressing of N fertilizers when infection is seen.
• Panicle initiation to booting: At 2 to 5% leaf area damage spray Edifenphos or Carbendazim or Pyroquilon or 1 BP 48 @0.1 %.

Flowering and after

• At 5 % leaf area damage or 1 to 2 % neck infection Spray Edifenphos, Carbendazim @ 0.1 % or Triclyclazole @ 1 gm /lit of water.

Sheath Blight

Control Measures

• Selection of healthy seeds, application of split (3-4) nitrogenous fertilizers, weed control in bunds and fields reduces the disease incidence.
• Spray application of Propiconazole @1ml/lit or hexaconazole 2ml/lit or validamycim at 2ml/lit twice at 15days interval when the first symptoms are noticed or at maximum tillering stage effectively controls the Sheath blight disease.

Bacterial Leaf Blight

Classification

Class:Schizomycete
Order:Pseudomonada
Family:Pseudomonadaceae

Occurrence

Earliest known plant disease Also known as rotten neck or rice fever. Reported from 80 rice-growing countries. First recorded in China (1637). Later from Japan (1704), From Italy (1828), from USA (1876), from India (1918). Expected grain loss : 70 to 80%

Disease Cycle

• Inoculum source - seed husk, seed endosperm, soil, plant stubbles, debris, collateral host grasses (Leersia spp. and Cyprus spp.)

Epidemiology

• Rainy (cloudy) weather, dull windy days, temperature between 22 - 26°C is conducive. Close planting enhances the disease incidence

Nature and Symptoms of Damage

• Bacteria induce either leaf blight or wilting of plant (Kresek)
• In Kresek stage plants show wilting symptoms (3 - 4 weeks)
• Leaf blight phase - appears small water soaked lesions (5 - 10cm length near tip of leaf)

Lesions gradually enlarge - infection starts from downwards either on one side or both sides of leaf margins. Affected portion gradually dryup - leaf margins remain green on the affected portions small amber colored droplets of bacterial ooze takes place - on drying these droplets form minute crusts and give rough touch when the leaves passed between fingers. This is the earliest known plant disease

Lesions give dark brown colour with saprophytic fungi cover Premature drying on severity of disease Brown colored discoloration in the xylem vessels of vascular bundles of stem disintegrates xylem vessels and restricts translocation of nutrients to growing points results in wilting and death of plants

Control Measures

• Secure disease free seed
• Grow nurseries preferably in isolated upland conditions
• Balanced fertilization, avoid excess N - application
• Skip N - application at booting (if disease is moderate)
• Drain the field (except at flowering stage of the crop)
• Destruction of wild collateral hosts
• Avoid flow of water from affected fields
• Grow tolerant varieties (Swarna, Ajaya, Deepti, Badva mashuri, MTU-9992).

Sheath Rot

Classification

Casual Organism:Sarocladium oryzae
Class:Deuteromycetes
Order:Moniliales
Family:Moniliaceae

Occurrence

Earlier this disease was considered as minor. But now it has assumed importance with its sporadic occurrence in some places of Andhra Pradesh.

Disease Cycle

• Primary source of inoculum is by means of infected plant debris.
• Secondary spread is by means of air borne conidia produced on the leaf sheath.
• Conidia are colorless, single celled and cylindrical in shape.

Epidemiology

• Night temperatures of 20°C, dew (mist), Cold weather, high humidity, more use of Nitrogen fertilizers are favorable for development of this disease.

Nature and Symptoms of Damage

• Small water soaked lesions on the upper most leaf sheaths (boot leaf sheath)
• Lesions gradually develop into grey colour irregular shaped spots, which are surrounded by brown coloured margins.
• In severe cases the infection reaches the panicle and glumes.

Control Measures

• Destruction of the infected plant debris by burning.
• Seed treatment with Carbendazim at 1.0 gm/kg seed.

Chemical Control

• Spraying of Mancozeb at 2.5 gm or Carbendazim at 1.0 gm/lit or Benomyl 0.5 gm/lit of water at flowering stage may be taken up.

Brown Spot

Classification

Causal organism: Helminthosporium oryzae
Class: Deuteromycetes
Order: Moniliales
Family: Dematiaceae

Occurrence

Also called as sesame leaf spot or Helminthosporiose or fungal blight Mostly seen in West Bengal, Orissa, A.P and Tamil Nadu

Disease Cycle

• Not soil borne
• Over winters mainly in infected plant parts
• Seedlings from diseased seed (primary source of inoculation)
• Seedlings show infection symptoms soon after germination
• Disease occurs on as many as 20 species of oryzae
• Spores on seedlings cause secondary infection (wind - borne)

Epidemiology

• Optimum temperature is 25 - 30°C for conidia germination
• Around 90% humidity favours infection
• Darkness more favoured for fungus spread over sunlight
• Flowering phase is more susceptible
• Heavy N - monsoon rains cloudy days favour the disease
• High N - application aggravate the disease
• Low pH soils, deficient in essential and trace elements (especially low available K) favourble to disease
• Older leaves are more susceptible over younger ones

Nature and Symptoms of Damage

• Occur in nursery as well as main crop
• Causes blight of seedlings
• Leaf spotting is very common
• Isolated brown, round to oval (resemble sesame seed)
• Spots measures 0.5 to 2.0mm in breadth - coalesce to form large patches.

Seed also infected (black or brown spots on glumes) (spots are covered by olivaceous velvety growth) Infection also occur on panicle neck with brown colour appearance 50% yield reduction in severe cases

Control Measures

• Use disease free seed (since it is seed borne)
• Treat the seed with Carbendazim (1g/kg seed) or Thiram or Mancozeb (2.5g/kg seed)
• Correct potash deficiency
• Avoid excess N - application

Chemical Control

• Spray Mancozeb (2.5g/lit) or Carbendazim (1g/lit) or EdiPhenphos (1ml/lit) - 2 to 3 times at 10 - 12 day intervals before appearance of initial symptoms
• Spray preferably during early hours or afternoon hours at flowering and post - flowering stages.

False Smut

Classification

Causal organism : Ustilaginoidea viridis Class : Deuteromycetes Order : Moniliales Family : Moniliaceae

Occurrence

• Also known as green smut
• First reported from Tamil Nadu in 1878
• Later reported from Japan, USA, Philippines, Indo - China, Burma, Srilanka
• Severe in Eastern States of India
• Not a serious disease in A.P
• Disease more prevalent - in seasons of favourable growth and high yield
• Indication of good harvest (farmers impression)

Disease Cycle

• Grasses and wild rice species are alternate hosts
• Spores - air - borne (main source of inoculum)
• Ascospores produced from scleratia - source of primary infection
• Chalmydospores - secondary infection , air - borne, abundant at heading stage

Epidemiology

• Rainfall accompanied by cloudy days are favourable
• Appear between flowering and maturity of grain

Nature and Symptoms of Damage

• Occurs on ear heads
• Ovaries are transformed into large, velvety green masses
• Round to oval, irregular sclerotial bodies
• Few spikelets affected

Glumes are not affected Sclerotial bodies - slightly flattened, smooth, yellow - covered by a membrane Membrane bursts leads to further growth

Control Measures

• Use certified seed
• Collect and destroy diseased grains check secondary spread of disease helps in reducing inoculum for the next year

Chemical Control

• Spray Carbendazim (1g/lit) or Copper Oxychloride (2.5g/lit) at panicle initiation stage and 7 - 10 days later.

Tungro Virus

Causal Organism:Rice Tungro Virus

Occurrence

Virus diseases are neglected initially with an impression of physiological disorders. Two types of viruses i.e. Tungro and Grassy stunt are reported. Tungro is severe in A.P. Reported in India in 1967. Appeared in epidemic form in N - E states of India (1969 & 1973) and Kerala (1964 ).

• Yield loss - 38 - 71% (less susceptible varieties) - 84 - 100% (highly susceptible varieties)

Disease Cycle

• Wild collateral grasses - Eleusine indica, Echinochloa colonum are the primary sources of inoculum
• Green leaf hoppers are the secondary source of infection (female hopper is more efficient over male hopper)
• Virus is non - persistent in the vector
• Four strains of virus reported in India
• Virus particles are spherical (27.3 to 44.5mµ diameter)

Epidemiology

• Mineral nutrition and N - fertilization had marked influence on development of disease
• September to November and March to April the insect vector is more active and thus disease is more prevalent

Nature and Symptoms of Damage

• Disease can infect paddy at all growth stages and all aerial parts of plant (Leaf, neck and node).
• Among the three leaf and neck infections are more severe.
• Small specks originate on leaves - subsequently enlarge into spindle shaped Spots(0.5 to 1.5cm length, 0.3 to0.5cm width) with ashy center.
• Several spots coalesce -> big irregular patches

Stunted growth, leaf colour is yellow to orange Mottled appearance and slight twisting in young leaves Rusty blotches in old leaves, discolored rusty blotches spread downwards from leaf tip

• Delayed flowering (less susceptible varieties)
• Leads to death before flowering (highly susceptible varieties)
• Virus transmitted by green leaf hopper (Nepholettix virescens)

Control Measures

• The isolated plants having virus infection symptoms in the beginning and destroy them by burning so that the insect does not get inoculum to spread the disease.
• The green stubbles, voluntary plants should be uprooted and burnt after harvest.
• Adopt balance fertilizer application.
• Destroy weeds both in field and on bunds.
• Leaf yellowing can be minimized by spraying 2 % urea mixed with Mancozeb at 2.5 gm/lit.
• Instead of urea foliar fertilizer like multi-K (potassium nitrate) can be sprayed at 1 per cent which impart resistance also because of high potassium content.
• Grow tolerant varieties like MTU 9992, MTU 1002, MTU 1003, MTU 1005, Surekha, Vikramarya, Bharani, IR 36 etc.,
• In epidemic areas follow rotation with pulses or oil seeds.

Chemical Control

• Green jassids acting as vectors are to be controlled effectively in time by spraying Monocrotophos at 1.6 to 2.2 ml/lit or Edifenphos @1.5 ml/lit or by applying carbofuron 3 G @ 10 kg/acre.
• In nursery when virus infection is low, apply Carbosulfan granules @ 1 kg a.i./ha to control vector population.
• During pre-tillering to mid-tillering when one affected hill/m is observed apply carbofuran granules @ 1 kg a.i./ha or spray monocrotophos @ 1.6 to 2.2ml/Lit to control insect vector.