Thursday, October 27, 2011

Black Gram(Urad Dal) Diseases

Anthracnose

Causal Organism
Colletotrichum lindemuthianum, C. capsisi

Damage 


The fungus attacks all aerial part parts and at any stage of plant growth.
Symptoms are circular, black, sunken spots with dark center and bright red orange margins on leaves and pods.
In severe infections, the affected parts wither off.
Seedlings get blighted due to infection soon after seed germination.

Survival & Favourable Conditions
The pathogens survive on seed and plant debris
Disease spreads in the field through air-borne conidia.
The disease is more sever in cool and wet seasons.

Cultural Control
Hot water treatment at 54 degree centigrade for 10 min.
Use disease free seed.
Follow crop rotation

Chemical Control
Spray mancozeb 0.3% or carbendazim 0.5/Litre.                                                                                           

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Bacterial Leaf Blight

Causal Organism
Xanthomonas phaseoli

Damage 

It is characterized by many brown, dry and raised spots on the leaf surface.
When the disease is severe several such spots coalesce, the leaves become yellow and fall off prematurely.
The lower surface of the leaf appears red in colour due to the formation of raised spots.
The stem and pods also get infected.

Survival & Favourable Conditions
The bacterium is seed-borne and through vines grow perennially.
Rain splashes play an important role in the development and spreading of the disease.

Cultural Control
Grow tolerant varieties of the disease.
Use disease free seed

Mechanical Control
Destruction of debris and stubbles.

Chemical Control
Soaking the seed in 500 ppm Streptocycline solution for 30 min. before sowing followed by two sprays of     Streptocycline combined with 3 g of Copper Oxychloride per litre at an interval of 12 days is recommended.

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Cercospora leaf spot

Causal Organism
Cercospora canescens

Damage 

Spots produced are small, numerous in number with pale brown centre and reddish brown margin. Similar spots also occur on branches and pods.
Under favourable environmental conditions, severe leaf spotting and defoliation occurs at the time of flowering and pod formation.

Survival & Favourable Conditions
The fungus is seed-borne and also survives on plant debris in the soil.
High humidity favours disease development.

Cultural Control
Cultivate resistant varieties.
Intercrop the moong with tall growing cereals and millets.
Follow clean cultivation.
Use disease free seed.
Maintain low crop population density and wide row planting.

Biological Control
The crude extracts of cassava, spiny amaranth, poinsettia, ipil-ipil, alascuatro, tagetes, garlic, mayana and zinger are applied for controlling the disease effectively.

Mechanical Control
Mulching reduces the disease incidence resulting in increase yield.                                                               
Chemical Control                                                                                                                                       
Cercospora leaf spot was effectively controlled by only a spray of Carbendazim (0.05%) at 30 days after       sowing.                                                                                                                                                         

 
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Corynespora Leaf Spot

Causal Organism
Corynespora cassiicola

Damage 

By this disease yields decrease drastically.
Symptoms of this disease develop on leaves when the crop reaches flowering stage.
Lesions begin as dark reddish brown circular spot usually on the upper surface of the leaf and they expand to become larger spots.
In advanced stages the spots coalesce to form patches. Shot-holing and severe defoliation is a marked symptom in advanced stages of infection.

Survival & Favourable Conditions
The fungus is seed-borne and can survive on host debris for two years.

Cultural Control
Use tolerant varieties LBG 167.

Chemical Control
Corynespora leaf spot was effectively controlled by only a spray of                                                               

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Leaf Curl

Causal Organism
Leaf Curl Virus

Damage 

An important and potential killer of green gram plants, more severe in Kharif season.
The earliest symptoms appear on youngest leaves as chlorosis around some lateral veins and its branches near the margin.
The leaves show curling of margin downwards.
Some of the leaves show twisting.
The veins show reddish brown discolouration on the under surface which also extends to the petiole.
Plants showing symptoms within 5 weeks after sowing invariably remain stunted and majority of these die due to top necrosis within a week or two.
Plants infected in late stages of growth do not show severe curling and twisting of the leaves but show conspicuous venial chlorosis any where on the leaf lamina.

Survival & Favourable Conditions
The disease develops in the fields mainly through seed or rubbing of diseased leaves with the healthy ones.

Cultural Control
Timely sowing.
Complete field and crop sanitation.
Take control measures for thrips.

Chemical Control
The virus is transmitted by thrips, Scirtothrips dorsalis, and hence can be managed by controlling thrips by spraying 1 g Acephate or 2 ml Dimethoate per litre.
 
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Leaf Crinkle Virus

Causal Organism
Rhizotonia solani

Damage 

The disease usually attacks black gram in all seasons.
Characterized by enlargement of leaves followed by crinckled surface of leaf lamina.
The crinckling is more pronounced on younger leaves.
Flowering is delayed by 8-10 days.
Inflorescence turns bushy in appearance.
Pod setting is curtailed which decreases the yield drastically.

Survival & Favourable Conditions
The virus is seed transmitted. Whiteflies, aphids and epilachna beetles also transmit the disease.

Cultural Control
The viral diseases can be controlled by applying following measures.
The crop must be sown timely.
The spacing between the lines should be maintained at 30 to 40 cms.
Only certified seeds should be used for sowing.
If the seeds are not treated then seed treatment should be done.
In endemic areas only tolerant and resistant varieties should be used.
Weeds plants should be rouged out at their inception.
Insect, fungal and nematode vectors should be controlled using suitable pesticides.
Control white fly as it spreads the virus.
Grow resistant varieties like ADT-3.
Removal and quick burning of the infected plant.

Chemical Control
Seed-borne infection can be eliminated by hot water treatment of seed at 55 deg C for 30 minutes              
Spraying insecticides 3 weeks after sowing to control sucking pests can help checking the spread of the          disease.                                                                                                                                                        

 
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Macrophomina Blight

Causal Organism
Macrophomina phaseolina

Damage 

In pre-emergence stage, the fungus causes seed rot and rotting of germinating seedlings.
In post-emergence stage, seedlings get blighted due to soil or seed borne infection.
Decay of secondary roots and shredding of the cortex region of the tap root are symptoms.
Small, circular, brown spots appear on the cotyledons or on young leaves.
At podding stage, some of the veins in the leaf develop copper colour.
As the severity increases, drooping of leaves occurs due to weakening and breakage of the veins. Such leaves droop, dry and shed.

Survival & Favourable Conditions
The pathogen can survive through seed, soil, diseased plant parts and host plants.
The severity of the disease increases with the increase in temperatures.
Fungus survives in upper layers of the soil and enters plant through stem.

Cultural Control
Deep ploughing.
Clean cultivation.
Crop rotation with non pulse crop.

Mechanical Control
Destroy the diseased plant debris by burning of burying in the soil.

Chemical Control
Seed treatment with carbendazim + Thiram 1:2.                                                                                             
 
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Powdery Mildew

Causal Organism

Erysiphe polygoni DC

Damage 

White powdery patches appear on leaves and other green parts which later become dull coloured. These patches gradually increase in size and become circular covering the lower
surface also.
When the infection is severe, both the surfaces of the leaves are completely covered by whitish powdery growth. Severely affected parts get shriveled and distorted.
In severe infections, foliage becomes yellow causing premature defoliation. The disease also creates forced maturity of the infected plants which results in heavy yield losses.

Survival & Favourable Conditions
The pathogen has a wide host range and survives in oidial form on various hosts in off-season.
Secondary spread is through air-borne oidia produced in the season.

Cultural Control
Use resistant varieties
The seeds must be sown early in the month of June to avoid early incidence of the disease on the crop.

Chemical Control
Powdery mildew could be controlled by spraying Carbendazim (0.05%) and Penconalzole (0.05%)            
Two spray of Carbendazim or Thiophanate Methyl 1 g ml or Tridemorph 1 ml per litre, one dose immediately after the disease appearance and the second dose 15 days later effectively manage                                      
the disease                                                                                                                                                
  

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Root Rot and Leaf Blight


Causal Organism
Rhizoctonia solani

Damage 

The pathogens cause seed decay, root rot, damping-off, seedling blight, stem canker and leaf blight in green gram.
The disease occurs commonly at podding stage.
In the initial stages, the fungus causes seed rot, seedling blight and root rot symptoms.
The affected leaves turn yellow in colour and brown irregular lesions appear on leaves.
On coalescence of such lesions, big blotches are formed and the affected leaves start drying prematurely.
Roots and basal portion of the stem become black in colour and the bark peels off easily.
The affected plants dry up gradually.
When the tap root of the affected plant is split open, reddening of internal tissues is visible.

Survival & Favourable Conditions
The pathogen is soil-borne.

Cultural Control
Grow resistant varieties.
Avoid moisture stress in the soil especially at podding stage.

Biological Control
Seed treatment with 4g Trichoderma viride formulation

Chemical Control
Seed treatment is effective is reducing the disease incidences.                                                                      
Seed treatment with Thiram + Carbendazim (2:1) 0.25% seed reduces the disease.                                        


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Rust
 
Causal Organism

Uromyces phaseoli

Damage

The disease appears as circular reddish brown pustules which appear more commonly on the underside of the leaves, less abundant on pods and sparingly on stems.
When leaves are severely infected, both the surfaces are fully covered by rust pustules.
Shriveling followed by defoliation resulting in yield losses.

Cultural Control
Use tolerant varieties

Chemical Control
Spray Mancozeb 3g to control of the disease.                                                                                               
 
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Seed and Seedling Rot

Causal Organism
Rhizoctonia solani, Macrophomina phaseolina
Pythium aphanidermatum, Sclerotium rolfsii

Damage


Several fungi growing on the seed coat of green gram cause rotting of the seeds resulting in failure of germination.
Leaves of affected seedlings dry and die suddenly.
Basal portion of the stem weakens and appears brown in colour.
Dried seedlings are seen sparsely here and there in the field within 3 weeks after sowing.

Survival & Favourable Conditions
The pathogens are soil-borne.

Cultural Control
Green gram cultivars, PS 16 and Pusa Bisaki are tolerant.
Seed treatment is advised.

Biological Control
Seed treatment with 4g Trichoderma viride formulation

Chemical Control
Seed treatment with 3g Thiram per kilogram of seed can reduce the disease incidence.                                
 

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Stem canker

Causal Organism
Macrophomina phaseolina

Damage


In rice fallows, symptoms appear on 4 weeks old black gram crop as raised white cankers at the base of the stem.
These enlarge gradually and turn as raised brown streaks spreading upwards.
Plants are stunted and leaves dark green, mottled and reduced in size.
Normal leaves on the affected plants drop suddenly and dry.
Flowering and podding is greatly reduced.
When the affected plants are split open vertically from the collar downwards reddish discolouration of the internal tissues is clearly visible while the internal root tissues appear white.

Survival & Favourable Conditions
Fungus survives in upper layers of the soil and enters plant through stem.

Cultural Control
Use tolerant varieties.
Field and crop sanitation.
Summer ploughing.
Crop rotation.

Chemical Control
Seed treatment with carbendazim + Thiram 1:2.                                                                                             
 
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Yellow Mosaic Virus

Causal Organism
Yellow Mosaic Virus

Damage

The disease is prevalent on black gram.
Initially mild scattered yellow spots appear on young leaves.
The next trifoliate leaves emerging from the growing apex show irregular yellow and green patches alternating with each other.
Spots gradually increase in size and ultimately some leaves turn completely yellow.
Infected leaves also show necrotic symptoms.
Diseased plants are stunted, mature late and produce very few flowers and pods.
Pods of infected plants are reduced in size and turn yellow in colour.

Survival & Favourable Conditions
The disease is transmitted by whitefly, Bemisia, tabaci.

Cultural Control
Use reistant/ tolerant varieties.
The viral diseases can be controlled by applying following measures.
The crop must be sown timely.
The spacing between the lines should be maintained at 30 to 40 cms.
Only certified seeds should be used for sowing.
If the seeds are not treated then seed treatment should be done.
In endemic areas only tolerant and resistant varieties should be used.
Weeds plants should be rouged out at their inception.
Insect, fungal and nematode vectors should be controlled using suitable pesticides.
Control white fly as it spreads the virus.

Biological Control
Conserve Paecilomyces farinosus fungus, a parasite of whitefly.

Chemical Control
Apply 10% phorate granules at the rate of 1kg/ha in the soil before sowing.                                                    
OR                                                                                                                                                               
Control white fly using insecticides.                                                                                                                
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