Mustard Disease

Alternaria blight or Alternaria leaf spot

Caused by Alternaria brassicae

Introduction : 

• Mustard contributes 32 % of  the total oilseed production in India.
• Average yield losses about 30- 60 % due to Alternaria Blight.
• Mostly affects Cruciferous crop, including Broccoli and Cauliflower.  

About Pathogen: 

• Caused by Alternaria brassicae.
• Infection occurs in younger plants it caused Damping off.

Survival and spread:

• The disease is externally and internally seed borne.

• The pathogen survives through spores (conidia) or mycelium in diseased plant debris or weed.

Favourable conditions : 

• The diseases are favored by warm temperatures (60-78° F or (12-25 °C ) ) and at least 12 hours of relative humidity of 90 % or more. 
• Intermittent rains .

Disease symptoms:

• Mostly the disease occurs in lower leaf latar small circular brown necrotic spots which slowly increase in size.

Fig.: Alternaria leaf spot

Many concentric spots merge  to cover large patches  as a result blighting and defoliation occurs  in severe cases.

• Circular to linear, dark brown lesions also develop on stems and pods, which are elongated at later stage.
• Infected pods produce small, discolored and wrinkled  seeds.

PLANT PROTECTION:

Cultural control:

• Use of healthy seeds for sowing should be recommended.

• Use of certified/resistant/tolerant variety of seeds.

• Seed treatment.

• Adopt timely sowing between 10-25 October.

• Crop rotations with non-cruciferous crops (Pulses,Cereals,Tomato, Potato,leafy vegetables etc.).

• Collect and destroy the affected plant portions after the harvest of the crop.

• Follow proper field sanitation.

• Remove weeds particularly collateral host plants.

• Apply recommended dose of potash to reduce disease incidence.

• Avoid of irrigation at flowering and pod formation stages may help to reduce the disease infestans.

 Biological Control:

• Spray of soil isolates of Trichoderma viride @ 4-5 gram/Lit. of water at 45 and 75 days after sowing.
• Garlic  bulb  extract  @  15%  (w/v), 
• Neem  leaf  extract@  15%  (w/v),  
• Trichoderma harzianum @ 10g/ Lit. of water 

Chemical Control: 

• Foliar spray with Mancozeb (0.2%) at 45 DAS followed by Hexaconazole (0.05%) at 60 DAS was found most effective results.

• Spray Mancozeb 75% Wp @ 2.5 GM / Lit Of Water. (Dithane  M45 ,uthane ,manjit, indofil M45).

• Spray Metalaxyl-M/Mefenoxam 4% + Mancozeb 64% (68% Wp)  @ 2.5 GM  / Lit Of Water. (Ridomil Gold,siscon).

• Azoxystrobin 23% SC (Amistar,Miradore,Saras) @ 1 ml/Liter Of Water.

• Propiconazole 25% EC (Tilt,Result,Built,) @ 1.5 ml/ 2 Liter Of Water.

....THANK YOU FOR READING.....

SOURCE: WEBSITE AND SOME BENGALI BOOKS.