Rice blast: Magnaporthe grisea (Hebert) Barr (Deuteromycotina: Moniliales: Moniliaceae)

Kannada Name: Benki Roga

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.

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

Damage symptoms

• Rice blast affects the leaves, on which it causes diamond / spindle shaped white to gray lesion with dark green to brown borders surrounded by a yellowish halo, the lesion may enlarge coalesce and kill entire leaves.
• Blast also affects leaf collar, stem nodes, earheads, neck and internodes.

Neck blast	Leaf blast	Nodal blast

Management:

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).

Cultural practices:

• Avoid stagnating of water in the field
• Use IR-64/MTU-1005, Jaya and Jyothi varieties
• Do not use high dose of nitrogenous fertilizers

Biological control:

UAS, Dharwad recommendation

• 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

                                    Plates: Photographs showing seedling root dip by bavistin

Chemical control:

• Seed dress with either tricyclazole 75 WP or carbendazim 50 WP @ 2g/kg of seed.
• Spray 1g of carbendazim (780g/acre) or 1 ml edifenphos (780ml/acre) or 0.6g of  tricyclazole (120g/acre)  in 1 liter of water, depending on severity repeat spray at 10-12 days of first spray.