Identification

According to period and position, rice blast can be distinguished into seedling blast, leaf blast, knob blast, panicle blast and grain blast. Rice blast easily occurs when it is raining, fogging, dewing and with less sunshine. Blast largely occurs during tillering and heading stage. Infected straws and grains left in the field allows for overwintering and sources of new inoculum of the disease.

(1)seedling blast – before three leaves. Base of infected plants becomes gray and black and then wither. No obvious scabs.

(2)leaf blast – occurs during tillering and elongation stage. Scabs are fusiform with faint yellow outside, brown inside and hoary colour in the middle. There are necrotic lines extending along the veins from scabs. There are gray mold on the back of scabs when humidity is high (Fig 1).

(3)knob blast – occurs on lower knobs. Infected knobs turn black and rot, and then constringe. Knobs are easily broken when it is dry.

(4)panicle blast – occurs on necks and branches. Scabs are brown and there are molds when humidity is high (Fig 2).

(5)grain blast – occurs on grains. Scabs are oval, with hoary color at early stages and brown color at late stages.

Control options

Cultural control: Choose resistant varieties and rotate with different varieties. Select disease free fields for nursery. Reduce seed density for better aerated seedbeds. Remove infected straws and grains after harvest. Early sowing of seeds after the onset of the rainy season is advisable. Provide enough base fertilization and topdressing several times at small amounts each, avoiding over use of nitrogen. If blast is observed in your field, stop using N-applications. Keep shallow water first and then apply alternative wetting and drying from late tillering stage onwards. Don’t use seeds from fields infested by blast disease for sowing in the next season

Chemical control: A seed treatment may be applied in areas known for high blast occurrence and a fungicide may be sprayed when acute scabs are identified.