What it does

Blast is caused by the fungus Magnaporthe oryzae. It can affect all above ground parts of a rice plant: leaf, collar, node, neck, parts of panicle, and sometimes leaf sheath.

Leaf and collar blast commonly occur together.

Blast can kill rice plants even at seedling stage.

Why and where it occurs

Blast can occur wherever blast spores are present.

It occurs in areas with low soil moisture, frequent and prolonged periods of rain shower, and cool temperature in the daytime. In upland rice, large day-night temperature differences that cause dew formation on leaves and overall cooler temperatures favor the development of the disease.

Rice can have blast in all growth stages. However, leaf blast incidence tends to lessen as plants mature and develop adult plant resistance to the disease.

How to identify

Check the leaf and collar for lesions.

Initial symptoms appear as white to gray-green lesions or spots, with dark green borders. Older lesions on the leaves are elliptical or spindle-shaped and whitish to gray centers with red to brownish or necrotic border.

Some resemble diamond shape, wide in the center and pointed toward either end.
Lesions can enlarge and coalesce, growing together, to kill the entire leaves.

Blast lesions can commonly be confused with Brown Spot lesions. Leaf blast lesions are usually elongated and pointed at each end, while brown spot lesions tend to be more round, brown in colour and have a yellow halo surrounding the lesion.

Click on images to enlarge

Lesions on leaves

Collar blast

Large lesions have gray center

Blast can infect the crop at any stage

How to manage

The primary control option for blast is to plant resistant varieties.

Other crop management measures can also be done, such as:

• Adjust planting time. Sow seeds early, when possible, after the onset of the rainy season.
• Split nitrogen fertilizer application in two or more treatments.
• Excessive use of fertilizer can increase blast intensity.
• Flood the field as often as possible.

Learn more

View full fact sheet:
Blast (Leaf and Collar) on IRRI Rice Knowledge Bank