Rice blast is a harmful fungal disease that affects rice plants. It commonly occurs during the Boro and Aman seasons. Under favorable weather conditions, blast can cause up to 100% yield loss in susceptible rice varieties.

The disease can appear at any stage, from the seedling stage until the rice reaches maturity. It can attack the leaves, nodes, and neck or panicle of the rice plant. Based on the affected part of the plant, the disease is known as leaf blast, node blast, and neck or panicle blast.

During the Aman season, blast is particularly common in aromatic rice varieties. During the Boro season, panicle blast is more common in narrow-grain, early-maturing, and aromatic varieties, including BRRI dhan28, BRRI dhan50, BRRI dhan63, BRRI dhan81, BRRI dhan84, and BRRI dhan88.

Rice production can be severely affected by this single disease. However, taking the right measures at the right time can help protect rice plants from blast disease.

Symptoms of Rice Blast Disease

Leaf Blast

At first, small dark brown spots appear on infected leaves. Gradually, the spots become larger, with a gray or white center and brown edges. The spots are usually elongated and resemble an eye.

Several spots may merge together, eventually causing the entire leaf to dry up and die.

Node Blast

When a node becomes infected, the affected area turns black and becomes weak. Strong winds may cause the infected portion to break, although it may not completely separate from the plant.

Neck or Panicle Blast

During dew or drizzle, water can accumulate at the junction between the flag leaf and the base of the rice panicle. The spores of the blast fungus can attack this area and produce dark brown spots.

As the base of the infected panicle begins to rot, nutrients cannot properly reach the panicle. As a result, the panicle dries out and produces unfilled grains. Panicles infected at a later stage may break.

The fungus can also attack other parts of the panicle, not just its base.

How to Control Rice Blast Disease

  • When blast disease appears, keep water standing in the field, as blast tends to be more severe in dry fields.
  • If leaf blast appears, apply an additional 5 kg of potash fertilizer per bigha as a top dressing and stop applying urea fertilizer.
  • At the early stage of leaf blast, an appropriate fungicide used for panicle blast can be applied twice at 5–7 day intervals, preferably in the late afternoon.
  • Once panicle blast develops, there is no effective opportunity to control it. Therefore, when conditions become favorable for the disease—such as drizzle, hot days and cool nights, prolonged dew-covered mornings, cloudy weather, or stormy conditions—fungicide should be applied before the disease appears, whether or not symptoms are visible in the field.
  • Apply the first spray when the panicle emerges from the boot and the second spray 5–7 days later. For every bigha (33 decimals), mix 54 g of Tuper 75WP / Difa 75WP / Jill 75WP, or 33 g of Nativo 75WG, or an approved fungicide from the tricyclazole/strobilurin group, at the recommended dose, thoroughly in 67 liters of water and spray in the late afternoon.
  • Remember: To control panicle blast, fungicide must be applied before the disease develops.

Source: https://brri.gov.bd/pages/news/6922da0b933eb65569e02158