Rice blast
Spindle-shaped grey-centred leaf spots and rotted panicle necks — a fast fungus driven by excess nitrogen, dew and cool, humid nights.
- Pathogen
- Fungus (Magnaporthe oryzae)
- Spreads by
- Air-borne spores; seed & debris
- Favoured by
- Excess N, dew, high humidity, cool nights
- Main risk
- Scorched leaves; broken necks, empty grain
Overview
Blast is one of the most important fungal diseases of rice worldwide. On the leaves it makes the classic spindle- (eye-) shaped spots — a grey or whitish centre with a brown to reddish margin — which enlarge and merge so leaves dry as if scorched (leaf blast). The fungus also attacks the node, the collar and, most damagingly, the neck of the panicle (neck blast), where a blackish-brown rot girdles and breaks the neck so the head hangs, whitens and fills poorly or not at all.
Neck and panicle blast are the costly phases because they directly empty the grain. Blast is favoured by excess and late nitrogen, long dew periods, high humidity, cool nights with warm days, and drought stress in upland/aerobic rice. It spreads fast by air-borne spores and carries over on debris and seed. Management combines balanced nitrogen, resistant varieties, clean seed and a protective fungicide timed to leaf blast and again at booting/heading to guard the neck.
How to identify it
- Leaf blast: spindle- or eye-shaped spots with a grey/whitish centre and a brown to reddish margin, enlarging and merging so leaves dry as if scorched.
- Node blast: blackened, shrunken nodes that the stem may break at.
- Neck/panicle blast: a blackish-brown rot girdling the neck just below the panicle, so the head bends, whitens and fills poorly — the costliest sign.
- Worst in a lush, over-nitrogen crop and after cool, dewy, humid nights.
What causes it and when
- The fungus Magnaporthe oryzae, spread by air-borne spores and carried over on infected debris and seed.
- Favoured by excess and late nitrogen, long leaf-wetness/dew, high humidity, and cool nights with warm days.
- Upland and aerobic rice under drought stress are especially prone; nursery and early crop can show leaf blast, the head stage shows neck blast.
- Spreads very fast in a susceptible, well-fed crop once conditions turn favourable.
Cultural & organic control
- Grow resistant varieties — the most reliable control — and use clean, healthy seed.
- Apply nitrogen in balanced, correctly timed splits; avoid a single heavy or late dose that makes the crop lush and blast-prone.
- Avoid drought stress in aerobic/upland rice and maintain the recommended water.
- Use recommended spacing and destroy infected debris/stubble that carries the fungus over.
Chemical control
- For leaf blast, spray a CIB&RC-registered fungicide (e.g. tricyclazole or isoprothiolane) as soon as the disease starts, before it runs through the crop.
- To protect against neck blast, spray at booting to heading — a protective spray at this stage is key because neck blast decides grain loss.
- Rotate fungicide groups and cover the crop well; observe the pre-harvest interval.
- Confirm the current product, dose and timing for your area with your local KVK.
Prevent it coming back
- Base the crop on resistant varieties, clean seed and balanced, correctly split nitrogen.
- Plan the booting/heading protective spray in advance where neck blast is regular, rather than reacting after the necks rot.
- Manage water to avoid drought stress, keep spacing open, and destroy infected stubble/debris after harvest.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Frequently asked questions
My rice leaves have spindle-shaped spots with grey centres. Is this blast?
Yes — spindle- or eye-shaped spots with a grey/whitish centre and a brown to reddish margin, enlarging until leaves dry as if scorched, are leaf blast. It spreads fast in a lush, over-nitrogen crop after dewy, humid nights. Cut back excess nitrogen, and spray a registered fungicide (e.g. tricyclazole) as soon as it starts. Watch especially for neck blast at heading, which is the yield-robbing phase.
What is neck blast and why is it the worst phase?
Neck blast is blast attacking the neck of the panicle — a blackish-brown rot girdles the neck just below the head, so it bends, whitens and cannot fill the grain, leaving empty or half-filled panicles. It is the most damaging phase because it directly empties the grain you were about to harvest. The key defence is a protective fungicide spray at booting to heading, plus a resistant variety and balanced nitrogen.
How does nitrogen affect rice blast?
Excess and late nitrogen make the crop soft and lush, which strongly favours blast — the disease runs faster and harder through a heavily fed crop. Applying nitrogen in balanced, correctly timed splits rather than one heavy or late dose keeps the crop less susceptible. Combine that with a resistant variety, clean seed, good water management and well-timed protective sprays for dependable control.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.