Divisi
Rice blast
Magnaporthe oryzae · Fungal
Photo: Donald Groth, Louisiana State University AgCenter, Bugwood.org · Public domain
Rice blast is a fast-moving fungal disease of rice (caused by the fungus Magnaporthe oryzae) that attacks the leaves, stem joints and — most damagingly — the neck just below the grain head. Its spores ride on wind and rain-splash and need a wet leaf to take hold, so it explodes in cool, cloudy, humid weather with long dews and on lush, over-fertilised crops. It is the single most destructive disease of rice worldwide.
Why it matters
On a susceptible crop in wet, humid weather, rice blast can destroy up to 80% of your harvest — more than almost any other rice disease. The cruellest damage comes late: the fungus rots the neck just below the grain head, so the head turns pale and empty and the grains never fill — a field that looked green and healthy can end up giving you almost nothing. Once the neck has rotted, no spray can bring the grain back, and the fungus lives on in the straw and seed to strike again next season. So blast has to be stopped early and prevented, not cured.
When to act
Spray when spindle-shaped leaf lesions spread on young crops, and protect the neck at heading if the field has any blast history under humid weather.
This guidance is general, compiled from published agronomic references including FAO and CABI. Thresholds and timing shift with your crop, your variety and the season.
In much of the region a spray is simply called mushonga — medicine. But a chemical group you cannot name is one you cannot rotate, and a product you did not write down has no pre-harvest interval you can observe. Mushonga, and other farming words →
The full rice blast field guide
- Identify it
- Scout for it
- Control it
13 field-guide sections in the app
The full guide to rice blast — every symptom to check, how and when to walk your field looking for it, and the controls that actually work, ranked. Built into your crop plan, so you are told to look before it costs you a harvest.
Crops it affects
Frequently asked questions
How do I identify rice blast?
The first thing you see (leaf blast): small spots on the leaves that grow into spindle- or diamond-shaped ('eye-shaped') lesions, pointed at both ends — from about the size of a rice grain up to your thumbnail. The centre is dead grey or ash-white, ringed by a brown to reddish-brown edge. When the weather stays wet the spots multiply and join up until whole leaves and patches of the field look scorched, as if burned.
When should I take action against rice blast?
Spray when spindle-shaped leaf lesions spread on young crops, and protect the neck at heading if the field has any blast history under humid weather.
How do I control rice blast?
Prevent it — start with a resistant variety: the strongest single defence is to plant a blast-resistant rice variety suited to your area (ask your extension officer or seed dealer which ones hold up locally). Because the fungus can slowly break a variety's resistance (learn to attack it), rotate or mix the varieties you grow rather than planting the same one every season.
Which crops does rice blast affect?
Among the crops covered here: Finger millet, Rice.
Catch it before it costs you a harvest
Divisi builds scouting into your crop plan — it tells you when to walk your field, what to look for at that stage, and what to do when you find it. Free for farmers, works offline.
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