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This page does not yet carry a machine-readable rule_card. An earlier revision of this note said it did. It does not, and no page in this documentation does — the rule_card schema exists at Risk Model and Crop Cycle Models as a definition, with no page yet conforming to it.So the Risk Monitoring card, the Activity & Alerts bindings and the grounded response of Ask the advisor are not driven from this page. The thresholds below are written for a human reader. Treat them as the source for a rule card when one is authored, not as one.
Rice blast, caused by Pyricularia oryzae, is the most damaging disease of rice worldwide. It attacks the leaf, collar, node, neck, and panicle. Neck blast is the most destructive form because a rotted neck causes complete grain loss on that panicle.

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When rice is most vulnerable

Leaf blast: from seedling through tillering. Neck and panicle blast: from booting through heading. Cool, humid, cloudy weather with heavy dew or fog strongly favors epidemics.

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How rice blast shows in satellite data

  • Rapid NDVI drop across zones with dense canopy and heavy N application, especially after several days of cool, humid weather.
  • Whiteheads at heading show as pale patches in high-resolution imagery, similar to drought whiteheads - separate them with weather history (blast follows humidity; drought follows dryness).
  • Pattern is often field-scale during epidemics and does not respect topography (unlike abiotic stress).
Satellites narrow where to scout but cannot confirm the disease. Blast, brown spot, and abiotic stress can look similar in imagery. Always confirm with a scout before spraying.

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Field symptoms

  • Leaf blast: diamond-shaped or spindle-shaped lesions with gray centers and brown borders on leaves
  • Collar blast: brown lesion where the leaf blade meets the sheath
  • Node blast: blackened, rotted node; stem may break at the node
  • Neck blast: brown to black rotted collar just below the panicle, causing the panicle to hang, dry out, and produce whiteheads
  • Panicle blast: lesions on panicle branches; poor grain fill

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Reduce the damage by

  • Grow resistant varieties - the primary control; rotate resistance genes across seasons where possible.
  • Avoid excessive N and split N applications - lush high-N canopies are highly susceptible.
  • Balance N with K, Si (silicon), and appropriate P.
  • Improve field drainage and avoid continuous deep flooding on susceptible fields.
  • Apply fungicide (tricyclazole or isoprothiolane) preventively at booting on susceptible varieties in high-risk environments - not curatively after neck blast is visible.
  • Destroy stubble and volunteer rice to break the disease cycle.

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Set an alert for early warning

Turn the diagnosis into a trigger. Combine a weather-based blast risk alert with an NDVI drop alert to flag susceptible fields before neck blast can develop.
Recommended settings for blast on rice:
  • Weather alert - cool nights (below 22 C) and high humidity (above 90%) sustained for 3+ nights, especially at booting.
  • NDVI drop alert - trigger on a drop of 0.10 or more during booting to heading on susceptible varieties.