> ## Documentation Index
> Fetch the complete documentation index at: https://badixth-dc85e378.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.
# Diagnose and Respond to Rice Blast
> Identify rice blast (leaf, neck, panicle) from diamond-shaped lesions and neck rot causing whiteheads, and control it with resistant varieties, balanced N, and timely fungicide.
**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](/concepts/risk-model) and [Crop Cycle Models](/concepts/crop-cycle-models) as a definition, with no page yet conforming to it.
So the Risk Monitoring card, the [Activity & Alerts](/guides/activity-and-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.
## 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.
## 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.
## 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
## 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.
## 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.
## Related
* [Rice Diagnosis](/guides/Crop/Rice/rice-abiotic-stress)
* [Nitrogen](/guides/Crop/Rice/nutrient/nitrogen) - over-application increases blast risk.
* [Activity & Alerts](/guides/activity-and-alerts) - unified feed for satellite, weather, scout, and team activity.
* [Field Alerts](/guides/alerts-notifications) - configure the four data-driven alert types.