> ## 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 Sheath Blight in Rice

> Identify sheath blight from oval greenish-grey lesions on lower sheaths spreading upward in dense canopies, and control it with lower plant density, balanced N, and fungicide at booting.

Sheath blight, caused by *Rhizoctonia solani*, is the second most damaging rice disease after blast. It thrives in dense high-N canopies with high humidity at the base. It survives between seasons as sclerotia in the soil.

## When rice is most vulnerable

Most damage from panicle initiation through grain filling. High plant density, high N, and continuous flooding are the classic risk factors.

## How sheath blight shows in satellite data

* **NDVI decline in the densest, highest-N zones** during booting to grain filling - the opposite pattern from N deficiency (which shows lower NDVI on the poor zones).
* **Lodging patches** may appear late season as stems weaken.
* Poor separation from other basal diseases in imagery alone; confirm on ground.

<Warning>
  Sheath blight is a canopy-base disease. It hides under the top leaves and is easily missed by both satellites and quick walk-throughs. Scout by parting the canopy.
</Warning>

## Field symptoms

* Oval, greenish-grey water-soaked lesions on lower leaf sheaths near the waterline
* Lesions enlarge and turn straw-colored with dark-brown margins
* Disease climbs the plant to upper sheaths and leaves in dense canopies
* White fluffy mycelium and small brown sclerotia (like mustard seeds) on infected tissue
* Weakened stems, lodging, and poor grain fill

## Reduce the damage by

* **Reduce plant density and avoid excessive N** - the two most effective preventive controls.
* **Balance N with K** - adequate K reduces severity.
* **Grow moderately resistant cultivars** and avoid highly susceptible high-yielding hybrids on chronic sheath-blight fields.
* **Deep plowing and stubble incorporation** to bury sclerotia.
* **Crop rotation** with non-host crops where practical.
* **Fungicide** (validamycin, hexaconazole, or azoxystrobin) at maximum tillering to booting - only if scouting confirms an active outbreak.

## Set an alert for early warning

<Tip>
  Turn the diagnosis into a trigger. Configure alerts on the high-density high-N zones - the disease consistently starts there.
</Tip>

Recommended settings for sheath blight on rice:

* **NDVI zone alert** - flag high-NDVI zones that suddenly drop by 0.08 or more during booting to grain filling.
* **Weather alert** - sustained relative humidity above 95% for 3+ days during booting.

## Related

* [Rice Diagnosis](/guides/Crop/Rice/rice-abiotic-stress)
* [Potassium](/guides/Crop/Rice/nutrient/potassium) - K deficiency worsens sheath blight.
* [Set up automated crop alerts](/guides/alerts-notifications)