Rice Diagnosis: Decide What an Alert Means and What to Do

The starting point for interpreting rice field alerts. Covers abiotic stress today (drought, salinity, poor soil, submergence), with room for biotic stress and nutrient deficiency next.

When an alert fires on a rice field, the platform tells you something changed. This guide helps you decide what changed and what to do. Use it as the bridge between a triggered alert and a field action.

For the standard walk and inspection sequence a scout should follow on the ground, see Field Walk Protocol.

What this guide covers

Rice diagnosis is organized around three pillars, matching the decision tree a scout actually uses in the field.

Abiotic Stress

Environmental causes: drought, salinity, poor soil, submergence. Best-detected group by satellite.

Nutrient Deficiency

N, P, K, Zn, S, and iron toxicity. Highest platform value: NDRE is designed for this.

Biotic Stress

Diseases, insect pests, and weeds. Imagery narrows where to scout; a scout confirms what.

How to use the three pillars

Use the pattern in the imagery to decide which pillar to open first:

What you see	Start with
Whole field or whole zones stressed after weather event	Abiotic stress
Uniform yellowing without a clear environment cause	Nutrient deficiency
Patchy, spreading, or symptoms concentrated on individual plants	Biotic stress
A field that never green-fills despite adequate inputs	Check all three - overlapping causes are common

Growth-stage vulnerability

Different stresses hurt rice at different growth stages. Match the stage to the likely cause before opening a specific stress page.

Three stage vocabularies are in use across the rice pages, and they do not match. This table has four classes, the field walk record asks for one of six, and Rice Ecosystems resolves bands against five — with two more names again on the flood-prone table.

The ecosystems page is the authority for anything that resolves a band. Everything else maps onto it:

Field walk records	This page calls it	Band phase on the ecosystems page
Seedling	Seedling / transplanting	Transplanting / early vegetative
Tillering	Tillering	Tillering (flood-prone: tillering / elongation)
Booting	Booting to flowering	Panicle initiation / booting (flood-prone: reproductive)
Heading	Booting to flowering	Heading / flowering
Grain fill	Grain filling	Ripening / maturity
Maturity	Grain filling	Ripening / maturity

Two joins are lossy and worth knowing about. Booting to flowering here covers two band phases with different bands — on irrigated lowland, 0.65 – 0.80 and 0.75 – 0.90. And grain fill and maturity both land on one band phase, so a scout distinguishing them gains nothing a band can read.

A recorded stage alone never resolves a band. The band resolves from the establishment date and the ecosystem; the stage is what the scout saw, and the two are reconciled here rather than assumed equal.

Growth stage	Most damaging causes
Seedling / transplanting	Salinity, submergence, zinc deficiency, bakanae, tungro
Tillering	Drought, poor soil, N and P deficiency, gall midge, sheath blight
Booting to flowering	Drought (highest yield impact), salinity, K deficiency, blast, stem borer, false smut
Grain filling	Drought, submergence, brown planthopper, rice bug, sheath blight

The three pillars

Abiotic stress

Environmental causes account for the majority of yield loss worldwide and show clearly in satellite imagery. Start here when the pattern follows topography, water flow, or a weather event.

Drought

NDWI drops before NDVI. Leaf rolling, stunted growth, burning leaf tips, whiteheads at flowering.

Salinity

Patchy NDVI in low-lying or coastal zones. Brown leaf tips, chlorotic patches, white panicle branches.

Poor soil / low fertility

Persistently low NDVI and NDRE across the whole field or repeatable weak zones season after season.

Submergence

Sudden NDVI collapse in flood-prone zones after heavy rain. Full or partial disappearance of canopy.

Nutrient deficiency

Nutrient limitation looks similar to abiotic stress but responds to fertilizer, not to weather or drainage. NDRE is the leading spectral indicator - use it from tillering onward.

Nitrogen

Uniform pale-green canopy, older leaves first. Low NDRE.

Phosphorus

Dark-green stunted plants, reddish-purple older leaves.

Potassium

Yellow-brown scorching along older leaf margins. Increased lodging.

Zinc

Patchy dusty-brown blotches at early tillering on high-pH soils.

Sulfur

Pale-yellow young leaves (opposite of N). Field does not respond to N top-dressing.

Iron toxicity

Bronze-orange stippling on lower leaves in acid, waterlogged zones.

Biotic stress

Living causes: diseases, insect pests, and weeds. Satellites narrow where to scout, but ground confirmation is essential before treatment.

Satellites are excellent at abiotic and good at nutrient. Biotic detection needs ground truth. Always confirm the identification with a scout before applying pesticides.

Diseases

Blast

Diamond-shaped lesions; neck blast causes whiteheads.

Bacterial leaf blight

Yellow wavy lesions from leaf tips; bacterial ooze in morning.

Sheath blight

Greenish-grey lesions on lower sheaths in dense high-N canopies.

Tungro

Yellow-orange stunted plants; transmitted by green leafhopper.

Sheath rot

Discolored flag-leaf sheath; panicle fails to emerge properly.

False smut

Yellow-green fungal balls replacing grains. Preventive fungicide at booting only.

Bakanae

Abnormally tall, pale, thin seedlings. Seed-borne.

Insect pests

Brown planthopper

Circular hopperburn patches; honeydew at plant base.

Stem borers

Deadhearts at vegetative stage; whiteheads at heading.

Leaffolder

Folded leaves with white longitudinal streaks.

Rice bug

Empty, spotted grains at milk stage; strong bug odor.

Gall midge

Silver shoots (onion leaves) replacing normal leaves. No panicle on affected tillers.

Armyworms

Sudden defoliation moving in waves; nocturnal.

Weeds

Grasses

Barnyardgrass; mimics rice early. Highest weed-driven yield loss.

Sedges

Triangular stems; nutsedge tubers persist across seasons.

Broadleaf

Wide leaves and showy flowers. Suppressed by shallow flooding.

Decision flow

1. Note the growth stage of the crop

   Check the season record for the field. Match the stage to the vulnerability table above.

2. Look at which index moved and how

   • NDWI drops first, NDVI follows: think drought.
   • NDVI collapses suddenly after rain: think submergence.
   • NDVI patchy and stable-low, coastal / low-lying: think salinity.
   • Field-scale low NDRE, uniform yellowing: think N deficiency (or S if N top-dressing did not help).
   • Circular expanding pale patches: think hopperburn (BPH).
   • Rapid, large drop between passes: think armyworm or BLB after a storm.
3. Confirm with field symptoms

   Open the matching stress page and compare the symptom list to what a scout sees on the ground. Symptoms rule stresses in or out faster than imagery alone.

4. Act, then set an early-warning alert

   Apply the recommended action. Then use the Alerts page to configure a follow-up alert so the same stress is caught earlier next time.

Related

• Field Walk Protocol - the standard scout inspection sequence this diagnosis feeds into.
• Healthy NDVI ranges for paddy across rice ecosystems - baseline values to compare an alert against.
• Set up automated crop alerts - configure the triggers that surface these stresses.
• Monitor crop health across fields - view the imagery that alerts are derived from.
• Analyze crop performance across a full season - the right tool for chronic zone problems.

This diagnosis covers the three major stress groups in rice. Rare stresses (cold, heat, herbicide phytotoxicity, mechanical damage) are not yet documented and can be added as separate short pages when needed.