high severity

Rice Sheath BlightIdentification & Treatment Guide 2026

Rhizoctonia solani AG-1 IA · Family: Ceratobasidiaceae

Rice sheath blight (Rhizoctonia solani) causes oval gray-green water-soaked lesions on leaf sheaths that enlarge with gray centers and brown borders. Sclerotia float in paddy water and infect at the waterline. Manage with moderate nitrogen, avoiding excess plant density, validamycin or azoxystrobin fungicide at panicle initiation, and incorporating crop residues after harvest.

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Quick Diagnosis

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Rice Sheath Blight

Affects: leaf sheathsleavespanicles
Peak Season: Mid to late season, during warm (28-32°C) humid weather with dense canopy closure
Spread Risk: Moderate
Spread By: Sclerotia floating in irrigation water, mycelial growth between touching leaves and tillers, infested crop debris

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Symptoms: What does Rice Sheath Blight look like?

Visual identification guide — tap each stage for details

Oval water-soaked lesion on rice leaf sheath at waterline — Initial oval lesion on leaf sheath at the waterline

Expanding rice sheath blight lesions with gray centers and brown borders — Characteristic lesions with gray-white centers and dark brown margins

Severe rice sheath blight with sclerotia visible and canopy blight — Severe canopy blight with sclerotia visible on stem surfaces

Early Stage

Oval water-soaked lesions on sheaths at waterline
Oval to irregular, gray-green, water-soaked lesions appear on leaf sheaths near the water level. Lesions are 1-3 cm long with indefinite margins.

Mid Stage

Expanding lesions with gray centers and brown borders
Lesions enlarge and develop characteristic gray-white centers with dark brown margins. Multiple lesions coalesce, girdling sheaths. White mycelium and small brown sclerotia (1-5 mm) may be visible on lesion surfaces.

Late Stage

Canopy blight and lodging
Disease moves upward to flag leaf and panicle. Severely affected tillers produce partially filled or unfilled grains. Weakened stems may lodge (fall over). Panicle infection (sheath blight reaching the panicle) causes the worst yield losses.

Causes: Why is my plant getting Rice Sheath Blight?

Environmental triggers and disease cycle

High nitrogen fertilization producing lush dense canopies
Excessive planting density
Continuous rice monoculture building up soil sclerotia
Warm stagnant water in paddies
Previous season's sclerotia surviving in soil for 2+ years

Disease Lifecycle

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Host Plant

Susceptible crop

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Pathogen

Rhizoctonia

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Conditions

Mid to late season, during warm (28-32°C) humid weather with dense canopy closure

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Infection

Penetrates tissue

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Symptoms

Visible signs

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Spread

Sclerotia floating in irrigation water

Often confused with: Rice Blast, Rice Bacterial Leaf Blight. See our comparison guide.

How to Treat Rice Sheath Blight

Tick each step as you complete it — works offline too

🌿 OrganicSafe for all farms

Organic Treatment Steps

4 steps

Apply balanced nitrogen — do not exceed recommended rates. Split nitrogen applications to avoid lush early growth.
Reduce seeding rate to decrease canopy density and improve air movement.
Incorporate crop residues by plowing after harvest to bury sclerotia and accelerate their decomposition.
Apply Trichoderma viride (5 g/L) as soil treatment before flooding to parasitize Rhizoctonia sclerotia.

🧪 ChemicalUse protective equipment

Chemical Treatment Steps

4 steps

Apply validamycin (Validacin 3L) at 2 ml/L at panicle initiation if sheath blight lesions are present on >25% of tillers.
Azoxystrobin (Amistar) at 1 ml/L provides excellent control when applied at boot to heading stage.
Hexaconazole (Contaf 5EC) at 2 ml/L as alternative systemic fungicide.
Direct sprays at the base of the canopy where infection originates, not at the top of the canopy.

Prevention & Seasonal Calendar

Year-round protection plan for your crops

Pre-Planting

Use moderate nitrogen rates — avoid over-fertilization
Plant at recommended spacing — avoid broadcast sowing at high rates

Mid-Season

Rotate with non-host crops (legumes, vegetables) to reduce soil sclerotia
Drain fields briefly mid-season to lower humidity at the canopy base

Post-Harvest

Plow in crop stubble after harvest to bury and decompose sclerotia
No commercially resistant varieties exist — management relies on cultural practices and timely fungicide

🛡️ Resistant Varieties

No highly resistant varieties — all commercial rice is susceptibleTetep (moderate resistance, used in breeding)LSBR lines from IRRI

View full seasonal calendar for your region →

Frequently Asked Questions

Common questions about Rice Sheath Blight

How do sclerotia spread sheath blight?

Sclerotia are small (1-5 mm) brown, hard survival structures produced on infected sheaths. After harvest, they fall to the soil. When fields are flooded for the next rice crop, sclerotia float to the water surface, drift to plant stems, and germinate to infect sheaths at the waterline. This is why initial infections always appear at the base of the plant.

Why is there no resistant rice variety for sheath blight?

Sheath blight resistance is quantitative (controlled by many genes with small effects) rather than qualitative (single gene). This makes breeding for resistance slow and difficult. No complete resistance has been found in any rice germplasm. Breeding programs have made incremental improvements in tolerance, but no variety is highly resistant. This is a major contrast with blast (many resistance genes) and BLB (Xa genes).

When is the best time to apply fungicide for sheath blight?

The critical timing is panicle initiation through heading (approximately 40-55 days before harvest). This protects the flag leaf and developing panicle, which are most important for yield. Applying before panicle initiation is usually too early (disease may not have developed), and after heading is too late to prevent major yield loss.

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Related Disease

Rice Blast

Magnaporthe oryzae

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Related Disease

Rice Bacterial Leaf Blight

Xanthomonas oryzae pv. oryzae

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Affected Plant

Rice

Oryza sativa

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Treatment Guide

Full Treatment Protocol

Detailed spray schedule & dosage guide

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