Plant Disease · Plant disease
Brown Spot of Rice
Bipolaris oryzae (teleomorph Cochliobolus miyabeanus)
Also known as: Helminthosporium leaf spot of rice, Sesame leaf spot
Brown spot is a fungal disease of rice caused by Bipolaris oryzae. It produces numerous small, brown, oval leaf spots and is strongly associated with nutrient-poor, stressed soils, making it a classic indicator of poor crop nutrition.
Brown spot of rice, caused by the fungus Bipolaris oryzae, is a widespread disease that affects the leaves and grains of rice. It is historically notable as a disease strongly linked to nutrient deficiency and soil stress, and it was associated with severe famine-era rice losses where crops were grown on impoverished soils.
Because the disease is so closely tied to plant stress, it is often described as a disease of poor soils and undernourished crops. It produces numerous small brown spots on the leaves and can also discolour and shrivel grain, and both seed and residue carry the fungus between crops.
Symptoms and identification
Brown spot produces numerous small, circular to oval brown spots scattered across the leaves. As they develop, the spots often show a brown margin with a greyish or tan centre, and heavy infection can give leaves a speckled, sesame-seed appearance. The fungus also attacks the grain, producing brown to black discoloration and shrivelling, and can cause seedling blight from infected seed.
Pathogen and disease cycle
Bipolaris oryzae survives on infected seed and crop residue and can also persist on weed hosts. Spores (conidia) produced on lesions and residue are dispersed by wind and rain splash to infect leaves and grains. Infected seed can carry the fungus into new crops and cause seedling infection, and warm, humid conditions with leaf wetness favour infection and sporulation.
- Infected seed and residue carry the fungus between crops
- Wind- and rain-dispersed conidia infect leaves and grains
- Infected seed can cause seedling blight in new crops
- Plant stress from poor nutrition greatly increases susceptibility
Hosts and favourable conditions
Rice is the primary host. The single most important factor in severe brown spot is plant stress, particularly nutrient deficiency and unfavourable soils, which weaken the crop and make it far more susceptible. Warm, humid weather with prolonged leaf wetness then favours infection, and drought-stressed or poorly managed crops are especially vulnerable.
- Nutrient-deficient, degraded, or otherwise stressful soils
- Warm, humid weather with prolonged leaf wetness
- Use of infected seed carrying the fungus
- Drought stress and other conditions that weaken the crop
Management principles
Because brown spot is fundamentally a disease of stressed, undernourished crops, correcting soil fertility and reducing plant stress are the most effective measures, supported by healthy seed and resistant varieties.
- Correct soil fertility and nutrient deficiencies through balanced fertilisation
- Use clean, tested, or treated seed to avoid seed-borne infection
- Grow resistant or tolerant varieties where available
- Manage water and other stresses to keep the crop vigorous
- Remove infected residue and volunteer hosts to reduce inoculum
Relationships
Evidence-backed connections in the knowledge graph.
Affects
Risk increases under
Scope & limitations
Geographic scope: Global in rice-growing regions; particularly severe on nutrient-poor and degraded soils in rainfed and stressed production systems.
Climate context: Favoured by warm, humid weather with prolonged leaf wetness, but severity is driven above all by plant stress from poor soil nutrition.
- This is a general overview and does not replace field diagnosis or region-specific extension guidance.
- Severity depends heavily on soil fertility and crop stress, which vary widely between fields and seasons.
- Control-product recommendations are jurisdiction-specific and are deliberately not provided here.
Sources
This article draws on the following authoritative sources. See our sources & methodology for how they are selected.
- [1]IRRI — International Rice Research Institute (opens in a new tab)High
International Rice Research Institute (IRRI)
Cited for: Rice-specific biology, nutrition links, and integrated management
- Type:
- Research institute
- Jurisdiction:
- Global
- Accessed:
- 2026-07-12
- [2]CABI Digital Library — Crop Protection Compendium (opens in a new tab)High
CABI (Centre for Agriculture and Bioscience International)
Cited for: Pathogen biology, disease cycle, and host range
- Type:
- Reference database
- Jurisdiction:
- Global
- Accessed:
- 2026-07-12
- [3]EPPO Global Database (opens in a new tab)Authoritative
European and Mediterranean Plant Protection Organization (EPPO)
Cited for: Pathogen nomenclature and distribution
- Type:
- Reference database
- Jurisdiction:
- Global
- Accessed:
- 2026-07-12