Brown spot of rice: symptoms, causes and control in paddy

Photo at the top: Brown spot on a rice leaf: oval spots with a light centre and a dark brown edge, Photo: Donald Groth, Louisiana State University AgCenter, CC BY 3.0 US

Quick answer

Brown spot of rice is a fungal disease of paddy. It makes oval brown spots with a grey or light brown centre on leaves, and dark spots on grains. Badly hit nurseries look burnt, and grains stay light. Control it with clean seed, good soil fertility and a label-approved fungicide at the threshold.

The fungus is Bipolaris oryzae. Older books call it Helminthosporium oryzae, and its sexual stage is Cochliobolus miyabeanus. Tamil Nadu Agricultural University (TNAU) also calls the disease sesame leaf spot, because the young spots look like sesame seeds.

How to identify brown spot of rice disease

In Hindi the disease is called bhura dhabba rog, and in Telugu godhuma aaku machha tegulu. TNAU notes that the fungus attacks the crop from the seedling stage to the milky grain stage. It can infect the seedling, leaf blade, leaf sheath and the husk of the grain, but the spots are easiest to see on the leaf blade and on the grains.

Symptoms of brown spot of rice on leaves, sheaths and grains

• Seedlings: small round, yellow-brown or brown spots on the first leaves. The International Rice Research Institute (IRRI) notes that spots can circle the young shoot and twist the first leaves. Seedlings die, and a badly hit nursery looks scorched from a distance.
• Young leaf spots: from tillering, tiny dark brown to purple-brown dots appear on the leaves.
• Full-grown leaf spots: round to oval. The centre turns grey or light brown and the edge stays dark reddish brown. TNAU notes a yellow halo (a pale ring) around many spots. On susceptible varieties IRRI gives spot length as 5–14 mm. Many spots join up, and the leaf dries.
• Leaf sheath: spots like those on the leaves.
• Grains: dark brown to black spots on the husk, or the whole husk turns dark. Grains fill poorly, are light, and the rice can be spotted inside. Infected seed often fails to sprout.

Look-alikes and how to tell them apart

• Blast: blast spots are spindle-shaped, wide in the middle and pointed at both ends, like an eye. Brown spot spots are round or oval, with no pointed ends. IRRI advises checking for a round, brownish spot with a grey centre and a reddish edge to confirm brown spot. See our rice blast guide for leaf and neck blast.
• Narrow brown leaf spot: short, thin brown streaks that run along the leaf veins, not round spots. See our narrow brown leaf spot guide.
• Zinc shortage (khaira): rusty brown patches on older leaves a few weeks after transplanting, often in patches of the field, with stunted plants. The spots do not have the neat grey centre and dark ring. See our guide to zinc deficiency and khaira disease in rice.
• Grain discolouration: dark grains can come from several fungi, not only brown spot. Read more in our dirty panicle and grain discolouration guide.

Life cycle and when it attacks

The fungus lives through the gap between crops mainly in infected seed and in stubble left in the field. TNAU notes that spores on infected grain stay alive for 2 to 3 years. Infected seed gives rise to infected seedlings. From there, spores (the tiny "seeds" of the fungus) travel by air to new leaves, in the nursery and in the main field. TNAU also names two grassy weeds that carry the fungus: Leersia hexandra and Echinochloa colona (jungle rice).

Conditions that favour the disease:

• Warm, humid weather: TNAU gives 25–30 °C with relative humidity above 80% as highly favourable.
• Wet leaves: IRRI notes that leaves must stay wet for 8–24 hours for the fungus to get in.
• Poor or unbalanced soil: IRRI notes the disease is common in fields that are not flooded, in soils short of nutrients, and in soils where toxic substances build up. TNAU adds that too much nitrogen also makes it worse. Both point to the same answer: feed the crop in balance, as a soil test shows.

Brown spot can appear at any stage, but IRRI notes the most harmful infection comes from maximum tillering to ripening. In Telangana and Andhra Pradesh, watch closely in humid kharif spells and in fields with poor or under-fed soil.

Crops it attacks

Paddy: brown spot is a disease of rice. The national rice IPM package lists it as one of the major rice diseases of national importance in India. In the nursery it kills seedlings. In the main field it cuts green leaf area from tillering onwards. At flowering and grain filling it spots the grains, so they fill poorly and lose weight and quality. IRRI notes an average yield loss of about 5% in lowland rice across South and Southeast Asia, and up to 45% in badly infected fields. IRRI also notes that brown spot is considered a major factor behind the Bengal famine of 1943.

When to spray for brown spot (economic threshold)

The economic threshold (ETL) is the level of disease at which a spray starts to pay for itself. The Integrated Pest Management Package for Rice (NCIPM, DPPQS and NIPHM) gives the brown spot threshold, from early to late tillering, as:

• 2–3 spots per leaf, and 2–3 infected plants per square metre.

The rice IPM package advises checking the field every 3 to 5 days. Start from tillering, and do not skip checks in humid, cloudy spells. Walk across the field, not just along the bund. Look at the upper leaves as well as the lower ones. A fungicide protects healthy leaves; it cannot heal a leaf that is already dried out. So act when the field reaches the threshold, not after the leaves turn brown.

Brown spot control without chemicals

• Fix the soil first: IRRI calls better soil fertility the first step against brown spot. Test your soil and apply the fertiliser it needs, including micronutrients, as your local recommendation says. For soils low in silicon, IRRI advises calcium silicate slag before planting. Avoid too much nitrogen. TNAU advises slow-release nitrogen fertiliser.
• Clean seed: use certified, disease-free seed. Do not save seed from a field that had spotted grains.
• Hot water seed treatment: IRRI advises soaking seed in cold water for 8 hours, then dipping it in hot water at 53–54 °C for 10–12 minutes before sowing. Keep the temperature exact, because hotter water can damage the seed.
• Seed treatment: the rice IPM package advises treating seed against seed-borne diseases with a fungicide or with a biological agent such as Trichoderma or Pseudomonas. Ask your local agriculture officer or Krishi Vigyan Kendra (KVK) for a product labelled for seed treatment on paddy. None of the products in the table below is labelled for seed treatment against brown spot.
• Resistant varieties: TNAU lists CO 51, CO 52, CO 53, CO 55, CO 56, ASD 18 and IR 64 as resistant or moderately resistant in Tamil Nadu. Ask your KVK which varieties suit your area and season.
• Water: keep water in the field as recommended for your crop. IRRI notes the disease is common in unflooded fields.
• Field hygiene: remove infected stubble and straw after harvest, and keep bunds and channels free of grassy weeds, as TNAU advises.

Fungicides for brown spot: chemical control in paddy

Only the products below list paddy and brown spot on their official label or leaflet. Doses are per acre, worked out from the label's per-hectare dose. Spray one product at a time. Do not mix products in one tank.

Paddy

Product	Contains	Label dose per acre	Water per acre	Wait before harvest
Reflect Top Fungicide	Isopyrazam 11.5% + Difenoconazole 11.5% w/w SC	162 ml	200 L	30 days
Motive Fungicide	Mancozeb 68% + Hexaconazole 4% WG	506 g	200 L	30 days
Avtar Fungicide	Hexaconazole 4% + Zineb 68% WP	405–506 g	200 L	34 days
Merger Fungicide	Tricyclazole 18% + Mancozeb 62% WP	405–506 g	200 L	25 days
Polyram - Fungicide	Metiram 70% WG	607–809 g	200 L	51 days

Notes from the labels:

• Reflect Top, Motive, Avtar and Merger each hold two active ingredients in one pack. These are ready-mixed products approved on the label. They are not tank mixes.
• Reflect Top: first spray when the disease starts, and a second spray 10–15 days later only if needed. No more than 2 sprays per season. The label also gives the strength as 0.8 ml per litre of water.
• Motive: spray when symptoms appear, at the vegetative or reproductive stage, in the morning or evening. 1–3 sprays depending on how bad the disease is.
• Merger: spray when symptoms appear, in the morning or evening, with a high-volume knapsack sprayer. 1–3 sprays depending on how bad the disease is.
• The Merger, Motive, Avtar and Polyram labels also list blast on paddy, and the Reflect Top, Motive and Avtar labels list sheath blight. If your field has more than one of these, one label-approved product can cover them. Read the label to check.

Mind the waiting period. Polyram needs 51 days between the last spray and harvest, and Avtar 34 days. For a late spray near grain filling, count the days left to harvest before you pick a product.

Rotate to avoid resistance

If you spray the same type of fungicide again and again, the fungus can stop responding to it. Fungicides are grouped by how they work, using the FRAC code (FRAC is the international Fungicide Resistance Action Committee). Change the group from one spray to the next.

FRAC group	Active ingredient	Products in this article
3 (triazoles)	Difenoconazole, hexaconazole	One part of Reflect Top, Motive and Avtar
7 (SDHI)	Isopyrazam	One part of Reflect Top
16.1	Tricyclazole	One part of Merger
M03 (multi-site contact)	Mancozeb, zineb, metiram	Polyram, and one part of Motive, Avtar and Merger

Reflect Top, Motive and Avtar all carry a group 3 triazole, so do not use them in back-to-back sprays. A simple plan: if the first spray was Reflect Top (groups 7 and 3), make the second one Merger (groups 16.1 and M03) or Polyram (group M03). Contact fungicides in group M03 carry a low risk of resistance, but they only protect the leaf surface they cover. Keep to the number of sprays each label allows.

Safety and waiting period

• The waiting period before harvest (PHI, pre-harvest interval) for each product is in the table above. Count the days from the last spray.
• Wear gloves, a mask, full-sleeve clothes and boots while mixing and spraying. Do not eat, drink or smoke while spraying. Wash well afterwards.
• Spray in the morning or evening, not in strong wind or just before rain.
• Fish: the Merger and Motive labels warn that they are toxic to fish and water life. Do not use them near ponds, tanks or fish culture.
• Re-entry: the Merger label says to keep people out of the sprayed field for 48 hours, and the Motive label 24 hours.
• Read the label and leaflet before use.

Frequently asked questions

What is brown spot of rice disease?

It is a fungal disease of paddy caused by Bipolaris oryzae (old name Helminthosporium oryzae). It spots the leaves, sheaths and grains, kills seedlings in the nursery and leaves grains light and discoloured.

What are the symptoms of brown spot of rice?

Small dark brown dots on the leaves that grow into round or oval spots with a grey or light brown centre, a dark reddish-brown edge and often a yellow halo. Spots join and leaves dry. Grains get dark brown to black spots, and badly hit nurseries look scorched.

Is brown spot in paddy caused by poor soil?

The cause is a fungus, but poor soil makes the crop much more likely to suffer. IRRI notes the disease is common in soils short of nutrients and in fields that are not flooded. TNAU adds that too much nitrogen also makes it worse. Test your soil and feed the crop in balance.

Can brown spot spread through seed?

Yes. Infected seed is one of the main ways the disease starts. Use certified seed, and treat it before sowing with hot water or a seed treatment your local agriculture officer recommends.

Which fungicide controls brown spot in paddy?

Use one whose label lists paddy and brown spot. In our store these are Reflect Top, Motive, Avtar, Merger and Polyram. The doses are in the table above. Spray at the threshold, change the FRAC group between sprays, and check the waiting period before harvest.

Related reading

• Rice blast in paddy: symptoms and control of leaf and neck blast
• Sheath blight of rice: symptoms, causes and control in paddy
• Khaira disease in rice and zinc deficiency: signs and correction
• All paddy products
• All fungicides

Sources

• National Centre for Integrated Pest Management (NCIPM, ICAR), DPPQS and NIPHM, Integrated Pest Management Package for Rice (2014).
• Tamil Nadu Agricultural University, TNAU Agritech Portal: brown spot of rice, symptoms and favourable conditions and management.
• International Rice Research Institute, Rice Knowledge Bank: brown spot.
• Fungicide Resistance Action Committee, FRAC Code List 2026.
• Official labels and leaflets of the products named in this guide.