Brown spot (rice)
Oval brown spots peppering the leaves and discoloured grain — a fungal spot strongly tied to poor, starved or stressed soils.
- Pathogen
- Fungus (Bipolaris oryzae)
- Spreads by
- Seed-borne; air/rain-splashed spores; debris
- Favoured by
- Poor, deficient, drought-stressed soils
- Main risk
- Leaf & grain spotting; poor grain & germination
Overview
Brown spot is a fungal disease of rice (Bipolaris oryzae) that spots the leaves and the grain. On leaves it makes numerous small, oval to circular brown spots, often with a grey or whitish centre and a brown margin, evenly scattered over the leaf (unlike blast’s spindle spots). It also spots and discolours the glumes and grain, giving a dirty, "dirty-panicle" look and reducing grain quality and germination.
Brown spot is famously a "poor-soil" or "hunger" disease: it is far more severe on nutrient-deficient, poorly-managed, drought-stressed or problem soils (low nitrogen, potassium or micronutrients), which is why a well-nourished crop suffers much less. It is seed-borne and also carries over on debris. Management therefore leans heavily on correcting soil fertility and stress, plus clean/treated seed, resistant varieties and, where needed, a fungicide.
How to identify it
- Numerous small, oval to circular brown spots, often with a grey/whitish centre, evenly scattered over the leaf.
- Even scatter distinguishes it from blast’s spindle- (eye-) shaped lesions.
- Spotting and discoloration of the glumes and grain — a dirty-looking panicle — with poorer grain and germination.
- Much worse on nutrient-deficient, drought-stressed or otherwise poor, problem soils.
What causes it and when
- The fungus Bipolaris oryzae, which is seed-borne and also spreads by air- and rain-splashed spores and carries over on debris.
- Strongly favoured by poor, nutrient-deficient (low N/K/micronutrient) and drought-stressed or problem soils.
- A well-nourished, unstressed crop is far less affected — hence its name as a "hunger disease".
- Shows on the leaves through the crop and on the grain/panicle later.
Cultural & organic control
- Correct soil fertility and stress — balanced nitrogen, potassium and any deficient micronutrient — which is the core control.
- Use clean, healthy (treated) seed and grow tolerant varieties.
- Improve problem soils and water management so the crop is not drought- or nutrient-stressed.
- Destroy infected debris and use a bio-agent seed treatment where recommended.
Chemical control
- Treat seed with a recommended fungicide to reduce seed-borne carry-over.
- Where the disease is significant, spray a CIB&RC-registered fungicide for rice at the recommended stage.
- Remember the fungicide supports, but does not replace, correcting the underlying soil fertility/stress.
- Confirm the current seed-treatment and spray for your area with your local KVK.
Prevent it coming back
- Make balanced nutrition, corrected problem soils and unstressed water management the routine — this is the real key to brown spot.
- Use clean/treated seed and tolerant varieties, and destroy infected debris.
- Add a fungicide only where needed, on top of good soil and crop management.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Frequently asked questions
My rice leaves are covered in small oval brown spots. Is this blast?
Probably not — numerous small, oval to circular brown spots evenly scattered over the leaf (often with a grey centre) are brown spot, not blast; blast makes spindle- or eye-shaped lesions. Brown spot also spots the grain and is much worse on poor, nutrient-deficient or drought-stressed soils. Correct the soil fertility and stress (balanced N, K and micronutrients), use clean/treated seed and tolerant varieties, and add a fungicide only if needed.
Why is brown spot called a "hunger disease"?
Because it is strongly tied to poor, starved and stressed soils: brown spot is far more severe where the rice crop is nutrient-deficient (low nitrogen, potassium or micronutrients), drought-stressed or grown on problem soils, and a well-nourished, unstressed crop suffers much less. Historically it was associated with famine-era, poorly-fed rice. That is why the main control is correcting soil fertility and stress, rather than relying on fungicide.
Will fertiliser alone control brown spot?
Correcting soil fertility and stress is the single most important step and often reduces brown spot dramatically, because the disease thrives on starved, stressed crops. But it works best combined with clean/treated seed, tolerant varieties and destroying infected debris, and in a bad season a registered fungicide may still be needed. Think of balanced nutrition as the foundation and the other measures as support on top of it.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.