Karnal bunt (wheat)
A partial bunt that blackens the germ-end of scattered grains and gives a fishy smell — a quality and quarantine problem more than a yield one.
- Pathogen
- Fungus (Tilletia indica)
- Spreads by
- Soil-borne spores; seed; wind at flowering
- Favoured by
- Cool, humid, cloudy weather at flowering
- Main risk
- Fishy smell, downgrade & quarantine rejection
Overview
Karnal bunt (named after Karnal in Haryana, where it was first described) is a fungal disease of wheat grain. Unlike loose smut, it usually infects only part of a grain — typically the germ (embryo) end — converting it into a black, powdery mass of spores, while the rest of the grain may look normal. Only a proportion of grains in a head, and only some heads, are affected.
Because the bunting is partial and scattered, Karnal bunt rarely causes a large yield loss. Its importance is in quality and trade: the black spore powder has a fishy (trimethylamine) smell that taints flour, and grain lots above a tolerance are downgraded or rejected. It is a strict quarantine disease for export. It is favoured by cool, humid, cloudy weather with light rain around wheat flowering, and it carries over as long-lived spores in soil and on seed. Management combines resistant varieties, clean/treated seed and a protective fungicide at flowering where the risk is high.
How to identify it
- Scattered grains with the germ (embryo) end converted to a black, powdery spore mass, the rest of the grain often looking normal.
- A characteristic fishy or foul smell from bunted grain (trimethylamine) — often the first thing noticed at threshing.
- Only a proportion of grains per head, and only some heads, affected — the bunting is partial, not the whole ear.
- Best confirmed by examining the grain at and after harvest, not the standing crop.
What causes it and when
- The fungus Tilletia indica, whose long-lived spores survive in the soil and on the seed and release wind-borne sporidia that infect the flowering head.
- Favoured by cool, humid, cloudy weather with light rain or high humidity around wheat flowering.
- Worse with late sowing that pushes flowering into cooler, more humid conditions, and with heavy irrigation/nitrogen giving a dense crop.
- Carries over for years as soil-borne spores, so once a field is infested the inoculum persists.
Cultural & organic control
- Grow resistant or tolerant varieties — the most practical control against a soil-borne disease.
- Sow on time (avoid late sowing) so flowering escapes the cool, humid window the fungus needs.
- Use clean, certified, disease-free seed and avoid seed from infested lots.
- Avoid excessive irrigation and nitrogen that create a dense, humid canopy at flowering.
Chemical control
- Treat seed with a recommended fungicide to reduce seed-borne carry-over.
- Where the risk is high, a CIB&RC-registered fungicide (e.g. propiconazole) sprayed at ear-emergence/flowering protects the head during the infection window.
- Soil-borne spores cannot be sprayed out, so the flowering-time spray is a protectant, timed to the weather.
- Confirm the current variety recommendation and spray schedule for your area with your local KVK.
Prevent it coming back
- Make resistant varieties, timely sowing and clean/treated seed the routine in bunt-prone areas.
- Keep flowering out of the cool, humid window through sowing date, and avoid a lush, over-irrigated crop.
- Do not save or trade seed from bunted lots — it both spreads the fungus and risks quarantine rejection.
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
Some of my wheat grains are black at one end and smell fishy. What is it?
That partial blackening of the germ (embryo) end, with a fishy smell, is Karnal bunt — a fungal bunt of wheat grain. Only some grains and some heads are affected, so yield loss is usually small, but the smell taints flour and the grain is downgraded or rejected above a tolerance. Manage it with resistant varieties, timely sowing, clean/treated seed, and a flowering-time fungicide where the risk is high.
Why does Karnal bunt matter if it barely cuts yield?
Because its damage is to quality and trade, not tonnage. The black spore powder carries a fishy (trimethylamine) odour that taints flour, and grain lots above the permitted tolerance are downgraded, rejected or fail export quarantine. So even a low level of bunting can cost you the market or the price, which is why the focus is on keeping infection below the tolerance, not just on saving yield.
How do I keep Karnal bunt out of my wheat?
Grow resistant/tolerant varieties, sow on time so flowering avoids the cool, humid, cloudy window the fungus needs, and use clean, certified, treated seed. Avoid excess irrigation and nitrogen that make a dense, humid canopy at flowering, and where the risk is high add a protective fungicide (e.g. propiconazole) at ear-emergence. Never re-sow or trade seed from bunted lots. Confirm the variety and schedule with your KVK.
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.