False smut of rice: symptoms, causes and control in paddy

Photo at the top: Rice ears with orange false smut balls. Each ball has taken the place of one grain, Photo: Crop Trust, CC BY-SA 4.0

Quick answer

False smut of rice is a fungal disease of paddy. It turns single grains in the ear into velvety balls, orange at first and greenish black later. It strikes at flowering in rainy, cloudy weather, mostly in crops given too much nitrogen. Use clean seed, split urea doses, remove smutted ears and ask your KVK about a spray at booting.

How to identify false smut of rice

In Hindi the disease is called mithya kanduwa or haldi rog (मिथ्या कंडुआ, हल्दी रोग), and in Telugu manipandu tegulu (మానిపండు తెగులు). It is also known as Lakshmi disease. It is caused by the fungus Ustilaginoidea virens. You can only see it after the ear (panicle) comes out of the leaf sheath, from flowering to grain filling.

False smut of rice symptoms

• Single grains turn into balls: the fungus takes over the inside of a grain and grows out of the husk as a round, velvety ball. It is bigger than a normal grain.
• Colour changes with age: a young ball is smooth, slightly flat and yellow, covered by a thin skin. The skin breaks and the ball turns orange. As it matures it becomes yellowish green and then greenish black.
• Only a few grains per ear: most ears have from one to a few smut balls. The rest of the grains look normal, but the grains next to a smut ball are often empty.
• Powder on your hand: rub a mature ball and a yellow-green or dark green powder comes off. These are the spores of the fungus.
• Scattered in the field: you will see smutted ears here and there across the field, often more where the crop is thick, dark green and lush.

Look-alikes and how to tell them apart

• Kernel smut (bunt): the grain keeps its normal shape. Black powder sits inside it, and you may see a thin black line where the husk opens. False smut makes a ball that grows outside the husk and is bigger than the grain.
• Dirty panicle (grain discolouration): grains get brown or black spots and stains on the husk, but they do not turn into velvety balls. Read about dirty panicle and grain discolouration in paddy.
• Neck blast: the neck below the ear turns grey-brown and rots, and the whole ear turns white or breaks over. See our guide to rice blast in paddy: leaf blast and neck blast.
• White ear from stem borer: the whole ear is white and empty, and it pulls out easily. There are no coloured balls on it. Read about stem borer in paddy: dead heart and white ear.

Life cycle and when it attacks

The fungus survives between crops in two ways. Hard resting bodies called sclerotia fall from smut balls into the soil. TNAU (Tamil Nadu Agricultural University) notes that these sclerotia sprout and release spores. These spores start the disease in the next crop. The powdery spores on mature smut balls are carried by wind and spread the disease further. Spores on seed taken from a sick crop can also carry it into a new field.

IRRI notes that the fungus infects the crop at the flowering stage. It then grows in place of the grain. So by the time you see a smut ball, the infection has already taken place.

The weather decides how bad a season will be. TNAU names rain and cloudy weather during flowering and grain filling, and high soil nitrogen, as the main favourable conditions. IRRI (International Rice Research Institute) adds that the disease occurs where air humidity is above 90% and temperatures are between 25 and 35 °C. A late-planted crop that flowers in rainy weather is more at risk. TNAU notes that early-planted crops get fewer smut balls.

In Telangana and Andhra Pradesh, false smut shows up mostly in the kharif crop, when flowering falls in rainy, cloudy spells. It can also appear in rabi paddy if flowering meets wet weather. The national IPM package for rice, from NCIPM, DPPQS and NIPHM, lists false smut among the five major rice diseases of national importance in India.

Crops it attacks

Paddy (rice): false smut is a disease of the rice ear. It attacks at flowering, and the damage shows from flowering to harvest. Each smut ball is one lost grain, and the grains around it often stay empty. IRRI notes that affected crops give chalky, lighter grain and seed with poorer germination, and that losses can reach 25% in damp weather. The smut balls also lower the quality and market value of the harvest.

When to act

We could not find an economic threshold (the disease level at which control starts to pay) for false smut of rice from a recognised public source, so we do not give one. Two things make this disease different from most:

• Once a smut ball has formed, nothing can turn it back into a grain. Control has to be planned before flowering.
• The risk depends on your field history and the weather. If your field or your neighbours' fields had false smut last season, and the crop is lush and flowering is near while the sky stays cloudy and wet, treat it as a high-risk year.

From panicle initiation (when the young ear starts to form inside the stem) to flowering, watch the weather forecast and the crop. After the ears come out, walk the field and count the smutted ears. This record helps you plan for the next season.

False smut of rice control without chemicals

• Clean seed: use certified seed or seed from a healthy crop. Never keep seed from a field that had false smut.
• Hot water seed treatment: IRRI lists soaking seed in hot water at 52 °C for 10 minutes. Ask your KVK (Krishi Vigyan Kendra) to show you how to do it without harming germination.
• Moderate nitrogen in split doses: too much urea makes the crop soft and lush and raises the risk. TNAU advises splitting nitrogen into several doses instead of one heavy dose. Follow a soil test or a leaf colour chart. Our guide to nitrogen deficiency in plants explains how to read your crop's colour.
• Plant on time: early or timely planting, so flowering does not fall in the wettest weeks. TNAU notes that late-planted crops get more smut balls.
• Tolerant varieties: TNAU names CO 59 as moderately resistant in Tamil Nadu. Varieties differ by region, so ask your KVK or state agricultural university which local varieties show less false smut, and grow those.
• Remove smutted ears: where only a few ears are hit, cut them off carefully and put them in a bag. Do this before the balls burst into powder. Burn or bury the bag away from the field.
• Remove sick plants at harvest: TNAU advises removing and destroying affected plants at harvest, so sclerotia do not fall into the soil.
• Destroy infected straw and stubble: do not leave smutted straw and stubble lying in the field or on the bunds.
• Clean bunds and channels: keep field bunds and irrigation channels free of weeds and grasses.
• Water: IRRI suggests alternate wetting and drying instead of keeping the field flooded all the time, to lower humidity in the crop. Ask your agriculture officer whether this suits your soil and water supply.
• Spacing: use the recommended spacing, so air can move between the plants and the crop dries faster after rain.

Chemical control: spray before flowering, not after

No product in our store has false smut on paddy in its label record, so we do not name one here. A spray after the smut balls appear does not cure the ears that are already infected. That is because the infection happened at flowering.

TNAU advises a preventive fungicide spray at the booting stage, when the ear swells inside the leaf sheath, and again just before flowering. This matters most in fields with a history of false smut and in a wet, cloudy season. Ask your local agriculture officer or KVK for a product labelled for false smut on paddy. Use the product and dose printed on its label. You can browse our fungicides and products for paddy, but use only a product whose label names false smut on paddy.

If you do spray:

• Use one product at a time. Do not mix products in one tank.
• Cover the upper part of the plant and the flag leaf sheath, where the ear is forming.
• If you spray more than once in a season, ask your KVK to suggest a fungicide from a different group for the next spray. This slows down resistance.

Safety

• Wear gloves, a mask, full-sleeve clothes and boots while mixing and spraying. Do not eat, drink or smoke while you work. Wash well afterwards.
• When you cut smutted ears by hand, wear gloves and a mask. The spore powder rises into the air when you touch mature balls.
• Spray in the morning or evening, not in strong wind or hot afternoon sun.
• Keep the waiting period before harvest that is printed on the label of the product you use.
• Keep sprays and washings away from ponds, canals and wells.
• Read the label and leaflet before use.

Frequently asked questions

What are the symptoms of false smut of rice?

Single grains in the ear turn into round, velvety balls. They are yellow or orange at first and greenish black when mature. Only a few grains in each ear are affected, and the grains next to them are often empty. Rubbing a mature ball leaves a green-yellow or dark green powder on your hand.

Is false smut a sign of a good harvest?

No. Some farmers call it Lakshmi disease because it often shows up in thick, healthy-looking crops. But that is because a lush crop with heavy nitrogen is more likely to get it. Every smut ball is a lost grain, and it lowers the quality of the rest.

Can I spray after I see the smut balls?

A spray at that stage does not save the ears that already have smut balls. The infection happened at flowering. Remove the smutted ears and plan a preventive spray at booting for the next crop. Ask your KVK for a product labelled for false smut on paddy.

Can I keep seed from a field that had false smut?

It is better not to. Spores stick to the grain and can carry the disease into your next crop. Use certified seed, or seed from a healthy field, and ask your KVK about seed treatment.

How does false smut spread to my field?

Wind carries the powdery spores from mature smut balls to nearby crops at flowering. Hard resting bodies left in the soil from last season's crop also start new infections. Infected seed can carry it to a new field.

Related reading

• Rice blast in paddy: symptoms and control of leaf and neck blast
• Sheath blight of rice: symptoms, causes and control in paddy
• Dirty panicle (grain discolouration) in paddy
• Stem borer in paddy: dead heart, white ear and how to control it
• Products for paddy and all fungicides

Sources

• Tamil Nadu Agricultural University, TNAU Agritech Portal: False smut / Lakshmi disease of rice
• International Rice Research Institute (IRRI), Rice Knowledge Bank: False smut
• National Centre for Integrated Pest Management (NCIPM, ICAR), DPPQS and NIPHM: Integrated Pest Management Package for Rice