Bacterial blight of rice: symptoms, spread and control in paddy

Photo at the top: Bacterial blight on rice leaves at grain filling. The straw-white stripes start at the tip and run down the leaf, Photo: Donald Groth, Louisiana State University AgCenter, Bugwood.org, CC BY 3.0 US (cropped)

Quick answer

Bacterial blight of rice (BLB) is a disease caused by bacteria. Leaves get yellow to straw-white stripes that start at the tip or edge and run down with a wavy border, and young plants can wilt and die. There is no cure once leaves dry. Control it with resistant varieties, less nitrogen, good drainage and clean fields.

The bacterium is Xanthomonas oryzae pv. oryzae. It is one of the most serious diseases of paddy in India, and it is worst in kharif after heavy rain and wind.

Bacterial leaf blight symptoms: how to identify it

In Telugu this disease is called endaku tegulu (ఎండాకు తెగులు), and in Hindi jivanu patti jhulsa (जीवाणु पत्ती झुलसा). Tamil Nadu Agricultural University (TNAU) describes three forms: kresek (wilting of young plants), leaf blight, and a pale yellow leaf form. Leaf blight is the one you will see most often.

Kresek: wilting of seedlings and young plants

• Shows up about 1–2 weeks after transplanting, as TNAU notes. The bacteria get in through cut or broken leaf tips and spread inside the plant.
• Leaves turn greyish green and roll up. Then they turn yellow to straw-coloured and wilt. The whole seedling or tiller can dry up and die.
• In the nursery, TNAU describes round yellow spots at the leaf edge that grow, join up and dry the leaves.

Rice bacterial blight symptoms on older plants

• Start: water-soaked, see-through stripes near the leaf tip or leaf edge, or where the leaf was damaged.
• Spread: the stripes grow longer and wider towards the leaf base. The border between sick and green tissue is wavy, not straight.
• Colour: within a few days the stripe turns straw yellow. Later the whole leaf blade can turn white or straw-coloured and dry.
• Morning drops: early in the morning, look for milky drops on young stripes. This is bacterial ooze. It dries into small yellowish beads or a white crust on the leaf.
• Old stripes: they turn greyish white and may get black dots. These are other fungi growing on the dead tissue, not the cause.
• Grain: TNAU notes that affected grains can have discoloured spots.

The glass of water test

This simple test helps you confirm it in the field. Cut a piece of leaf across a young stripe. Stand the cut end in a clear glass of clean water. Wait a few minutes, then hold the glass against the light. If the water near the cut end turns cloudy or milky, that is bacterial ooze. TNAU and the International Rice Research Institute (IRRI) both describe this test.

Look-alikes and how to tell them apart

• Stem borer dead heart: the centre shoot dries, like kresek. But a dead heart pulls out easily, and the stem has a bore hole. A kresek plant does not pull out easily, and IRRI notes that if you squeeze the lower end, yellowish ooze comes out. See our guide to stem borer in paddy: dead heart and white ear.
• Rice blast: eye-shaped spots, pointed at both ends, with a grey centre and brown border. BLB makes long stripes from the tip or edge, not separate spots. See our rice blast guide for leaf and neck blast.
• Sheath blight: grey-green patches on the leaf sheath near the water line, not stripes on the leaf blade. See sheath blight of rice: symptoms and control.
• Nitrogen or potassium shortage: nitrogen shortage turns older leaves pale yellow evenly, with no wavy border and no ooze. Potassium shortage browns the tips and edges of older leaves. Neither one gives milky drops or a cloudy glass test. See potassium deficiency symptoms in plants.

How rice bacterial blight spreads and when it attacks

The bacteria survive between crops in infected stubble and straw, in rice ratoons (regrowth from old stubble), in self-sown seedlings and in weeds. IRRI notes the disease is most likely where these are left in or near the field. From a sick leaf, the ooze drops are carried by rain splash and strong wind to healthy leaves. Water flowing from a sick field into the next one can carry it too. The bacteria enter through wounds and the natural openings at the leaf edge.

TNAU lists the conditions that favour it:

• Clipping the tips of seedlings at transplanting, which leaves fresh wounds.
• Heavy rain, heavy dew, flooding and deep standing water.
• Strong wind and warm weather of 25–30 °C. IRRI gives a range of 25–34 °C with humidity above 70%.
• Too much nitrogen, especially a late top dressing of urea.

In Telangana and Andhra Pradesh, watch for it most in kharif paddy, after spells of heavy rain, storms or cyclone weather. Fine-grain varieties grown widely here, such as Samba Mahsuri, are susceptible. That is why ICAR-IIRR bred a resistant version (see below).

Crops it attacks

Paddy: this article covers rice only. The disease can strike from the nursery to grain filling. IRRI notes that the earlier it starts, the bigger the loss, and that losses can reach 70% in susceptible varieties when the weather suits the disease. Kresek in the first weeks kills plants and leaves gaps. Leaf blight before flowering dries the leaves the plant needs to fill grain. IRRI notes that when it starts only at booting, it does not cut yield, but grain quality drops and more grains break during milling.

Cotton has a different bacterial blight, caused by a different bacterium. It does not spread from paddy.

When to act on bacterial blight of rice (economic threshold)

The economic threshold (ETL) is the level of disease at which control action starts to pay. The Integrated Pest Management Package for Rice (NCIPM, DPPQS and NIPHM, Government of India) gives these levels for BLB:

• Nursery, kresek form: 2–3 affected plants per square metre.
• Early to late tillering: 2–3 infected leaves per square metre.

Walk through the field, not just along the bund, twice a week after heavy rain or wind. Look early in the morning, when the milky drops are easy to see. If you reach these levels, stop extra nitrogen at once and call your local agriculture officer or KVK (Krishi Vigyan Kendra, the farm science centre in your district).

How to control bacterial leaf blight without chemicals

IRRI calls resistant varieties the most reliable and cheapest way to control bacterial blight. The other steps below cut the chance of an outbreak and slow the spread.

• Resistant varieties: the rice IPM package lists varieties with BLB resistance, including Ajaya, IR 36, IR 64, Swarna and Improved Samba Mahsuri. Improved Samba Mahsuri was developed by ICAR-IIRR and CSIR-CCMB in Hyderabad. It carries three BLB resistance genes and keeps the fine grain of Samba Mahsuri. Ask your KVK which resistant variety suits your area and season.
• Healthy seed and nursery: use disease-free seed and raise a healthy nursery. Do not take seedlings from a nursery that shows yellow, drying leaf edges.
• Do not clip seedling tips: TNAU names clipping at transplanting as a cause, because the bacteria enter through the cut tips. In fields with a history of BLB, plant the seedlings whole.
• Nitrogen in small split doses: do not overdose urea, and avoid a heavy late top dressing. The rice IPM package advises cutting nitrogen where BLB appears, and giving only small doses split over more rounds if the crop needs it. To judge whether the crop really needs more, see nitrogen deficiency symptoms and how to correct them.
• Water: avoid deep standing water. The rice IPM package advises alternate wetting and drying in areas where bacterial blight keeps coming back. Make sure the nursery and field can drain.
• Stop water flowing from sick fields: do not let water from an infected field run into a healthy one.
• Clean fields and bunds: remove weeds from bunds and channels. Remove and destroy badly infected plants.
• After harvest: plough under the stubble, straw, ratoons and self-sown seedlings. IRRI advises letting fallow fields dry out, which helps reduce the bacteria left in the soil and crop waste.

Chemical control: fungicides do not cure bacterial blight of rice

Bacterial blight is caused by bacteria, not a fungus. Fungicides for blast or sheath blight do not cure it, so do not spray them for BLB. No spray can heal a leaf that has already dried. Most of the control comes from the variety you choose, how much nitrogen you give and how you manage water.

If the disease crosses the action level above, ask your local agriculture officer or KVK for a product labelled for bacterial leaf blight on your crop. Before you buy, check that the label names both paddy (rice) and bacterial leaf blight. We have not listed a product here because we have not yet confirmed one in our range with this use on its label. You can browse our paddy products, but use only a product whose label names this disease.

Safety if you spray

• Read the label and leaflet before use. Use only the crop, dose and number of sprays printed on it.
• Note the waiting period before harvest on the label, and 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, and wash well afterwards.
• Spray in the morning or evening, not in strong wind or just before rain. Keep sprays away from ponds and fish.

Frequently asked questions

What are the first symptoms of rice bacterial blight?

Water-soaked, see-through stripes at the leaf tip or edge. They turn straw yellow with a wavy border and run down the leaf. In the morning you may see milky drops on them. Young plants 1–2 weeks after transplanting may wilt and die (kresek).

Is bacterial leaf blight a fungus? Will a fungicide cure it?

No. It is caused by bacteria, so fungicides do not cure it. Resistant varieties, less nitrogen, good drainage and clean fields are the main control. For a spray, ask your agriculture officer or KVK for a product labelled for BLB on paddy.

How can I tell bacterial leaf blight symptoms from nitrogen shortage?

Nitrogen shortage makes older leaves evenly pale. BLB makes stripes from the tip or edge with a wavy border. Do the glass of water test: if the water turns milky near the cut leaf, it is bacterial blight.

Does too much urea cause bacterial blight?

Urea does not bring the bacteria, but too much nitrogen, especially a late top dressing, makes the disease much worse. Give nitrogen in small split doses and stop extra urea when you see BLB.

Which rice variety resists bacterial blight?

The rice IPM package lists several, including Improved Samba Mahsuri, Swarna, IR 64 and Ajaya. Ask your KVK which one suits your area and season.

Will bacterial blight of rice come back in the next crop?

It can. The bacteria survive in stubble, straw, ratoons and weeds. Plough them under after harvest, let the field dry, keep bunds clean and sow a resistant variety next time.

Related reading

• Rice blast in paddy: symptoms and control of leaf and neck blast
• Sheath blight of rice: symptoms, causes and control in paddy
• Stem borer in paddy: dead heart, white ear and how to control it
• Nitrogen deficiency in plants: symptoms, causes and how to correct it
• Potassium deficiency in plants: symptoms, causes and how to correct it
• All paddy products

Sources

• Tamil Nadu Agricultural University, TNAU Agritech Portal: Bacterial leaf blight of rice
• International Rice Research Institute (IRRI), Rice Knowledge Bank: Bacterial blight
• National Centre for Integrated Pest Management (NCIPM, ICAR), DPPQS and NIPHM, Government of India: Integrated Pest Management Package for Rice
• ICAR-Indian Institute of Rice Research (ICAR-IIRR): Improved Samba Mahsuri