🌾Cereal & Fibre Crop Diseases — Pathogens, Symptoms, and Management

From Field to Lab — When Cereal Crops Fall Sick

India produces over 300 million tonnes of foodgrains annually, with rice, wheat, maize, and bajra forming the backbone of food security. Yet every season, diseases silently rob farmers of 10–30% of their potential yield. The blast in a rice nursery can burn entire fields to the ground. Brown spot of rice caused the devastating Bengal Famine of 1943. Loose smut turns wheat ears into masses of black powder. Rust can spread across hundreds of kilometres on wind currents, devastating wheat crops in days.

Knowing the pathogen, recognising the symptoms, and applying the right management strategy is what separates a successful harvest from a failed one.

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Diseases of Rice

Rice Diseases — Quick Reference Table

Disease	Causal Organism
Blast	Pyricularia oryzae (teleomorph: Magnaporthe grisea)
Sheath Blight	Rhizoctonia solani
Brown Spot	Helminthosporium oryzae (syn. Bipolaris oryzae)
Foot Rot / Bakanae	Fusarium moniliforme
Bacterial Leaf Blight	Xanthomonas oryzae pv. oryzae
False Smut	Ustilaginoidea virens
Udbatta Disease	Ephelis oryzae
Bunt / Kernel Smut	Tilletia barclayana
Khaira Disease	Zinc deficiency (not a pathogen)
Tungro	Rice tungro bacilliform virus (RTBV) + Rice tungro spherical virus (RTSV)
Grassy Stunt	Rice grassy stunt tenuivirus
Ufra Disease	Ditylenchus angustus (nematode)

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1. Blast — Pyricularia oryzae

Most severe disease of rice, also called “Rich men’s disease”. The teleomorph (sexual stage) is Magnaporthe grisea.

Symptoms:

• Leaf Blast, Nodal Blast & Neck Blast are the major symptom types
• Lesions appear as small bluish-green flecks that enlarge under moist weather to form characteristic spindle-shaped spots with grey centre and dark brown margin (Leaf blast)
• Severely infected nursery and field appear as burnt
• Infected pedicels result in non-production of seeds (blanking)

Management:

• Seed treatment with Carbendazim or Tricyclazole
• Spray Tricyclazole 0.06% or Edifenphos 0.1%
• Use resistant varieties

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2. Brown Leaf Spot — Helminthosporium oryzae

This disease caused The Great Bengal Famine of 1943 — one of the most devastating plant disease epidemics in history.

Symptoms:

• Fungus attacks from seedling to milky stage
• Minute circular to oval spots on coleoptile, leaf blade, leaf sheath, and glumes
• Most prominent on leaf blade and glumes
• Disease is severe on potash-deficient soils

Favourable Conditions:

• Temperature of 25-30°C with relative humidity above 80%
• Excess nitrogen aggravates disease severity

Management:

• Seed treatment with Thiram or Captan at 2 g/kg
• Spray Mancozeb 2 kg/ha or Edifenphos 1 ml/litre
• Apply balanced fertilization, especially potash

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3. Foot Rot or Bakanae Disease — Fusarium moniliforme

Also known as “Foolish seedling disease” because infected plants grow abnormally tall.

Symptoms:

• Infected seedlings in nursery are lean and lanky, much taller and die after some time
• In main field, affected plants have tall lanky tillers
• Plants are killed before earhead formation or produce only sterile spikelets
• When culm is split open, white mycelial growth can be seen

Management:

• Fungus is externally seed-borne
• Seed treatment with Thiram or Captan or Carbendazim at 2 g/kg

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4. Bacterial Leaf Blight — Xanthomonas oryzae pv. oryzae

Symptoms:

• Disease usually noticed at time of heading but can occur earlier
• Seedlings in nursery show circular yellow spots in margins that enlarge, coalesce, and cause drying of foliage
• ”Kresek” symptom — seen in seedlings 1-2 weeks after transplanting; bacteria enter through cut wounds in leaf tips, become systemic, and cause death of entire seedling
• Blighting starts from tip of leaves to the base

Management:

• Avoid clipping of seedling tips during transplanting
• Spray Streptocycline 500 ppm
• Use resistant varieties

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5. False Smut — Ustilaginoidea virens

Symptoms:

• Fungus transforms individual ovaries/grains into greenish spore balls of velvetty appearance
• Only a few spikelets in a panicle are affected

Favourable Conditions:

• Rainfall and cloudy weather during flowering and maturity

Management:

• Spray Copper oxychloride 0.25% at boot leaf stage
• Avoid excess nitrogen

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6. Udbatta Disease — Ephelis oryzae

Symptoms:

• The entire ear head is converted into a straight compact cylindrical black spike-like structure since the infected panicle is matted together by fungal mycelium

Management:

• Pathogen is internally seed-borne
• Hot water seed treatment at 45°C for 10 minutes effectively controls the disease

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7. Khaira Disease — Zinc Deficiency

Khaira disease is NOT caused by a pathogen — it is a nutritional disorder due to zinc deficiency.

Symptoms:

• Chlorotic/yellow patches at leaf base on both sides of midrib
• Restricted root growth; main roots turn brown

Management:

• Apply ZnSO4 @ 25 kg/ha at the time of sowing
• Foliar spray of 0.5% ZnSO4

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8. Rice Viral Diseases

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9. Sheath Blight — Rhizoctonia solani

Symptoms:

• Oval or elliptical greenish-grey lesions on leaf sheath near water level
• Lesions have grey-white centre with brown margin
• Under severe conditions, lesions spread to upper leaf sheaths and leaf blades

Management:

• Avoid excess nitrogen and close spacing
• Spray Validamycin 3L or Hexaconazole 1 ml/litre

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Diseases of Wheat

Wheat Rusts — Comparison Table

Feature	Black/Stem Rust	Brown/Leaf Rust	Yellow/Stripe Rust
Pathogen	Puccinia graminis tritici	Puccinia triticina (P. recondita)	Puccinia striiformis
Alternate Host	Berberis vulgaris	Thalictrum spp.	None known
Pustule Colour	Reddish-brown → black	Orange → brown	Bright yellow
Pustule Location	Leaves, sheaths, culms, floral parts	Mostly on leaves	Mostly on leaves, in linear rows
Pustule Shape	Oblong, merging	Round, scattered	Linear stripes
Favourable Temp	15-20°C	15-20°C	< 10°C (coolest)
Common Name	”Killer” disease of wheat	Most common rust in India	—

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1. Black or Stem Rust — Puccinia graminis tritici

Known as the “Killer” disease of wheat. Alternate host is Berberis vulgaris (barberry).

Symptoms:

• First symptom is flecking of leaves, leaf sheaths, culms, and floral structures
• Flecks develop as oblong, reddish-brown uredo-pustules that frequently merge and burst to expose brown uredospores

Favourable Conditions:

• Low temperature (15-20°C) and high humidity during November-December

Management:

• Grow resistant varieties
• Eradicate Berberis (alternate host) near wheat fields
• Spray Mancozeb 2.5 kg/ha or Propiconazole 0.1%

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2. Brown or Leaf Rust — Puccinia triticina (P. recondita)

Most common and widespread rust of wheat in India.

Symptoms:

• Minute, round, orange sori irregularly distributed on leaves
• Rarely on leaf sheath and stem
• Sori turn brown with maturity

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3. Yellow or Stripe Rust — Puccinia striiformis

Symptoms:

• Mainly on leaves (not sheaths or stems)
• Bright yellow pustules arranged in linear rows as stripes
• Stripes are yellow to orange-yellow

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4. Loose Smut — Ustilago nuda tritici (Ustilago tritici)

Symptoms:

• Difficult to detect until heading — infected heads emerge earlier than normal heads
• Entire inflorescence covered by olive-black spores under a thin grey membrane
• Internally seed-borne disease
• Entire ear except rachis and awns is smutted — black powder produced in place of grains

Management:

• Seed treatment with Vitavax (Carboxin) @ 2 g/kg
• Solar heat treatment of seeds — given by Luthara & Suttar (1934)

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5. Flag Smut — Urocystis tritici

Symptoms:

• Symptoms seen on stem, culm, and leaves from late seedling stage to maturity
• Leads to twisting and drooping of leaves followed by withering

Management:

• Seed treatment with Carboxin at 2 g/kg

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6. Karnal Bunt — Neovossia indica

First reported in India from Karnal (Haryana) by Mitra in 1931. This is a quarantine disease of international importance.

Symptoms:

• Infection occurs at flowering stage by air-borne spordia
• Symptoms most readily detected on seed after harvest
• Few grains are partially converted into black sooty powder
• Characteristic foul, fishy odour caused by production of trimethylamine by the fungus

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7. Hill Bunt or Stinking Smut — Tilletia caries / T. foetida

Symptoms:

• Fungus attacks seedlings of 8-10 days old and becomes systemic
• At flowering, hyphae concentrate in inflorescence and transform the ovary into smut sorus of dark green colour with masses of chlamydospores
• Produces foul, fishy odour (similar to Karnal bunt)

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8. Ear Cockle of Wheat — Anguina tritici (Nematode)

This is a nematode disease, not fungal.

Symptoms:

• Leaf blades generally twisted
• Infected ears shorter, remain green longer, with awns more spreading
• Affected grains transformed into small hard galls (cockles)

Management:

• Seed floatation in 20% salt solution — galls float and can be removed

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9. Tundu Disease — Corynebacterium tritici + Anguina tritici

Tundu is a complex disease requiring both a bacterium and a nematode together.

Symptoms:

• Twisting of stem, distortion of ear head, and rotting of spikelets
• Profuse oozing of yellow liquid from affected tissues — the ooze contains masses of bacterial cells
• Agglutinated inflorescence; seeds not formed; grains transformed into small hard galls

Management:

• Floatation of seeds in 20% salt solution

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10. Other Wheat Diseases

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Diseases of Pearl Millet (Bajra)

1. Downy Mildew / Green Ear Disease — Sclerospora graminicola

Most important disease of pearl millet. Infection is mainly systemic.

Symptoms:

• Leaves show patches of light green to light yellow on upper surface; corresponding lower surface bears white downy growth of sporangiophores and sporangia
• Yellow discolouration often turns to streaks along veins — young plants dry and die
• Symptoms may appear first on upper leaves
• Inflorescence gets completely or partially malformed with florets converted into leafy structures — typical symptom of “Green Ear”

Management:

• Seed treatment with Metalaxyl at 6 g/kg
• Spray Mancozeb 2 kg or Metalaxyl + Mancozeb at 1 kg/ha on 20th day after sowing
• Use resistant varieties (e.g., HHB 67 Improved)

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2. Smut — Tolyposporium penicillariae

Symptoms:

• Symptoms become apparent at grain setting
• Pathogen infects few florets and transforms them into large oval-shaped sacs (sori) containing black powder (smut spores)
• Initially sori are larger and greener than normal grains; on maturity they become dark brown and release millions of black smut spore balls

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3. Ergot or Sugary Disease — Claviceps fusiformis

Symptoms:

• Exudation of small droplets of light pinkish or brownish honeydew from infected spikelets
• Under severe infection, honeydew trickles along the earhead attracting insects
• Later, infected ovary turns into small dark brown sclerotium projecting out of the spikelet

Management:

• Adjust sowing date to avoid flowering during September (high rainfall and humidity)
• Immerse seeds in 20% common salt solution and remove floating sclerotia (ICAR & TNAU recommend 10% salt solution)
• Spray Carbendazim 500 g or Mancozeb 2 kg or Ziram 1 kg/ha at 5-10% flowering and again at 50% flowering

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Diseases of Maize

1. Downy Mildew / Crazy Top

Three types of downy mildew affect maize:

1. Sorghum downy mildew — Peronosclerospora sorghi
2. Philippine downy mildew — Peronosclerospora philippinensis
3. Crazy top — Sclerophthora macrospora

Symptoms:

• Chlorotic streaks on leaves are the most characteristic symptom
• Plants exhibit a stunted and bushy appearance due to shortening of internodes
• White downy growth on lower surface of leaf
• Proliferation of auxillary buds on tassel stalk and cobs is common — giving the typical symptom of “Crazy top”

Management:

• Seed treatment with Metalaxyl at 6 g/kg
• Spray Metalaxyl + Mancozeb @ 1 kg on 20th day after sowing

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2. Leaf Blight — Helminthosporium maydis

Symptoms:

• Affects crop at young stage
• Small yellowish round to oval spots on leaves
• Spots gradually increase into bigger elliptical spots — straw to grayish-brown in centre with dark brown margins
• Spots coalesce giving blighted appearance
• Surface covered with olive-green velvetty masses of conidia

Management:

• Seed treatment with Captan or Thiram at 4 g/kg
• Spray Mancozeb 2 kg or Captan 1 kg/ha

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3. Rust — Puccinia sorghi

Symptoms:

• Circular to oval, elongated cinnamon-brown powdery pustules scattered over both surfaces of leaves
• As plant matures, pustules become brown to black

Management:

• Spray Mancozeb at 2 kg/ha

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4. Head Smut — Sphacelotheca reiliana

Symptoms:

• Symptoms on cob and tassel
• Large smut sori replace the tassel and the ear
• Sometimes tassel is partially or wholly converted into smut sorus
• Smutted plants are stunted, produce little yield, and remain greener

Management:

• Crop rotation with pulses
• Seed treatment with Captan or Thiram at 4 g/kg

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5. Charcoal Rot — Macrophomina phaseolina (Rhizoctonia bataticola)

Symptoms:

• Affected plants exhibit wilting symptoms with grayish streak on stalk
• Shredding of the interior of the stalk causes stalks to break in the crown region
• Crown region of infected plant becomes dark in colour

Management:

• Long crop rotation with crops that are not natural hosts
• Irrigate crops at earhead emergence to maturity
• Seed treatment with Carbendazim or Captan at 2 g/kg

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Diseases of Cotton (Fibre Crop)

1. Bacterial Blight / Angular Leaf Spot / Black Arm — Xanthomonas campestris pv. malvacearum

The bacterium attacks all stages from seed to harvest. Five common symptom phases:

Management:

• Acid delinting of seeds (conc. H2SO4)
• Seed treatment with Streptocycline
• Spray Streptocycline 100 ppm + Copper oxychloride 0.25%
• Use resistant varieties

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2. Wilt — Fusarium oxysporum f.sp. vasinfectum

Symptoms:

• Sudden drooping and wilting of leaves
• Brown discolouration of vascular bundles when stem is cut
• Plants die within a few days of wilting

Management:

• Long crop rotation (3-4 years)
• Seed treatment with Carbendazim 2 g/kg
• Use resistant varieties

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3. Root Rot — Rhizoctonia solani

Symptoms:

• Yellowing and wilting of seedlings
• Brown lesions on roots and lower stem near soil line

Management:

• Seed treatment with Thiram or Captan 3 g/kg
• Soil application of Trichoderma viride

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4. Anthracnose — Colletotrichum capsici

Symptoms:

• Small reddish-brown spots on leaves, stems, and bolls
• Lesions on bolls cause premature opening and fibre damage

Management:

• Spray Mancozeb 2.5 kg/ha or Copper oxychloride 0.25%

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5. Grey Mildew / Areolate Mildew / Dahiya Disease — Ramularia areola

Symptoms:

• Pale translucent spots on leaves with angular margins defined by veinlets
• White powdery fungal growth on lower surface of leaves (visible in early morning)
• Severe infection leads to premature defoliation

Management:

• Spray Copper oxychloride 0.25% or Carbendazim 0.05%
• Avoid dense planting

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6. Tirak / Bad Opening of Bolls — Physiological Disorder

Tirak is NOT a disease caused by a pathogen — it is a physiological disorder.

Symptoms:

• Premature defective opening of bolls and shedding of leaves

Causes:

• Soil with subsoil salinity
• Light sandy soil
• Nitrogen deficiency
• Low humidity, warm and dry weather during fruiting period
• Low moisture and nutrient availability during boll formation

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Other Cotton Diseases

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Rice Disease Field Diagnosis: Which Disease Is It?

When you see leaf/plant damage in rice, follow this diagnostic flowchart:

Exam trap: Khaira disease of rice is a nutritional disorder (zinc deficiency), NOT a pathogenic disease. Bakanae disease is caused by a fungus that produces GA₃ — the same plant hormone used commercially. Both are favourite trick questions.

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Summary Cheat Sheet