🍅Vegetable Crop Diseases — Pathogens, Symptoms, and Management

From Field to Lab — Defending India’s Vegetable Basket

A tomato farmer in Karnataka spots leaves with dark spots and concentric rings forming a “bull’s eye” pattern — that is Early Blight (Alternaria solani). In a nursery in UP, entire trays of seedlings topple over at the soil line overnight — Damping Off has struck. Potato fields in West Bengal showing water-soaked lesions that spread rapidly during cool, wet weather face the dreaded Late Blight — the same disease that caused the Irish Potato Famine. And curled, stunted tomato plants with leathery leaves signal Leaf Curl Virus, transmitted by whiteflies.

Vegetable crops are attacked by a wide range of pathogens including fungi, bacteria, viruses, and phytoplasmas. Understanding the causal organisms, symptoms, and management strategies is essential for competitive exams like IBPS AFO, NABARD, and FCI.

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Tomato Diseases

1. Early Blight — Alternaria solani

Symptoms:

• Attacks foliage causing characteristic leaf spots and blight
• Small, black lesions mostly on older foliage that enlarge to 6-7 mm diameter
• Concentric rings form a bull’s eye pattern in the centre of the diseased area
• Tissue surrounding the spots may turn yellow

Management:

• Spray Mancozeb 0.2% for effective disease control
• Remove and destroy infected plant debris
• Use resistant varieties

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2. Damping Off — Pythium aphanidermatum

Symptoms:

• Occurs in two stages: pre-emergence and post-emergence
• Pre-emergence: Seedlings killed before reaching soil surface; complete rotting of radical and plumule
• Post-emergence: Infection of young, juvenile tissues at the collar region (ground level); tissues become soft and water-soaked; seedlings topple over

Management:

• Drench with Copper oxychloride 0.2% or Bordeaux mixture 1%
• Seed treatment with Trichoderma viride (4 g/kg) or Thiram (3 g/kg)
• Spray Metalaxyl 0.2% in cloudy weather

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3. Fusarium Wilt — Fusarium oxysporum f.sp. lycopersici

Symptoms:

• First symptom is clearing of veinlets and chlorosis of leaves
• Younger leaves may die in succession; entire plant wilts and dies in few days
• Petiole droops and wilts
• In young plants: vein clearing and drooping of petioles

Management:

• Spot drench with Carbendazim (0.1%)
• Use resistant varieties
• Crop rotation with non-solanaceous crops

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4. Tomato Mosaic — Tomato Mosaic Virus (TMV)

Symptoms:

• Light and dark green mottling on leaves
• Often accompanied by wilting of young leaves on sunny days when plants first become infected
• Leaflets of affected leaves are usually distorted, puckered and smaller than normal

Management:

• Remove and destroy infected plants
• Control aphid vectors
• Use TMV-resistant varieties
• Wash hands with soap before handling plants (TMV is highly stable and mechanically transmitted)

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5. Tomato Leaf Curl — Tomato Leaf Curl Virus (ToLCV)

Vector: Whitefly (Bemisia tabaci) + Begomovirus

Symptoms:

• Severe stunting with downward rolling and crinkling of leaves
• Newly emerging leaves show slight yellow colouration, later show curling
• Older leaves become leathery and brittle

Management:

• Yellow sticky traps @ 12/ha to monitor whitefly
• Raise barrier crops (cereals) around the field
• Spray Imidacloprid 0.05% or Dimethoate 0.05% at 15, 25, 45 days after transplanting to control vector

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Potato Diseases

1. Late Blight — Phytophthora infestans

Symptoms:

• Affects leaves, stems and tubers
• Water-soaked spots on leaves that increase in size, turn purple-brown and finally black
• White growth develops on under surface of leaves — spreads to petioles, rachis and stems
• Frequently develops at nodes

Management:

• Protective spraying with Mancozeb or Zineb 0.2% to prevent tuber infection
• Avoid injuries at harvest; do not store visibly infected tubers
• Resistant varieties: Kufri Naveen, Kufri Jeevan, Kufri Alenkar, Kufri Khasi Garo, Kufri Moti

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2. Early Blight — Alternaria solani

Symptoms:

• Present in both hills and plains
• Brown-black necrotic spots — angular, oval shape with concentric rings (bull’s eye pattern)
• Spots coalesce and spread all over the leaf; shot holes on fruits

Management:

• Use disease-free seed tubers
• Remove and destroy infected plant debris (spores in soil are primary infection source)
• Early spraying with Zineb or Captan 0.2% every 15-20 days
• Resistant variety: Kufri Sindhuri

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3. Black Scurf — Rhizoctonia solani

Symptoms:

• At sprouting, dark brown colour appears on the eyes of tubers
• Affected xylem tissue causes wilting; infected tuber shows russeting of skin
• Hard dry rot with browning on internal tissue; spongy mass on infected tuber
• Seed tubers are source of spread
• Favourable conditions: moderately cool, wet weather at 23°C

Management:

• Treat soil with Pentachloronitrobenzene (PCNB) @ 70 kg/ha
• Plant well-sprouted tubers at shallow depth
• Leave land fallow for 2 years to reduce disease severity

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4. Common Scab (Corky Scab) — Streptomyces scabies

Symptoms:

• Corkiness of tuber periderm is the characteristic symptom
• Approximately 1/4 inch into the tuber surface showing russette appearance
• Slightly pitted on infected tuber
• Light brown to dark brown lesions; affected tissue attracts insects

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Brinjal (Eggplant) Diseases

1. Phomopsis Blight — Phomopsis vexans

Symptoms:

• Damping off of seedlings in nursery beds
• Leaf spots: large, irregular, grey-brown patches
• Fruit rot: sunken, discoloured lesions on fruits; fruits shrivel and mummify

Management:

• Seed treatment with Thiram 3 g/kg
• Spray Copper oxychloride 0.25% or Mancozeb 0.2%

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2. Little Leaf of Brinjal — Phytoplasma

Vector: Leafhopper (Cestius phycitis and Amrasca biguttula biguttula)

Symptoms:

• Characteristic smallness of leaves; petioles very short, leaves appear to stick to stem
• Leaves are narrow, soft, smooth and yellow; newly formed leaves much shorter
• Internodes shortened; axillary buds get enlarged giving plant a bushy appearance
• Mostly no flowering; if flowers form, they remain green
• Fruiting is rare

Management:

• Spray insecticides to control leafhopper vector
• Remove and destroy infected plants
• Use resistant varieties

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Chilli Diseases

1. Damping Off — Pythium aphanidermatum

• Same pathogen and symptoms as tomato damping off
• Pre-emergence and post-emergence phases

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2. Anthracnose / Die-back — Colletotrichum capsici

Symptoms:

• Ripe fruits turning red are most affected
• Small, black, circular spots appear on fruit skin
• Badly diseased fruits turn straw colour or pale white, lose their pungency

Management:

• Seed treatment with Thiram or Captan 3 g/kg
• Spray Mancozeb 0.25% or Copper oxychloride 0.3%
• Use disease-free seeds

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3. Chilli Leaf Curl — Leaf Curl Virus

Vector: Whitefly (Bemisia tabaci)

• Upward curling and puckering of leaves
• Stunting of plants; reduced fruit set

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4. Chilli Mosaic — Viral

• Mottling and distortion of leaves
• Stunted growth and reduced yield

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Onion Diseases

1. Purple Blotch — Alternaria porri

Symptoms:

• Disease occurs mainly at the top/tip portion of leaves
• Infection starts with whitish minute dots on leaves with irregular chlorotic areas
• Circular to oblong concentric black velvety rings appear in the chlorotic area
• Lesions develop towards the base of the leaf
• Spots join together and spread quickly to the entire leaf area
• Leaves gradually die from the tip downwards

Management:

• Spray Mancozeb 0.25% or Copper oxychloride 0.3%
• Proper spacing for air circulation
• Avoid overhead irrigation

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2. Onion Smut — Urocystis cepulae

• Black powdery mass of spores in leaves
• Seedlings are most susceptible
• Soil-borne; seed treatment with Thiram recommended

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3. Downy Mildew — Peronospora destructor

• Pale green or yellowish patches on leaves
• Grey-violet fuzzy growth on leaf surface
• Leaves bend and fall; tips die back

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Pea Diseases

1. Fusarium Wilt — Fusarium oxysporum f.sp. pisi

Symptoms:

• First symptom is drooping of plants followed by sudden death
• Leaves turn yellow and drop off prematurely

Management:

• Seed treatment with Carbendazim or Thiram
• Crop rotation (3-4 years)
• Use resistant varieties

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2. Powdery Mildew — Erysiphe polygoni

Symptoms:

• Disease appears on foliage and pods
• First apparent as small, slightly darkened areas which later become white powdery spots
• Spots enlarge and cover entire leaf area
• Severely infected leaves become chlorotic and distorted before falling
• Affected pods are small in size and malformed

Management:

• Spray Wettable sulphur 0.2% or Karathane 0.1%
• Use resistant varieties
• Early sowing to escape disease

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3. Pea Rust — Uromyces fabae

Symptoms:

• Serious in humid regions
• Plants dry up quickly; yield considerably reduced
• Initial symptoms: flecking of leaves
• Flecks develop into reddish-brown pustules, frequently merging, finally bursting to expose brown spores
• Entire leaf blade and affected parts give brownish appearance from a distance

Management:

• Spray Mancozeb 0.2% or Zineb 0.2%
• Remove and destroy crop debris
• Use resistant varieties

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Quick Reference: Vegetable Crop Diseases

Complete Disease-Pathogen Summary Table

Crop	Disease	Pathogen	Type	Key Diagnostic Feature
Tomato	Early blight	Alternaria solani	Fungal	Bull’s eye concentric rings on older foliage
Tomato	Damping off	Pythium aphanidermatum	Oomycete	Pre- and post-emergence seedling death
Tomato	Fusarium wilt	F. oxysporum f.sp. lycopersici	Fungal	Vein clearing, chlorosis, wilting
Tomato	Mosaic	TMV	Viral	Light-dark green mottling, puckered leaves
Tomato	Leaf curl	ToLCV	Viral	Downward rolling, crinkling; whitefly vector
Potato	Late blight	Phytophthora infestans	Oomycete	Water-soaked spots, white growth below leaf
Potato	Early blight	Alternaria solani	Fungal	Concentric rings, angular-oval spots
Potato	Black scurf	Rhizoctonia solani	Fungal	Dark brown on eyes, russeting of skin
Potato	Common scab	Streptomyces scabies	Actinomycete	Corky periderm, russette appearance
Brinjal	Phomopsis blight	Phomopsis vexans	Fungal	Fruit rot, mummification
Brinjal	Little leaf	Phytoplasma	Phytoplasma	Tiny leaves, bushy habit; leafhopper vector
Chilli	Anthracnose/Die-back	Colletotrichum capsici	Fungal	Black spots on ripe fruits, loss of pungency
Chilli	Leaf curl	Leaf curl virus	Viral	Upward curling; whitefly vector
Onion	Purple blotch	Alternaria porri	Fungal	Concentric black rings at leaf tips
Onion	Smut	Urocystis cepulae	Fungal	Black powdery spore mass in leaves
Onion	Downy mildew	Peronospora destructor	Oomycete	Grey-violet fuzzy growth
Pea	Fusarium wilt	F. oxysporum f.sp. pisi	Fungal	Drooping, sudden death
Pea	Powdery mildew	Erysiphe polygoni	Fungal	White powdery spots on foliage and pods
Pea	Rust	Uromyces fabae	Fungal	Reddish-brown pustules, merging

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Vectors and Their Associated Diseases

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Key Exam Points to Remember

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Summary Cheat Sheet