Onion Crop Care Guide: Complete Global Diseases, Pests, Nutrition & High-Yield Farming System

1. Introduction: Why Onion Needs Precision Care

Onion is a shallow-rooted, slow-starting crop with hollow leaves and a tight bulb structure. These traits make it highly sensitive to moisture stress, nutrient imbalance, thrips outbreaks, fungal leaf diseases, and bulb rots. Profit comes only with preventive care, not late treatment.

2. Climate & Soil Requirements

Ideal climate:

Temperature: 15–25°C (bulb formation best at 20–25°C)

Humidity: Medium; high humidity triggers leaf diseases

Sunlight: Full sun

Soil:

Texture: Sandy loam to loam, well drained

pH: 6.0–7.0

Avoid heavy clay and waterlogging (causes basal rot)

3. Land Preparation & Bed Design

Deep ploughing to remove clods and pests

Raised beds improve drainage and reduce rot

Organic matter is critical for uniform bulb size

Per acre soil boost:

FYM/compost: 3–4 tons

Neem cake: 200–250 kg

Biochar (optional): 25–30 kg

Trichoderma mixed with compost

4. Nursery & Transplanting Care

Seed treatment (mandatory): Trichoderma + Pseudomonas (reduces damping-off, basal rot).

Nursery rules:

Raised beds, light irrigation, no stagnation

Weekly neem spray to deter thrips

Avoid dense sowing (reduces disease)

Seedling age:

6–8 weeks (15–20 cm height)

Transplanting:

Evening transplanting

Spacing: 15 × 10 cm (bulb onions); wider for seed crop

Light irrigation immediately after transplant

5. Irrigation Management

Onion roots are shallow; irregular watering ruins bulbs.

Rules:

Frequent light irrigations

No waterlogging

Stop irrigation 10–15 days before harvest (for better curing)

Problems:

Overwatering → basal rot, soft bulbs

Underwatering → small bulbs, doubles, splitting

6. Nutrient Management (Onion Nutrition Science)

Basal: Balanced NPK + organic matter
Vegetative: Nitrogen in splits (avoid excess)
Bulb initiation: Potassium increases size & storage life
Micronutrients: Sulphur (pungency), Zinc (growth), Boron (uniform bulbs)

Deficiency symptoms:

N low → pale thin leaves

K low → soft bulbs, poor storage

S low → less pungency

B low → malformed bulbs

7. Major Onion Diseases (A–Z)

7.1 Purple Blotch (Alternaria porri)

Symptoms: Purple lesions with yellow halo on leaves.
Damage: Reduced photosynthesis, poor bulb size.
Favouring conditions: Warm + humid.
Care:

Wider spacing, airflow

Balanced nitrogen

Preventive fungicide rotation / copper-based sprays

Organic: Neem + compost tea preventive

7.2 Downy Mildew

Symptoms: Greyish growth on leaves, sudden collapse.
Care:

Avoid overhead irrigation

Improve drainage

Preventive sprays before cool, humid weather

7.3 Basal Rot (Fusarium)

Symptoms: Bulb base rots, plants topple.
Cause: Poor drainage, infected soil.
Care:

Crop rotation

Trichoderma soil application

Avoid excess moisture

7.4 Stemphylium Blight

Symptoms: Small tan spots turning brown; leaf drying.
Care:

Remove affected leaves

Maintain K nutrition

Timely protective sprays

7.5 Bacterial Soft Rot

Symptoms: Watery, foul-smelling bulbs (often post-harvest).
Care:

Gentle harvesting

Proper curing

Dry, ventilated storage

8. Onion Pests (A–Z)

8.1 Thrips (Most dangerous onion pest)

Damage:

Silvery streaks

Leaf curling

Bulb size reduction up to 50%
Season: Dry, warm weather
Care:

Blue sticky traps

Maintain humidity lightly

Neem-based sprays early

Threshold-based selective insecticides

8.2 Onion Maggot

Damage: Larvae feed at bulb base → wilting.
Care:

Deep ploughing

Clean field sanitation

Avoid fresh manure

8.3 Cutworms

Damage: Seedlings cut at ground level.
Care:

Clean nursery

Evening monitoring

Neem cake in soil

9. Weed Management

Weeds compete early and host thrips.

Early hand weeding

Mulching reduces both weeds and disease splash

Clean borders are essential

10. Bulb Development, Harvest & Curing

Signs of maturity:

50–70% neck fall

Leaves yellow and dry

Harvest:

Dry weather harvest

Avoid bruising

Curing:

Shade cure 7–10 days

Proper curing = longer shelf life

11. Storage Management (Major Loss Stage)

Store only cured onions

Cool, dry, ventilated storage

Remove damaged bulbs immediately

Avoid high humidity (causes rot & sprouting)

12. FAQs

Why onion bulbs remain small?
Irregular irrigation and low potassium.

Why tips dry early?
Thrips damage or nutrient imbalance.

Best fertilizer for bulb size?
Potassium with balanced nitrogen.

Why onions rot in storage?
Poor curing and high humidity.

Can excess nitrogen harm onions?
Yes, it reduces storage life and increases disease.

Best control for thrips?
Early monitoring + neem + threshold-based control.

Why leaves turn purple?
Purple blotch or nutrient stress.

When to stop irrigation?
10–15 days before harvest.

Why bulbs split or double?
Irregular water and excess nitrogen.

Best yield booster?
Uniform moisture + potassium + healthy leaves.

Conclusion

Onion farming success depends on even moisture, thrips control, balanced nutrition, airflow, and proper curing. Preventive field management and careful post-harvest handling decide both yield and market value. This guide gives farmers a complete, practical system used across major onion-growing regions worldwide.

✍️Farming Writers Team
Love farming Love Farmers.

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