Onion is an important cash crop for farmers across India, grown in both rabi and kharif seasons. Although it is a hardy crop, onions are easily affected by several fungal, bacterial, and viral diseases. These diseases can cause leaf spots, rotting, yellowing, poor bulb formation, and heavy yield loss if not managed in time. Understanding the common diseases and following a proper management plan can help farmers maintain a healthy onion crop and get good-quality bulbs.
1. Purple Blotch
Purple blotch is one of the most common diseases in onions. It appears as small water-soaked spots on leaves, which later turn purple with yellow margins. In severe cases, leaves dry and bend down.
Management:
Avoid overhead irrigation, especially late evening watering.
Maintain good spacing to improve air circulation.
Remove and destroy infected leaves.
Spraying recommended fungicides at early stages gives good control.
2. Stemphylium Blight
This disease often appears along with purple blotch. Symptoms start as small, light-brown spots that enlarge and turn dark with concentric rings. These spots weaken the leaves and reduce bulb size.
Management:
Follow crop rotation and avoid planting onions in the same field every year.
Use disease-free seeds or seedlings.
Apply protective fungicide sprays during humid weather.
3. Downy Mildew
Downy mildew thrives in cool and moist weather. It appears as pale yellow patches on leaves with a purple or grey fungal growth on the underside. Leaves may curl, dry, and fall early.
Management:
Avoid excess irrigation and improve drainage.
Use wider spacing to reduce humidity.
Keep the field weed-free.
Use preventive fungicide sprays when the weather is favorable for disease.
4. Basal Rot
Basal rot is a soil-borne fungal disease. It starts at the base of the plant and causes yellowing, wilting, and rotting of bulbs. The infected area becomes soft and emits a foul smell.
Management:
Avoid waterlogging and ensure proper drainage.
Use well-rotted compost only; avoid fresh manure.
Practice crop rotation with cereals or legumes.
Remove and destroy infected plants immediately.
5. Bacterial Soft Rot
This disease is common during storage and transport. Bulbs become soft, watery, and have a bad smell. High moisture and mechanical injury make the disease worse.
Management:
Harvest bulbs only after the neck has dried properly.
Avoid damage during harvesting and handling.
Store onions in well-ventilated, dry rooms.
Do not store injured or diseased bulbs.
6. Viral Diseases
Onions are also affected by viral diseases that cause mosaic patterns on leaves, stunted growth, and malformed bulbs. These diseases spread mostly through insects like thrips and aphids.
Management:
Control insect vectors through timely spraying.
Use resistant varieties if available.
Remove infected plants early to prevent spread.
7. General Best Practices for Disease Prevention
Use certified seeds and healthy seedlings.
Maintain proper spacing to reduce humidity.
Avoid overhead irrigation at night.
Keep the field clean and remove infected plant debris.
Follow crop rotation for at least 2–3 years.
Use balanced fertilizers—excess nitrogen can increase disease problems.
