This article teaches you how to treat the leaf blotch disease of onion. You can also learn more about the causes and symptoms of the disease. This management will be easy for you to use as it results from tested research.

This disease is a significant economic threat to onion growers worldwide. Studies have estimated that this disease alone causes approximately $500 million in losses. It destroys the crop and makes onions unmarketable due to unsightly brown spots on the leaves and stems of the affected plants.

What Causes Leaf Blotch of Onion?

This disease is caused by a fungus called Alternaria porri belonging to the Pleosporaceae family. The disease survives in the soil over winter in addition to infected crop debris; Wet weather causes its spores to start their life cycle anew. Spores can also spread to healthy plants and soil through wind, irrigation water, or rain showers. 80-90% relative humidity and 20-30°C temperature are favorable conditions for this disease. 

What Are The Symptoms?

You can easily identify this disease by seeing two main symptoms.

• • When this disease attacks, long spots are seen along the veins of the leaves.
  • A dark brown coating of the fungus is seen on the affected leaves.

Affected Onion Leaf.

How To Treat Leaf Blotch Disease of Onion? Its an Integrated Suppression Management System

1. 1. It would be best if you kept the land clean. 
   2. Cultivate a crop other than onion/garlic several times in the ground and then cultivate garlic/onion again. That is, you should do farming according to the crop stage. Do not cultivate onion/garlic again and again in the same land.
   3. It’s best to avoid planting onions close to each other.
   4. Infected leaves and seeds should be pruned and destroyed.
   5. Balanced fertilizer application and inter-cares should be done.
   6. It would help to irrigate onion land regularly every 12-15 days according to soil requirements.
   7. Fungicides of propiconazole group (eg: Tilt) at 0.5 ml per liter of water. Mix and spray twice every 12 days.
   8. If humid and warm weather prevails, you should mix Mencozeb-64% +Metalaxyl-8% fungicide (Ridomin Gold MZ-68WP) with 2 grams per liter of water and spray every seven days.

Conclusion: 

Integrated Suppression Management is the most effective way to prevent and treat onion leaf blotch. If you have any questions about this disease, you can contact us. We will continue to bring articles about symptoms, causes, and prevention of more than nine important onion diseases. 

Admin

Md. Gaushoul Agam 
Co-Founder & CEO, ToAgriculture
Experienced Horticulture Officer | Sustainable Farming Advocate

I am a passionate and experienced Horticulture Officer with over 14 years in the Department of Agricultural Extension, Bangladesh. My goal is to transform agriculture through knowledge, innovation, and sustainable practices.

I founded ToAgriculture to empower farmers and agriculture enthusiasts with science-backed knowledge and modern farming solutions. The platform addresses global challenges like food safety, shrinking arable land, and climate change—while promoting practical, localized strategies.

What I Do at ToAgriculture:

• Control pests and manage plant diseases using eco-friendly methods.
• Promote modern, climate-smart farming techniques.
• Support farmers with irrigation, crop rotation, and grafting guidance.
• Encourage sustainable vegetable and fruit farming practices.

I have hands-on experience in field crops and horticulture, with deep knowledge of soil health, pest control, and irrigation systems.

Join me on this journey as I share real-world insights and practical tips to help you grow healthier crops, improve yields, and build a resilient farming future.