Affected leaf by onion leaf blotch disease

How To Treat Leaf Blotch of Onion?

Through this article, you will know 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 really easy for you to use as it is the result of tested research.

This Disease is a major economic threat to onion growers worldwide. Studies have estimated that this disease alone causes approximately $500 million in losses. It not only destroys the crop but also 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 actually causes its spores to start their life cycle anew.  Spores are also able to spread to healthy plants and soil through wind, irrigation water, or rain showers. 80-90% relative humidity and a temperature of 20-30°C are favorable conditions for this disease. 

What Are The Symptoms?

Affected leaf by onion leaf blotch disease

Affected Onion Leaf.

This disease can be easily identified 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.

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

    1. Onion land should be kept clean.
    2. Cultivate a crop other than onion/garlic several times in the land and then cultivate garlic/onion again. That is, farming should be done according to the crop stage. Do not cultivate onion/garlic again and again in the same land.
    3. Do not plant onions too densely.
    4. Infected leaves and seeds should be pruned and destroyed.
    5. Balanced fertilizer application and inter-cares should be done.
    6. Onion land should be irrigated 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, Mencozeb-64% +Metalaxyl-8% fungicide (Ridomin Gold MZ-68WP) should be mixed with 2 grams per liter of water and sprayed every 7 days.


Onion leaf blotch can be easily prevented and successfully treated if the above-mentioned Integrated Suppression Management is followed. 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 9 important onion diseases.

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