My rabi onion leaves are dying back from the tips with brown and purple patches in cool humid weather. The bulbs stay small. What is wrong?
Cool, humid, dewy weather in rabi onion brings on leaf diseases like Stemphylium blight, purple blotch and sometimes downy mildew, all of which dry the leaves from the tips down, cut photosynthesis and leave you with small bulbs. Because the leaves feed the bulb, protecting the foliage is what protects your yield. Use clean seed, follow crop rotation away from onion and garlic, give proper spacing for air movement, and avoid evening irrigation that keeps leaves wet through the dewy nights. Start protective fungicide sprays such as mancozeb when the weather turns conducive and switch to a recommended systemic under high pressure, rotating groups and adding a sticker because onion leaves are waxy and shed spray. Balanced potash and avoiding excess nitrogen help. Follow label doses and waiting periods and confirm the schedule with your KVK as several diseases can look similar.
A sticker in the spray was essential for me on onion. Without it the fungicide rolled straight off the waxy upright leaves and the blight kept spreading. Once I added a wetting agent the spray held and finally worked.
Spraying ahead of the cool dewy spell, not after the leaves are already drying back, made the difference here. By the time the patches are widespread the leaf area is lost and the bulbs stay small. Watching the weather and protecting the foliage early saved my bulb size.
Avoiding evening watering helped, because the leaves staying wet through the dewy nights fed the disease. I water earlier so the foliage dries by evening, and I give proper spacing so air moves between the rows. These cultural steps reduced how often I needed to spray.
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