How to control Stemphylium blight and downy mildew leaf damage in rabi onion (pyaaz)?

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.