Purple Blotch of Onion & their control

Purple Blotch: Purple blotch is caused by Alternaria porri . The disease occurs under favourable conditions of temperature 28-30ºC and 80-90% relative humidity. It is more common in kharif season in Maharashtra. Small, sunken, whitish flecks with purple coloured centres are common symptoms occurring on leaves and flower stalks. Further, large purple area develops forming dead patches. The intensity of disease varies from season-to-season. It causes losses of 25% in rabi, 50% in kharif in Maharashtra, while in Northern and Eastern parts 25-90% damage in bulbs and seed crop occurs when the disease appears along with stemphylium blight.

Control: For managing the disease effectively, healthy seed should be used. Crop rotation of 2-3 years with non related crops should be followed. Further, mancozeb @ 0.25% or chlorothalonil @ 0.2% or rovral @ 0.25% should be sprayed at fortnightly interval commencing from one month after transplanting. The sticker triton/sandovit should be mixed in spray solution.