EFFECT OF HEAT-TREATMENT OF BULB AND SPRAY OF FUNGICIDES IN MANAGEMENT OF PURPLE BLOTCH NALTERNARIA-PORRI) OF ONION (ALLIUM-CEPA)

An experiment was conducted during winter seasons (rabi) of 1989-90 and 1990-91 to study the effect of heat treatment of bulbs alone and in combination with a spray of metalaxyl + mancozeb (Ridornil MZ) for the control of purple blotch [Alternaria porri (Ellis) Cif.] of onion (Allium cepa L.). Heat treatment to onion bulbs at 35-degrees-C for 8 hr before sowing followed by single prophylactic spray of metalaxyl + mancozeb @ 0.25% at bolting stage or only 3 sprays of metalaxyl + mancozeb @ 0.3% at 15-day intervals (from the appearance of disease) gave the most effective control of purple-blotch disease. Heating of bulbs at 40 and 45-degrees-C reduced the crop growth. Spray of metalaxyl + mancozeb @ 0.3% proved superior to those of copper oxychloride 0.25%, captafol 0.2% and mancozeb 0.25%.