Efficacy of Some Fungicides against Post-infection Control of Downy Mildew of Onion

Three consecutive post infection sprays of Ridomil MZ (metalaxyl+mancozeb)@ 0.25 per cent at an interval of 10 days were found highly effective against downy mildew of onion caused by Peronospora destructor (Berk) Casp. and gave 96.51 per cent disease control in bulb and seed yield by 3.66 and 21.41 times over check (untreated). Next best fungicides were Galben M-8-65 (benalaxyl +mancozeb) @ 0.2%, Galben R-4-33 (benalaxyl + copper oxychloride) @ 0.2%, followed by propineb (0.2%) and fungicides from oxadixyl group namely; SAN 516 (oxadixyl+mancozeb) and SAN 506 (oxadixyl+copper oxychloride). Amongst other fungicides, Bordeaux mixture (0.8%), controlled the disease to an extent of 75.97 and 76.27 per cent both in bulb and seed crop, respectively. Mancozeb (0.25%), chlorothalonil (0.2%), aliette (0.05%), captan (0.2%) and copper oxychloride (0.3%) were almost equally effective and exhibited per cent disease index ranging between 25.16 - 29.09 and 29.67 - 32.17 in bulb and seed crop, respectively. Zineb and prothiocarb were less effective, however, were superior over the control (untreated).