Relative efficacy of fungicides in managing onion purple blotch incited by Alternaria porri

Onion purple blotch incited by Alternaria porri (Ellis.) Cif. is a serious bottleneck in onion seed production and has become a major concern for farmers and research fraternity. In vitro studies on efficacy of fungicides indicated the pre-eminence of Amistar Top (azoxystrobin 18.2% + difenoconazole 11.4% w/w SC @ 1000 ppm) and Score (difenoconazole 25 % EC @ 1000 ppm) in mycelial growth inhibition of test pathogen. The fungal isolates did not differ significantly with respect to chemo sensitivity towards fungicides. Under field conditions, foliar spray of Score (difenoconazole 25 % EC @ 0.1%) at fortnightly intervals outperformed by exhibiting substantial disease control (43.08 per cent) with AUDPC value of 497 and exhibiting minimum infection rate (0.009) with consequential increase in seed yield (7.78 per cent) over control.