Field evaluation of fungicides against Purple Blotch (Alternaria porri) of bulb onion (Allium cepa).

Abstract

Seven fungicides were evaluated during a dry season and a wet season for efficacy on disease incidence and disease severity of purple blotch of bulb onion. The fungicides used were benomyl, 50% WP, 10% a.i.; mancozeb, 80% WP. 0.16% a.i.; captan, 80%> WP, 0.10% a.i.; chlorothalonil, 50% EC, 0.10%) a.i.; metalazyl, 72% WP. 0.036%) a.i.; copper-oxychloride 50%, WP. 0 10%o a.i. and manzeb, 80%o WP, 0.16%> a.i. Fungicidal treatments reduced the rate of purple blotch incidence and severity in the wet season. All the fungicides tested resulted in higher yields. Mancozeb was most effective in both the dry and wet seasons. Yield losses in unprotected plots were estimated at 53.8% and 67.5%o for the dry and wet seasons of disease index (CODEX).