MANAGEMENT OF PURPLE BLOTCH OF ONION FOR SEED PRODUCTION

Abstract

The experiments were conducted both in Seed Health Laboratory, Department of Plant Pathology and in the farm of the Sher-e-Bangla Agricultural University, Dhaka, Bangladesh, during the winter cropping season 2007-2008 to determine the efficacy of fungicides, botanicals and micronutrients against purple blotch of onion. Initially, five chemical fungicides and two botanicals were assayed for the efficacy against Alternaria porri by in vitro test. Among the fungicides, Rovral 50 WP @ 0.2% reduced the highest mycelial growth of Alternaria porri followed by Ridomil Gold MZ-72 @ 0.2% and Dithane M-45 @ 0.45% compared to control. Between two botanicals, Neem leaf extract (1:6 w/v) gave better result than Allamanda leaf extract (1:6 w/v). A field experiment was laid out using onion variety Taherpuri to evaluate the nine (9) different treatments viz. Allamanda leaf extract (1:6 w/v) + micronutrients, Neem leaf extract (1:6 w/v) + micronutrients, Cupravit 50 WP @ 0.7% + micronutrients, Rovral 50 WP @ 0.2% + micronutrients, Dithane M-45 @ 0.45% + micronutrients, Ridomil Gold. MZ-72 @ 0.2% + micronutrients, Bavistin 50 WP @ 0.1 % + micronutrients, Only micronutrients and Untreated Control (No fungicides, botanicals & micronutrients). A positive and significant effect of fungicides, botanicals and micronutrients was found in respect to % leaf infection, % leaf area diseased (LAD), PDI (leaf & stalk), % seed stalk infection and % stalk area diseased (SAD). The highest performance in reducing disease incidence and severity of purple blotch of onion was found by the application of Rovral 50 WP @ 0.2% + micronutrients followed by Ridomil Gold MZ-72 @ 0.2% + micronutrients. The seed yield and yield contributing characters also influenced by the application of the treatments. The highest onion seed yield (650 kg/ha) was recorded in case of application of Rovral 50 WP @ 0.2% + micronutrients followed by Ridomil Gold MZ-72 @ 0.2% + micronutrients. Between two botanicals, Neem leaf extract performed better than Allamanda leaf extract in reducing the disease incidence, severity and in improving seed yield and yield contributing characters. III