Efficacy of fungicides in controlling purple leaf blotch (Alternaria porri) of onion (Allium cepa)
1989
Rahman, L. | Ahmed, H.U. | Mian, I.H.
Six fungicides namely Antracol (Propineb) 65 WP, Bordeaux admixture Copper sulphate and lime), Cupravit (Copper oxychloride) 50 WP, Dithane M-45 (Mancozeb) 80 WP, Rovral (Iprodione) 25 EC and Trimiltox forte (Cu-salts and Mancozeb) 47 WP were evaluated for their efficacy against leaf blotch (Alternaria porri) of onion (Allium cepa). For preliminary evaluation, bioassay of the chemicals was performed against the fungus following paper disc method. The concentrations of Rovral and Bordeaux mixture were 250, 500, and 1000 ppm with an additional concentration of 10,000 ppm for Bordeaux mixture. The other 4 fungicides were used at 250, 500, 1000 and 2000 ppm. All the concentrations of Rovral and Dithane M-45 gave significant reduction in the growth of the fungus. Significantly wider inhibition zones were recorded at 250 to 5000 ppm of Trimiltox forte and at 1000 ppm or higher concentrations of the other 3 fungicides. All of the fungicides were evaluated against leaf blotch of onion under natural field conditions using only their highest concentration. Altogether 4 sprays were applied with 10 days interval, beginning from first appearance of the disease. All of the fungicides gave significant reduction in disease severity but increase of onion yield was achieved with only Rovral, Dithane M-45 and Bordeaux mixture. Maximum reduction in disease severity was achieved with Rovral, Dithane M-45 and they caused 61, 36 and 29% yield increase respectively.
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