The potential use of plant extracts for controlling northern leaf blight on organic sweet corn production

Northern leaf blight caused by Helminthosporiumturcicum is the most frequently occurring foliar diseases in sweet corn plants grown under humid environments. Finding an effective control measure for controlling the disease can be a challenging issue for organic growers. The present study was undertaken to investigate the potential use of plant products as the botanical fungicides for controlling northern leaf blight in sweet corn. The aqueous solutions of extracts mixture and its individual constituent extracts made from neem leaf, betel leaf, clove leaf, lemon grass leaf, and galangal rhizome were tested in petri dishes assay for their antifungal activity against H. turcicum. Lemongrass+galangal rhizome exhibited the most effective solution in suppressing the growth of H. turcicum (55%), as followed by galangal rhizome (50%), lemongrass+clove leaf (50%), betel leaf+galangal rhizome (50%), and cloveleaf+neem leaf(47.5%). Accordingly, these 5 solutions were selected and tested for their efficacy in controlling northern leaf blight on sweet corn plants under field condition. Lemongrass+galangal rhizome, galangal rhizome, lemongrass+clove leaf, betel leaf+galangal rhizome, and cloveleaf+neem leaf had similar effectiveness in reducing disease intensity ranged from 55% to 66% and leaf disease severity ranged from 44% to 52% as compared to the control. Betel leaf+galangal rhizome was relatively effective in reducing disease intensity (43.4%) but less effective in reducing leaf disease severity (24%). Application of the selected solution had reduced the ear length but improved the ear weight excluding betel leaf + galangal rhizome.