Effect of oil cakes and lemongrass essential oil on purple blotch (Alternaria porri) disease of onion (Allium cepa L.)

Onion (Allium cepa L.) which is also called as “bulb onion”, “Queen of kitchen” or “Princess of vegetables”, is one of the important cultivated crops belonging to the genus Allium and family Amaryllidaceae. Purple blotch of onion which is caused by Alternaria porri is major disease in the onion. The neem cake (S.A.) + lemongrass essential oil (Cymbopogon citratus) (F.S.), mustard cake (S.A.), castor cake (S.A.), coconut cake (S.A.), groundnut cake (S.A.), sesame cake (S.A.), were tested under field conditions during Rabi 2022 - 2023 for their efficacy against the disease. Study on disease severity of onion in field conditions revealed that the minimum disease intensity (18.51) was obtained in mancozeb treated plants followed by neem cake + lemongrass essential oil (26.55%), mustard cake + lemongrass essential oil (30.25%) and groundnut cake + lemongrass essential oil (38.66%) and the highest was recorded in control (untreated check) (54.70%). Among the treatments the plant height (cm) significantly increased in mancozeb treated plant (49.07 cm) followed by neem cake + lemongrass essential oil (48.14 cm), mustard cake + lemongrass essential oil (47.09 cm) and groundnut cake + lemongrass essential oil (45.50 cm) and the minimum height was recorded in treatment control (untreated check) (38.73 cm). The number of leaves plant^-1 significantly highest in mancozeb treated plant (10.09) followed by T₁ neem cake + lemongrass essential oil (8.85), mustard cake + lemongrass essential oil (8.30) and groundnut cake + lemongrass essential oil (7.88) and the minimum leaves plant^-1 was recorded in treatment control (untreated check) (5.09).