Damping off Disease of Onion & their control

Damping off: Caused mainly by Fusarium oxysporum fungus, this is very common in almost all onion-growing pockets. Pythium sp. has also been reported to cause damping off disease in some pockets. The disease is more prevalent in Northern and Eastern parts of the country during kharif season, causing 60-75% damage. Two types of symptoms are observed.

Pre-emergence damping off : The fungus kills the radicle and plumule of seed before emergence from soil.

Post-emergence damping off : The pathogen attacks the collar region of seedlings on the surface of soil. The collar portion rots and ultimately the seedlings collapse and die.

Control: For managing the disease, healthy seeds should be selected for sowing. The seed should be treated with thiram @ 2g/kg before sowing. Continuous raising of nursery in a particular plot should be avoided. Top soil of nursery should be treated with thiram @ 5 g/m² area and nursery should be drenched with the same chemical @ 2 g/litre of water at fortnightly interval. Soil solarization using 250-gauge polythene for 10 days before sowing and application of Trichoderma viride in soil @ 1,250 g/ha is also effective to control damping off to a considerable extent.