Onion (Allium cepa var. aggregatum L.) once considered as the poor man's staple spice, is flying out of the reach of even middle class families.. Onion is affected by various plant pathogens of which leaf blight was reported to be one of the major diseases in India and it causes severe yield loss. It is caused by Alternaria alternata and it destructs the leaf tissue which destroys the stimulus for bulb initiation and delay for bulbing and maturation. Modern agriculture is highly dependent on chemical pesticides. However, the repeated use of such chemicals may result in the environmental pollution and may lead to development of resistance in the target organisms. Environmental considerations have highlighted the requirement for sustainable solutions in agriculture and consumer pressures for green alternatives have accompanied a boom in the organic farming sector. This has awakened new interest in natural products as a source for novel industrial plant protection strategies. This book is written as a text book primarily for research workers and its covers the plant oils, extracts and oil cake used for the management of onion leaf blight disease.