ABSTRACT: The research work entitled “Studies on preventive measures to reduce the postharvest losses in onion (Allium cepa L.)” was carried out at NIFTEM, Sonepat, Haryana, India during Rabi seasons of 2014-15 and 2015-16. The research work was carried out with objectives of studying the effect of application of organic formulations (applied as pre-harvest foliar spray viz., Neem based formulation (Besara) at the rate of 20ml/L; Panchgavya at the rate of 100ml/L; Trichoderma viride (Bio Shield) at the rate of 50g/L) on growth period of selected onion varieties (Pusa Madhavi, Pusa Riddhi, Pusa Red, NHRDF Red and Agri found Light Red) grown during Rabi season in Haryana region. The formulations were applied as four pre-harvest foliar sprays starting from 30 days after transplanting and repeated at an interval of 15 days. The main aim of this experiment was to isolate and identify the pathogenic fungi causing spoilage of stored onion bulbs under cold and ambient conditions. Additionally, the efficacy of organic formulations against the isolated pathogenic fungi was studied under both the onion storage conditions. Fungal isolates responsible for disease and rotting as identified under cold storage condition were Penicillum purpurogenum, Penicillum griseofalvum, Penicillum citrinum and as Aspergillus niger under ambient storge contion. Under invitro condition, Neem based formulation (Besaara) was most effective for inhibition of fungal growth. The efficacy of organic formulations in restricting the fungal growth was higher with higher concentration (i.e. at 20%).