Substantial yield losses have been reported during the storage of Allium cepa L., and effective methods to minimize postharvest losses are currently lacking. Therefore the objectives of this study were to investigate the impact of pre-treatment with Trichoderma asperellum and Trichoderma virens on post-harvest losses during storage and to evaluate factors associated with these losses. The storage behaviors of Allium cepa L. bulbs after different field treatments with Trichoderma spp. were examined using a complete randomized design. The common onion bulb diseases encountered during storage were basal rot and black mould diseases, with Fusarium sp., Mucor sp., Penicillium sp., Aspergillus niger and Aspergillus flavus being associated with diseased bulbs. The results regarding the percentage of diseased bulbs showed that pre-harvest treatments with Trichoderma asperellum and Trichoderma virens did not have a significant effect on disease control during storage. Furthermore, storage losses of onions were attributed to sprouting, rooting and wilting, which were exacerbated by the prevailing temperature (~30-32°C) and relative humidity (~77%-79%) during the storage period.