Bulb rot diseases such as black mould, basal rot, neck rot and bacterial soft rot attack onion bulbs during storage and causing losses in onion bulb weight. Black mould and bacterial soft rot recorded the highest considerable disease incidence during three and six months of storage at 2014/2015 and 2015/2016 seasons, followed by basal rot, while neck rot recorded the least incidence in this respect. Most of foliar spraying with fungicides as pre-harvest treatment plus biocides as post-harvest treatment significantly decreased these bulb rots. The most effective combinations in reducing incidence of bulb rots were Bio Nagi plus King star, Acrobat Mancozeb, Ridomil gold plus, or Antracol and Bio Arc combined with Acrobat Mancozeb or Antracol, respectively. Reductions (%) in onion bulbs weight during storage periods, resulted from rots infections, were significantly minimized using most of the combination treatments (pre- plus postharvest) ested.