Control of onion neck rot caused by Botrytis allii and a decrease in black mould caused by Aspergillus niger were obtained on onion (cv Giza 20) with promot. Promot strongly inhibited radial growth of patho‌gens on potato dextrose agar when it was conditioned at 20°C for 12 hr or at 30°C for 4 hr. Moreover, area of inhibition increased when promot was conditioned at 20°C or 30°C for 12 hr. On dry onion, however, promot was ineffective on dry onion fleshy fresh scales after dipping in promot (conditioned at 22 ± 2°C for 4, 12 or 24 hr). It promoted the growth of the inoculated discs, of B.allii or A.niger, on the concave surface of scales giving high infection rate with expanded rotted area. The level of control of neck rot through post harvest simulation was determined at room temperature for the bulbs resulting from dip treatment of onion seedlings in promot suspension before planting fol‌lowed by three spray applications at 15 day intervals four months after planting. Infections were significantly reduced to 27% and 23%. The dip treatment in Benlate solution (half dose 0.5 g./L) followed by the same spray application of promot was not satisfactory. Similar results were obtained in the control of black mould rot, where the percentage of infection of the same dip and spray treatments with promot was approximately 50% of the control treatment, Mean‌while, spray treatments with both of Ridomil plus (half dose 75 g./L) and promot was comparable. On the other hand, the treatment of Rido‌mil using recommended dose (1 50 g./L) was much less effective. According to the obtained results Trichoderma product (promot) as dip or spray could protect onion plants against B.allii and A.niger and could result in enhanced plant growth and better bulb development, thus help in escaping infection.