The effects of some microorganisms, e.g. Trichoderma harzianum (T1), T. viride, (T2) mixture of T1+T2, Bacillus subtilis and commercial biocide product namely Blight Stop were studied on the incidence and disease severity of downy mildew of squash caused by Pseudoperonospora cubensis under field conditions during two successive growing seasons (2013 and 2014). All the biocontrol agents tested caused significant reduction in both disease incidence and disease severity of downy mildew on the five tested squash cultivars. The lowest percentage of disease incidence was recorded on Blonky 180 cv. during the two successive growing seasons. Among the tested bioagents, B. subtilis treatment caused significant reduction in both disease severity and disease incidence during 2013. However, the commercial product Blight Stop was the best in this respect during season 2014. All bioagent treatments caused significant increases in some growth parameters, i.e. fruit number/plant, plant height and yield of fruits.