Two field trials and one laboratory experiment were carried out during 1996 and 1997 maize growing seasons at El-Gemmeiza Research station, Gharbia governorate. The objective was to investigate the performance of some selective herbicides i.e. Gesaprim 80%, Lasso/atrazine, Starine and Basagran 50% compared with hand hoeing 3 times and Unweeded check, as well as, their effect on maize downy mildew infection caused by Peronosclerospora sorghi (Weston and Uppal) C.G. shaw. Laboratory results showed that, Starine was the most inhibiting of used herbicides to both root and shoot systems of maize seedlings until at the lower concentrations. Basagran had phytotoxic effect to both root and shoot at recommended dose. Lasso/atrazine and Gesaprim had no remarkable phytotoxic effects on the shoot system, while its effects on root system were moderate in their phytotoxicity at the lower concentrations. Field data revealed that, the percentages of downy mildew infection were varied with the different treatments under this study. All selected herbicides and hand hoeing showed clear effect on downy mildew incidence when compared with unweeded check. Hand hoeing was the best of all treatments in reducing downy mildew infection percentage followed by Lasso/atrazine, Gesaprim, Basagran and starine, Respectively, Results also indicated that, the post emergence herbicide Starine at 200cm3/Fed and hand hoeing gave the highest percent reduction in fresh weight of broad leafed weed species that surveyed in 1996 season. In contrast, pre-emergence herbicides lasso/atrazine and Gesaprim were effective on broad-leafed and grassy weeds in 1997 season.