A field trial was conducted at the Corozal Substation, to determine the effect of two time intervals (6 and 12 weeks) and four frequencies (once, twice, three and four times) of glyphosate application on weed control, phytotoxicity and yield of plantain (Musa acuminata x M. balbisiana AAB) throughout a planting cycle. The effectiveness of glyphosate at 1% increased with reduced time interval and increased frequency of application. Plantain injury was more pronounced with increased time interval and increased number of applications. The maximum yields in terms of number and weight of fruits were obtained with three applications at a 6-week interval from planting onward. The lowest number and weight of fruits were obtained in the non-weeded check. On the basis of weed control, phytotoxicity and yield data, optimum time interval and frequency of glyphosate application during a planting-to-harvest cycle was three applications of glyphosate at 1% every 6 weeks.