Greenhouse studies were conducted to examine the effect of non-ionic ‘Induce’ and the organosilicone ‘Silwet L-77’ adjuvants on the rainfastness of glyphosate applied to a broadleaf weed-wild mustard. Glyphosate was tank mixed with and without adjuvant at three different concentrations. No rainfall and six simulated rainfall treatments at 30 min, 1, 2, 4, 6 and 24 h after glyphosate treatment were applied to the treated plants. With the addition of either adjuvant, absorption of 14C glyphosate was enhanced, which presumably led to increased rainfastness as indicated by good control of wild mustard plants even when simulated rainfall occurred 30 min after application. Addition of both adjuvants also improved translocation of 14C glyphosate. Simulated rainfall immediately after glyphosate application washed off chemical from the foliage, leaving not enough chemical to have phytotoxic effects. Simulated rainfall that occurred 30 min after application did not affect the efficacy of glyphosate as a significant amount of 14C glyphosate had already been absorbed. Use of the organosilicone adjuvant achieved higher per cent control of weeds than the nonionic adjuvant, presumably through increased rainfastness of glyphosate. Addition of non-ionic adjuvant ‘Induce’ at 0.25% in and organosilicone ‘Silwet L-77’ at 0.1% was better in achieving effective control of wild mustard than other rates of adjuvants with glyphosate under different simulated rainfalls. Thus, addition of an adjuvant helped in absorption and translocation of 14C glyphosate as quickly as 30 min after treatment.