Experiments were conducted to examine the influence of adjuvant, growth stage, air temperature, and soil moisture on nicosulfuron activity, absorption, and distribution in quackgrass. Foliar absorption of 14C-nicosulfuron by quackgrass was greater in one-leaf than five-leaf plants. Total translocation of 14C-nicosulfuron was similar regardless of growth stage. However, nicosulfuron was more phytotoxic to three- and five-leaf than one-leaf quackgrass. Of the absorbed 14C, at least 71 % remained as 14C-nicosulfuron 168 h after application in three-leaf plants. 14C-Nicosulfuron absorption, translocation, and accumulation increased with increasing temperatures and was independent of soil moisture. Under adequate soil moisture conditions (-0.03 MPa), nicosulfuron activity was not influenced by temperature. Nicosulfuron efficacy was not influenced by soil moisture at a cool (11/6 C) temperature. As plant moisture stress increased, due to low soil moisture and increasing air temperature, nicosulfuron efficacy declined. Differences in nicosulfuron efficacy due to growth stage or environmental conditions could not be explained by differential 14C recovery, absorption, translocation, or accumulation. The addition of 28% urea-ammonium nitrate liquid fertilizer (UAN) to 14C-nico-sulfuron plus petroleum oil adjuvant (POA) provided greater 14C absorption than POA alone. Translocation of 14C with POA alone 168 h after treatment (HAT) was similar to POA plus UAN 24 HAT. However, 168 HAT there was no difference in the total amount of radiolabelled material translocated among the adjuvants.