This research was aimed at understanding how far and how fastglyphosate-resistant (GR) Palmer amaranth will spread in cotton and theconsequences associated with allowing a single plant to escape control.Specifically, research was conducted to determine the collective impact ofseed dispersal agents on the in-field expansion of GR Palmer amaranth, andany resulting yield reductions in an enhanced GR cotton system whereglyphosate was solely used for weed control. Introduction of 20,000 GRPalmer amaranth seed into a 1-m2 circle in February 2008 was usedto represent survival through maturity of a single GR female Palmer amaranthescape from the 2007 growing season. The experiment was conducted in fourdifferent cotton fields (0.53 to 0.77 ha in size) with no history of Palmeramaranth infestation. In the subsequent year, Palmer amaranth was located asfar as 114 m downslope, creating a separate patch. It is believed thatrainwater dispersed the seeds from the original area of introduction. Inless than 2 yr after introduction, GR Palmer amaranth expanded to theboundaries of all fields, infesting over 20% of the total field area.Spatial regression estimates indicated that no yield penalty was associatedwith Palmer amaranth density the first year after introduction, which is notsurprising since only 0.56% of the field area was infested with GR Palmeramaranth in 2008. Lint yield reductions as high as 17 kg ha−1were observed 2 yr after the introduction (in 2009). Three years after theintroduction (2010), Palmer amaranth infested 95 to 100% of the area in allfields, resulting in complete crop loss since it was impossible to harvestthe crop. These results indicate that resistance management options such asa “zero-tolerance threshold” should be used in managing or mitigating thespread of GR Palmer amaranth. This research demonstrates the need forproactive resistance management.