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Purple threeawn is a grass species which is considered as undesirable to cattle production due to its low palatability and poor forage quality. This grass has been causing problems mainly in western grasslands in US, affecting negatively cattle production. There have been several attempts to control it using chemicals and fire but there is no information about the seasonal effect of fire on threeawn survival coupled to drought conditions. The objective of this study was to evaluate the long-term effects of a single fire treatment application during different phenological stages on purple threeawn (Aristida purpurea) survival rates in the Southern Great Plains. This research was conducted in the Texas Tech University, Native Rangeland, Lubbock, TX. Eighty plants were randomly selected regardless plant size at each phenological stage. Forty plants were burned individually using portable propane burner, which was calibrated using a combination of pressure (PSI) and time (sec) to simulate the temperatures present during a wildfire in a shortgrass prairie. Forty more plants were used as a control. Plants were identified individually with color flags and numbered tags. Mortality vas evaluated at the beginning of the 2011 growing season and 2 growing seasons later during the fall of 2012. Statistical analyses to detect possibly differences among treatments were performed using GLMMIX and CATMOD procedures in SAS. During the first mortality evaluation, on April of 2011, plant mortality was significant higher (P<0.05) on all burned treatments than on control plants, being the fire application during reproductive stage the treatment that promoted the greater mortality rates (25%). On the other hand, the second evaluation reveled that mortality rates on all treatments continued increasing, being the greater increase on those plants burned on post-reproductive stage (62.5%). The increase in mortality even on control plant suggests and adverse effect on plants survival of the severe drought conditions presented during 2011 and 2012 growing season. The results of this study can be considered by rage managers in order to design strategies to control purple threeawn on invaded rangelands on the South Great Plains of US.