|Abstract:||Palmer amaranth has been spreading from the southern United States into the Midwest, and the extent of damage this weed can inflict to Illinois row crops is not yet known. Palmer amaranth is known for rapid biomass accumulation and multiple emergence events, making this weed difficult to control. Field and greenhouse experiments were conducted in 2015 and 2016 to evaluate the biology and management of Palmer amaranth in Illinois. Chapter 1 includes a literature review of herbicides pertinent to these experiments and a section of Palmer amaranth biology. Chapter 2 characterizes the growth accumulation and emergence patterns of Palmer amaranth in Illinois to determine when and how long this weed will compete with field crops. Results indicate that Palmer amaranth can germinate for at least 10 weeks in Illinois. Due to the rapid biomass and height accumulation of Palmer amaranth, post emergence herbicides were evaluated in Chapter 3 to determine the herbicide efficacy at different Palmer amaranth heights. Results showed chlorimuron (13 g ai ha-1), imazethapyr (70 g ai ha-1), and mesotrione (105 g ai ha-1) did not achieve Palmer amaranth control ≥73%, regardless of application timing in all experiments. New technology has enabled extensive usage of synthetic auxin herbicides as an option for control in resistant-soybean varieties; therefore, Chapter 4 discusses dose response experiments of Palmer amaranth in Illinois to 2,4-D and dicamba. Results indicate that dicamba ratings did not exceed 86% of Palmer amaranth control under field conditions at the maximum labeled rate for dicamba-resistant soybean. Single or multiple applications of glufosinate, or glufosinate plus residual herbicides were compared in Chapter 5 to determine the overall control of biomass and emergence of Palmer amaranth in glufosinate-resistant soybean. Results indicate that Palmer amaranth biomass reduction is greatest when multiple applications of glufosinate are used, regardless of the addition of a residual herbicide. Preemergence herbicides were evaluated in Chapter 6 to determine the length of control and reduction in biomass of Palmer amaranth. Further research is needed for evaluation of length of residual control.