Twospotted spider mites, Tetranychus urticae, are an important agricultural pest of many field crops worldwide. Insecticides and acaricides play a primary role in controlling T. urticae populations on agricultural crops. Here, we used greenhouse and field applied foliar spray tests and leaf dip bioassays to examine the susceptibility of T. urticae to glufosinate ammonium in cotton. Leaf dip bioassay results indicated that T. urticae is highly susceptible to concentrations of formulated glufosinate ammonium. The LC50 value was determined to be 10.31 ppm. Field-applied glufosinate ammonium at 1.61 and 3.14 L ha−1 provided 48.9 and 80.2% control, while fenpyroximate provided 89.6% control five days after treatment in 2015. Greenhouse applications resulted in 55.4% control 14 days after treatment with 0.73 L ha−1, while 1.61 L ha−1 resulted in 72.9% control and 3.14 L ha−1 resulted in 91.9% control of T. urticae populations. Treatment with glufosinate ammonium resulted in significant phytotoxic effects to drought-stressed cotton in the 2015 field trial. These results suggest that glufosinate ammonium may be a useful tool for integrated pest management of weeds and spider mites in cotton. Due to the high cost associated with glufosinate ammonium and possibility of phytotoxic effects under certain conditions, this herbicide it is not considered a viable treatment targeting spider mites but may prove useful for managing mites when utilized for weed management.