A field experiment was conducted to determine the most appropriate cotton growth stage or stages to apply Roundup Ultra^® (RU^®) herbicide to maximize control of silverleaf nightshade in Roundup Ready cotton. Treatments (TR) included were : (1) TR1 - control, 2 cultivations, (2) TR2 - application of (RU^®) over the top at 4-leaf stage, (3) TR3 - TR2 followed by RU^® post directed, 21 days later, (4) TR4 - 2 cultivations plus RU^® semi-directed at 20% open bolls, (5) TR5 - TR2 plus TR4, and (6) TR6 - TR3 plus TR4. Treatments were arranged in six completely randomized blocks. Approximately 30%, 59%, 63%, and 89% weed control was achieved with TR2, TR3, TR5, and TR6, respectively, when compared to the control. During the eleven weeks growth period between 3 weeks after planting (1 day before TR2 application) and 14 weeks after planting (1 day before TR4 application) silverleaf nightshade numbers tripled in both the control (from 831 to 2413 stems/ac) and in TR4 plots (from 1616 to 4878 stems/ac). Sixteen weeks after planting the surviving silverleaf nightshade stem numbers were 8 times and 10 times higher in the control (2304 stems/ac) and in TR4 (2539 stems/ac), respectively than in TR6 (264 stems/ac). Plant height was highest with TR3. Total bolls were greatest in TR3 and lowest in TR1 but, gin turnout was highest in the control. Lint yield was greater in treatment TR3 or TR6 than in the control (393 or 385 vs 360 lbs/ac). Weed competition (on a biomass basis) was lower with TR2, TR3, TR5, and TR6 when compared to TR4. Lint yield reflected weed competition. This one year study shows that not controlling silverleaf nightshade early in the growing season may result in reduced lint yield.