Response of Cogongrass to Imazapyr Herbicides on a Reclaimed Phosphate-Mine Site in Central Florida, USA

Cogongrass {Imperata cylindrica) is a globally recognized invasive weed; it has caused land management problems and threatened critical habitat in the southeastern United States as well as on most continents. We tested four rates of imazapyr (1.17, 2.34, 3.51 and 4.68 L/ha), the most effective active ingredient available for cogongrass control, as two formulations (Chopper and the new generation Chopper known as Chopper GEN2) on cogongrass cover over a 27-month period in central Florida. One month after the |une treatment, Chopper GEN2 provided significantly greater cover reduction than the original Chopper formulation. Twelve months after treatment, cogongrass top regrowth cover was similar among all herbicide treatments, ranging from 1% to 3%. However, 15 months after treatment, cogongrass cover was significantly higher at the lowest rates of Chopper treatments than for the Chopper GEN2 treatments, and this trend continued throughout the experiment. Overall, Chopper GEN2 provided immediate control (one month after treatment) that continued to 27 months after treatment.