In the southeastern United States, cogongrass (Imperata cylindrical (L.) Beauv.) is an aggressive non-native herbaceous species that has hampered reforestation efforts throughout the region by forming dense monotypic stands that inhibit species diversity and reduce forest productivity. Herbicides play an important role in cogongrass management and imazapyr is an effective active ingredient often used for cogongrass control. The objective of this study was to evaluate the effects of four levels of two imazapyr herbicides, Chopper and second generation Arsenal, on cogongrass cover on a reclaimed phosphate-mine site in central Florida, USA. We hypothesized that we would see increased control of cogongrass with increased herbicide rates and that second generation Arsenal would be more effective at reducing cogongrass cover compared to Chopper. We tested the effectiveness of nine treatments, four rates of two herbicides, Chopper (imazapyr) and second generation Arsenal (imazapyr), plus a control (no treatment), on cogongrass control over a twenty-seven month period.

Results/Conclusions

All herbicide treatments showed a > 99% reduction in cogongrass cover and were significantly lower than the control 12 months after treatment (MAT) (P < 0.05). In addition, planned contrast of Chopper and second generation Arsenal herbicide treatments revealed greater cogongrass control using second generation Arsenal 15 and 27 MAT (P < 0.003). Our results indicate that while all of the rates tested for both herbicides provided cogongrass control 12 MAT, use of second generation Arsenal may be required to ensure cogongrass control for an additional length of time.