Various Timings and Rates of Fluazifop Tank-mixed with Triclopyr for Bermudagrass Control in Zoysiagrass Turf.

Eliminating bermudagrass (Cynodon dactylon) contamination from zoysiagrass (Zoysia spp.) turf is an arduous task.  Few selective herbicides are available to provide bermudagrass suppression without injuring the desired zoysiagrass.  Previous research demonstrates that aryloxyphenoxypropionate (AOPP) herbicides suppress bermudagrass but cause phytotoxicity to zoysiagrass.  Additional research indicates that the AOPP herbicide fluazifop tank-mixed with triclopyr increased bermudagrass suppression and decreased zoysiagrass injury.  Research was conducted to determine the best timing and rate of fluazifop tank-mixed with triclopyr for bermudagrass control in zoysiagrass turf.  Treatments included fluazifop applied at 0.11, 0.16, 0.21, and 0.26 kg ai/ha alone or tank-mixed with triclopyr (1.12 kg ai/ha) at two or four week intervals.  Sequential applications were made every 7 or 14 days, depending on treatment, for a total of four applications of each treatment.  At two week intervals, all rates of fluazifop alone provided bermudagrass suppression (≥88%) but caused excessive zoysiagrass cover reduction (≥56%).  When tank-mixed with triclopyr, all rates of fluazifop provided excellent bermudagrass suppression (≥95%) and provided a safening effect on zoysiagrass, but cover reduction was unacceptable (≥28%).  At four week intervals, fluazifop alone applied at 0.11 kg/ha provided bermudagrass suppression (56%) with minimal zoysiagrass cover reduction (6%).  Higher rates of fluazifop alone increased bermudagrass control (≥73%), but caused unacceptable zoysiagrass cover reduction (≥15%).  When tank-mixed with triclopyr, all rates of fluazifop suppressed bermudagrass (≥60%) and safened application to zoysiagrass (≤12% cover reduction).  These data indicate that triclopyr safens fluazifop on zoysiagrass when applied at two and four week intervals while providing effective bermudagrass suppression.  Due to unacceptable zoysiagrass cover reduction at two week intervals, four week intervals of fluazifop tank-mixed with triclopyr are the safest strategy for controlling bermudagrass in zoysiagrass turf.