Characterizing Oxadiazon Resistance and Improving Postemergence Control Programs for Goosegrass (Eleusine indica) in Bermudagrass (Cynodon spp.)
Cox, Michael Christopher
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Goosegrass is a problematic weed of golf courses, sports fields, and residential lawns that decreases playability and aesthetic quality of turf. With the recent banning of MSMA in sports fields and intensive restrictions in golf and sod production, turfgrass managers are seeking alternatives for postemergence goosegrass control and how to utilize currently labeled goosegrass control products more effectively. Studies were conducted to investigate a suspected-resistant (SR) goosegrass accession in Richmond, VA and characterize the resistance mechanism if present. The SR accession showed a hypersensitive response to oxadiazon treatment and reached maximum electrolyte leakage quicker than the susceptible (S) accession, but had significantly lower electrolyte leakage indicating less tissue damage and suggesting there is a physiological resistance mechanism within the SR accession. In absorption and translocation studies, percent oxadiazon absorption and translocation was not significantly affected by goosegrass biotype. Roots of both the S and resistant (R) biotypes contained over 95% of total detected oxadiazon, while the plant tissue above the treated foliage only contained small quantities. These results suggest that absorption or translocation is not the mechanism conferring oxadiazon resistance in the goosegrass biotype from Richmond, VA. Greenhouse and field trials were conducted to determine the lowest rate at which topramezone, with or without the addition of triclopyr, controls goosegrass while maintaining commercially-acceptable bermudagrass quality. In field trials, topramezone rate did not significantly affect goosegrass cover at 56 and 70 days after initial treatment (DAIT). All treatments reduced goosegrass cover below 3 and 7% with and without the addition of triclopyr, respectively at 70 DAIT. A significant herbicide effect on bermudagrass cultivar showed higher injury from topramezone within three weeks of application, but injury persisted longer from treatments containing triclopyr. Bermudagrass cultivars completely recovered by 4 weeks after treatment (WAT) from all treatments. Greenhouse trials were conducted to determine if goosegrass growth stage affects efficacy of nine postemergent herbicides or programs documented to have goosegrass activity. As goosegrass growth stage increased from four- to five-leaf to greater than eight-tiller stage, goosegrass control and biomass reduction decreased among all of the herbicides except topramezone and MSMA plus metribuzin at 4 and 8 WAT. These data suggest that one application of sulfentrazone is only effective for seedling stage (pre-tiller) goosegrass control; foramsulfuron, topramezone, and metribuzin suppress all growth stages of goosegrass; and diclofop, sulfentrazone plus metribuzin, fenoxaprop, and metamifop control up to three-tiller stage goosegrass.
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