Metribuzin-Resistant Goosegrass (Eleusine indica) in Bermudagrass Turf

Applications of metribuzin plus MSMA have been used to control goosegrass in bermudagrass turf for over 20 yr. In 2003, two goosegrass biotypes on the island of Kauai, Hawaii were found to be resistant to applications of metribuzin plus MSMA. Metribuzin plus MSMA applied at rates of 0.28 kg ai/ha plus 2.2 kg/ha, respectively, followed by MSMA at 2.2 kg/ha 7 d later, provided 100% control of two susceptible goosegrass biotypes, but no control of two resistant biotypes. At the flowering growth stage, metribuzin applied at a rate of 0.28 kg/ha controlled both susceptible biotypes (> 92%), but did not control the two resistant biotypes. Two applications of MSMA applied at a rate of 2.2 kg/ha (7 d apart) did not control any of the four biotypes at the flowering growth stage. The two resistant biotypes were approximately 100 to 200 times less sensitive to increasing rates of metribuzin than the two susceptible biotypes. The two biotypes that were resistant to metribuzin plus MSMA were also resistant to applications of simazine plus MSMA. However, all four biotypes were susceptible to applications of glyphosate and foramsulfuron.