Bermudagrass Control in Alfalfa Using Clethodim (Prism) and Two Formulations of Sethoxydim (Past Plus, Ultima)

Two successive applications of Poast Plus (60 oz. product /A, 0.47 lb. sethoxydim /A), Ultima 160 (46 oz. product /A, 0.47 lb. sethoxydim /A), and Prism (34 oz. /A, 0.25 lb clethodim/A) were made on May 31 and June 27, 1996 to control bermudagrass (Cynodon dactylon) in a commercial alfalfa field. A crop oil concentrate was added to all herbicide solutions. Applications were made two days after the irrigations that followed removal of the cuttings. The bermudagrass density was high with extensive stolon development; the grass formed almost a complete mat in most of the plots. Percent control was visually estimated on June 27 (prior to second application) and on July 25, 28 days following the second application and after cutting of the alfalfa. Percent control was 84.5, 71.2, and 65% for Poast Plus, Ultima, and Prism, respectively, after one application. Percent control was 87.5, 72.5, and 90.5% for Poast Plus, Ultima, and Prism, respectively, after two applications. A single application of Poast Plus resulted in good bermudagrass control but single applications of Ultima or Prism resulted in marginal control. The second application of Prism significantly improved bermudagrass control but the second application of Poast Plus or Ultima did not improve control. The Poast Plus formulation of sethoxydim appeared to be superior to the Ultima 160 formulation of sethoxydim