ANNUAL BLUEGRASS CONTROL WITH METHIOZOLIN ON GOLF PUTTING GREENS IN THE UNITED STATES AND KOREA. B. McNulty*, S. Koo, and S. Askew, Virginia Tech, Blacksburg, VA (87)

Methiozolin (MRC-01) is a potential new turf herbicide currently being developed by Moghu Research Center in South Korea. It is being investigated for its selective control of annual bluegrass (Poa annua) in creeping bentgrass (Agrostis stolonifera) golf course putting greens as well as fairways and tees of cool- and warm-season turf. Methiozolin is in the isoxazoline class of chemistry, yet its mode of action (MOA) is not fully understood. Its MOA is believed to be related to cell wall biosynthesis inhibition, but more work is needed for confirmation. Methiozolin has substantial postemergence activity on annual bluegrass and roughstalk bluegrass (Poa trivialis) and suppresses seedheads of annul bluegrass when applied at the flowering stage. Methiozolin also has residual and preemergence activity, but the soil half-life is about 2 weeks. Methiozolin is reported to control other grasses including crabgrass (Digitaria sp.) and goosegrass (Eleucine indica). Turfgrass species that are tolerant to methiozolin include creeping bentgrass, perennial ryegrass (Lolium perenne), Kentucky bluegrass (Poa pratensis), tall fescue (Festuca arundinacea), bermudagrass (Cynodon dactylon) and zoysiagrass (Zoysia japonica). Methiozolin received labeling and registration in South Korea in April of 2010. Methiozolin has been used successfully on over 100 of the approximately 350 golf courses in the first year of its release in Korea, and registration is currently sought in the United States and Japan. Research on methiozolin began in the US in 2008, with putting green experiments conducted at Auburn University and Virginia Tech (VT). At VT, a variety of studies have been conducted through 2010 including tolerance, efficacy, programs, and rate response trials. At two university research putting greens, methiozolin did not injure A4, L-93, and Declaration creeping bentgrass when applied at rates of 500 to 4000 g/ha. At Hanover Country Club near Richmond, VA, methiozolin at 2000, 3000, and 4000 g/ha injured L-93 creeping bentgrass 25 to 40% and significantly decreased normalized difference vegetative index at 39 DAT but not at later rating dates. During this period, the Richmond Virginia area experienced the hottest June on record and extended drought. In an adjacent study, methiozolin at 500 and 750 g/ha did not injure creeping bentgrass while cumyluron at 1720 and 2300 g/ha injured bentgrass 43 and 79% on August 3, 2010. At Spotswood Country Club near Harrisonburg, VA, methiozolin at 500 and 750 g/ha applied once in spring and once in fall during the 2009 and 2010 seasons decreased annual bluegrass populations 20 and 40% and more than cumyluron, bensulide, and oxadiazon. Single treatments of 1500 to 3000 g/ha at this golf course in fall reduced annual bluegrass populations over 70% in whole putting green demonstrations treated by the superintendent. Trials conducted to date suggest two to three treatments of 1000 g/ha at 1 month intervals provide the best annual bluegrass population reduction while maintaining creeping bentgrass safety. Additional work is underway to confirm this assumption.