Methiozolin (PoaCure) a new herbicide developed by the Moghu Research Center in Daejeon, Korea for safe and selective removal of annual bluegrass (Poa annua) from creeping bentgrass (Agrostis stolonifera) turf.  Methiozolin is a member of the isoxazoline class of chemistry and works by either inhibiting cell wall biosynthesis or through inhibition of the enzyme tyrosine aminotransferase.  Ethephon (Proxy) is a plant growth regulator which is used on putting greens to temporarily suppress annual bluegrass seedheads.  Applications of ethephon improve the aesthetic quality and playability of putting greens during peak seedhead production on putting greens.  Previous research conducted on two Virginia golf courses in 2011 indicated ethephon may negatively impact methiozolin efficacy for annual bluegrass control and creeping bentgrass response.  The objective of this study was to determine whether or not the addition of ethephon to methiozolin programs would influence annual bluegrass control and creeping bentgrass safety.  This trial was initiated on March 13, 2012 at the Blacksburg Country Club in Blacksburg, Virginia on a mixed variety creeping bentgrass putting green.  Sequential applications were made on March 13 and April 16.  Methiozolin was applied alone at 500, 1000 and 2000 g ai/ha, and 500, 1000 and 2000 g ai/ha + 3818 g ai/ha ethephon.  A comparison treatment of 1000 g ai/ha methiozolin + 3818 g ai/ha ethephon+ 48 g ai/ha trinexapac-ethyl as well as an untreated check were also included.

Initial annual bluegrass cover ranged from 43 to 57%.  At the time of the first application, 82% of the annual bluegrass plants were producing seedheads.    At two weeks after the initial treatment (WAIT), methiozolin at 1000 and 2000 g ai/ha controlled annual bluegrass 22 and 53%, respectively, and all other treatments controlled annual bluegrass less than 15%.  At 4 WAIT, methiozolin at 2000 g ai/ha controlled annual bluegrass 73% when applied alone and 53% when applied in a mixture with ethephon.  At 6 WAIT, all treatments except methiozolin at 500 g ai/ha controlled annual bluegrass over 87%. At 8 WAIT, methiozolin alone did not significantly injure bentgrass regardless of rate while combinations of ethephon with 1000 or 2000 g ai/ha methiozolin injured creeping bentgrass 23 and 80%, respectively.  In addition, normalized difference vegetative index was significantly decreased when ethephon was added to any rate of methiozolin.   By mid- October (28 WAIT), methiozolin with or without ethephon or trinexapac ethyl at 1000 and 2000 g ai/ha controlled annual bluegrass 85% or higher.  Methiozolin at 500 g ai/ha with and without ethephon controlled annual bluegrass 43 and 40%, respectively.  All bentgrass injury had recovered and voided areas of turf caused by removal of annual bluegrass had recovered.  Visually estimated bentgrass texture, however, was significantly lower in plots previously injured by ethephon + methiozolin.  These data suggest ethephon should not be mixed with methiozolin to avoid increased creeping bentgrass injury and delayed recovery of areas voided by controlled annual bluegrass.