Chemical Options to Selectively Control Annual Bluegrass (Poa annua L.) On Kentucky Bluegrass (Poa pratensis L.)Turf.

Annual bluegrass (Poa annua L.) is difficult to manage in cool-season turf, such as Kentucky bluegrass (Poa pratensis L.).  The objective of this research was to evaluate post-emergence control options for annual bluegrass without compromising Kentucky bluegrass turf quality.  A preliminary study conducted at the University of Missouri in 2012 found that various herbicides, including methiozolin, mesotrione, bispyribac-sodium, and ethofumesate exhibited certain levels of selectivity on annual bluegrass over Kentucky bluegrass plants.  Phytotoxicity was observed, however, it was only from one treatment with bispyribac-sodium and at a tolerable level.  In 2013, a field study was established on plots with established Kentucky bluegrass in Columbia, Missouri.  The experiment was designed as a randomized complete block with four replications with each plot measuring 1.5 by 3.0 m.  Five plugs of annual bluegrass, which measured 10 cm in diameter, were transplanted and established into each plot 3 months prior to chemical applications.  Treatments included methiozolin at 0.5 and 1.0 kg ai ha^-1, mesotrione at175 g ai ha^-1, bispyribac-sodium at 111 g ai ha^-1 and ethofumesate at 341 g ai ha^-1, in addition to an untreated control.  Methiozolin was applied repeatedly on 14- or 28-day intervals with a total of 4 or 2 applications for rates at 0.5 or 1.0 kg ai ha^-1, respectively.  Mesotrione and bispyribac-sodium was re-applied every 14 days for a total of three applications, and ethofumesate was re-applied every 28 days and received two applications.  Data collected included turf quality, phytotoxicity, percent annual bluegrass cover, and normalized difference vegetation index (NDVI) on a weekly basis.  Data in 2013 is currently being analyzed and results will be presented.