Multi-Year Autumn Applied Methiozolin for Poa Annua Control On Golf Greens.

Creeping bentgrass (Agrostis stolonifera L.) golf greens infested with annual bluegrass (Poa annua L.) can be hard to manage, unattractive, and have reduced playability.  Methiozolin is a relatively new isoxazoline herbicide that has shown selective Poa annua control in golf greens.  Our objective was to evaluate multi-year, single autumn applications of methiozolin to control low populations of Poa annua in bentgrass greens.  Research was conducted on ‘T-1’ creeping bentgrass, sand-based greens (< 5% Poa annua) at the Palouse Ridge Golf Club in Pullman, WA.  A single application of methiozolin was applied at 750 or 1500 g a.i./ha in late September, mid October, or early November 2010 (3 wk intervals following initial application) and reapplied to the same plots in 2011.  The study was repeated on a separate green in 2011-2013.  Experimental design was a randomized complete block with three replications.  Initial plant counts/929 sq. cm (two random counts per plot) were made in September at initial application and subsequently monthly during the following summer.  In the non-treated control, Poa annua increased by 80% in the 2010-2012 study and 120% in the 2011-2013 study.  In general, Poa annua control increased with methiozolin rate and late applications in the autumn.  There was no phytotoxicity observed at any time during either study.  All treatments (except for the late September methiozolin application at 750 g a.i./ha during 2010-2012; reason unknown) reduced Poa annua compared to the non-treated control.  Single applications of 1500 g a.i./ha in early November of 2010 and 2011 completely eliminated Poa annua by summer 2012.  In the repeat study, a single application of 1500 g a.i./ha on 2 Nov. 2011 reduced the Poa annua population by 75% (0.5 plants/929 sq. cm) the first year (2012); summer 2013 data will also be presented.  Multi-year (2 yr), single autumn applications of methiozolin provided excellent control of Poa annua in bentgrass greens having an initial low Poa annua population.  Methiozolin should be considered as a management tool to mitigate the invasion of Poa annua into newly established bentgrass golf greens.