Fall Applications of Methiozolin for the Control of Annual Bluegrass In Sand-Based and Push-up Greens.

Methiozolin is a new isoxazoline herbicide being investigated for selective postemergence annual bluegrass control in creeping bentgrass putting greens. Research was conducted from 2010 to 2012 in Tennessee and Texas to evaluate annual bluegrass control efficacy with two methiozolin application rates (500 and 1000 g ha^-1) and six application regimes [October, November, December, October followed by (fb) November, November fb December, October fb November fb December] on sand- and soil-based putting greens. A non-treated check was included for comparison. Treatments requiring sequential applications were applied on a four-week interval. Creeping bentgrass injury was visually evaluated on a 0 (i.e., no injury) to 100% (i.e., complete kill) scale at 7, 14, 21, 28 days after initial treatment (DAIT). Annual bluegrass control was assessed visually at 133 and 166 DAIT using a similar 0 (i.e., no control) to 100% (i.e., complete kill) scale relative to the non-treated check. Annual bluegrass plant counts were taken at the conclusion of each experiment to provide a quantitative assessment of annual bluegrass control.  A 1-m² grid with 100 intersection points was placed in the center of each plot. Minimal to no phytotoxicity was observed in response to methiozolin treatments throughout the length of the trial. Annual bluegrass control with methiozolin at 1000 g ha^-1 on sand-based greens ranged from 70 to 72% compared to 87 to 89% on soil-based greens 166 DAIT. Treatment at 500 g ha^-1 controlled annual bluegrass 57 to 64% on sand-based greens compared to 72 to 80% on soil-based greens 166 DAIT. Sequential methiozolin application regimes controlled annual bluegrass greater than single applications. On sand-based greens sequential application programs controlled annual bluegrass 70 to 79% compared to 85 to 92% on soil-based greens 166 DAIT.