Methiozolin is a new cellulose biosynthesis inhibitor being evaluated for selective control of annual bluegrass (Poa annua L.) in creeping bentgrass (Agrostis stolonifera L). Research was initiated in 2010 evaluating the efficacy of single and sequential methiozolin programs for annual bluegrass control.

Research was conducted at Lambert Acres Golf Course (Alcoa, TN) on ‘Penncross’ creeping bentgrass green naturally infested with annual bluegrass. Turf was established as a native soil pushup green. Turf was mowed daily at 3 mm and irrigated to promote optimum creeping bentgrass growth.  Fertility was applied at 4.9 kg N ha^-1 per week using a complete fertilizer (18N: 3P₂O₅: 6K₂O). Applications of triticonazole, chlorothalonil, fosetyl-al, iprodione, and mefenoxam were applied on as-needed basis at labeled rates.

Methiozolin was applied singly and sequentially at 0.5 and 1 kg ha^-1 at three fall timings: October, November, and December. Programs of two and three sequential methiozolin applications (applied on a three-week interval) were evaluated at each timing and compared to a sequential application program (three week interval) of paclobutrazol at 0.28 kg ha^-1 initiated in October. Experimental design was a randomized complete block with three replications. All treatments were applied using a CO₂ powered boom sprayer calibrated to deliver 30 gpa using four, flat-fan, 8002 nozzles at 18 psi, configured to provide a 1-m spray swath. Creeping bentgrass injury was rated on a 0 (no turf injury) to 100% (complete kill of all turf) scale relative to an untreated control throughout the fall and winter of 2010. Annual bluegrass control was rated on a 0 (no control) to 100% (complete kill) scale in the spring of 2011. Annual bluegrass plant counts were made 25 weeks after initial treatment (WAIT) using a 1-m by 1-m grid with 100 intersection points.

Applications of MRC-01 effectively controlled annual bluegrass in this study. Annual bluegrass control increased throughout the spring with control ranging from 73 to 100% by 25 WAIT. With the exception of a single application in October, annual bluegrass control 25 WAIT with methiozolin at 1 kg ha^-1 exceeded 90% regardless of application frequency. All MRC-01 treatments controlled annual bluegrass greater than paclobutrazol at 25 WAIT as well. By 28 WAIT, all sequential methiozolin programs at 1 kg ha^-1 reduced annual bluegrass plant counts > 90% compared to 49% for paclobutrazol. Results suggest that MRC-01 is highly efficacious for annual bluegrass control in creeping bentgrass putting greens in Tennessee. However, additional research is needed to evaluate programs involving both fall and spring applications on sand and soil-based rootzones.