Methiozolin Rate and Spring Application Timing Affect Annual Bluegrass Control On Putting Greens.

Methiozolin is a new herbicide reported to control annual bluegrass (Poa annua) in creeping bentgrass (Agrostis stolonifera) golf course putting greens. However, the appropriate application timing and rate to maximize efficacy is still not clear. The objective of this experiment was to determine the optimum rate and timing of spring applications for annual bluegrass control. The experiment was conducted in Knoxville, Tennessee and West Lafayette, Indiana. Individual timings in March, April and May, or programs of March + April, April + May or March + April + May at two methiozolin (MRC-01) application rates (0.5 or 1.0 kg/ha) were tested.  Applications were made at the first of each month in Tennessee and the middle of each month in Indiana.  Results from both locations concluded that sequential applications which contained the early spring (March) applications provided the best efficacy compared to later application timings in April and May.  In Indiana, plots receiving 1.0 kg/ha methiozolin sequentially applied March + April + May controlled annual bluegrass up to 44%, whereas in Tennessee the same treatment provided 99% annual bluegrass control.   Treatments sequentially applied in March + April also provided annual bluegrass control in both Tennessee and Indiana. A single March application was not effective (0% control) in Indiana but provided 97% control in Tennessee.  Additionally, Tennessee reported up to 40% annual bluegrass control with either a single April or May application at 1.0 kg/ha, whereas no control was observed in Indiana. Annual bluegrass was not controlled from the 0.5 kg/ha applications in Indiana, but in Tennessee the 0.5 kg/ha rate provided control that was similar to 1.0 kg/ha. Differences between locations were likely due to different annual bluegrass biotypes at each location, and emphasize the importance of conducting annual bluegrass research at multiple locations.  In general, methiozolin proved to be a useful tool for annual bluegrass control in creeping bentgrass.