Efficacy and Safety of Methiozolin for Pre-Emergence Control of Annual Bluegrass (Poa annua L.) On Creeping Bentgrass (Agrostis stolonifera L.) Putting Greens.

Annual bluegrass (Poa annua L.) is the most problematic weed on golf course putting greens. Besides plant growth regulators (PGRs), there are limited options to control Poa.  Despite several pre-emergence herbicides available for use, concerns exist regarding phytotoxicity to creeping bentgrass (Agrostis stolonifera L.). This study was established to investigate the efficacy and safety of a cell wall biosynthesis inhibitor, methiozolin, when applied in late summer or early fall as a pre-emergence herbicide. Two field studies were established on creeping bentgrass greens, with one located in St. Louis, Missouri, and a second one in Stillwater, Oklahoma. The experiment was designed as a randomized complete block with 4 replications. Treatments included methiozolin at different rates from 0.25 to 1.00 kg ai/ha at various re-application intervals. Commercially available pre-emergence herbicides bensulide and dithiopyr were also included in addition to an untreated control. In Missouri, the initial application was made in early September 2011, prior to Poa emergence.  After fall and spring applications, methiozolin treated plots resulted in less than 5% Poa in spring 2012, while in untreated plots, Poa comprised up to 30% by the May evaluation.  For the commercially available herbicides, bensulide and dithiopyr, Poa encroachment increased over the course of the study, comprising 10 to 15% of the plots by May.