Annual bluegrass (Poa annua L.) is a problematic weed on golf courses, sports turf, sod production fields, and irrigated lawns, but few options exist for control of annual bluegrass in Kentucky bluegrass (Poa pratensis L.). However, mesotrione has shown promising activity against annual bluegrass and adequate turf safety on Kentucky bluegrass. Experiments were completed from 2004 through 2010 in Urbana, IL, and/or West Lafayette, IN, to refine application strategies for annual bluegrass control with mesotrione in the fall. Though acceptable control (> 80%) was obtained in some experiments, control was inconsistent or marginal depending on the location and year. Our current recommendations for fall‐applied mesotrione would include three applications, starting in mid‐ to late September, at rates between 0.11 and 0.17 kg ai/ha per application, and without follow‐up applications in April. Further research will have to improve consistency of Poa annua control with mesotrione for widespread commercial use.

Roughstalk bluegrass (Poa trivialis L.) is a troublesome weed on golf courses, home lawns, and athletic fields from the Midwest to the mid-Atlantic states. Bispyribac-sodium and sulfosulfuron have recently been labeled for roughstalk bluegrass control, but their use needs to be refined. Our objective was to determine the most effective herbicide strategies for control of roughstalk bluegrass. Initial studies were conducted during 2005 in Illinois and Indiana and follow-up studies in 2006 in Indiana, Illinois, South Dakota (partial shade and full sun), and Wisconsin. Applications starting in the warmer temperatures of late May and June 2005 were more effective than those starting in mid-May. Bispyribac-sodium (a.i.) was applied at 74 or 114 g·ha−1 four times at 2-week intervals decreased roughstalk bluegrass cover to 1% and 0% 12 weeks after initial treatment (WAIT) in Illinois and Indiana in 2005, respectively, whereas sulfosulfuron (a.i.) at 13 or 27 g·ha−1 applied twice at 2-week intervals decreased cover to no less than 18%. In 2006, bispyribac-sodium was most effective in Indiana and Illinois decreasing cover to as low as 4%, whereas sulfosulfuron was most effective in South Dakota resulting in a decrease in cover to as low as 7%, and both herbicides performed similarly in Wisconsin. Three applications of sulfosulfuron (a.i.) at 27 g·ha−1 at 2-week intervals or four applications of bispyribac-sodium (a.i.) at 56 or 74 g·ha−1 at 2-week intervals were most effective for roughstalk bluegrass control.

Bispyribac and sulfosulfuron are labeled for selective control of roughstalk bluegrass(Poa trivialis L.), but previous research indicates inconsistent control. Our primary objective was to determine whether response of bispyribac or sulfosulfuron was consistent among eight cultivars of roughstalk bluegrass. Studies were conducted in Indiana at 1.25 and 5.0 cm mowing heights in 2006 and 2007. Herbicide treatments included an untreated control, sulfosulfuron at 13 g ai/ha per application applied twice on a two‐week interval, and bispyribac at 37 g ai/ha per application applied four times on a two‐week interval. Herbicide treatments were chosen as the lowest effective application strategy in our previous research. Applications were made in June and July to eight cultivars of mature roughstalk bluegrass. All roughstalk bluegrass cultivars were more susceptible to control from bispyribac than to sulfosulfuron. When mowed at 5.0 cm, there was some indication that ‘Laser’ or ‘Bariviera’ may be more susceptible to herbicidal control whereas ‘Pulsar’ may be more tolerant. This variability did not occur consistently in the two years of study at either mowing height, but this may partly explain variability in control typically seen in roughstalk bluegrass from bispyribac or sulfosulfuron.

Roughstalk bluegrass (Poa trivialis L.) contamination is problematic on golf course fairways from the Midwest to the mid-Atlantic regions of the United States. Bispyribac–sodium and sulfosulfuron have potential to selectively control roughstalk bluegrass. Our objectives were to determine the most effective herbicide treatments for short- and long-term roughstalk bluegrass control and to determine if interseeding with creeping bentgrass (Agrostis stolonifera L.) after herbicide treatments will improve long-term control of roughstalk bluegrass or conversion to creeping bentgrass. Plots were treated with bispyribac–sodium or sulfosulfuron and then half of each plot was interseeded with creeping bentgrass in early August, 2 weeks after the final herbicide application in 2006, 2007, and 2008 in Indiana. Roughstalk bluegrass cover reduction was highest when treated with bispyribac–sodium at 56 or 74 g·ha−1 a.i. applied four times or sulfosulfuron at 27 g·ha−1 a.i. applied three times. Interseeding with creeping bentgrass improved long-term roughstalk bluegrass control and quickened conversion to creeping bentgrass. Furthermore, bispyribac–sodium and sulfosulfuron appeared to be more effective in the first 2 years of the study when seasonal heat stress was greater, which appeared to improve long-term roughstalk bluegrass control and promoted creeping bentgrass establishment. Chemical names used: {2,6-bis[(4,6-dimethoxypyrimidin-2-yl)oxy] benzoic acid} (bispyribac–sodium), {1-[4,6-dimethoxypyrimidin-2-yl]-3-[2-ethanesulfonyl-imidazo(1,2-a)pyridine-3-yl) sulfonyl]urea} (sulfosulfuron).