CONTROLLING ANNUAL BLUEGRASS AND ROUGHSTALK BLUEGRASS IN COOL SEASON LAWNS WITH METHIOZOLIN. B. McNulty* and S. Askew, Virginia Tech, Blacksburg, VA (25)
Annual bluegrass (Poa annua) and roughstalk bluegrass (Poa trivialis) are annual grassy weeds that commonly infest home lawns in the United States. In cool climates, lawns are typically comprised of tall fescue (Festuca arundinacea), perennial ryegrass (Lolium perenne), and Kentucky bluegrass (Poa pratensis). Methiozolin is a new herbicide under evaluation by the Moghu research Center in South Korea for use in several turfgrass species. Three trials were initiated at the Glade Road Research Facility in Blacksburg, VA on April 19, 2010 to evaluate annual and roughstalk bluegrass control and turfgrass response to methiozolin compared to an industry standard. The first trial location was perennial ryegrass infested with annual and roughstalk bluegrass mown at 3.81 cm. The second location was Kentucky bluegrass contaminated with white clover (Trifolium repens) maintained at 3.81 cm. The third site was a weed-free area of tall fescue mown at 6.35 cm. Treatments were replicated 3 times in a randomized complete block design (RCBD) and applied using a CO2 backpack sprayer calibrated at 280 L/ha. Treatments included; methiozolin at 500, 1000, 1500, 2000, 3000, and 4000 g ai/ha, bispyribac-sodium (Velocity) at 74 g ai/ha, and a non-treated check (NTC). All methiozolin treatments 2000 g ai/ha or less and bispyribac-sodium treatments were repeated one month after initiation on May 19, 2010. Methiozolin did not injure any turf species at any timing. Bispyribac-sodium injured perennial ryegrass 20%, tall fescue 15%, and Kentucky bluegrass 60% at nine days after the second treatment. At rates above 1500 g ai/ha, methiozolin suppressed annual bluegrass seedheads by at least 85% one week after the first treatment. Bispyribac-sodium also reduced annual bluegrass seedheads by 85% at the same timing. Bispyribac-sodium controlled white clover at two locations, while methiozolin did not affect white clover populations at any rating. At 29 days after treatment (DAT), methiozolin at 2000 g/ha applied twice and 3000 or 4000 g/ha applied once controlled roughstalk bluegrass 60, 90, and 92%, respectively, compared to 90% control from bispyribac-sodium. At 49 DAT, methiozolin at 1500 and 2000 g ai/ha applied twice controlled annual bluegrass 84% and 94% respectively. Methiozolin at 3000 and 4000 g ai/ha applied once controlled annual bluegrass 85% and 93%, respectively at the same rating date. Bispyribac-sodium applied twice controlled annual bluegrass 38% 49 DAT. These results suggest that methiozolin could be a safe and effective herbicide for post emergence control of both annual and roughstalk bluegrass in a variety of cool season turfgrass situations.