Creeping Bentgrass and Perennial Ryegrass Seedling Tolerance to Bispyribac-sodium

Establishing creeping bentgrass [Agrostis stolonifera L. (CBG)] and perennial ryegrass [Lolium perenne L. (PRG)] from seed can be hampered by competition from annual bluegrass (Poa annua L.). Bispyribac-sodium (BPS) is a postemergence annual bluegrass herbicide that may have applications for use when establishing these grasses. This field study was undertaken to determine if BPS could be applied safely to CBG and PRG seedlings. Ethofumesate (ETHO) was applied sequentially (840 + 840 g.ha(-1) a.i.) and served as a standard. In 2004, BPS was applied once (49, 74, 111, and 148 g.ha(-1) a.i.) or sequentially (49 + 49 and 74 + 74 g.ha(-1) a.i.) to CBG and PRG seedlings 4 weeks after emergence in Maryland. In 2004, BPS discolored CBG and PRG and reduced PRG cover, whereas ETHO reduced CBG cover but was not injurious to PRG. In 2005, a single (148 g.ha(-1) a.i.) and sequential (25 + 25, 49 + 49 and 74 + 74 g.ha(-1) a.i.) applications of BPS were made to CBG and PRG 2 and 4 weeks after seedling emergence (WASE) in Maryland and Connecticut. Treatments applied 2 WASE generally resulted in more injury when compared with applications made 4 WASE. In Maryland in 2005, CBG only sustained long-term loss of cover when treated 2 WASE with 148 g.ha(-1) a.i. of BPS. The PRG was more sensitive to BPS and 148 g.ha(-1) a.i. applied once and sequential treatments 49 g.ha(-1) a.i. or greater applied 2 and 4 WASE generally caused the greatest loss in PRG cover. Conversely, CBG was severely injured by all BPS treatments and ETHO in Connecticut. In PRG, only 25 + 25 g.ha(-1) a.i. of BPS and ETHO in both timings did not cause a loss in cover in Connecticut or Maryland. High levels of precipitation and probably other unknown factors may have enhanced the phytotoxicity observed in Connecticut. Ethofumesate generally was safer than BPS for use on PRG seedlings.