Sulfonylurea herbicides can be effectively used to control various weeds including annual bluegrass before overseeding cool-season grasses like perennial ryegrass or Poa trivialis on dormant bermudagrass. These herbicides can also be used to remove cool-season grasses during spring transition. Experiments were conducted at the California State Polytechnic University, Pomona with trifloxysulfuron, foramsulfuron, rimsulfuron and sulfosulfuron during the fall of 2004 and spring 2005. Sulfosulfuron treatments controlled 88-99% of the annual bluegrass 3 weeks after treatment (WAT) but the high rates applied 7 days prior to overseeding injured 11-24% of the perennial ryegrass 3 WAT. Rimsulfuron controlled 100% of the annual bluegrass but injured 50-62% of the ryegrass 5 WAT. Trifloxysulfuron applied at 17.3 and 29.4 g a.i/ ha, 21, 14, 10 days before overseeding with perennial ryegrass on a ‘GN-1' and ‘Tiffgreen' bermudagrass. At nine days before overseeding (DBO) the bermudagrass sustained minimal injury (>3%) when applied at 21 DBO for both high and low rates and moderate injury (11-13%) when applied at 14 DBO at both rates. Perennial ryegrass injury at 14 DAO with trifloxysulfuron was minimal for both rates of when applied at 21 DBO, but sustained more injury when applied 14 and 10 DBO. Formasulfuron was very effective in removing clumpy ryegrass in a bermudagrass base during spring transition.
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