Perennial Ryegrass Overseeding Tolerance to Residual SP25052 Activity.

Research was conducted from August to December 2011 on a common bermudagrass fairway at Reese Golf Course (Lubbock, TX) and a ‘Tifway 419’ hybrid bermudagrass fairway at the Rawls Golf Course (Lubbock, TX). Plots were arranged in a 2 x 4 factorial where the main factor was herbicide rate and the sub-factor was application timing [weeks before overseeding (WBO)]. Treatments included thiencarbazone + foramsulfuron + halosulfuron (SP25052) at 136 and 271 g ai ha^-1 + MSO at 0.5% v/v applied on August 15, 2011 (8 WBO), August 29, 2011 (6 WBO), September 12, 2011 (4 WBO), and September 26, 2011 (2 WBO). Treatments were applied with a CO₂ powered boom sprayer equipped with XR8004VS nozzle tips calibrated to deliver 375 L ha^-1 at 221 kPa. The entire experimental area was overseeded with perennial ryegrass at 392 kg ha^-1 on October 10, 2011. The research area was verticut and seeded with perennial ryegrass seed in two directions. Perennial ryegrass cover was evaluated bi-monthly through December 2011 using digital image analysis. As SP25052 rate increased and applications were made closer to overseeding, perennial ryegrass establishment decreased. Untreated check plots exhibited 80% perennial ryegrass cover on December 14, 2011. Similar ryegrass cover (75 to 76%) was observed on December 14, 2011 in plots sprayed with SP25052 at 136 g ai ha^-1 applied 6 and 8 WBO, respectively. Ryegrass cover in response to SP25052 at 136 g ai ha^-1 applied 4 and 2 WBO was 45 and 36%, respectively. No SP25052 treatment at the 271 g ai ha^-1 rate exhibited similar ryegrass cover to the untreated check, regardless of application timing. Ryegrass cover in response to SP25052 at 271 g ai ha^-1 applied 8, 6, 4, and 2 WBO was 54, 40, 43, and 16%, respectively.