Experiments were conducted to compare rates and formulations of quinclorac for postemergent control of slender speedwell in cool-season turf. A 50% ae wettable powder formulation (50WP) was compared with two granular formulations, a 1% clay granule (1G) and a 0.4% corn cob granule (0.4G). Each formulation was applied at 0.3, 0.6, 0.8, and 1.1 kg ha−1. Additionally, 2,4-D at 1.1 kg ha−1 was applied alone and in combination with quinclorac 50WP at 0.8 kg ha−1. Slender speedwell control with the 50WP or 0.4G formulations was superior to that obtained with the 1G. At lower rates, slender speedwell control with the 50WP was greater than with the 0.4G; however, the rates required to obtain 95% control were not significantly different. Tank mixing quinclorac 50WP at 0.8 kg ha−1 with 2,4-D at 1.1 kg ha−1 did not improve slender speedwell control but increased roughstalk bluegrass injury. Kentucky bluegrass, perennial ryegrass, and tall fescue were not injured by quinclorac. Roughstalk bluegrass and chewings fescue were temporarily discolored. Turf injury was rate-related and more severe with the 50WP than the 1G formulation.
