Response of Creeping Bentgrass (Agrostis stolonifera) to Fall Applications of Bensulide and Dithiopyr

Bensulide and dithiopyr may be used in late summer–fall as a preventative treatment to reduce the potential of annual bluegrass encroachment onto newly constructed or renovated creeping bentgrass putting greens. In 1999, no herbicide treatment reduced bentgrass cover or root mass 1 mo after treatment (MAT). In April of 2000, root mass was lower with bensulide applied at 11.2 kg/ha in October and 22.4 kg/ha applied at both timings or by dithiopyr applied at all rates and timings compared with the untreated bentgrass. In April, bentgrass cover was reduced by bensulide applied at 22.4 kg/ha and dithiopyr applied at 0.4 and 0.8 kg/ha at both timings. In contrast to 1999, significant reductions in root mass were observed 1 MAT in 2000 with bensulide applied at 22.4 kg/ ha and all rates of dithiopyr. Reductions in root mass and bentgrass cover continued into April of 2001 with dithiopyr at 0.4 or 0.8 kg/ha applied at either application timing. Bentgrass cover was lower than the untreated with dithiopyr applied at 0.8 kg/ha until August of 2001. These results suggest that bensulide may be used on creeping bentgrass greens in late summer–fall with a greater degree of safety than dithiopyr.