Studies were conducted to determine the effectiveness of 11 multiple treatment combinations of bensulide in controlling a perennial and an annual subspecies of annual bluegrass. Bensulide controlled 97% of the annual subspecies with annual applications of 11 kg ai ha–1 (Jan.) + 6 kg ha–1 (Feb.) + 6 kg ha–1 (Mar.) totaling 92 kg ha–1 in 4 yr. The annual subspecies appeared to have a germination period from mid November to early January. None of the bensulide treatments controlled the perennial subspecies acceptably. The common occurrence of these two subspecies in mixed stands may account for the erratic weed control reported by many researchers. Bentgrass showed good tolerance to bensulide totals over 4 yr of 160 kg ha–1 applied in a U.S. Golf Association rootzone green.
