The news that glyphosate-resistant turfgrasses are under development is terrific. The potential to control weeds with one herbicide is awesome to consider. Both Kentucky bluegrass and bentgrass are being studied. What if, however, you need to renovate Kentucky bluegrass turf? Or what if bentgrass grows beyond its boundary? How can you control them? Researchers from Purdue, University of Maryland, Virginia Tech and Rutgers performed field experiments on glyphosate-resistant Kentucky bluegrass (GRKB) to determine which herbicides can be used to control GRKB. They treated GRKB plots with seven different herbicides in addition to glyphosate. The herbicides were fluazifop-p, clethodim, sethoxydim, glufosinate, rimsulfuron, trifloxysulfuron and formasulfuron (which are from varying groups of chemicals). Glyphosate controls weeds through inhibition of an amino acid. The experimental herbicides control through inhibition of different amino acids or inhibition of fatty acid enzymes, etc. The results varied greatly between locations. In general, the group of herbicides composed of clethodim, fluazifop-p and sethoxydim did not provide consistent control and will probably not help with GRKB control. However, the sulfonylureas, consisting of rimsulfuron, trifloxysulfuron and formasulfuron, provided fairly good control at all locations (though they sometimes needed two applications). Researchers caution that subsequent seeding and overseeding options need to be delayed at least six weeks after treatments with trifloxysulfuron. Glufosinate provided good control, as well, but sometimes required two applications, depending on location, and left no residual to delay seeding operations.

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