Turf Weeds at Virginia Tech

With the potential introduction of glyphosate-resistant kentucky bluegrass (GRKB) (Poa pratensis L.), postemergence herbicides must be identified for renovation from glyphosate-resistant stands or control escaped GRKB. Field experiments were conducted in Indiana, Maryland, New Jersey, and Virginia from July to September 2004 to investigate efficacy of postemergence herbicides for Kentucky bluegrass control. Herbicides tested included clethodim at 0.28 kg•^{ha -1} (a.i.), fluazifop-p at 0.43 kg•^{ha -1}(a.i.), formasulfuron at 0.03 kg•^{ha -1} (a.i.), glufosinate at 1.12 kg•^{ha -1} (a.i.), glyphosate at 1.68 kg•^{ha -1} (a.i.), rimsulfuron at 0.03 kg•^{ha -1} (a.i.), sethoxydim at 0.53 kg•^{ha -1} (a.i.), and trifloxysulfuron at 0.03 kg•^{ha -1} (a.i.). One and two applications of each herbicide were applied to separate plots with the sequential applied 4 weeks after initial treatments (WAIT). Single applications of glyphosate completely controlled kentucky bluegrass 4 WAIT in Maryland, New Jersey, and Virginia. Glufosinate completely controlled kentucky bluegrass with one application in Maryland and New Jersey but single and sequential applications provided only 80% to 88% control in Indiana and Virginia. Foramsulfuron and rimsulfuron required sequential applications for complete kentucky bluegrass control 8 WAIT in New Jersey and Maryland but <82% control was obtained in Indiana and Virginia. Trifloxysulfuron controlled kentucky bluegrass 95% to 100% with single applications in Maryland, New Jersey and Virginia. Single applications of clethodim, fluazifop, and sethoxydim provided minimal stand reductions but sequential applications controlled kentucky bluegrass 65% to 100 %. Results suggest glufosinate and trifloxysulfuron have the greatest potential for controlling GRKB while other herbicides provided erratic control and require sequential applications.