Heat Tolerant Bluegrass Response to Preemergence and Postemergence Applied Herbicides.
Travis C. Teuton1, Christopher L. Main2, J. Scott McElroy1, John C. Sorochan1, and Thomas C. Mueller1. (1) University of Tennessee, 2431 Joe Johnson Drive, 252 Ellington Bld., Knoxville, TN 37996, (2) Clemson University, 2200 Pocket Drive, Florence, SC 29506
Field studies were conducted near Knoxville, TN in 2004 to evaluate the response of ‘Thermal Blue' a new heat tolerant Kentucky bluegrass hybrid to preemergence (PRE) and postemergence (POST) herbicide applications. Thermal Blue exhibited significant injury to all seven preemergence herbicides tested when applied at seeding; dithiopyr, oryzalin, oxadiazon, pendimethalin, prodiamine, quinclorac, and trifluralin. Quinclorac at 840 g ai ha-1 showed the least injury (81 %) 25 weeks after treatment (WAT). Established Thermal Blue exhibited tolerance to ten postemergence ALS herbicides applied at 1 and 2X the normal use rates; bispyribac-sodium, chlorosulfuron, foramsulfuron, halosulfuron, imazapic, imazaquin, metsulfuron, rimsulfuron, sulfosulfuron, and trifloxysulfuron. Foramsulfuron and trifloxysulfuron at 87 g ai ha-1 and 35 g ai ha-1 showed 36 and 26% injury 5 WAT. However, at 10 WAT the greatest injury (7%) occurred with trifloxysulfuron at 36 g ai ha-1. Established Thermal Blue also displayed excellent tolerance to four postemergence graminicides applied at 0.5, 1, and 2X normal use rates. Unacceptable injury (>15%) was observed with clethodim (1 and 2X) at 280 and 560 g ai ha-1, fluazifop (2X) at 420 g ai ha-1 and sethoxydim (2X) at 630 g ai ha-1. However, at 10 WAT the greatest injury (14%) occurred with clethodim at 560 g ai ha-1. Overall, Thermal Blue is very susceptible to preemergence herbicides and precaution should be used when applying these products at seeding. Thermal Blue has excellent tolerance to many postemergence herbicides; however manufacturers suggested use and application rates for Kentucky bluegrass apply and should be followed carefully.