Field studies were conducted near Knoxville, TN, from 2003 to 2005 to evaluate the response of ‘Thermal Blue’, a new interspecific hybrid Kentucky bluegrass to commonly applied PRE and POST herbicides for weed management. Dithiopyr, oryzalin, oxadiazon, pendimethalin, prodiamine, quinclorac, and trifluralin applied at seeding injured hybrid bluegrass greater than 81% and reduced hybrid bluegrass cover greater than 57%. In a second study, established hybrid bluegrass was treated POST with acetolactate synthase–inhibiting herbicides including bispyribac-sodium, chlorosulfuron, foramsulfuron, halosulfuron, imazapic, imazaquin, metsulfuron, rimsulfuron, sulfosulfuron, and trifloxysulfuron at low and high rates (one and two times the suggested use rates in Kentucky bluegrass or other turfgrasses). By 5 wk after treatment (WAT), foramsulfuron at 88 g ai/ha and trifloxysulfuron at 35 g ai/ha injured hybrid bluegrass greater than 26% and reduced visually estimated quality and chlorophyll meter indices. However, hybrid bluegrass injury was no longer evident at 10 WAT. In a third study, established hybrid bluegrass was treated with clethodim, diclofop-methyl, fluazifop-p-butyl, and sethoxydim applied at low, medium, and high rates (0.5, 1, and 2 times the registered Kentucky bluegrass or other turfgrass use rates). Clethodim applied at 280 and 560 g ai/ha, fluazifop at 420 g ai/ha, and sethoxydim at 630 g ai/ha injured hybrid bluegrass 5 WAT. These treatments also reduced quality (to less than 5 on a scale of 1 to 9) and chlorophyll meter indices (24 to 37%) when compared to the untreated control. By 10 WAT, only clethodim at 560 g ai/ha caused injury (14%). By 10 WAT, hybrid bluegrass had recovered and injury was only observed in plots treated with clethodim at 560 g ai/ha. No differences in chlorophyll indices or quality were observed at 10 WAT for any POST graminicides.

Nomenclature: Bispyribac-sodium, chlorosulfuron, clethodim, diclofop-methyl, dithiopyr, fluazifop-p-butyl, foramsulfuron, halosulfuron, imazapic, imazaquin, metsulfuron, oryzalin, oxadiazon, pendimethalin, prodiamine, quinclorac, rimsulfuron, sethoxydim, sulfosulfuron, trifloxysulfuron, trifluralin, Kentucky bluegrass, Poa arachnifera Torr. × P. pratensis L. ‘Thermal Blue’