Common Kentucky bluegrass (Poa pratensis L.) sod-plugs were grown in the greenhouse in soil freshly treated with 11 herbicides and in soil collected from the 0 to 2 and 2 to 4-inch depths of field plots treated 10 months earlier with the same herbicides. Fresh herbicide treatments reduced significantly the root regrowth of the bluegrass plants. The 12-lb/A rate of the fresh application of 1-(2-methylcyclohexyl)-3-phenylurea (siduron) caused the least chemical inhibition of root regrowth. The most phytotoxic fresh applications were 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) and 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), both killing the bluegrass plants at the 4 lb /A rate. Root regrowth of bluegrass grown in the herbicide residue samples was significantly reduced for all treatments. Herbicides which tended to persist in the 0 to 2-inch soil level and were most phytotoxic to root regrowth were simazine, polychlorodicyclopentadiene isomers (hereinafter referred to as bandane), N-(2-mercaptoethyl)-benzenesulfonamide S-(O,O-diisopropyl phosphorodithioate) (bensulide), and 2,6-di-tert-butyl-p-tolyl-methylcarbamate (terbutol). Those herbicides which tended to leach into the 2 to 4-inch soil level and cause the greatest reduction of root regrowth were N-butyl-N-ethyl-alpha, alpha, alpha-trifluoro-2,6-dinitro-p-toluidine (benefin), α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin), atrazine, and O-(2,4-dichlorophenyl) O-methyl isopropylphosphoramidothioate (DMPA). Herbicides which tended to leach uniformly throughout the 0 to 2 and 2 to 4-inch soil layers were siduron, an equal mixture of 1,1-dimethyl-4,6-diisopropyl-5-indanyl ethyl ketone and 1,1-dimethyl-4,6-diisopropyl-7-indanyl ethyl ketone (hereinafter referred to as sin-done), and dimethyl 2,3,5,6-tetra-chloroterephthalate (DCPA).
