Tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} at 2 or 4 ppmw placed 0 to 3, 8 to 11, or 15 to 18 cm deep in soil columns reduced root and shoot weights of buffelgrass [Pennisetum ciliare (L.) Link # PESCI] 30 days after emergence. Plains bristlegrass (Setaria macrostachya H.B.K.) seedling shoot weights were not reduced when 2 ppmw tebuthiuron was placed 8 to 11 cm deep or deeper. Effects of tebuthiuron at 0.13 to 0.50 ppmw on buffelgrass shoot and net tiller production were not moderated by the presence of honey mesquite (Prosopis glandulosa # PRCJG) in the pots. However, regardless of tebuthiuron dosage, average height and shoot weight of buffelgrass seedlings were greater when seedlings were grown in soil collected from beneath honey mesquite canopies compared to growth in soil from interspaces. Therefore, spatial variations in buffelgrass response to applications of tebuthiuron for control of invading shrubs may largely be attributed to soil changes induced by woody plants rather than to presence of shrubs.
