Cut-leaved teasel is an invasive weed along highway corridors and is classified noxious in four states, including Missouri. Few herbicides have been examined for cut-leaved teasel control. Herbicides were evaluated for efficacy on established plants and residual activity for suppressing seedling emergence. Various growth regulator herbicides, amino acid inhibitors, and paraquat were applied on established teasel at two locations in central Missouri in fall 2003 and spring 2004, and two additional locations in fall 2004 and spring 2005. At 2 wk after treatment (WAT), paraquat resulted in the highest injury of teasel (85), but injury declined over time. At 4 WAT, teasel control was most consistent with dicamba + diflufenzopyr applied in spring, ranging from 75 to 94 control. At 8 wk, glyphosate, dicamba + diflufenzopyr, metsulfuron-methyl, imazapyr, and combinations of growth regulator herbicides with 2,4-D were most effective, with teasel control froth 86 to 100. Control with 2,4-D alone was inconsistent; sulfosulfuron, sulfometuron-methyl, and paraquat were ineffective. Residual herbicides did not reduce teasel seedling emergence the following year. A number of herbicides were effective in managing emerged plants but reinfestations of treated sites is likely, even with the residual herbicides used in this research.
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