Canada thistle control in no-tillage corn was studied in Western Maryland from 1990 to 1992. The best treatment at planting for controlling Canada thistle was a tank mixture of 2240 g/ha glyphosate plus 560 g/ha 2,4-D. Clopyralid applied at 210 and 280 g/ha alone and 106 g/ha tank mixed with 560 g/ha 2,4-D effectively controlled Canada thistle in no-tillage corn (85 to 96%). Nicosulfuron applied at 35 g/ha and 20 or 40 g/ha primisulfuron suppressed Canada thistle (59 to 75%). Tank mixtures of nicosulfuron or primisulfuron with 2,4-D or dicamba generally increased Canada thistle control (75 to 87%) compared with control by these herbicides applied alone. Treatments that controlled Canada thistle generally increased corn yields compared with the weedy controls. Yield increases were most dramatic in 1991 when precipitation was low.
