About dicamba：utilized a combination of nitrogen fertilizers rates and herbicide treatments

reported that all herbicide treatments were effective on both thistles with or without fertilizer. They indicated that fertilized plots had a greater thistle biomass than the unfertilized check in the three-year experiment. They further reported that ammonium nitrate with either clopyralid in 1978, clopyralid + 2, 4-D in 1979 and dicamba + 2, 4-D in 1980 reduced grass biomass compared to non-fertilized plots; however, there was no determination that biomass was reduced due to herbicide injury, which was observed in some treatments in 1978 (Reece and Wilson 1983). Donald (1993) studied the effectiveness of long-term herbicide treatments applied in late September for the control of Canada thistle shoot density on non-cropped, untilled abandoned farmland. Clopyralid, glyphosate and picloram were effective in reducing Canada thistle at certain high rates in the first two years of the trial. The fall-applied treatments of clopyralid and picloram took fewer years of treatments to reduce shoot density than did glyphosate or dicamba. Clopyralid at 840 g/ha or picloram at 560 g/ha applied in the fall for three consecutive years inhibited, or almost prevented, shoot emergence the third growing season, while glyphosate and dicamba did not reduce shoot emergence. Miller and Lym (1998) conducted several field experiments on the control of Canada thistle with herbicides and cultivation treatments in corn and soybeans. Photoperiod determinations of Canada thistle and clopyralid absorption and translocation at different stages of growth were evaluated. The herbicide and cultivation treatments resulted in clopyralid and bentazon having 42% and 44% control 4 MAT in corn and soybeans, respectively.  

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