Recently, roundleaved mallow, redroot pigweed, and annual smartweed species have become problems for flax producers in the Canadian prairies. The use of thifensulfuron to enhance weed control with commonly used herbicide mixtures was tested at Indian Head, SK and Morden, MB. Visible crop injury and reduced height, yield, and quality occurred at rates as low as 0.5–1.0 g/ha. Improved control of broadleaf weeds was not consistent and antagonism of grassy weed control with sethoxydim occurred.