Denise McWilliams recommends early cultivation of fields with a thistle problem, preferably before the three-inch weed stage. "Continue routine field scouting and cultivating as needed," says McWilliams.
Several herbicides and herbicide combinations are effective against thistles, she adds. U of M extension educators in each county can recommend specific chemicals.
"Long-term thistle control requires an integrated approach using both mechanical and chemical controls," says McWilliams. "Timely application of chemicals will maximize control of current thistles and help reduce thistle seed banks and root reserves."