ST. PAUL -- Animal pastures and Conservation Reserve Program fields are continually stressed with a succession of noxious weeds and woody trees and shrubs throughout the growing season. University of Minnesota Extension conducts weed control research on crops and landscapes and shares this information with Minnesota residents.
Fall is the best time to control perennial broadleaf weeds. This time of year, perennial plants are storing carbohydrates for winter. Actively growing weeds will readily take up herbicides until a hard frost.
Thistles are a major problem in pastures and on CRP lands. There are several labeled broadleaf selective herbicides that do not kill grasses, but will effectively treat thistles and other common broadleaf weeds.
Red cedar, boxelder, cottonwood, and green ash trees can overtake pastures or CRP fields. Buckthorn is a woody invasive species typically affecting Minnesota forests and woodlands that is also treated in the fall and winter.
Woody-plant seedlings can be pulled, but a cut stump treatment is recommended for thicker stems and trees -- cut the stem or tree and apply herbicide to the exposed bark layer on the cut stump. Some woody-plant herbicides are labeled for use throughout the winter months. A labeled brush killer should be used for woody plants.
Herbicides labeled for use in animal pastures may have a grazing restriction or interval for animals. Look on the label for these grazing intervals and precautions.
To control weeds, select an herbicide labeled for the targeted weeds and landscapes. Always read and follow label directions. If you are uncertain about what weeds you have and how best to control them, visit the following University of Minnesota websites for more information:
- University of Minnesota Extension's Gardening Information diagnostic tool "Is this Plant a Weed?" www.extension.umn.edu/
- University of Minnesota Extension recommendations for treating animal pastures and CRP fields (PDF document), www.
- University of Minnesota agricultural weed control recommendations, www.
Gary Wyatt is a natural resource management educator with University of Minnesota Extension.