Reproduced with permission from
/ Weed District Tech Advisor / / April 2011
Early spring is the time ranchers and farmers may be composting or spreading livestock manure and/or bedding on fields and pastures. Small acreage landowners may also be spreading manure and compost on their gardens. This common practice can have consequences if the manure or plant material contains herbicide residues.
Aminopyralid is the active ingredient in several herbicides under the brand names Milestone®, ForeFront® R&P, Chaparral™, and Opensight®. Based on registration and label directions, they are used by farmers, ranchers and vegetation managers for effective control of deep-rooted perennial weeds in grassland, such as thistle, ragweed, knapweed and some woody species. When grassland is sprayed with aminopyralid, the target weeds are killed but the grass is not affected.