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®, GrazonNext® HL, 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. However, when treated grass is eaten by animals, either out in the field or as hay or silage, a small amount of aminopyralid may be in the resulting manure and urine. Herbicide residues may also remain on hay and forage grass used for feed or bedding. Aminopyralid can be released as the plant tissues decay and are broken down by soil microbes. Any susceptible plants present at the time of decay of plant tissues may be affected. The length of time for treated hay/forage or manure to break down is dependent upon many different factors such as soil type, temperature, aeration of the soil, compaction etc. Therefore, it is impossible to give a timescale on decay times as each situation will be different. NOW is the time to remind your agricultural producers to prevent possible injury to desirable plants by reading and following the herbicide label section on “Plant Residues or Manure” when handling compost, manure or hay/livestock bedding that may contain aminopyralid residues.
More information: http://www.dowagro.com/range/aminopyralid_stewardship.htm