What herbicide residues should be avoided in commercial-scale composting?
Answer: Most agricultural herbicides and pesticides break down quickly in the environment. There are a few exceptions, however, particularly Clopyralid and Picloram. Picloram has shown up in compost residues throughout the country for as much as two years with concentrations as low as 2 parts per billion in compost and straw. Clopyralid is a long-lasting herbicide that is commonly used on turf and has surfaced in municipal composting facilities that compost lawn and leaf residues and Picloram is used to control broad-leafed weeds such as Canadian Thistle. It is currently banned for use on lawns in some states, and agricultural producers are required to have a pesticide applicators license to spray it.An indication of herbicide damage on your plants is curled and burned leaves. Certain plants are particularly susceptible to herbicide damage, however, including peppers, peas, tomatoes, red clover, and cucumbers. If only these plants are damaged, then most likely herbicide residue is the culprit.When you source compost and straw for mulch in the future, be sure to ask if the source of your material had Cloropyralid applied.