Herbicide products containing clopyralid have been used by the lawn-care industry for more than 15 years. The chemical is extremely effective against persistent weeds, such as dandelion, yellow starthistle, and Canada thistle. For the past 2 years, however, this popular herbicide has shown up as a contaminant in composting facilities from Pennsylvania to Washington.Clopyralid-contaminated compost can be toxic to sunflowers, peas, beans, tomatoes, and potatoes. The problem is that clopyralid doesn't break down under normal composting processes, and it can be a hazard to these plants even at low concentrations.
The contamination is mostly due to the collection and composting of clippings from lawns treated with the herbicide. To ease the problem, the manufacturer, Dow Chemical, recently agreed to prohibit the use of clopyralid on residential lawns. The chemical can still be used on commercial properties.
Plants damaged by clopyralid often have curling and deformed leaves. If you suspect clopyralid contamination in your garden, follow these suggestions to neutralize the toxin. Plant non-susceptible crops, such as asparagus, onions, garlic, broccoli, spinach, and beets, in the affected areas; keep the area moist during the growing season; and incorporate uncontaminated compost into the soil to enhance biological activity. To learn more, call the Natural Lawn and Garden Hotline at (206) 633-0224.