Herbicide Found in Compost

Herbicide Found in Compost

Trace amounts of a herbicide that kills broadleaf weeds have been found in the City of Lincoln’s compost. The source of the herbicide, called clopyralid (pronounced lo-peer-uh-lid), is grass clippings collected from Lincoln residents.

The city has launched an education campaign to discourage the use of the herbicide since finding clopyralid in the city’s LinGro compost at levels of 13 to 23 parts per billion (ppb). The city also wants to assure users of the compost that damage to vegetable gardens and broad-leaf ornamentals can be avoided if the compost is applied according to city-developed guidelines.

Clopyralid is an ingredient in many lawn-care herbicides available to Nebraskans. According to information posted on the City of Lincoln web site, clopyralid-contaminated compost is known to damage plants including carrots, carnations, lupines, and lettuce, and certain sensitive plant families, including:

Legumes, such as peas, beans, lentils, and clover;
Solanaceous, including tomatoes and potatoes; and
Composite, such as sunflower, petunias, daisies, and asters.

Clopyralid is not known to harm other plants, including trees, lawns, and shrubs. Compost contaminated with clopyralid is not harmful to people or animals, and vegetables grown in compost containing clopyralid are safe to eat.

Sensitive plants should not be harmed if the compost is thoroughly mixed with existing soil, according to Gene Hanlon, Recycling Coordinator for the City of Lincoln. “The recommended application rate of compost for vegetable and flower gardens is one inch of compost mixed thoroughly in six inches of soil,” Hanlon said.

“Our goal is to reduce the amount of herbicide sent to our compost facility,” he added. Hanlon offered the following tips to people using herbicides on their lawn:

Leave your grass clippings on your lawn. This returns nutrients (and herbicides) to the soil, saves mowing time, and saves the expense of hauling the clippings away;
When purchasing lawn care products, check the ingredients label and avoid buying products that contain clopyralid; and
If you use a lawn maintenance company, ask that they not use clopyralid-containing products on your lawn.

Other composting operations in the state may have the same clopyralid-related problem as Lincoln does, according to David Haldeman, Department of Environmental Quality Waste Management Division Administrator. “Compost operations should review their sampling and testing procedures to evaluate compost quality and determine if clopyralid is present in their finished product. Local greenhouses may be able to perform the testing, called a bioassay, for the compost facility. The University of Nebraska at Lincoln can also conduct bioassays for a nominal fee.”

Additional information about Clopyralid, and a list of Clopyralid-containing products, are available on the City of Lincoln web site at: www.ci.lincoln.ne.us/city/pworks/waste/recycle or by calling (402) 441-8215.

Additional information about bioassays performed by UNL can be obtained from Brady Kappler, Weed Science Educator, at (402) 472-1544, or bkappler@unl.edu.