WSDA Samples Compost for Herbicide Residue for Second Year; Ban Reduces Levels of Clopyralid in Compost.

News & Business Editors/Environment & Agriculture Writers

OLYMPIA, Wash.--(BUSINESS WIRE)--June 20, 2003

Data collected by the state Department of Agriculture (WSDA) indicates gardeners have less need to be concerned about herbicide residues in compost than last year. Testing completed by WSDA shows the level of the herbicide "clopyralid" found in compost has dropped an average of 80 percent or more. WSDA banned the use of clopyralid on residential and commercial lawns last year after consumers and compost facilities complained that clopyralid residue in compost was damaging sensitive plants, such as asters, sunflowers, tomatoes and beans.

Clopyralid is used to kill broadleaf weeds such as dandelions, clover and thistle. However, clopyralid does not completely break down during the composting process. The ban is intended to keep clippings from grass that has been treated with clopyralid from being sent to municipal compost facilities. Clopyralid may still be used on golf courses and some agricultural crops as long as grass clippings and other waste are not sent to a compost facility.

"It appears the ban is working," says Cliff Weed, Pesticide Compliance Program manager at WSDA. "Part of our success can be attributed to extensive public education efforts designed to reduce the flow of clopyralid-tainted products into compost facilities. Our efforts involved extensive collaboration with state and local government officials, farmers, and the lawn and garden, pesticide and compost industries."

In December 2002, WSDA staff collected and analyzed samples from 12 Washington compost facilities. An average of all 34 samples collected contained 18.47 parts per billion (ppb) of clopyralid. By contrast, the average of close to 50 samples taken from nine compost facilities in 2001 contained 96.89 ppb.

"The tests confirm that grass clippings are the largest contributor of clopyralid in compost," says Weed. At one compost facility, where grass clippings alone were sampled in both years, the levels of residue were much higher than those found at other facilities. Samples taken from all the other compost facilities included mixed yard waste, such as leaves, twigs, branches, shrubs, and other garden waste.

"Lower residues of clopyralid in compost samples show the ban is working," Weed said. "WSDA plans to conduct similar statewide testing this fall." Oregon and California have followed Washington's effort to protect compost from contamination by adopting rules that limit the use of herbicides that contain clopyralid. For more information, visit WSDA's Web site at agr.wa.gov and click on "Clopyralid in Compost."