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Herbicide Contamination A Growing Problem for Composters

PULLMAN, Wash. — For the second year in a row, a broadleaf herbicide has contaminated compost processed in Pullman and Spokane. Commercial composters fear it may become a growing problem across the nation.

Last year Washington State University’s compost was contaminated by picloram, a broadleaf herbicide that killed fruit and vegetables in many gardens in which the soil was amended with the compost.

This spring another broadleaf herbicide, clopyralid, was found in compost at WSU. It also was found in the Spokane Regional Compost Facility last year, and again this spring, said Dan Caldwell, WSU farm and compost manager.

WSU is responding by certifying vendors of grass hay and straw, which ends up in compost it processes and sells. Vendors will have to guarantee their product is free from herbicide contamination.

Picloram and clopyralid present a problem for composters because they don’t break down quickly and persist in the finished product. Compost contaminated with these chemicals may be safely applied to turf grass, but may harm broadleaf ornamentals and vegetables.

Caldwell explains that herbicides containing picloram or clopyralid aren’t legally available to home gardeners, but can be a problem for back-yard composters if they compost clippings from lawns that commercial applicators have treated with broad leaf herbicides.

However, picloram and clopyralid sometimes make their way into compost sold commercially, in which case they may harm garden plants.

No chemicals known to leave harmful residues in compost are approved for application by home owners.

WSU was unable to sell any compost this spring after discovering the clopyralid contamination. Caldwell said WSU crews retrieved 300 cubic yards of compost that hadn’t been sold in 2000, and disposed of another 9,000 cubic yards this year.

WSU has diverted contaminated compost into safe channels. Caldwell said last year’s contaminated compost was applied to grass pastures. This year’s contaminated compost is being used in a rock quarry reclamation project.

Damon Taam, Spokane Regional Solid Waste System manager, said Spokane’s Colbert compost facility is limiting sales of 47,000 yards of clopyralid-contaminated compost to customers who sign a statement acknowledging the presence of clopyralid and that the compost shouldn’t be used around ornamentals or in vegetable gardens.

Tim Manifcalo, Dow AgroSciences LLC, spokesperson, Indianapolis, Ind., said clopyralid contamination of compost has arisen suddenly.

Although the compound has been used on turf grasses since 1989, reports of contamination of compost began only recently.

Dow has responded by asking distributors and commercial applicators in the Spokane area to stop using clopyralid anywhere that the chemical could wind up getting into compost. “If there is a potential to get into composting systems, we’ve asked them not to use it, at least for the time being,” Manifcalo said.

Meanwhile, Dow AgroSciences is planning research at the Colbert compost facility in an attempt to discover why clopyralid is persisting in compost and to determine if there might be a way to speed breakdown of clopyralid in compost, Manifcalo said.

Dow also is testing compost at other facilities to see if clopyralid is a problem in other areas of the country. The company is the only manufacturer of clopyralid.

The compound is sold under the trade names of Confront, Curtail, Stinger, Transline, Reclaim and Lontrel for control of broadleaf weeds in a variety of crops. Clopyralid must be applied by licensed applicators.

In May, David Bezdicek, a WSU soil scientist, presented an invited paper on contaminated compost, at the 31st Biocycle National Conference in St. Paul, Minn.

“The recycling and compost industries are extremely worried that persistent herbicides such as clopyralid may end up in compost for sale to the public from feed stocks inadvertently treated with clopyralid, even though the label may have been followed.

“The public is often not aware that the desire to have weed-free lawns and crops may have hidden dangers from persistent herbicides,” Bezdicek said.

“In today’s world where green wastes are often not allowed in landfills, recycling through composting is one of the only means for responsible stewardship,” Bezdicek said. “Many large composting facilities have millions of dollars invested where the public and commercial sources bring in feed stocks for composting and often purchase the compost for many uses.”

Bezdicek reported intense interest across the country in the potential for persistent herbicide contamination of compost.

The Washington Organic Recycling Council is asking all composting facilities to start performing growing trials to monitor for clopyralid. “If they do find herbicide effects in their bioassays, we recommend they follow up with chemical tests,” said Jeff Gage, WORC president and a member of the board of directors of the U.S. Composting Council. Bioassaying involves growing herbicide sensitive plants like tomatoes, peas or beans for a few days and watching for signs of stress. They are very sensitive and much cheaper than chemical tests.

Gage said the council has 70 members. He reported about 20 Western Washington government bodies — county and city governments — recently met with Dow officials to question them and convey concerns regarding the impact of clopyralid on their recycling systems. They agreed to express concerns in letters to the Environmental Protection Agency and the Washington State Department of Agriculture.

Caldwell recommends gardeners who are concerned about the possibility of contaminated compost conduct their own bioassay before using it to amend their garden soil. To do this, mix 25 percent compost and 75 percent soil or potting soil and plant peas or beans.

These vegetables are highly sensitive to picloram and clopyralid. Peas are most sensitive and can indicate a potential problem before the whole garden is affected. Beans may grow a little, but if the second true leaf doesn’t fully develop, the compost may be contaminated, Caldwell said.

He recommends conducting the test in a protected place. Temperature extremes could delay sprouting and growth and produce unusual symptoms.

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EDITORS: Dan Caldwell can be reached for comment on WSU aspects of this story by calling 509-336-1354.