Killer Compost Update: Herbicide Damage Still a Major Problem

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Curled plant leaves, like the leaves on this eggplant, are a telltale sign of herbicide damage.
Curled plant leaves, like the leaves on this eggplant, are a telltale sign of herbicide damage.
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Potent chemicals are contaminating compost and manure supplies, a problem we've termed
Potent chemicals are contaminating compost and manure supplies, a problem we've termed "killer compost." 

We need to demand that the Environmental Protection Agency ban the potent, persistent herbicides that continue to contaminate commercial compost and manure supplies.

For more than a decade, gardens and farms have been damaged by compost or mulch that was contaminated with persistent herbicides. These potent chemicals are applied to lawns, pastures, hayfields and roadsides, and continue to be highly toxic even after residues on grass or hay have been composted. When livestock graze on treated pasture or hay, these herbicides even remain potent in their composted manure. We’ve termed this recurring problem “killer compost.” (For one reader’s report on this herbicide contamination, see Dear MOTHER February/March 2013.)

In June 2012, employees at Green Mountain Compost in Williston, Vt., began fielding reports from gardeners about suspected herbicide damage following application of compost purchased at the facility. Initial tests of the compost revealed the presence of two herbicides?–?picloram and clopyralid?–?known to be persistent in compost. Green Mountain, which is now under the management of the Chittenden Solid Waste District (CSWD), immediately suspended sale of its bagged and bulk compost and began seeking the source of the contamination. It also started making reparation arrangements with customers who had reported damage. Picloram and clopyralid are produced by Dow AgroSciences to control broadleaf weeds on turf grass, pastures and rangelands. Both compounds are under restricted use in Vermont; picloram may only be applied by licensed applicators. According to the Vermont Agency of Agriculture, there was no reported use of picloram in the state on any potential composting feedstock between 2009 and 2011.

The Plot Thickens

So how did these chemicals turn up in the compost? In early August 2012, CSWD identified area horse farms as the source of the contamination and sent letters to those farms indicating it could no longer compost their manure. Puzzled as to how the herbicides had gotten into the manure, CSWD asked those farms to indicate which commercial horse feed they had used, and then took the bold step of having samples of that feed tested. Bingo. According to initial lab results, several samples of off-the-shelf Purina horse feed were contaminated with clopyralid at levels between 142 and 465 parts per billion! Susceptible garden plants?–?such as beans, eggplant, peas, peppers, potatoes, sunflowers and tomatoes?–?are harmed at exposure levels as low as 30 ppb, five to 15 times lower than the levels detected in the horse feed.

CSWD also sent the same lab?–?Anatek Labs Inc. in Moscow, Idaho?–?84 samples of compost from other regional facilities as well as common local compost feedstocks, including bedding, manure, hay, straw and municipal grass clippings. The lab found picloram and/or clopyralid in 67 out of the 84 samples80 percent! Meanwhile, on behalf of the Vermont Agency of Agriculture, Dow sent samples of manure, manure with bedding, compost, feed, hay, grass, and straw collected from across Vermont to its own contracted lab, Carbon Dynamics. The tests detected no picloram, but did find low levels of clopyralid in five samples, all of them commercial livestock feed.

A Long and Checkered Past

Dow voluntarily withdrew clopyralid for legal use on residential lawns a decade ago following compost contamination issues in California, Pennsylvania and Washington state. By 2004, levels of clopyralid in compost had dropped significantly across the Pacific Northwest thanks to tighter label restrictions. But then in 2010, Washington state farmers were hit again, this time with another Dow plant-killer, aminopyralid, and tainted compost caused extensive crop damage on organic farms and gardens. In 2011, DuPont (not Dow) began aggressively marketing another similar compound?–?aminocyclopyrachlor?–?under the brand name Imprelis.

The chemical companies consider these highly persistent herbicides “green” because a little goes a long way and because they remain effective over time. This staying power actually turns out to be an enormous problem.

Absurd Label Restrictions Aren’t Helping

In May 2011, the U.S. Composting Council (USCC) alerted members about Imprelis, the new persistent pesticide on the block, and the “do not compost” warning buried within its lengthy label. “One problem is that the warning is on page seven of a nine-page label, and unfortunately not everyone reads or follows the label,” former USCC Executive Director Stu Buckner wrote in a memo to members. “We are requesting the U.S. Environmental Protection Agency (EPA) initiate a special review of the registration due to the likelihood of residual herbicide levels in compost damaging non-target plants.” That turned out to be the understatement of the year. Certain species of trees began dying in alarming numbers in areas where Imprelis had been applied, and DuPont was faced with lawsuits seeking multimillions. The company voluntarily began recalling the product a week before the EPA issued an official Stop Sale Order. (See Imprelis: Another Deadly Herbicide, This Time From DuPont for more details.)

Fox Guarding the Henhouse

CSWD General Manager Tom Moreau says it has been frustrating to learn that the EPA has no standard procedures for testing persistent herbicides in compost or feedstocks down to the levels at which garden plants are affected, depending instead upon the companies to develop their own test protocols. “There is no approved standard procedure or certification process,” says Moreau. “The labs have to ask Dow and DuPont and get permission to use their proprietary testing procedures. It’s akin to the fox guarding the henhouse.”

What this essentially means is that when chemical companies market their chemicals, often they are the only ones who know how to run tests to detect contamination?–?and they then charge labs for the right to use the tests.

Given how widespread the contamination was in the Vermont tests, this problem likely transcends the state’s borders. Remember: The testing of dozens of Vermont samples found herbicide contamination in 80 percent of manure, hay and grass clippings. Dow and DuPont are, again, poisoning compost across the United States.

On Aug. 16, 2012, members of the U.S. Composting Council met with 10 EPA officials in Washington, D.C. According to the Council, the EPA was amenable to the idea of developing a testing method to pre-screen herbicides for their fate in compost. Considering how powerful the chemical companies are, however, it’s going to take pressure from the public to force the EPA to finally protect us from this “herbicide roulette.” 

It’s Time to Outlaw Persistent Herbicides

We simply cannot allow chemical giants to continue to peddle such persistent and powerful pesticides. It is well past time for the EPA to fix this problem. The solution is simple?–?stop allowing companies to profit by selling these plant-killers while hiding behind “do not compost” warnings buried in nine-page labels. Our guess is that while the Composting Council agrees with us, it doesn’t want the public to know about this issue because then we might stop buying its products. Well, as much as it pains us to say it, we believe the time has come for the public to stop buying compost or manure products unless they come from suppliers that are able to afford testing and can screen feedstocks for herbicide residues. A few companies have told us this is the only way they know of to deliver safe compost to their customers, but the added costs for testing make competing tough. And now we’ve learned that these Dow and DuPont herbicides are even contaminating our livestock feeds!

This has to stop. Clearly, EPA labeling requirements and state regulations aren’t working. Recycling organic wastes to maintain soil fertility is essential if we want a sustainable food-production system. Picloram, clopyralid, aminocyclopyrachlor and all similar chemicals should be banned, period.

To express your view on the use of these persistent pesticides, we suggest you send your comments to Richard Keigwin, director of the EPA’s Special Review and Reregistration Division, at

Cheryl Long, Editor-in-Chiefof MOTHER EARTH NEWS

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