A Herbicide in Compost Kills Crops

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Photo by Istockphoto/John Fuller
A herbicide in compost kills crops. Aminopyralid can persist in manure or previously treated straw, threatening tomatoes, lettuce, beans and other sensitive crops with which these come into contact. Here’s how you can protect your garden, even if the EPA won’t.

Home food gardens are falling victim to a persistent pesticide found in some forms of compost, this herbicide in compost kills crops.

Gardeners beware — straw, manure and maybe even compost can kill your garden, thanks to the folks at the Dow chemical company. An herbicide called aminopyralid, released by Dow Agroscience in 2005 and aggressively marketed to horse and cattle owners to control perennial weeds, has been associated with an herbicide in the compost that kills crops and the loss of thousands of home gardens in Great Britain this year. So can it happen here? You bet! Previously treated straw and even well-rotted manure may carry enough persistent plant killer to kill tomatoes, lettuce, beans and other sensitive crops.

Dow’s Clouded History

This is the second time that Dow herbicides that were supposed to degrade within days were found to persist for years. In 2001, Dow’s clopyralid (still sold as Confront), was found to be the contaminant in compost that killed home garden and nursery plants in Washington, Pennsylvania and New Zealand. (For more on clopyralid in compost, see Ann Lovejoy’s article, Beware of Herbicide-Laced Compost.) Aminopyralid, the active ingredient in common herbicides Milestone and Forefront, belongs to the same class of chemicals that includes clopyralid.

Dow’s behavior defies environmental corporate responsibility. They know their product is capable of causing significant environmental harm, yet they continue not only to sell it, but develop and sell new products that pose equal or greater risks. And shame on the U.S. Environmental Protection Agency EPA) for letting this happen again!

How Did the Contamination of This Compost Happen?

A close read of the EPA’s paper trail shows that the half-life (the time it is expected to persist) of aminopyralid in soil was never clearly determined. Still, the EPA decided that aminopyralid was “safe for humans and the environment.” The license to sell was granted despite the fact that Dow’s own data showed a half-life of up to 533 days. Despite that, only two studies were done to investigate its persistence in soil. Even though clopyralid was known to persist in compost, specific inquiries were never made into the newer herbicide’s fate in manures. In their 2004 response to Dow’s registration application, three EPA scientists said that both of Dow’s soil dissipation studies were of “questionable validity.”

Regardless, Milestone and Forefront were fast-tracked for EPA approval through the Reduced Risk Pesticide Initiative. The Initiative says that if new pesticides, when compared to those that came before them, are clearly less toxic to people and animals, less scientific data is required to win EPA registration. The environment — and the right of people to grow uncontaminated food — hardly gets a seat at the policy table.

Keeping Your Garden Safe

Thousands of acres of North American pasture and rangeland have been treated with aminopyralid, so gardeners should ask questions before buying manure or compost that contains manure. If the seller doesn’t know if it’s safe, don’t buy it.

You may be able to help prevent hundreds of garden disasters by spreading the word about this problem. If you know of friends or neighbors who might use herbicides to control weeds in their pastures, tell them! Alert your local composting facilities, too, because gardeners work too hard to lose their food to corporate greed and government loopholes.

For more on this topic, see Contaminated Compost: Coming Soon to a Store Near You and the Ask Our Experts post that explains how to test your compost.

Cheryl Long is the editor in chief of MOTHER EARTH NEWS magazine, and a leading advocate for more sustainable lifestyles. She leads a team of editors which produces high quality content that has resulted in MOTHER EARTH NEWS being rated as one North America’s favorite magazines. Long lives on an 8-acre homestead near Topeka, Kansas, powered in part by solar panels, where she manages a large organic garden and a small flock of heritage chickens. Prior to taking the helm at MOTHER EARTH NEWS, she was an editor at Organic Gardening magazine for 10 years.Connect with her on.