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Imprelis: Another Deadly Herbicide, This Time From DuPont

Spruce TreeThis post was updated Aug. 12, 2011.   

Since 2008, we’ve been reporting on the dangers of pyralid herbicides (including Milestone, Forefront and other trade names), which turn grass clippings, manure or hay into killer compost or mulch that can ruin gardens and farmland for years.

Despite ample evidence that these deadly herbicides are damaging fields and gardens — and despite our calls for the companies and the Environmental Protection Agency (EPA) to solve this problem — we learned another dangerous pyralid herbicide, aminocyclopyrachlor, had been widely sold in the spring of 2011 following its approval by the EPA in August 2010. Invented by scientists at DuPont and sold as “Imprelis,” aminocyclopyrachlor was marketed to control weeds in cool-season lawn grasses, especially bluegrass.

After one season of use, Imprelis has been implicated in the injury or death of thousands of trees. Conifers that are growing in or near grassy areas treated with Imprelis, and are showing new growth that is brown and twisted, have been reported in Pennsylvania, Minnesota, Iowa, Delaware , Indiana, Nebraska , Wisconsin, and several other states. Michigan State has published an advisory on What to Do With Imprelis-Affected Trees, and Purdue University in Indiana has set up channels for Imprelis related herbicide complaints, as have Nebraska and Wisconsin. And what will happen when the chipped wood from these poisoned trees ends up at compost facilities? DuPont never denied Imprelis-treated lawns would create killer compost. Lost in a 19-item bulleted list on Page 7 of the nine-page Imprelis label, we found this language:

“Do not use grass clippings from treated areas for mulching or compost, or allow for collection to composting facilities. Grass clippings must either be left on the treated area, or, if allowed by local yard waste regulations, disposed of in the trash. Applicators must give verbal or written notice to property owner/property managers/residents to not use grass clippings from treated turf for mulch or compost.” 

Come on, people! How likely is it that most users will remember this from a 9-page label, let alone warn others not to use clippings for hay, mulch or compost? Despite our knowledge of the severe problems these herbicides are causing, the EPA continues to allow chemical companies to sell them and hide behind their “the label is the law” excuse by putting unrealistic instructions and a liability release on the product labels.

Somehow, DuPont’s “over 400 field trial protocols” failed to detect that Imprelis would kill trees. As damage reports began to surface in late spring, DuPont’s response was to send a letter to turf management professionals asking for help as they “continue their work.” The letter said “to be careful that no spray treatment, drift or runoff occurs that could make contact with trees, shrubs or other desirable plants, and stay well away from exposed roots and the root zone of trees and shrubs” when applying Imprelis. It also said to “consult a certified arborist if you are uncertain about the root zone of specific tree species.” Tree roots often spread three times as wide as the branches, so following these guidelines, few properties could be safely treated with Imprelis.

On July 5, 2011, DuPont issued recommendations for handling trees affected by aminocyclopyrachlor. The company’s justification for selling this deeply flawed product was that it had been approved by the EPA. We think the government shouldn’t have to force chemical companies to do the right thing, but regardless, the EPA must stop allowing herbicides to be registered with such unrealistic guidelines for legal uses.

On Aug. 5, DuPont finally halted sales of Imprelis after the EPA threatened to force it to do so. University extension services in 22 states have received reports of damage consistent with that caused by Imprelis, and a team of specialists at Purdue University has stated this chemical should not be used until we know more about its effects. Numerous lawsuits have been filed alleging damage from what DuPont labeled “the most scientifically advanced turf herbicide in over 40 years.”

The world is running out of oil, and that means we are running out of chemical fertilizer. We must expand our systems to capture and recycle organic materials if we are to maintain the fertility of our soils.

You can express your concern about persistent herbicides to Dan Kenny, EPA herbicide branch chief: 703-305-7546; To contact DuPont directly, call its Imprelis hotline at 866-796-4783 or email Mike Kuflik, DuPont sales manager for U.S. turf and ornamentals: 

Related Reading:

Oct 2008: Watch Out For Killer Compost 

July 2009: Milestone Herbicide Creates Killer Compost 

September 2009: Contaminated Compost — Coming Soon to a Store Near You  

Contributing editor Barbara Pleasant gardens in southwest Virginia, where she grows vegetables, herbs, fruits, flowers and a few lucky chickens. Contact Barbara by visiting her website or finding her on .

Photo: Purdue University Extension 

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, Kan., 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 .

barbara pleasant_3
8/4/2011 8:49:05 AM

As of this week, Jeff Schalau, extension agent in Yavapai County, says there have been no reports of Imprelis damage in Arizona. He notes that it is not recommended for use on bermudagrass, and most Arizona lawns are bermuda. The related herbicide that has polluted the compost stream in Washington and other states, clopyralid, also is rarely used in Arizona because it has been found to kill many species of native cacti. You do need to be concerned about aminopyralid, which is used to control weeds in ditches in Arizona. States seem to have more power than the EPA to say no to these dangerous and persistent pesticides. Contact your state congress people about banning these pesticides in your state.

8/2/2011 4:10:02 PM

Since "warmer" climates are mentioned can I safely say that hay grown in Arizona would be considered safe? Most of it is grown in Fort Mohave, a VERY warm place. Thank You.

7/31/2011 10:37:58 AM

With apologies to Joyce Kilmer, 1886–1918 TREES I think that I shall never see A weed as lovely as a tree A tree whose ugly brown is prest Against the poisoned earth’s flowing breast; A tree that may in summer wear A nest of toxins in her hair, A tree that looks to God all day, And lifts her leafy arms to pray, “Why did you Imprelis spray?” Poems are made by fools like me, But only DuPont can kill a tree. funfundvierzig…funfun..July 31, 2011 @ 8:33 AM EDT

7/14/2011 8:46:59 PM

It gets worse. I just checked EPA's registration for Imprelis (chemical name: aminocyclopyrachlor). This herbicide is touted as being safe for humans, but when you look more closely, it turns out that a breakdown product called cyclopropane carboxylic acid is 100 times more toxic than the parent compound. Administered orally, this breakdown product inhibits oxidation of fatty acids, leading to accumulation of fat droplets in cells, especially the liver, which becomes inflamed and undergoes "necrosis" (cell death!). These effects were observed in rabbits, which were tested for just one to 14 days. No fear however. Based on 1-14 day long tests on rabbits, we are assured that infants won't be exposed to more than 9-13% of a dangerous dose in drinking water! This herbicide is persistent, with a half life of 100 to over 300 days, and it leaches into groundwater. EPA admits the need for a "repeated dose study" to assess the toxicity of this hazardous degradate, but went ahead and approved Imprelis without that study. As usual, EPA doesn't consider synergistic effects of exposure to multiple pesticides. This stuff should never have been approved. See "final registration decision" at

7/13/2011 2:10:56 PM

DuPont's bumbling marketing execs are bragging their intractably flawed Imprelis has "proven performance" and has been subjected to "over 400 tests". Apparently and amazingly none of those field tests involved any trees and shrubs in the field, in particular spruces and pines, ubiquitous in the yards of millions of homeowners? ...funfun..

7/13/2011 11:02:09 AM

What is it going to take to stop this kind of stuff? Are you kidding me?

7/13/2011 8:59:13 AM

...“Do not use grass clippings from treated areas for mulching or compost, or allow for collection to composting facilities. Grass clippings must either be left on the treated area, or, if allowed by local yard waste regulations, disposed of in the trash. Applicators must give verbal or written notice to property owner/property managers/residents to not use grass clippings from treated turf for mulch or compost.”.... I believe this would qualify the grass clippings as a toxic waste in most states, requiring the clippings to be taken to a toxic waste dump for legal disposal.

7/12/2011 2:59:50 PM

DuPont's secretive and evasive "leaders" have yet to say a public word of apology or accountability for turning evergreens into everbrowns en masse! Through low-level PR flacks, they have attempted to blame lawn care operators and homeowners, implying misuse of their defective "new" product. With Orwellian irony, DuPont execs tout Imprelis as "environmentally friendly." WHAT? A conifer-killing, compost-killing, soil-poisoning toxic turf herbicide is "friendly" to the environment? That's like saying Casey Anthony is maternal....funfun..