Aminopyralid (sold as Milestone, Milestone VM, Milestone VM Plus, Chaparral, CleanWave, ForeFront, GrazonNext, Opensight and PasturAll) was released by Dow Chemical Company in 2005 and was marketed to horse and cattle owners to control perennial weeds. Use of the chemical quickly became widespread, and by 2008, thousands of home gardens in Great Britain perished as a result of herbicide-contaminated “killer compost”. In 2009, the problem surfaced here at home, with gardeners and farmers reporting damaged or lost crops from Milestone contamination. The herbicide was rightly pulled from the UK market in late 2008 pending further study?—?but it was reintroduced in 2010, despite fears from farmers and gardeners.

We’ve been reporting on this widespread problem of pyralid herbicide contamination since it first surfaced. The herbicides end up in gardens and on vegetable farms through what should be a natural cycle?—?pasture to manure to compost. Here’s what happens: The EPA allows Dow and others to sell these potent weed killers to ranchers, who then spray their pastures and hayfields. When animals graze on the treated pasture or hay, the chemicals pass through the animals and persist in the manure for several years?—?even if the manure is processed into compost. Gardeners use the contaminated hay, grass clippings, manure or compost on their crops, bringing damage or slow death to plants. These poisons are so powerful that they can damage sensitive crops at levels as low as 10 parts per billion, according to Ohio State University.

Tomatoes are highly sensitive to contamination. In a former North Carolina hay field treated with Milestone in June 2006, residue levels were high enough to damage tomatoes three years later. Symptoms include curled, cupped leaves and wilting new growth?—?problems often misdiagnosed as disease. The herbicide residues also affect carrots, potatoes, spinach, beans, peas, eggplant, peppers, lettuce, raspberries, strawberries and more.

This entire aminopyralid problem is a repeat of damage that surfaced in 2000 in the United States from another persistent Dow herbicide, clopyralid. Clopyralid was used for broadleaf weed control on residential lawns, and it contaminated grass clippings used to make municipal composts. Researchers eventually traced mysterious damage in gardens across the United States to the herbicide residues in compost.

The problem is, Dow hides behind the product label, which says never to use treated materials or manure when making compost. “One load of contaminated grass clippings can ruin a batch of compost,” says Eric Philip of Anatek Labs in Moscow, Idaho. The source of pyralid pollution can be impossible to trace. For example, a horse stable may use hay brought in from a neighboring state, without knowing that it’s laced with pyralid herbicides. If the horse’s manure or stable litter is composted and later ends up in a garden, the gardener’s crops will die or become deformed. Most gardeners won’t have any idea that the cause was hay the horses consumed.

Today, Milestone and other related herbicides collectively known as pyralids (sold under the brands Confront, Curtail, Forefront, Hornet, Lontrel, Millennium Ultra, Reclaim, Stinger and Transline) are still surfacing in gardens throughout the United States, with devastating results. This is not a minor or isolated problem. In Montana, laboratory tests confirmed pyralid toxicity in soil samples from 17 counties across the state. Numerous North Carolina vegetable growers have lost crops to contaminated mulch, hay or compost. Whatcom County in Washington has been hit especially hard, with losses to community gardens and several organic farms estimated at hundreds of thousands of dollars.

The half-life (the time it is expected to persist) of aminopyralid in soil was never clearly determined. The EPA gave aminopyralid “conditional” approval in 2005, despite inconsistencies in the Environmental Fate and Ecological Risk Assessment submitted by Dow and despite Dow’s own data showing a half-life of up to 533 days. According to the EPA’s own scientists, “the persistence of aminopyralid [in soil] may be underestimated in this assessment.” When aminopyralid was approved, reliable lab tests didn’t even exist to identify the herbicide’s residue levels in soil, and today such tests cost several hundred dollars per sample.

The EPA recently asked Dow to make aminopyralid’s environmental risks more prominent on labels, but it’s not reasonable to expect this approach to work. When we pressed EPA officials to say what they plan to do about this issue, they said they intend to reevaluate aminopyralid, with data completion in 2014.

Thousands of acres of North American pasture and rangeland are treated with pyralid herbicides. To protect your garden, ask local stores not to sell pyralids, and ask questions before importing any compost, manure, mulch or topsoil. If you do bring outside amendments or mulch onto your property, test them before use to be sure they don’t contain traces of toxic herbicides (find testing instructions at http://goo.gl/BDukx.) Help yourself and other growers avoid killer compost by contacting the EPA and demanding that they stop allowing these super-potent herbicides onto the market. 

Related Killer Compost Articles

Problems Persist with Persistent Herbicides From the U.S. Composting Council 

The EPA and U.S. Composting Council are working together to solve the problem of killer compost made from persistent-herbicide-contaminated vegetation and manure.

Imprelis: Another Deadly Herbicide, This Time from DuPontBy Barbara Pleasant and Cheryl Long 

We’ve been warning you about aminopyralid-containing killer compost for quite some time. Now there’s a new deadly herbicide on the market, Imprelis, and it’s wreaking havoc in at least seven states.

Keep Your Garden Safe From Killer Compost By Barbara Plesant 

Gardens across the nation are experiencing the devastating, long-lasting effects of aminopyralid and related herbicides, which are in many popular brands, including Milestone and Confront. These herbicides are finding their way into compost through manure from animals that grazed on treated pastures, and they appear to have the ability to persist in soil for years at a time. Want to make sure this doesn’t happen to you? Here’s how.

One Reader Shares Personal Experience With Killer Compost on Her Homestead By Jennifer Kongs 

One reader from central Oregon shares her personal encounter with killer compost laced with aminopyralic, a toxic chemical herbicide, and the affects it has had on her small organic farm. Read about her experience, and find out what you can do to protect your own farm or garden.

 Use a Simple Compost Test to Avoid Contaminated Materials in Your GardenBy Barbara Pleasant 

Keep your garden safe by testing your organic materials for herbicide residue. A few simple tests can help you avoid harming your plants. 

Contaminated Compost: Coming Soon to a Store Near YouBy Barbara Pleasant 

Two powerfully toxic herbicides, clopyralid and its close cousin, aminopyralid, persist in compost and endanger gardeners and the environment. 

Milestone Herbicide Creates Killer Compost By Barbara Pleasant 

U.S. gardeners, organic farmers and commercial growers have reported damaged or lost tomato crops from Milestone herbicide contamination.

Watch Out For Killer Compost By Cheryl Long and Barbara Pleasant 

An herbicide produced by Dow AgroScience, aminopyralid, has been responsible for killing thousands of home gardens across Great Britain. The chemical is found in two brands of herbicide commonly sold in the U.S. and used in pastures grazed by horses, cattle and other livestock. 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.