Killer Compost Update: Herbicide Damage Still a Major Problem

Persistent herbicides continue to contaminate the compost supply — and the herbicides are turning up in new places, including livestock feed. Learn about this serious problem affecting gardeners.

  • Curled Leaves Indicate Herbicide Damage
    Curled plant leaves, like the leaves on this eggplant, are a telltale sign of herbicide damage.
    Photo By David Goodman
  • Watch Out for Killer Compost
    Potent chemicals are contaminating compost and manure supplies, a problem we've termed "killer compost." 
    Photo By iStockphoto/Markswallow

  • Curled Leaves Indicate Herbicide Damage
  • Watch Out for 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.

8/20/2016 4:49:42 PM

We made some raised beds about six months ago. This the first time we had enough outdoor space for gardening in ten years. We thought we were being careful with a mix of 2 parts topsoil, two parts compost, 1 part peat moss. I amended the soil with crab shells and kelp meal. We then planted tomatoes, corn, pole beans, etc at anxiously waited. Everything looked great for about a month. Then the growth stalled. We did everything we could think of, but eventually all the crops failed, except for the radishes. We also planted a few peppers in buckets, not using the composted Cow manure that we put in the beds (we ran out room in the beds). The peppers in the buckets are big and bushy. There is one pepper plant still alive in the raised beds and it's about 5ins tall after six months!! We are inexperienced gardeners in the zone we live in (10b) and assumed we started everything too late in the season. After reading this and a few other resources I'm beginning to think it was the cow manure. I read that charcoal can help. I'm going to try that, as I just planted a new crop of peppers in one of the beds and they don't seems too happy.

5/20/2014 7:11:32 PM

To anyone that has ever ran into a herbicide carry over I have the answer that will help you. I work for company that provides a natural approach to herbicide in the soil. Oh and did I mention it is usda certified organic. This product is called Reclaim. Reclaim stimulates the existing microbes in the soil to create a barrier between the roots and the herbicide. this prevents the toxins from entering the plant and allows the mirco biology to break the chemical chains of the herbicide apart. This is a concentrate so you only need a quart per acre. this is a crop saving miracle that I wish more small scale farmers new of!!! If any one would like to get this product email me @

4/22/2013 7:17:43 PM

So, do I need to worry about the manure that I am getting from daughter's rabbits? How are we supposed to any manure is safe? Is there any plan to test the different feeds for traces of this stuff in it?

This just another reason I would like to move to my own island and raise all my own food.




Fall 2021!

Put your DIY skills to the test throughout November. We’re mixing full meal recipes in jars, crafting with flowers, backyard composting, cultivating mushrooms, and more!


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