Persistent herbicides in composts, manures, hays and grasses

George Monbiot posted an article a few days ago in the Guardian about the negative garden effects of a persistent herbicide called Aminopyralid. Aminopyralid is a broadleaf herbicide used to control “weeds” in turf grasses, pastures and rangeland.  Manures from animals eating these grasses still contain non-degraded Aminopyralid and therefore if applied to soil growing broadleaf plants will damage those plants.  I made a comment post on George’s article and I think it is worth repeating here. We all need to keep our eyes open when dealing with manure and compost feedstocks that may contain persistent herbicides:


Please excuse the long post but this is very important for those of us making composts and/or using manures as soil fertilizers. You might want to print this comment out and put it on your fridge.

The problem goes beyond aminopyralid and just manures.

First, people should know that Monbiot got his aminopyralid definition incorrect. Aminopyralid is not a pesticide; its a hormone-based persistent herbicide used to control broadleaf “weeds” on range, pastures and turf.

A persistent herbicide is chemically designed to have a very slow soil degradation process, lasting several growing seasons depending on the type of soil and climate where its used. Only having to apply the persistent herbicide every few years is its selling feature. Most herbicides are microbiologically broken down or degraded within a few days or weeks (like 2,4-D) in the soil and leave no lasting herbicidal impacts.

A broadleaf herbicide does not kill or affect monocot grasses. It severely stunts (leaf tip curl and whithering) and/or kills broadleaf “weeds” and every other broadleaf plant like a tomato plant and all the other annuals in our gardens. Aminopyralid often results in very deformed fruits, like small pear shaped tomates.

A couple of years ago (I think 2007-08) aminopyralid caused big problems first in the northwest US (Washington state) when grasses sprayed with it were eaten by dairy cows. The dairies couldn’t use all of the inhouse produced manures for field applications. Dow instructions for aminopyralid use are to apply the aminopyralid manures back on the same aminopyralid sprayed grasses. The excess manures HOWEVER, were shipped off site and used to make compost. One Washington farmer who used the aminopyralid contaminated compost lost over $200,000 USD in crop losses.


Persistent herbicides like aminopyralid do not break down in a composting process.

Though many of us talk about the amazing detoxifying capabilities of a humus and microbiologically rich compost (microbe rich compost IS an amazing soil bioremediator), some human made chemicals are persistent tough molecules and degrade slowly. Its important to know what you put into your composts and whether you have a persistent chemical.

And, aminopyralid does not move or leach through the soil either, staying in place for the multi-year degradation. That means you either wait and plant nothing or remove the soil and bring in new uncontaminated soil.


It can still take 2 or 3 years for the persistent herbicide to degrade even after going through a composting process, THERMOPHILIC OR NOT. There are some human made chemicals designed to be persistent that do not degrade through composting. Whatever these persistent chemicals are designed to do will then be an effect of using the compost. As a result an aminopyralid contaminated compost becomes a broadleaf herbicide. So, when you use your freshly made microbe rich compost, you and your plants will literally get burned.

And, aminopyralid is only the one of a few persistent herbicides (and pesticides) we have to worry about and its not the latest. Here’s the list of persistent stuff you need to watch out for starting with the latest one, Aminocyclopyrachlor, just coming onto the market in the US this year (2011):

maker: DuPont
brand name: Imprelis, Perspective, Plainview, Streamline, Viewpoint

use: Hormone-based herbicide used to control broadleaf “weeds” on turf grass, bare soil, for road side weed and brush control. CURRENTLY, up for USEPA review for use on range and pasture.

status: US Composting Council sent a letter to the USEPA about the Dow label restrictions prohibiting composting Aminocyclopyrachlor sprayed turf grass. DuPont has partnered with Scotts to make and market for residential use (Imprelis is the common name).

maker: Dow
brand name: Chaparral, CleanWave, ForeFront, GrazonNext, Opensight, Milestone

use: Hormone-based herbicide used to control broadleaf “weeds” on turf grass, pastures and rangeland.

status: despite Dow label warnings about not exporting Aminopyralid off farms in contaminated hay or manure, aminopyralid, as Monbiot outlines above, continues to be a problem for veggie growers big and small.

FMC Corporation
brand names: Talstar, Maxxthor, Capture, Brigade, Bifenthrine, Ortho, Home Defense Max, Bifen IT, Bifen L/P, Scotts LawnPro Step 3

use: Sythetic pyrethroid insecticide used to control fire ants, termites and stink bugs

status: seen as everywhere in compost made from yard trimmings with fire ant prevalence, USDA Nat. Organic Program considers bifenthrin an Unavoidable Residual Organic Contaminant.

maker: Dow
brand name: Cloypry AG, Confront, Lontrel, Mellenium Ultra, Reclaim, Stinger Transline

use: Hormone-based herbicide used to control broadleaf “weeds” on turf grass (home use where legal), pastures and rangeland.

status: Crop failures in Washington state in 1999 traced back to compost containing Clopyralid. Also, found in California, New Jersey, Oregon, and Pennsylvania. Major composts inputs were grass clippings and hay. Some US states have banned Clopyralid for home use.

I understand that the Canada Composting Council has sent a letter to Health Canada about Dow’s Aminocyclopyrachlor. Aminocyclopyrachlor or Imprelis is currently not for sale in Canada but I think Dow has applied for some type of selling approval. Don’t know if Dow has applied for approval to sell In other countries. If you have a national composting council or organization you should contact them to ask about Aminocyclopyrachlor and Let them know if they don’t already about what’s happening in the US and Canada.

On that note, what I covered here is US and Canada stuff including the common brand names. You may need to do some checking in other parts of the world especially for what the common brand name is.

So, when you’re putting together a compost pile you really need to trace back your hay (grass) and ruminant (cow, sheep, goat, bison, etc.) and cecal digester (horse, donkeys, rabbits) manures to see if a persistent herbicide has been sprayed on the grass feed. You’ll need to make your own judgement about how far you trace back. Just remember that many farmers have been burned by contaminated hays and manures that were said to be clean. So do the checking you need to be comfortable. As more of thee products come out we’ll all have to be more vigilant.

Buena suerte.

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