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Herbicide Contaminants in Purchased Straw, Compost, Manure & Dairy Waste

Herbicide Contaminants in Purchased Straw, Compost, Manure & Dairy Waste


by Tom Allen 


For the coming season be very careful what off-site inputs you bring into your garden or farm. Though they have been de-listed for lawn use, the herbacides Clopyralid, and Aminopyralid can still turn up in mulch and compost. They are used in industrial ag. as a weed killer in grain fields and pasture. They are very effective herbicides and persist in soil for several years. They pass through the digestive systems of ruminants unscathed and break down very slowly in the composting process. This means that manure from animals fed non-organic grain may contain herbicide residue. That threatens the entire local/organic food movement as we typically require animal waste as fertilizer.


If you have not already done so, do not use commercial straw in your garden. If you buy organic straw, trace its chain of custody back to the source. Don't rely on assurances of organicness from vendors. The risks are just too high.


Consider my experience.


For two years (09 & 10) I bought straw mulch from two different feed stores and have had crop failures of plants known to be sensitive to broadleaf herbicides; that is, peas, beans and potatoes and tomatoes. The culprit may be Clopyralid, Aminopyralid or both. 


There was a known problem several years ago with Seattle city yard waste containing Clopyralid entering the waste stream composted by Cedar Grove. It was reported in an article in The Seattle Times, cited in the wikipedia article on Clopyralid below. I had assumed the problem went away, misunderstanding that Clopyralid had not been banned outright. It had been de-listed for lawn use but not for agricultural use.


If you think your garden may be contaminated, WSU suggests a bioassay (See below) with a limited number of known sensitive plants in a test bed filled with suspect soil or compost. I essentially did this last season and have determined that the known sensitive plants  did not flourish. The chemicals mentioned have a detrimental effect on Potato/tomato family, Fabaceae, which includes peas and beans, brassicas, and Asteraceae,  the sunflower family. 


Once you determine that you have a problem you need a solution. I contacted Dr. Richard Haard retired professor at WWSU and he has offered a solution that I include following the WSU Extension pages.


From WSU Extension

Aminopyralid Residues in Compost and
other Organic Amendments

Pepper, 2010



Effects of aminopyralid residues in dairy organic matter (manure, composted manure, silage) applied to broadleaf crops on farms and gardens in Whatcom County have been seen in 2009 and 2010. Aminopyralid is an auxinic herbicide that will cause damage to sensitive broadleaf plants such as tomato, beans and peas; these plants will usually not die, but will produce no or few, low quality fruit.


What is aminopyralid?

Aminopyralid is a broadleaf herbicide registered for use on grassland and rangeland. It is registered under several product names to control many broadleaf weeds, including invasive and noxious weeds, on grass crops as rangeland, permanent grass pastures, as well as non-cropland areas.


Why is aminopyralid used?

It has long-lasting effects against target weeds when applied at low rates. Aminopyralid has low toxicity to humans and animals.


How did aminopyralid get into my compost/manure/topsoil mix?

Aminopyralid was probably used to control weeds on grassland for dairy farms. The grass was cut and fed to dairy cattle. Aminopyralid in the feed does not harm livestock and is rapidly excreted in urine and manure. Manure is often separated into solid and liquid portions on the dairy farm. The soilds are collected from the dairy and distributed to a farm (to be applied directly as organic matter and nutrient source) or to a composter (to produce compost for farms and gardens). Aminopyralid breaks down slowly or not at all in the digestive system of a cow or in the composting process, instead remaining with the organic matter through the process.

Dairy manure is a significant component of compost in Whatcom County and manure solids are distributed throughout the county as an organic soil amendment. It is often used in "topsoil" mixes, such as "3-way" or "5-way" mixes, for use in home gardens and landscapes.


What can herbicide residues do to my plants?

Residues of aminopyralid in manure, composts or soils can cause damage to sensitive plants at levels as low as 1 part per billion. Some plant species are more sensitive than others, but all broadleaf plants are considered sensitive to this molecule. Damage includes cupped leaves, twisted stems, distorted apical growing points, and reduced fruit set (see pictures).


Are fruits and vegetables grown in aminopyralid contaminated soil safe to eat?

According to Dow AgroSciences, "If aminopyralid has been introduced into your garden, and plants are showing symptoms of herbicide damage consistent with aminopyralid, but produce a harvestable yield, these inadvertent aminopyralid residues are at a level low enough that you can eat the produce from the garden. Produce from the garden cannot, however, be sold."


How do I know if my organic matter is safe?

Before planting in soil that contains organic matter from a dairy, perform a bioassay. This entails growing a small number of the desired plant in the soil or media to be used; the plants should be grown to full maturity to determine if damage will occur. The bioassay should be performed before the organic matter is applied to the farm or garden, but can also be done after the organic material has been added to your field, garden or landscape. This can be done by planting seeds of plants with known susceptibility, such as peas, beans or tomatoes, in small pots with a mix of suspicious material and peat based potting mix. For instructions for this bioassay, see the WSU publication at:


What can I do if I know that my organic matter contains herbicide residue?

Aminopyralid is slowly broken down by microorganisms commonly found in soil. If organic matter is found to contain herbicide residues, it should be incorporated into the soil and irrigated heavily; a second and third mixing with the soil may speed the decomposition of the material. An additional bioassay should be performed before planting a new broadleaf plant into the material.

Other options may be to 1) plant a cover crop (such as winter wheat), then remove the plants to either burn them or shred and apply them to a non-sensitive area, 2) plant crops that have a higher tolerance to aminopyralid, or 3) remove the organic material that was applied and spread it on a non-sensitive crop area, such as grassland.


What is being done to reduce the impact of this issue?

Washington State University Extension is working with Washington State Department of Agriculture and other agriculture organizations to determine the best way to use remaining dairy derived organic matter containing aminopyralid residue. It is expected that the use of aminopyralid on dairy forage crops will be greatly reduced to lessen the risk of contaminated organic matter in the future. Residues may remain in the soil, plant tissue, and dairy waste for another year or more; the farming and gardening communities need to work together to fully understand this issue and take steps to manage it.

Colleen Burrows and Craig MacConnell; June 29, 2010



Washington State Department of Agriculture: Herbicides in animal manure, compost raise concerns for growers and gardeners.

Dow AgroSciences. Manure Matters Website

Washington State University and Washington State Department of Ecology. 2002. Bioassay test for Herbicide Residues in Compost: Protocol for Gardeners and Researchers in Washington State.

Rynk, R. 2002. Prevalence and Fate of Clopyralid in Compost. BioCycle.

Bezdicek, D, M. Fauci, D. Caldwell, R. Finch and J. Lang. 2001. Persistent Herbicides in Compost.


A Possible Solution


There is some question as to whether activated charcoal as recommended below is effective. Dr. Haard believes so. Per Michael Pilarski, old-growth permaculture teacher and farmer.

"Richard Haard is one of the most knowledgeable people in the state of Washington on this topic." 

I have bought a bucket of activated charcoal and applied it to the affected areas. It is likely that the charcoal will also trap nitrogen and make is unavailable to plant roots. I'll make allowances for that. We shall see how my experiment turns out. I will report back. 



Pilarski also offered this:

Some further recent resources

Albert Bates has a new book and website on the topic.

James Bruges book The Biochar Debate (Green Books)


Per Dr. Haard




What I have been recommending is the use grosafe activated carbon, made by Norit corporation. Likely it is coconut charcoal run thru the process. It is a nice product and is easy to handle.

I have purchased so far 2 - 2 gallon pails from buyactivatedcharcoal


Are a reliable company and good shipping.


You should be able to use your soil right away. The deactivation is essentially instant. My work so far has been only with preemergent herbicides and is working very good. In addition, I notice some stimulation in seed germination and seedling vigor. It could be deactivation of natural allelopathic compounds. (my theory)


here is my poster


Best wishes


Rich Haard


Citations From Wikipedia:



Molecular formula C6H3Cl2NO2

(3,6-dichloro-2-pyridinecarboxylic acid) is a selective herbicide used for control of broadleaf weeds, especially thistles and clovers. For control of Creeping Thistle, Cirsium arvense, a noxious, perennial weed, clopyralid is the only effective herbicide available.

Clopyralid is in the pyridine family of herbicides, which also includes picloram, triclopyr, and several less common herbicides. It is particularly active on members of the Asteraceae and the Fabaceae. It does not affect members of the Poaceae (grasses).

Clopyralid is notorious for its ability to persist in dead plants and compost, and has accumulated to phytotoxic levels in finished compost in a few highly publicized cases. In Seattle, Washington, clopyralid was widely used for weed control in lawns until prohibited in 1999. There, a city-mandated curbside grass clipping collection and composting program produced compost with measurable levels of clopyralid. Subsequently, DowAgro, the manufacturer of clopyralid, voluntarily deregistered it for lawn uses.

Clopyralid is still licensed for lawn use in France and is available under the following names: Bayer Jardin: Désherbant jeune gazon and Scanner Sélectif gazon Vilmorin: désherbant Gazon LONPAR


And its relative 



From Wikipedia, the free encyclopedia

Jump to: navigation, search



IUPAC name[hide]

4-amino-3,6-dichloropyridine-2-carboxylic acid

Other names[hide]

4-amino-3,6-dichloropicolinic acid


CAS number 











Molecular formula 


Molar mass 

207.01416 g/mole


Off-white powder


1.72 (20°C, relative to water at 4°C)

Melting point 

161.75 - 16523°C

 (what is this?)  (verify)

Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

Infobox references 

Aminopyralid is a selective hormone-based herbicide manufactured by Dow AgroSciences for control of broadleaf weeds on grassland, such as docks, thistles and nettles. It was first registered for use in 2005, in the USA under the brand name "Milestone".[2]

Aminopyralid is of concern to vegetable growers as it can enter the food chain via manure which contains long lasting residues of the herbicide. It affects potatoes, tomatoes and beans, causing deformed plants, and poor or non-existent yields. Problems with manure contaminated with Aminopyralid residue surfaced in the UK in June and July 2008, and at the end of July 2008 Dow AgroSciences implemented an immediate suspension of UK sales and use of herbicides containing Aminopyralid. A company statement explained:

"Consistent with its long-standing commitments to product stewardship, and in cooperation with United Kingdom regulators, Dow AgroSciences has asked the Pesticide Safety Directorate (PSD) for a temporary suspension of sales and use of herbicides containing aminopyralid. The suspension shall remain in place until assurances can be given that the product and subsequent treated forage and resultant animal wastes will be handled correctly."[3]



Tomato plant affected by aminopyralid herbicide residue from contaminated manure, grown July 2008, Cheshire, UK. Note tightly curled leaves, which is a symptom of aminopyralid contamination.

As of July 2008 the following herbicide products that include aminopyralid in the UK include: Banish, Forefront, Halcyon, Pharaoh, Pro-Banish, Runway, Synero and Upfront.

An online petition to the British government to "halt the use of Aminopyralid as a weed killer in British agriculture" gathered 1,459 signatures and the following response:

"Unfortunately the label prohibition on using manure that could contain aminopyralid on susceptible crops has not always have been followed when manure has been supplied to allotment holders and gardeners resulting in damaged crops. However the Government confirms that this has no implications for human or animal health."

"The manufacturers of aminopyralid products have now withdrawn their products from sale and the Government has formally suspended their approvals whilst they investigate the options for mitigating against a recurrence of this problem. Only when the Government is satisfied that the necessary measures to achieve this can be put in place will aminopyralid products be allowed back on the market."[4]

Despite restrictions, symptoms of aminopyralid damage were recorded on crops growing in allotments in Edinburgh UK as recently as June 2010; enquiries traced the source of contamination to a farm supplying hay to the stables from where bags of manure had been obtained.


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Comment by Tom Allen on June 26, 2012 at 10:51am

To follow up on my post of last spring, 2011, I had some difficulty getting beans to grow in the affected spot even after the charcoal treatment. This spring, 2012, the beans are doing well in the same spot with no further treatment. So, it may take some time for the charcoal to work. Other crops did very well after the charcoal treatment. However, I added worm casting tea to the mix and that may have helped too. I now have a 12 foot cardoon plant in the bed that was treated. Wow! Kale grew to about 4 feet tall before bolting last winter. So, I seem to have his on a good formula with the charcoal and worm tea.

Comment by Lacia Lynne Bailey on April 29, 2012 at 10:33am

Really good info and well presented Tom!   I wish I'd seen this before!


So what happened with your experiments?  It'd be great to see the outcome posted.

Comment by Tom Allen on April 6, 2011 at 12:16pm
Thought I give you an update on my tests.

I planted two flats with peas, one in purchased potting soil and one in my own compost that may be contaminated with decomposed straw. Peas in potting soil are emerging. Looks like a 50% rate after 17 days. Daytime temp in the low 40s. Soil temp today is 45 F on a partly cloudy day.
Peas in  suspect compost have not emerged, G.R. = 0%.

Spinach planted in suspect compost treated with activated charcoal has emerged after 17 days  at ~85% rate but show signs of yellow. Broccoli about the same GR but plants look better; also treated with A.C.

I drenched  with A.C. existing beds having wintered over plants. In nearly all cases those that were alive have perked up considerably within a few days following the drench 17 days ago. There are a couple of chard plants with badly misshapen leaves that haven't responded much. Other chard looks much better. Aliums and Collards haven't seemed to suffer but broccoli and brussels sprouts have not done well. Brussels sprouts have now put on a growth spurt and are bolting. Big Dinosaur Kale that normally would have gone to seed this season has died. Dwarfs planted late in the summer are bolting. They never reached a good size. Amongst the brassicas only collards did well.

I suppose the plants are responding to more daylight hours but the temperatures haven't changed much since January except that it's quit freezing at night. .

WSU extension got wind of my plight and want to test the straw so I gave some partially decomposed straw to Sue McGann who's the conduit to WSU. We'll see.

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