Curling Leaves On My Tomato Plant
Curling leaves.

If you’re going to buy manure or use manure in your organic garden, you’ll want to read this email I received from Janet, one of my readers. It’s a good story with a very important warning:

“I have a sad composting/soil tale to share that I’d like to share with as many gardeners in the area as possible so please pass this along.

As many of you know, I’ve been an organic gardener for many years, making my own compost, using natural ingredients. I might buy manure or find it free. Last week I diagnosed a problem with my soil, specifically with some of my tomato plants due to a batch of “killer manure.”

I start my own seedlings, which this year included 12 tomato plants. I planted half of my tomatoes in a bed with poor, compacted soil beside my house and half in a bed with superior soil in the organic garden.

The house bed plants have been looking peaked since they were set out, growing feebler each day. The new growth is “shoestring” looking, with the leaves curling into themselves so tightly they make hard little knots that won’t uncurl. See the photo below.

The new growth is pale. Every time I looked at them, I thought “herbicide damage” but thought that couldn’t possibly be the case because neither I nor any of my neighbors use herbicides. I checked with them all to make sure.

I looked up “curly top virus” and “cucumber mosaic virus.” Both showed similar but not exact matches for symptoms. I searched online for other diseases or pests but nothing matched. When I heard that plants I’d given to a couple of people died while others stayed healthy, I thought maybe I had the same thing – root nematodes or something.

I drenched the tomatoes with a foliar seaweed fertilizer and also with neem oil – slight response but still very sickly looking. Several of the fruits were mutant looking weird things while other fruits look okay. Meantime their siblings in the vegetable garden bed are growing sturdy, green and lush.

Last week my friend Kathy stopped by and affirmed my “herbicide damage” sense. When I told her neither I nor the neighbors use chemicals, she asked if I’d brought in any bulk soil or compost that might have been contaminated. No, I said. Then I remembered the manure.

I didn’t even buy manure. In mid-May, a family member delivered a gift of 1.5 cubic meters of 4 year old horse manure. On June 2, I used a couple of 5 gallon pails of that manure in the planting holes for tomatoes planted in my house bed, a couple of barrow loads in my new cucumber bed and, a week ago, a few scoops when transplanting the lupins someone gave me.

Other than that, the manure has been sitting in a heap on my front yard, waiting to be incorporated into my fall compost. Good thing.

With a little online searching, I found an exact photo match for my tomatoes on sites about “aminopyralid,” a component of several herbicides manufactured by DowAgro, a division of Dow Chemical.

For those of you as unfamiliar with herbicides as I am, aminopyralid is a selective, hormone-based, broad-leaf weedkiller, a component of herbicides for use on hay, grain corn and grass crops. The farmer sprays the herbicide on the hay to suppress broadleaf weeds.

The cows or horses eat the hay and their manure contains the herbicide which affects any non-grass crops which it is spread on. This is where my manure problem comes in. Aminopyralid is what is called “persistent” in chemical agriculture circles. It does not break down in animal digestion and travels intact in ground and surface water. Breakdown in manure or compost heaps takes 5 years or more.

Gardeners in UK (seriously affected since 2004), USA and Canada are reporting much slower breakdown than Dow suggests – up to 600 days to half-life. Tests done by the Canadian Regulatory Authorities suggest that in clay loam soils, it can take up to two years for the aminopyralid to be released.

According to DowAgro:

  • Most affected are potatoes, tomatoes, peas, beans, carrots, peppers, lettuce and similar crops (eggplant, arugula, asian greens, etc.).
  • Young trees are severely damaged or killed.
  • Some sensitivity: raspberries, gooseberries, blackcurrants, red currants (however, gardener reports are that these fruits are severely damaged even with a light top-dressing).
  • Heavy application may affect leeks, onions, shallots and garlic
  • Less sensitive are brassicas (cabbage, broccoli, etc) and mature top-fruit trees (apples, pears, etc)
  • Least sensitive are all grasses, including most grains and corn.
Tomato Damage From My Manure Problem
Unhappy tomato plant

I’m fortunate in that this manure problem didn’t affect my whole organic garden – I didn’t spread this manure all over my yard, just in a couple of beds. The cucumbers are exhibiting a bit of leaf-cupping and the three cukes I’ve harvested so far were less than half the size of normal. The lupins are not doing well – major leaf cupping and a sickly greyish tone.

My plan is to spread the pile on the boulevard. It’s far from any vegetable garden or trees and I doubt anyone will try to grow broadleaves there anytime soon. The beds I’ll cultivate well this fall (contrary to my usual no-dig soil management), then I’ll plant with brassicas or alliums next year. So far adjacent plants (veronica spicata, a heritage lily, ornamental allium, echinacea, rudbeckia and an Explorer rose) are not showing any signs of damage.

To prevent this manure problem from happening to you, make searching inquiries of the manure supplier to ensure that the animals have not been fed on grass treated with this weed killer. Many farmers and ranchers may not know “aminopyralid” by its chemical name, but rather by Dow’s market name (ie. Torchon or Grazon). See Dow Agro’s website for a list of aminopyralid products.

Many manure suppliers, especially those who purchase hay and feed or who lease graze, will be unable to confirm that their animals have not been fed with contaminated feed. If you cannot get absolute confirmation that the manure has not been contaminated with aminopyralid, it might be better to avoid that source of manure.

Once you have your manure, make sure that you test it for aminopyralid contamination, using a bioassay test (see Dow or other websites for instructions).”

Any questions about this?

If your goal is to improve your soil with manure, you’ll want to either compost it first or buy it already composted.


  1. Tq on January 14, 2012 at 5:21 pm

    We really need to play detective – every day for every choice we make.  Thank you so much for sharing this information.

    • Michael Maciorski on May 9, 2017 at 2:11 pm

      Have wrecked my brain trying to figure this one out! The beauty of it is I WAS LOOKING FOR MORE MANUREand this warning came up! My blessings and thanks! I know this is it!!!

    • Mery K. on June 27, 2017 at 12:08 pm

      Whoa, thanks so much for the information. I’m beginning to go totally organic in my vegetable garden and this year my potatoes, tomatoes , green sweet pepper and green beans have destroyed by the same disease. I took sample leaves to a nursery to be advised but no one seemed to be aware of the problem. Is there any remedy or treatment of the affected soil? Mery K. Georgia.

      • Phil on July 2, 2017 at 3:06 pm

        Applying beneficial microbes might help (compost, compost tea, effective microorganisms). Read Janet’s comment for more details.

  2. Early Riser on January 14, 2012 at 5:21 pm

    Oh yes. I am devastated. Several truck loads of manure from a dear friend who works hard to be organic were inadvertently contaminated by feed she gave her horses. My years of building soil and organic gardening have been wiped out. Be advised the affected plants contain the herbicide so do not re-compost them or plant a cover crop, it just soaks up the herbicide and the cycle continues. Dow needs to pull this off the shelf, it is just too strong to release into environment and not easily tracked. It can ruin our food chain. Summer 2011.

    • Phil on January 14, 2012 at 5:33 pm

      Wow, that’s actually surprising to me that the herbicide went through thehorses and still caused such major problems. How did you figure it out – didyou test the manure after? Just goes to show that we need to be careful ofwhat kind of organic matter we bring into the garden, including manure,straw, leaf mold, and other such things.

      • Jack Campbell on June 22, 2017 at 9:35 pm

        Would be good to buy manure that is heat treated before selling. Fresh might not be a good thing anymore.

        • Phil on June 25, 2017 at 1:24 pm

          I suppose it depends on what you’re using it for. Conceivably, heat treating could be useful in some situations. And yet it won’t get rid of most pesticide residue.

        • Eliot on April 20, 2019 at 10:07 pm

          If you go to manure go cow not horse manure for reasons I won’t get into hear. Also if it’s not aged it’s to strong and isn’t broken down just like any other compost. You would put raw kitchen scraps right onto your vegetables as they grow because whatever is breaking down your scraps will effect your plants. The Amish people have been growing vegetables forever with grate results. Broccoli heads as big as basketballs and I can go on. Aside from preparing your soil one needs more than manure but just because of misuse of it by some it shouldn’t be over looked as a nutrient building your soil. The only problem I have is I can’t find it in my area right now in affordable bulk and organic.

    • Lois Gertz on April 9, 2018 at 1:40 pm

      Will this herbicide be in the salad vegetables I throw in my compost bin????

      • Phil on April 10, 2018 at 1:06 pm

        Yes, sometimes, but in smaller amounts. I do compost food scraps even when they’re not organic.

    • Ben Smith on April 17, 2018 at 11:41 am

      They won’t take it off the shelf unless they make a better strain of it first. When it is that powerful. They keep it because it works well. I garde. Not farm. But a friend of mine uses stuff like this and loves it because it kills everything and when the animals eat it the manure goes back on the same fields keeping its effectiveness on the field and reducing the nessisary concentration for future sprays. It costs thousands to keep good fields. Farmers can’t afford a sub grade product.

  3. Tq on January 14, 2012 at 5:34 pm

    How would you test for these herbicides?  Could a soil lab tell you?  I would be interested to know who in BC would use such a chemical on their hay crops and how we can avoid it.

    • Phil on January 14, 2012 at 5:34 pm

      I’ve never gotten in to testing for pesticide residues, but I would beinterested to know, too. My labs don’t advertise this service. If anyoneknows, it would be great if you could tell us here.

    • Susan Chambless on July 2, 2018 at 3:42 pm

      I’ve read that growing some test plantings of beans beside controls in known good soil is a good test.

  4. Gardenlaura on January 14, 2012 at 5:35 pm

    maxxam lab in burnaby lists herbicides and pesticides as parameters they test for.  i’m not sure how specific their tests are but it would be well worth asking them 1-800-665-8566

  5. Joreme on January 14, 2012 at 5:35 pm

    May be a problem with using hay as a mulch cover: I planted potatoes and then bought a bale of hay from a well known hardware store to cover the soil. The plants look just like your picture! I was wondering what was going on. I have checked them for pests, etc. with no idea what else might be going on. Thanks for the info.

  6. Kay Gschwind on January 14, 2012 at 5:36 pm

    Late to this thread but just had to post.  Several of my tomato plants last summer had the same weird growth issue and yes, that bed was amended with aged composted horse manure from a commercial outfit here in the area.  Nothing this year has anything like the same deformities so perhaps it was only a small amount, I should be so lucky.  I appreciated the identification of the manure problem, though

  7. Janet on January 14, 2012 at 5:36 pm

    Realized I haven’t stopped by for several months. Canadian Organic Growers ( published this info and more of my experience and research findings in the “Readers Write” column n the fall 2011 issue of their magazine, TCOG magazine. I suspect they would welcome inquiries for copies of the article. I offered to do a followup article on the mitigating effects of using aerated compost tea and EM’s but they haven’t taken me up on it.Phil, if I may, I’ll answer some of the questions asked (feel free to edit or delete at will)…Tq, the best test for clopyralid, aminopyralid and picloram residues is a “bioassay” test, something you can do most easily yourself. Lab tests are expensive and actually less sensitive mostly because they need to detect extremely low levels of pesticides.Here’s how to test manure, compost or soil in which you suspect contamination:Thoroughly mix 1-2 parts manure, compost or soil with 1 part sterile commercial potting mix (the kind without additives) in a clean bucket. Prepare enough to fill three clean 4-inch pots.Fill another three clean pots solely with commercial potting soil. These will be the untreated comparisons.Place each of the pots in a separate saucer to prevent water from on pot reaching another. Water all and let sit for 24 hours.Plant each pot with three pea or bean seeds.Keep watered, give adequate light and observe growth for about 4 weeks, watching for symptoms such as cupped leaves, fern-like growth on new shoots, twisted stems or “shoestring” like leaves which indicate likely picloram, clopyralid or aminopyralid residues.Early Riser & Phil, what I learned about these herbicides that makes them so problematic is that they can pass through any animal’s digestive system unchanged. They can sit without breakdown for years and years in a manure pile. Composting doesn’t break them down. Nor does it break down in water – it only transports to another place. The only thing that breaks them down is metabolization by microorganisms in aerobic conditions. (Effective microorganisms to the rescue!!)Conventional recommendations are to aerate the soil to activate microorganisms. I thought I could do one better with my contaminated tomato patch. I brewed up aerated compost tea using Phil’s recipe and The Organic Gardener’s Pantry ingredients and drenched the soil and the foliage every 5 to 8 days. Within 2 weeks, you could see a visible difference in the plants. Above the weird and misshapen leaves and stems was a whole new band of healthy foliage – a dark green with well-shaped, appropriately sized leaves. Even the fruits changed (although we didn’t eat them. Ewwww.)In my research, I found the following conventional recommendations to ameliorate pyralid or picloram damage:1. Plant a cover crop (such as winter wheat), then discard it as toxic waste.2. Aerate the soil. Cultivate deeply every few days for the rest of the growing season (and perhaps the next couple as well).3. Plant resistant species next year. Crops such as squash and mint family are less sensitive – they can handle concentrations of about 300 ppb before succumbing. (however one can only eat so much minted squash).4. Replace the soil. That’s what I suspect my sister may need to do. I ended up spreading my pile of contaminated manure on the boulevard on my street. It’s already highly contaminated with road salt and exhaust emissions. Not the best solution but the only other was to haul it to the toxic waste site so it became someone else’s problem.5. Frequent bioassay testing. Because plants are affected by parts-per-billion levels, continue to do testing until residue is depleted.One of the primary issues with potential soil contaminants is that whenever we import inputs to our gardens, we rely on the producers of those inputs to know, remember and communicate to us what ever may have gone into or onto the soil or product. Trouble arises when, in situations like mine, my brother simply forgot or didn’t think it important to tell us.When asked, he thought back and said, ‘Why yes. I spray the pasture with Lontrel 360 (clopyralid) to get rid of the alsike clover because it’s poisonous to my grazing horses. Maybe that’s why even my nine year-old manure patch doesn’t have any weeds on it?”My belief is that contamination is far more frequent than we might think. My lesson learned this summer is that from now on, unless I’m absolutely certain of the pedigree of imported inputs, I’ll import nothing. No bio-materials in, no bio-waste out.Janet Reformed Peace River, AB gardener

    • Phil on January 14, 2012 at 5:39 pm

      Excellent work Janet. This is very useful information for all of us.

  8. payday2222 on January 14, 2012 at 5:40 pm

    We are told by our local radio organic gardener host (Bob Webster) to cover a broadleaf weed with the horse manure before composting.  If the weed dies within a couple of days or so after being covered, don’t use the horse manure!

    • Carleen on April 7, 2017 at 3:11 pm

      What a great idea! And so much faster and easier then planting seeds and waiting 4 wks. Thank u so much everyone!

  9. Dave on March 11, 2012 at 8:25 pm

    Absolutely incredible article. Janet, Phil, everyone else…thank you so much for sharing this. The information and experience presented here is priceless. I shall spread the word amongst my community. 

  10. Breezy Acres Farm on March 12, 2012 at 1:28 am

    I’ve been complaining for years that the use of manure on organic farms have no regulations in the organic standards. In my opinion the failure of the standards to regulate manure totally negates the organic certification program.

    • Phil on March 12, 2012 at 5:52 pm

      Ya, I think the certification program is a process. It probably takes a lot of years to get right, with a lot of vested interests trying to hold back progress. The SOUL Standard is pretty good, though.

  11. Haydn G on March 12, 2012 at 12:21 pm

    Thanks Janet for sharing this scary stuff.  I guess this means also we could be buying contaminated straw / hay  too for our compost making…………?!

    • Phil on March 13, 2012 at 7:54 pm

      Yes. I always try to find organic straw/hay. Most of the conventional stuff has Roundup residue. I don’t think that’s the end of the world, but I prefer organic.

  12. Brad on February 9, 2013 at 2:24 am

    Straw is less likely to be affected than hay as the aminopyralid doesn’t bind as well to the stalks as it does to grass.

    • Phil on February 11, 2013 at 2:17 pm

      Hmm, I would have thought since it is a systemic herbicide that it would exist throughout the entire plant.

  13. on June 15, 2015 at 7:01 am

    You’re actually right

  14. Indira on February 27, 2016 at 9:25 pm

    Hi, Thanks for the Tips, last three years i have been loosing all my plants flowers .Dahlia. marigold. chillies tomatoes, spinach.and all herbs God I could’not believe what was i doing wrong i was only buying organic manure direct from farmer i was only trying to grow more produce fruits veg and flowers thanks for the sharing this iformation

  15. Gudrun Scott on April 26, 2017 at 9:00 pm

    It is now 2016 and I just bought some manure and compost from Scott – about 30 lbs only $2 I should have been thinking it was too cheap. There was a pronounced smell to the manure – very chemical- I should not have used it but I used about 1/3 of the bag and did not touch the next back– I am briing that one to the store where I bought it along with this discussion here and I also will call my local soil and conservation department at the county level and see what they have to say. I think we need to report to the Food and Drug Administration FDA and fill out reports on this and Dow chemical has to at least educate the public and so on. This is alarming. Also- talk to your legislators !

  16. Helen scheiderer on May 1, 2017 at 8:57 pm

    Once already in the soil will it eventually decompose enough so it will no longer hurt plants ?

    • Phil on May 3, 2017 at 8:14 am

      Eventually. I’m not sure how many years it takes.

  17. Pat nielsen on June 7, 2017 at 2:07 pm

    Will it hurt to use the produce.

    • Phil on June 9, 2017 at 12:39 pm

      Hard to say for sure. It will depend on how much of the pesticide is present in the soil, on the characteristics of the soil itself, and on the types of plants. But I don’t have any experience with it myself.

  18. Gary on June 16, 2017 at 6:44 pm

    As the problem with aminopyralid based herbicides is related to cows or horses eating the contaminated hay which means manure produced by these cows or horses contains the herbicide, would there be a concern for this aminopyralid based herbicide contamination for other sources of manure such as pig, chicken, or other farm animals other that cows or horses?

    • Phil on June 17, 2017 at 11:54 am

      I’m not positive, but I’ve never seen any talk about this problem with other animals than cows and horses.

  19. John on July 9, 2017 at 1:41 pm

    Wow, certainly a cautionary tale for anyone – as we think we’re good to go (e.g. organic) when apply composted manure, with the reality being even the farmer/manure producer might be unaware of the chemistry lurking in his/her livestock’s feed source. I had chickens & sheep for years and bought my feed, of course, from the local feed store, which wasn’t contaminated, only because of that being decades ago. Today, I’d not be sure this feed source wasn’t cross contaminated, as well. Notwithstanding the misery of malaria, DDT had to go. Now this multi-year persistent weed killer must also be banned. Five+ years is like 4.9 years too long waiting for a toxic material to dissipate, all in the name of some agri-bus acreage to produce weed free crops, probably solely for the purpose to reduce manual labor at harvest. And yes, our reps and FDA should be made aware of this issue.

  20. john grierson on August 16, 2017 at 8:51 pm

    Dr. Michael Greger’s site, Nutrition Facts, explains that American rice is contaminated with arsenic because it is grown in fields that previously grew cotton. which was sprayed with arsenic. Problematic because rice takes the arsenic very well! Perhaps if you plant rice and discard the crop, that may help. Regards, John.

    • Michael Maciorski on August 20, 2017 at 11:29 pm

      This is real, took 4 years and many false hopes to isolate this pile of bad shit!!

  21. John Van Buiten on January 24, 2018 at 3:16 pm

    Do animals fed with Grazon pose a threat to human health if consumed ?

    • Phil on January 31, 2018 at 3:56 pm

      I haven’t looked at it in detail. Here’s an excerpt you may have read: “Lactating dairy cows should not graze in areas that have been treated with Grazon for at least a week after application, and meat animals should not graze in these areas for at least three days before slaughter. Areas treated with Grazon must not be harvested for hay within a month of application. If animals have grazed on treated pasture, they should graze on untreated areas for at least one week before being moved to areas with broadleaf crops, as their urine can kill sensitive plants. Manure from animals that have grazed on Grazon-treated areas is not suitable for compost.”

  22. Nancy Lucas on February 14, 2018 at 10:49 pm

    Thank you so much for this post. A few years back I looked for untainted horse manure in my area and found none. I decided to look again today and your article came up—and I am so glad it did. I had an old unopened bag of composted organic manure commercially sold . Because of injuries last spring a friend came by and set up large pots for me to grow on my deck since I could not physically access my garden. He used soil from my raised beds and then I had him add this bag of organic composted manure to the pots too. I put in organic tomato plants and a mint plant, but everything else was seeded. I had never seen anything like it–even the mint leaves etc did exactly what this lady Janet experienced. Peas, beans, tomatoes, marigold everything was very strange in the way it grew or didn’t grow and died. Everyone who saw it was perplexed–including longtime professional organic farmers. But I had tons of grass sprouting in the pots. It was so strange as my yard has no regular grass, only a few native grasses and native plants–which this grass in the pots was not. My yard has been completely organic, biodynamic since 2009. I’m out west in high dessert and I have been told by professionals ( I am just a home gardener) that I have the best soil in the area–and that’s the only thing that was added to my growing pots excepting that bag of composted organic cow manure. Now I know what happened–it was that bag of organic manure. I was going to return the soil from these pots to my raised beds this week and would have contaminated them if I did. Thank you so much for posting and keeping your feed updated.

  23. Landon on April 9, 2018 at 8:25 pm

    So I had a question on Aminopyralid, etc. effect / presence in poultry litter….if this is used on broadleaf pastures and hay operation, do we see a way that it would get into a poultry diet?

    Didn’t take too long looking to find this from Ohio State University
    which contradicts some of my previous reading:
    Feed stocks to which glyphosate was been applied as directed (4 kg AI/acre), exhibited phytotoxic effects after the feedstocks were composted when the compost was used as a 20% potting media amendment. The same composts made from untreated feed stocks showed no phytotoxicity. Concentrations in composts made from feed stocks to which the compounds were applied, contained more than 1 ppm of these compounds. These studies indicate that careful attention must be paid to the source and types of manure used for composting.

    • Phil on April 11, 2018 at 12:53 pm

      Thanks for sharing Landon. That link isn’t currently working for me, but thanks for pulling that quote.

  24. Liz on May 14, 2018 at 7:19 am

    Just for the record – I wanted to donate a pile of large bags, which were used for bought compost, to any farm where horse and farm manure is being sold or given free but I did not find any when I searched. I can remember the days when handwritten notices were seen by the roadside to announce that manure was available nearby, but this does not appear to be the case anymore. I am assuming that, with the information I have just read here, the availability of this soil improver has been curtailed. I had not known about the effect of animal feed on the environment, but I do now, so many thanks for this information. Also, there is the question of humans taking in these chemicals in our food, after all we do buy from farm shops, don’t we? One could get quite paranoid! However, I’m sure we are made of sterner stuff and will survive. And, as there are no takers, my large bags will have to be donated to our local dump.

  25. Chuck on May 16, 2018 at 9:46 am

    I was going to buy some mushroom compost this year then I found this blog post. So I was wondering if mushroom compost might also have a possibility of being contaminated in the same way since mushroom compost contains a lot of hay.

    Can anyone answer this?

    • Phil on May 18, 2018 at 10:08 am

      Non-organic mushrooms are often grown with a lot of pesticides, so they aren’t an ideal source of compost.

    • Chuckers on August 2, 2018 at 10:57 am

      Mushroom compost, since it’s made with hay, does have the possibility of containing contaminated hay. Also, they treat mushroom compost with fungicide so that your compost won’t sprout mushrooms.

      It has come to the point that we gardeners can’t trust any source for our soil amendments. You just have to bite the bullet and hope for the best or buy a farm and produce everything ourselves.

  26. Emjay on July 3, 2018 at 10:30 am

    Aminopyralid is also sold as Milestone, Banish and ForeFront. says it is “practically non-toxic to birds, fish, honeybees, earthworms and aquatic invertebrates…slightly toxic to aquatic organisms on acute basis.” I guess that’s someone’s opinion who’s paid by the company.

  27. Judy Urso on July 31, 2018 at 8:30 am

    So, my garden was terrible this year and I wanted to amend it before winter with horse manure. What should I do instesd? The ground is hard and compacted and I’m worried about not having a good garden next year.

  28. Richard on December 30, 2018 at 7:46 am

    Very interesting comments on this problem. My advise is avoid manure and use one of the growing manure from seed.then dig it in. People used to use recycled compost from household bin co llection but this was found to contain dumped medication in various forms. Keep to using household recycled material only.And sparingly with the nitrogen pellets.

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