Looking To Buy Manure? Read About This Manure Problem First

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 enquiries 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 it’s chemical name, but rather by Dow’s market name (ie. Torchon or Grazon). See Dow Agro’s website for a list 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? I can answer or pass them on to Janet. I know it may seem like a rare problem, but I imagine it’s more common than we think.


  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.

  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.

  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.

  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 (www.cog.ca) 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!

  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. Flatbud.com 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

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