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.