Gardeners' Alert:
Aminopyralid-contaminated manure - a problem that has not gone away.

June 20th 2011


A familiar and seemingly innocent sight: a heap of horse-manure lying in the corner of a small market-garden, waiting to be added to a compost-heap or mulched onto the beds ready for the first frosts of winter to get to work on it.


There was a time, back in the dim and distant past (well, before the closing years of the last decade to be more accurate), when that would be that. An everyday part of any vegetable-production area, from the suburban veggie-patch to the allotment. But a few years ago, that all changed.

Reports of vegetable-gardens decimated by herbicide present as residues in manure made the news in 2008 and, despite certain actions being taken to address the issue, the problem has, it seems, not gone away.

The herbicide involved in 2008 was Aminopyralid. Quoting the Health and Safety Executive (reference 1 at end of page):

"Aminopyralid is an effective herbicide with a low toxicity to mammals. However residues of it can remain in grass from treated land and pass into the manure of grazing livestock, where it remains tightly bound to the plant material until it decomposes. Similarly, the substance can also remain in grass fed as hay or silage to horses and housed cattle, again passing through the animals into the manure.

If manure is applied to soil or crops before the plant material in the manure has fully decomposed, susceptible crops may be damaged.

Labels of products which contain aminopyralid therefore include warnings not to use manure from livestock, which have eaten grass from treated land, on susceptible crops, or on land intended for growing such crops, until all plant material had fully decomposed.

However it would appear that in the past the label precautions in respect of manure may not always have been followed when manure has been supplied to allotment holders and gardeners."

I'll put it a bit more bluntly.

If this gets into your garden then you have a very big problem, and if that garden is your livelihood, then you have a disaster.

My friend Ann runs a market-garden here in the Dyfi Valley: two large polytunnels and a patchwork of beds provide her with a modest living. She and her partner John have worked their butts off to convert a poorly-drained paddock into a flourishing little venture over a number of years:

market garden, dyfi valley

All was going well until recently. On June 9th there was an email from Ann:

"I'm afraid that I'm the bringer of bad news: aminopyralid contaminated manure is back! If you want to see the damage it causes in gardens, just come and have a look at our patch!"

Yesterday - June 19th 2011 - [and on a second occasion a week or two later] I did just that.

I should first add that I am familiar with the place the manure in question comes from - some local people who keep horses, but because of limited storage space they give the manure away. I've collected some myself in the past and can verify that it is all fresh from recently mucked stables. It's the sort you'd want to leave awhile before applying.

In this case, the source seems likely to have been a rogue batch of hay, as explained as one of the potential problems in the HSE piece above. Ann explains:

"The manure that is affecting our crops was produced this winter just gone by horses who ate affected hay that was grown over the summer of 2010, this manure was then composted through a hotbed and used in planting and potting mixtures for our tomatoes, cucumbers etc. We also top dressed potatoes and other crops. So no old fodder or manure in our case."

Ann gave me a guided tour of her beds and polytunnels while I familiarised myself with the calling-cards of this unwelcome guest. This image shows sunflowers that began life at the same time. On the right, a bed which was free of this particular manure; on the left, a bed which had the manure added:

Ann & sunflowers

Here's a close-up of the tip of one of the affected sunflowers. Note the weird curling and twisting of young leaves - that's one distinctive sign....

sunflower affected by herbicide

The herbicide residue affects some groups of vegetables more than others. Here, Ann shows me tomato plants, their leaves curling:

aminopyralid damage - potato

Young plants are particularly prone and may be killed outright. Their growing-shoots become malformed and the leaves turn almost fern-like:

aminopyralid damage - tomatoes

They may still fruit, but the fruits tend to be misshapen, deformed in appearance:

aminopyralid damage - tomatoes

Cupping of leaves is a characteristic symptom. The leaves have a brittle, papery feel to them - like old parchment, if you gently crush one it will develop breaks. This plant was dug up and its roots rinsed before replanting in an uncontaminated bed, but Ann has no idea whether it will recover....

aminopyralid damage - courgette

Potatoes are likewise affected - again, the leaf-cupping and brittleness....

aminopyralid damage - potato

And the fernlike growing-tips.....

aminopyralid damage - potato

And the same with runner-beans:

aminopyralid damage - runner bean

Veins standing out on deep green leaves are another frequent sight....

aminopyralid damage - runner bean

I came away from my visit angry and bitterly frustrated for Ann and her partner - that all this hard work should be undone - for this year at least - by an invisible, insiduous contaminant in what should be an everyday gardening accessory - good old horse-shit. We should be able to trust such things, not have to view them with the same level of suspicion one might reserve for rusting barrels of weedkiller.

That we cannot trust horse-shit for being, well, horse-shit is a sad indictment of our times.


1) Health & Safety Executive's Aminopyralid advice page: