In recent years the hormone weed killer Aminopyralid has often been used by the agricultural / farming industry, to control broad leafed weeds in grassland.

This has led to a potential problem for gardeners who use farm yard manure that has been produced from animals that have grazed on treated land.

The problem is; the chemical remains active in plant matter even after it has been excreted by the animals and is then passed on to unsuspecting gardeners in the form of 'farm yard manure'.

It has been found to affect the cropping / yield of crops such as; Beans, Carrots, Lettuce, Peas, Potatoes, Sweet Peppers and Tomatoes.

The symptoms:

These are seen as stunted twisted foliage, as seen here:

Affected Beans
Affected Cape Gooseberries
Affected Potatoes
Affected Sweet Peppers

What is Aminopyralid?

Aminopyralid is an active ingredient in a number of weed control products produced by Dow AgroSciences.

What does Aminopyralid do?

Aminopyralid is designed as a selective weed killer to kills Docks, Nettles and Thistles, without affecting the grass.

How does it do it?

Aminopyralid is absorbed into the plants cellular structure where it stays until it is broken down by soil microbes.

There by hangs the problem, the Aminopyralid is still active and affects plantlife until such times as the microbes have broken the Aminopyralid down completely.

How long does it take for the Aminopyralid to be completely broken down?

It is impossible to give a timescale as the process is dependent upon a number of factors, for example; soil type, ambient temperature,and soil compaction / aeration etc.

How does one know if the manure they have received is not contaminated?

This is proving to be a grey area in so far as, one can ask the farmer they are recieving the manure from and then respond to the reply.

But it would seem that the chain extends further than this!

For example stables buying in straw / hay bedding and feeding can be passing it on unbeknown to them.

That is, because the straw / hay does not affect their animals, meaning they are unaware that the resulting manure is contaminated, and that they may be unsuspectedly passing the problem on to gardeners as a source of manure.

Then there is the national need to recycle to avoid using landfill sites, meaning compost suppliers who recycle this material may also be using contaminated ingredients in their composts!

Government Action:

The Government have been in touch with the manufacturers Dow AgroSciences which resulted in a temporary ban of its use.

The conclusion to this goverenment action (at the time of writing this article) was: Dow AgroSciences improved the paperwork accompanying their products.

This took the form of additional information on the packaging to warn the farmers not to pass treated crop residue on to the general public.

Although well meaning, this advice will only work if the farmers heed the advice, If they don't then the potential will alway be there for the general public to receive contaminated manure / composts.


The only control the gardener has is, is to sow a few seeds of a sensitive crop e.g. Beans in a compost mix containing some of the manure.

If the results are positive then it should be OK to use the manure, if the results are negative then it is safer to get rid of the manure.

Advice from Dow AgroSciences is that regular turning (aeration) of the manure prior to its use will dissipate the active ingredients quicker, but note! this action will not necessarily get rid of the problem.

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