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Herbicide Contamination of Manure and composts

Aminopyralid damage to courgette plants
Aminopyralid damage to courgette plants
(photo - Sally Cunningham)

July 2011 update - On-going issues with herbicide contamination of manure.

Once again Garden Organic has been receiving reports from gardeners with crops exhibiting signs of herbicide damage (cupped leaves and/or fern like growths) consistent with aminopyralid or clopyralid. In his Guardian blog on July 15th George Monbiot drew attention to the continued problems that gardeners are experiencing with contaminated manures. He highlighted the problems that his market gardener neighbours have had with devastated crops and called for similarly affected people to contact him through the website. http://www.guardian.co.uk/environment/georgemonbiot/2011/jul/15/vegetables-disease-aminopyralid-pesticide
Comments on this article are now closed but we would urge gardeners to keep vigilant and report any problems here. https://spreadsheets.google.com/viewform?formkey=dHhSbUZDbEgtLWxadW5RaWZZNHAzcHc6MQ

In February following discussions between WRAP (Waste Resources Action Plan), the Chemicals Regulation Directorate (CRD) and the herbicide industry aimed at improving the clarity of product labels containing clopyralid, a change of wording to appear on all amateur products containing clopyralid was insisted on, which must take place before 2014. "After treatment, leave the clippings from the first mowing on the lawn. The next three mowings should be composted well, for at least 9 months, before being used as a mulch. Do not dispose of the grass clippings via council composting schemes." Margi Lennartsson comments “Who is going to compost these mowings at home when large-scale composting schemes are not considered capable of dealing with them safely? Mowings will inevitably end up in the ‘non-recyclable waste’ collection bins, which is entirely counter to the UK landfill directive policy to reduce municipal waste going to landfill.”
http://www.pesticides.gov.uk/approvals.asp?id=2977

July 2010 Update: Manures and composts contaminated with weedkillers are still damaging plants.

In 2008, a flood of reports appeared from allotment holders and gardeners whose crops were showing unusual symptoms. The cause turned out to be manure contaminated with the very persistent weedkiller, aminopyralid. See below for more information.

This year, 2010, we have, yet again, received many reports of crops damaged by heribicide residues, most likely aminopyralid, in manures. This is despite the introduction, by Dow Agrosciences, of stringent conditions regarding the use of aminopyralid, to prevent it getting into manures.

It is unclear whether these new cases are due to failure of these new stewardship conditions, or due to the use of old stocks of contaminated manure, hay or silage.

The Soil Association and Organic Growers Alliance (OGA) issued a press release Soil Association/OGA press release in June calling on gardeners and growers to be on the lookout for symptoms, which include twisted, cupped, and elongated leaves; misshapen fruit; reduced yield; death of young plants; and poor seed germination, on susceptible crops.

For Dow AgroSciences’ response to this years incidents click here

Garden Organic calls for ban
After government lobbying by the Soil Association, OGA, Garden Organic, and others, and following many cases of damage to crops in 2008, products containing aminopyralid were withdrawn from sale by the manufacturers Dow AgroScience Ltd. They were re-instated in September 2009 by the Chemicals Regulations Directorate (CRD), with supposed ‘enhanced stewardship requirements, despite a petition on the Prime Minister’s website which raised over 1500 objections and a submission from concerned allotment holders.

Aminopyralid is a persistent chemical, which is causing serious damage many years after its original application so Garden Organic, together with the Organic Growers Alliance, and the Soil Association, is calling for it to be banned from sale. It can remain active, damaging subsequent crops, even after the crop to which it has been applied has been eaten by a horse or cow, passed through the animal, been stored as farm yard manure, and eventually applied to another crop.

Click here for a list of products containing aminopyralid.

Aminopyralid is not the only one
Herbicides containing clopyralid, (CLICK here for list of products) which can be used on domestic lawns and amenity grassland, can also cause similar damage. There is a risk that residues of this weedkiller may be present in green waste compost, from grass mowings from treated lawns. Garden Organic is also calling for a ban from sale of products containing clopyralid. It is totally unacceptable that valuable sources of fertility for gardeners should become a toxic waste.

Damage reporting
If you suspect that your crops have been damaged by herbicide contaminated manures or compost:

1.  It is important that you let Dow Agrosciences know. Visit their website http://www.manurematters.co.uk/ or email UKHotline@dow.com

2. Please also log the incident at this web address. This will help us to form a broader picture of the scale of the problem.



October 2009 Update: Aminopyralid is back

Despite protests ministers have approved the lifting of the suspension of aminopyralid approvals.

The approval of the Dow AgroSciences herbicide, aminopyralid, has been reinstated by ministers on the recommendation of the Advisory Committee on Pesticides.

The move lifts a voluntary suspension of approval for sales and use which the company sought in July 2007 after widespread contamination of sensitive crops on allotments and gardens affected by manure containing traces of the herbicide.

Aminopyralid is a weedkiller used by farmers to control pernicious and poisonous weeds such as ragwort, thistles and docks in pasture.

The active ingredient will be re-introduced with new recommendations and a stringent stewardship programme devised to prevent inadvertent movement of manure from farms. Key to this is the requirement that products containing aminopyralid are only applied to land that will be grazed by cattle or sheep; not land where forage will be conserved. This requirement aims to ensure manure generated from treated grassland remains on the pasture. Problems have arisen when conserved forage from treated pasture was fed to housed livestock and manure created in large quantities.

Last summer (2008) reports began to emerge of deformed, distorted and dying vegetable crops in gardens and allotments. It soon became clear that the problem was widespread. It was finally identified as damage caused by the weedkiller aminopyralid. The source? Contaminated manure.

As a result, the product was voluntarily withdrawn by the Dow Chemical Company.

The Advisory Committee on Pesticides, on June 30 2009, recommended that the approvals be reinstated, subject to strict conditions of the stewardship scheme being met.

Other than questioning the supplier, there is no way of knowing that manure brought in to allotments and gardens is not contaminated - and it seems that even if the manure has been stored for a couple of years, residues of aminopyralid can still damage plants.

The photograph shows courgette plants which were raised in large pots, and planted out a few weeks before this photo was taken in. The ground had been dressed with two year old manure in the spring - and potato, pea, onion and broad bean crops had already been affected. (photo - Sally Cunningham)

 

July 2008

Garden Organic has received an unprecedented number of calls from members and concerned public regarding widespread damage to home-grown crops.

Large manure heap
Large manure heap

Herbicide damage is a very common problem this year and the root of the problem seems to be herbicide residues in grass or silage fed to livestock which subsequently contaminates the manure and bedding straw which is then supplied to gardeners and allotment holders. The herbicides responsible are mainly sold under the trade name Forefront and Pharaoh containing aminopyralid as an active ingredient although other herbicides containing a similar chemical, clopyralid (e.g. Vitax Lawnclear 2, Verdone Extra, Charter) can have similar effects. The herbicide manufacturers of Forefront and Pharaoh (Dow Agrosciences) recommend that manure and slurry from treated land should not be sold for garden use but this seems to have been overlooked in the supply chain. The Pesticide Safety Directorate say that the risk from eating any crops resulting from these plants is minimal.

It is still unclear why the problem has been much more noticeable this year although aminopyralid has only been widely used in the UK from 2006 when the first product became available. Some of the references supplied below indicate that it has been known about for some time in the US, where damage due to clopyralid has been widely reported since about 2000. Although there are a number of routes by which contamination may occur the herbicide is absorbed into plants and can bind to lignin and other plant cellular structures, only being released when they breakdown and so can be a contaminant of animal feed. As it is water soluble it is rapidly excreted intact in urine by farm animals (cattle and horses) when they are fed on contaminated material and also causes contamination of manure and bedding straw.

The herbicide is released once the manure or bedding material breaks down and can exert its herbicidal action at this point. The manufacturers advise that it is safe to plant sensitive crops when the manure is no longer visible in the soil. The actual length of time for manure to breakdown depends on soil conditions. By this measure stacking manure or bedding is unlikely to completely destroy the herbicide. However, proper aerobic composting (at 60°C) is more likely to degrade the herbicide in manure and straw and it should not be such a problem in thoroughly composted manure. If sensitive plants are present when the organic material breaks down they will be damaged but otherwise soil microorganisms rapidly break down the aminopyralid so crops may grow if the contamination is not too serious.

Clorpyralids (e.g. Vitax Lawnclear 2, Verdone Extra) are also licensed for amenity and amateur use in the UK and there is a possibility that they could end up either in the green waste stream or even home composting heaps. However the manufacturers warn that all grass clippings from the first mowing must not be used as a mulch, either fresh or after composting, since it may damage desired plants. They advise that it should be disposed as household waste and not via council composting schemes. Subsequent mowings can be used as mulch only after composting well for at least nine months. This should not be an issue for organic gardeners who should not be using lawn herbicides but may be an issue if you get green waste compost.

Symptoms of contamination include:

Distorted growth, cupped leaves or fern-like growth. Growth is often stunted.

Sensitive crops include:

Peas, beans and other legumes, sugar beet and fodder beet (i.e. beets), carrots and other umbellifers, potatoes and tomatoes, lettuce and other compositae.

Insensitive crops include

Wheat (if sown one month after application) and maize, grasses and brassicas (if sown with a four month delay).

Herbicides responsible are:

Mainly sold under the trade name Forefront and Pharaoh containing aminopyralid as an active ingredient. Manufacturers, Dow Agrosciences, recommend that manure and slurry from treated land should not be sold for garden use but this is being overlooked in the supply chain.

As this is not a new chemical it is still unclear why the problem has been much more noticeable this year although some of the references supplied below indicate that it has been known about for some time in the US, especially in active ingredients from the same family of chemicals.

Garden Organic advises:

  1. If you suspect herbicide damage due to manure do not use any more of this manure.
  2. Make your manure supplier aware of the problem so that it can be addressed in the supply chain in future years.
  3. Do not use the land treated with this manure until Spring 2009. You can plant a green manure in this period (e.g. rye grass immediately or grass-clover after some delay)
  4. Before sowing expensive seeds or planting transplants in the spring, test the soil by trying to geminate seeds of a sensitive (but cheap!) crop like lettuce - if the germination is weak or non-existent, leave the soil in a green manure for another 12 months.
  5. The manure should be returned to the vendor for disposal or spreading on cereal stubble. Alternatively it could be composted and spread on suitable land but this would not be advisable at home where the heap could not be regularly turned.
  6. Take steps to reduce your reliance on external composts or manure by making your own at home or by planting more green manures in your rotation.

Obviously steps should be taken by vendors to prevent contaminated straw and bedding entering the garden supply chain in future seasons. Alternatively farmers should be encouraged to use alternative methods of weed management that does not involve these chemicals.

Useful links:

Knowledge Development Team
15 July 2008

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