Issues associated with the use of farm yard manure containing aminopyralid residues
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Aminopyralid is a chemical herbicide (weedkiller) which is used to control broad-leaved weeds on grassland/pasture. Products containing aminopyralid have been authorised in the UK following an evaluation of extensive safety data by the government’s Chemicals Regulation Directorate (CRD).
The first Aminopyralid products were authorised in 2006 with further authorisations being granted in 2007, 2008 and 2009.
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.
Susceptible crops include peas, beans and other legumes, carrots and parsnips, potatoes and tomatoes, and lettuce and similar crops.
The issue with aminopyralid first came to light in May/June 2008 when the Chemicals Regulation Directorate (CRD) started to receive complaints from members of the public who had allotments and had purchased farmyard manure from farms and stables during the winter of 2007/08.
CRD issued a Regulatory Update informing people of the dangers to sensitive crops being grown in land that had had farmyard manure incorporated into the soil, which had been produced by animals grazing on land treated with aminopyralid or which had been fed hay or silage containing residues of it.
Following the first reports of damage to crops on allotments and gardens in the spring and summer of 2008 an investigation was started by the Chemicals Regulation Directorate CRD . This included investigating whether the conditions of use for aminopyralid products regarding the use of manure were sufficiently well known and understood by the users of the products.
Samples of manure, treated soil and affected plants where taken and analysed by the government’s Food & Environment Research Agency (fera). The crop samples contained trace amounts of aminopyralid, these levels were found to be below the Limit of Quantification of 0.02 milligrams per kilogram.
At the request of the authorisation (previously called approval) holder, Dow AgroSciences, the sale and use of products containing aminopyralid were suspended whilst incidents of crop damage were investigated.
As CRD’s investigation has progressed a number of Regulatory Updates and other information have been produced by the directorate and published on the CRD Website.
Following suspension of the sale and use of aminopyralid products, Dow AgroSciences initiated a major awareness campaign, reminding all those involved in distributing and using the products to follow the label instructions and to only use manure on-farm and on certain crops. At the same time, through published articles, advertisements and contact with trade associations and allotment societies, attempts were made to alert all those who use manure to the issues and to provide advice on how to minimise the chances of any problems. Authorisation for new aminopyralid products were granted in October 2009.
Before authorisation for new aminopyralid products were granted in October 2009 (see Regulatory Update 32/2009) advice was sought from the independent Advisory Committee on Pesticides (ACP). The committee considered a number of issues relating to possible restrictions on the use of aminopyralid products including a Dow AgroSciences product stewardship programme, designed to ensure that users are fully aware of the particular requirements for correct use.
The ACP recommended that authorisations should be allowed for use on grassland and amenity grassland where the products offer very useful control for a wide range of weeds. These authorisations were subject to the following conditions:
- products may only be used on grassland for grazing (not for forage) or amenity grassland;
- product labels must state that manure derived from animals that grazed on grassland treated with aminopyralid should be returned directly to the grassland ie keeping it on farm;
- only grassland grazed by cattle and sheep may be treated – not that grazed by horses; and
- products are labelled with a warning that animal waste or plant material suspected of containing aminopyralid must not be used for composting or mulching.
The overall effect of these conditions should be to prevent aminopyralid residues from leaving farms where it has been used.
In addition to these restrictions, prior to sale of the product, potential purchasers are required to receive training from qualified advisors (British Agrochemicals Standards Inspection Scheme certified) so that the risks and how to prevent these are fully understood.
Dow AgroSciences is continuing to provide the government with regular reports detailing any complaints they have received about manure containing aminopyralid and what action they have taken.
The Chemicals Regulation Directorate (CRD) reviews details of all reported incidents. This is being undertaken on a 3 monthly basis for the first year and every six months thereafter. If there is evidence that matters are not improving as expected, further consideration of the situation will take place to determine if any further action is required.
Although aminopyralid is an effective weedkiller it is of low toxicity to mammals. Additionally the Chemicals Regulation Directorate (CRD) has assessed further information from the manufacturer that confirmed that using manure which may contain residues of aminopyralid in the ground used to grow vegetables does not have implications for human or animal health.
Even if the manure was derived from animals fed only grass, or silage made from grass treated with aminopyralid, and the plants took up all the aminopyralid present in that manure, the highest residues would not give rise to consumer health concerns and the vegetables should be safe to eat.
Irrespective of whether manure contains aminopyralid or not it is in any case inadvisable to use fresh manure on crops because this can actually cause damage itself. Allotment users and gardeners are therefore usually advised to use well-rotted manure.
Dow AgroSciences has set up an advisory website for allotment holders and gardeners to provide advice on the use or disposal of existing manure that may contain aminopyralid and will provide a ‘Bioassay’ (testing kit) to allow growers to check their manure. If the manure is found to contain residues of aminopyralid Dow AgroSciences will arrange for the manure to be removed.
Where aminopyralid is present in the manure, anything that will speed up the decomposition of the grass in the manure, for example rotavating or digging over affected plots a number of times and ensuring the manure is turned readily, will help alleviate the problem. In addition it is advisable not to replant susceptible crops until the following season, to ensure that all plant material has had sufficient time to decompose. Susceptible crops include peas, beans and other legumes, carrots and parsnips, potatoes and tomatoes, and lettuce and similar crops.
Because of the length of time manure is usually left before it is disposed of, it is unlikely that any well-rotted manure obtained by allotment users and gardeners from 2010 onwards would have been produced since aminopyralid was allowed back into use in the spring of 2010 under the new controls. So if crop damage has occurred as a result of the use of manure containing aminopyralid, this almost certainly results from the use of aminopyralid prior to suspension in July 2008. This would not indicate that the new restrictions on aminopyralid products are not working.
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