In June 2008 a number of gardeners and allotment holders noticed some unusual symptoms in their vegetable crops. It quickly became clear that the effects were most likely to be associated with hormonal herbicides. Cupping of leaves upwards is a typical sign of hormonal herbicide contamination and new growth may take on a fern-like appearance. Leaf texture may become leathery and veins may appear more prominent.
Problems continued into 2009 and a campaign to have products containing aminopyralid (Forefront, Pharaoh and Banish) withdrawn. Organisations involved included Garden Organic, Soil Association, Organic Growers Alliance, and a number of allotment holder organisations. The products were withdrawn temporarily by Dow Agrosciences pending investigation of the problems.
Aminopyralid is a herbicide used by farmers and horse paddock owners to control persistent perennial broadleaf weeds such as docks, thistles, ragwort and nettles. If the grass is subsequently cut for hay, haylage, etc. the residues survive passage through the digestive systems of the animals fed with this forage. The residues continue to survive in the manure stack because they have been quite strongly adsorbed. If this manure is incorporated into soil the aminopyralid is released as the organic matter breaks down causing the symptoms outline above.
An online petition against the re-introduction of these products was established on the Downing Street website but to no avail. The Chemical Regulations Directorate (formerly the Pesticides Safety Directorate) developed a set of restrictions which allowed the reintroduction. To ensure that their use does not lead to a repeat of the issues seen previously, their availability is now tightly controlled with a significantly amended label and a stewardship scheme which ensures farmers are aware of the implications for subsequent manure management. The herbicides cannot be used on grassland destined for hay and silage nor on grassland grazed by horses. This year sales are restricted to Scotland, South West England and Northern Ireland.
There have been some incidents this year but it is not clear whether this is because old manure is still being used. There have been few if any cases involving commercial organic growers but this kind of problem raises the issue of whether growers should be relying on brought in animal manures of potentially dubious provenance. It has also been suggested that some green waste compost could be affected by aminopyralid. This is an issue that needs wider discussion in the light of questions about GMOs in manures and composts, and the increasing use of food waste in the production of available composts. These issues will be discussed in a later article.
In the meantime anyone contemplating the use of brought in manure should either not do it or ask some detailed questions of the supplier.