[belfast]

"Contaminated farmyard manure can cause damage to vegetable crops in gardens and allotments. This contamination is caused by application of weedkillers to pastures, which are then eaten by stock.

Plants affected: Potatoes, tomatoes, beans, peas, but also other vegetable and salad crops. Some ornamental plants, including delphinium, phlox and roses.
What is it?

A recent surge of reports of weedkiller damage across many allotments and some gardens in the UK has been traced back to farmyard manures as the source of the contamination.
Symptoms

Typical symptoms include cupped leaves and fern-like growth on sensitive plants. The shoot tips become pale, narrow and distorted, with prominent veining on the foliage. Growth generally is stunted, leaving most crops unusable.
Potato crop affected by contaminated manure on an allotment. Image: Susan GarrattCause

The damage is caused by hormone-type weedkillers, approved for use on grassland to kill broad-leaved weeds. The active ingredient responsible for most of the damage is aminopyralid, though clopyralid, found in certain lawn weedkillers as well as agricultural products, can also give similar results.

The herbicide binds strongly to plant material which when grazed by or fed to cattle and horses in feedstuffs such as silage or hay, can pass through the animals without breaking down. Manure from animals fed on treated grass contains chemical residues sufficient to damage susceptible crops. Bedding materials such as straw are less likely to be affected as aminopyralid does not currently have approval for use on cereal crops from which straw is made.

The weedkiller is bound to the lignin in grass in the manure and released as the grass, hay or silage decays. Once released it affects broadleaved plants. However, the weedkiller is broken down by soil bacteria and should all be eliminated by the following year.

Because the weedkiller is bound to lignin, only costly laboratory chemical analysis can detect weedkiller within manure. Even then, the residue levels are so low that detection of the weedkiller in the laboratory is not guaranteed. "
rest of details in link below
https://www.rhs.org.uk/advice/profile...ler-manure.asp

https://www.glallotments.btik.com/p_C...ure.ikml#video
https://www.allotment.org.uk/garden-d...killing-crops/