If you think the previous two problems are awful, this one is truly devastating, almost too ugly for two words. And the two words are aminopyralid and chloropyralid
This is the active ingredients in an increasingly commonly used herbicide against broad leaf weeds in grassland. It is regularly used on horse grazing and domestic lawns in gardens. The chemical is particularly persistent and survives hot composting and sunlight, without much degradation.
Many growers have had their crops contaminated by importing manure from stables, but also from green waste compost made from plant materials only, so not just animal-based materials. Greenhouse/tunnel crops such as tomatoes, cucumbers, peas and beans are the usual type of crops, but there are many other crops affected too. The symptoms are a horrible distortion of leave and fruits, and the plant begins to stop growing. Sometimes there may be a partial recovery but the damage will severely reduce the crop. The problem can persist in the soil for many years and is difficult to deal with. The usual recommendation is to remove the topsoil and spread far and wide on a larger area and in time the material will break down by soil microbes.
Animals eating hay or grass treated with the chemical are not apparently affected. However, the manure will retain the chemical, even after many years of composting the risk is still there. Green waste compost may be taking in grass mowings from gardens and just one barrow load of the contaminated grass in 10,000 cubic metres of green waste compost will contaminate the entire heap. Green waste companies are presently not testing for the material, due to the lack of any reliable test for such tiny amounts. The only reliable way to test is to grow red clover in a pot containing a small amount of contaminated compost or soil. Red clover will fail at levels as low as one part per billion. This would be the same for most other crops.
Clearly this chemical should not be getting used at all, but Dow Chemicals are continuing to sell the product despite many complaints from the horticultural industry and gardeners. I personally have known a number of organic commercial growers who have suffered with this problem. Charles Dowding,, who has suffered twice did mount a campaign some years ago. If you go to his Facebook page, I think you will be able to find out more about it.
Many gardeners have had the problem but not realised it’s a contamination issue, blaming on something else. I suspect that there are organic growers who have tended to keep the problem quiet, as they risk losing their certification and their business for a whole year. Well known companies supplying plant raising substrates, and who are trying hard to remove peat from their mixes, have also been affected. So potentially thousands of users may have unwittingly brought the material into their land.
If you get this there is little you can do, other than wait for it to gradually go away on its own. I have designed a green manure system that may help to speed up the process, but not had anybody take it up to see if it works. The message really is clear, don’t import any materials from outside of your farm or garden without checking if there is potential contamination. If you are Stockfree organic or a veganic gardener then you won’t be using horse manure, but check out all composts and if you are not able to get a 100% assurance of purity, don’t use it. It is becoming increasingly important to rely only on what you can grow for fertility coming from your own land.