In order to control the growth of bracken in Scotland, farmers have been denied emergency access to a prohibited chemical.
Asulam has been given a special permit to be sprayed from helicopters for the past 10 years in order to treat bracken that threatens to cover entire hillsides.
According to the Scottish government, the advantages do not outweigh the risks to the environment and public health.
Sheep grazing areas would turn into wasteland without treatment, according to farmers who want to use Asulam.
Ministers must annually grant an emergency approval for the chemical's use, which was outlawed in 2011.
The Scottish government announced on Wednesday that, for the first time, the Health and Safety Executive (HSE) had advised against its use in 2023 for all four UK countries.
According to the statement, using the herbicide "does not meet the statutory requirements for emergency authorisation.".
This suggestion has received the support of Scottish ministers. Wales has reached the same conclusion.
Asulam, which is marketed under the trade name Asulox, was prohibited by the EU due to worries that it might be an endocrine disruptor that could interfere with hormone production.
The Scottish government, according to Rural Affairs Secretary Mairi Gougeon, is aware of the dangers posed by unchecked bracken and has based its position on scientific evidence.
She stated: "The Health and Safety Executive advised against authorizing the use of Asulox due to the risks it poses to human, animal, and environmental health. This advice was given to all four of the UK's member states.
The Welsh government has stated that they will also abide by the HSE's recommendations, and independent advice from the Chief Scientific Adviser and the Expert Committee on Pesticides supported this conclusion. ".
Asulam could potentially cause cancer, according to activists opposed to the use of risky chemicals, who argue that alternative control methods should be employed in its place.
Farmers assert that the terrain frequently makes those alternatives, like using cutting tools or letting cattle trample the bracken, impractical.
Despite the fact that bracken is not a food item, the spray drifting onto crops or getting into waterways is a source of concern.
Although more research is being done, there is no concrete proof of an association between Asulam and cancer.
