UK to Phase Out Dimethomorph Fungicide From Nov. 30

10 November 2026, London: The UK’s Health and Safety Executive (HSE) has confirmed that approval for the fungicide active substance dimethomorph will expire in Great Britain on November 30, 2026, after a scientific review concluded the chemical meets the criteria for classification as an endocrine disruptor in humans and as toxic for reproduction.

HSE first flagged the substance in a bulletin issued July 31, 2026, proposing withdrawal after new scientific information indicated dimethomorph might no longer satisfy approval criteria under assimilated Regulation (EC) 1107/2009, the retained EU law that governs pesticide active substances in Great Britain post-Brexit. The review specifically examined the compound’s potential to disrupt the oestrogen, androgen and steroidogenesis pathways in humans, collectively known as the EAS modalities, and found that dimethomorph met the threshold for that classification. The review separately concluded the substance is toxic for reproduction under category 1B, a classification reserved for substances presumed to impair human fertility based on the weight of evidence.

Following the July proposal, the withdrawal was referred to the World Trade Organization for a standard consultation period with the UK’s trading partners, a step required before Great Britain can finalize the removal of an approved active substance from its pesticide register. HSE said in its November 2 bulletin that this consultation has now concluded, and that the Department for Environment, Food and Rural Affairs together with the devolved administrations in Scotland, Wales and Northern Ireland have consented to the decision, clearing the way for the approval to lapse at the end of the month.

Phase-Out Timeline

The withdrawal will not take immediate effect for products already on the market. HSE has set a phased exit: companies holding authorizations for dimethomorph-based products may continue to sell and distribute existing stock for six months beyond the expiry date, until May 31, 2027. Farmers and other end users will then have a further twelve months to use up any stock they have already purchased, meaning dimethomorph-containing products can legally be applied in Great Britain until May 31, 2028, before all remaining authorizations lapse entirely.

Neither of HSE’s two bulletins names the specific commercial products, brand names or authorization holders affected by the decision, nor does either document specify which crops or production regions will feel the greatest impact. Dimethomorph is a morpholine-class fungicide historically used against oomycete diseases, a group of fungus-like pathogens that includes downy mildew and potato late blight, and has commonly been applied as a protectant spray, frequently in combination with mancozeb, across crops such as potatoes, onions and lettuce.

Wider Regulatory Context

HSE’s bulletin also flagged a broader point of uncertainty for the sector: pesticides remain within the scope of ongoing UK-EU talks over a Sanitary and Phytosanitary (SPS) agreement, which have not yet concluded. The regulator said it would issue further communication on any implications for dimethomorph, or for pesticide approvals more broadly, once those negotiations are finalized. An SPS deal could in principle align UK and EU pesticide approval timelines more closely, though HSE gave no indication of timing for when that clarity might arrive.

Since the UK left the EU’s own pesticide approval system, HSE has run its own parallel program of active substance reviews for Great Britain under assimilated Regulation 1107/2009, which covers toxicology, environmental fate and ecotoxicology criteria among other factors. A substance can lose its GB approval if a routine review reclassifies it as meeting endocrine-disrupting or reproductive-toxicity criteria, even without a specific trigger event such as a poisoning incident or an environmental contamination case.

GB-registered dimethomorph products remain on the market and usable without restriction until the approval itself expires on November 30, after which the six-month sell-off window and the subsequent twelve-month use-up period will govern how long existing stock can still legally reach a field in Great Britain, through May 31, 2028.

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