The loss of certain key pesticides under proposals being negotiated in Brussels would have a significant impact on crop yields and production costs, warns the Pesticides Safety Directorate.

A new PSD study into the agronomic effects of the new rules on pesticide approvals is nearing completion and it is understood that it will confirm that yield losses of up to 20% in cereals and 100% in carrots are on the cards.

Among the key points, the PSD will warn that the potential loss of many triazoles will completely undermine the control of septoria in wheat.

Much will depend on what definition of “endocrine disruption” – one of the four cut-off criteria – is finally chosen.

The PSD has considered three possibilities and, in all three, the active ingredient epoxiconazole will be lost.

Much will then depend on how prothioconazole is treated. If it too is banned, then yield losses due to septoria would amount to between 5% and 20%, depending on weather conditions and varieties grown.

The report is also expected to warn of dire consequences for potato growers, as the loss of mancozeb under all scenarios – a key product for containing blight – will seriously affect yields. Its loss will also lead to increased resistance to existing alternative products.

Several key herbicides are also under threat, including pendimethalin and linurin. The study will conclude that this will have a “substantive impact” on minor crops such as carrots, parsnips and onions.

And then there are the two additional cut-off criteria – neurotoxic and immunotoxic – which the European parliament wants to add to the list of reasons to ban pesticides.

A recent impact assessment by the PSD showed that this would lead to the loss of 23 insecticides, including the pyrethroids, carbamates and organophosphorous compounds.

This would leave nematodes almost unchallenged, with profound consequences for potatoes, carrots and onions. Aphids would also swiftly develop resistance, the PSD report will say.

Finally, the loss of methicarb, should the European parliament get its way in enforcing the two additional cut-offs, would come as a big relief to the UK’s slug population.