November 2008. New regulations on metaldehyde use.
EU: Growers reassess control of slugs
Cauliflower and potato growers have been revising slug control programmes this autumn following withdrawal of approval for metaldehyde pellets for use on these crops. Approvals were withdrawn by the Pesticides Safety Directorate (PSD) with effect from 1 September because use on cauliflower and potato under the current label recommendations would have carried a high risk of the crops exceeding the new EU-wide maximum residue levels (MRLs) of 1 mg/kg for cauliflower and 0.05 mg/kg for potatoes. Other on-label uses and their extrapolated specific off-label approvals (SOLAs) have not been affected.
The molluscicides methiocarb, ferric sulphate and biocontrols can still be used.
Potato Council knowledge transfer manager Rob Clayton said: “We understand manufacturers are working with PSD to review the situation. One immediate issue is that metaldehyde has always been used in cereal stubble to reduce slug populations and therefore aid control in a following potato crop. At the moment it is not clear if that use counts as part of the potato rotation. We’re talking to PSD about it to clarify the situation for growers. It has been a use that has been especially important for land with high slug populations.”
On cauliflower the lack of a recommended harvest interval was one reason for the withdrawal of approval for that crop. However, in practice growers would have been unlikely to apply pellets after the curd formed – early applications being more effective while late application ran the risk of pellets lodging in the curd leading to crop rejection by retailers.
It is likely that new usage and residue data will be required before approvals can be reconsidered. Meanwhile, Clayton said growers need to discuss alternatives, not only with their agronomists but with their customers. “Retailer protocols tended to put metaldehyde ahead of methiocarb so this change does not sit comfortably with retailer perception,” he said. “Methiocarb does have the edge on control – it is effective on a wider range of species – but is more expensive to use.”
Bayer CropScience, which markets methiocarb as Draza Forte, says it is faster to apply.
Growers using metaldehyde for other edible crops are reminded that there are risks of the ingredient being picked up by water company monitoring.
Precautions should be taken to ensure there is no risk of pellets entering watercourses. Application in high winds can cause pellets to drift, or they may be carried in run-off during heavy rain.