Big changes to the way metaldehyde slug pellets can be used are to be introduced after the active was widely detected in surface waters this autumn, prompting fears that it could be banned.

The strict guidelines will include limits on dose and the number of applications. Full details are expected to be announced next month, but Colin Myram, speaking on behalf of the Metaldehyde Stewardship Group told the AICC conference last week that proposed limits of 250g ai/ha for a single application and 700g ai/ha per crop per season in total were likely to be the maximum permitted.

A no-spread zone of 5m from the edge of field margins was also likely to be part of a promotional campaign to help ensure users applied the slug pellet responsibly, he added.

“Metaldehyde has some serious problems,” he said. Lack of residue data in some treated crops had led to the withdrawal of approval for the product in potatoes and cauliflowers after the harmonisation of maximum residue levels across Europe, he said.

“But, more importantly, residues have been found in surface waters to such an extent that Bob Breach, a respected consultant on water issues, recently said it was the biggest problem he had ever encountered.”

The ability to analyse water for metaldehyde had only been available since 2007. “In early 2008 levels above the drinking water standard of 0.1 parts per billion were found all across England.

“And the problem is, unlike some other pesticides found in water, that there is no reliable method available to remove it from water at present.

“This autumn high levels have again been found in raw surface water in an increasing number of locations, sometimes several times the permissible drinking water limit.”

That didn’t present a health issue, he stressed. “For there to be a human health issue you would need to exceed the limit by something like 3000 times.”

The high levels were often tied into high rainfall events, and connected to run-off from fields, he said. “But we don’t know how much is due to that, and how much is down to poor application, for example.”

But the discovery meant urgent action was needed. “We clearly need to get messages out to operators.”

To help with that the Metaldehyde Stewardship Group’s promotional campaign would include operator training events, as well as the new use guidelines, he said.

Metaldehyde manufacturers had also committed to improve packaging to reduce the incidence of split bags, and to improve pellet formulations to reduce dust. A study to assess whether there was a difference between wet or dry process pellets in reaching surface waters was also under way, he said. “Early indications suggest there is no difference.”

Industry estimates suggest a ban on metaldehyde could halve oilseed rape yields and reduce wheat output by 30%, costing growers up to £500m a year.

New proposed metaldehyde limits*

• Likely 5m no spread zone around water courses
• New limit on total active ingredient per season per crop of 700g
• New limit of 250g ai/ha application
• Application limit equivalent to 5kg/ha of 5%, 6kg/ha of 4%, etc.
• Industry launch – 11/12 February

*Subject to amendment following further studies