The last few months of record breaking rainfall means the threat of slug damage to crops will be significantly higher than in recent years.

Dr Dinah Hillier, Catchment Control Manager at Thames Water, says; “We now need to prove in a wetter autumn period, and when the slug pressure is higher, that the stewardship measures work and metaldehyde can be used without getting in to water."

Last autumn, the concentration of metaldehyde in river water was generally lower than in previous years and in the Thames Water region rarely exceeded 0.1 microgrammes per litre, which is the drinking water standard for pesticides.

But it was very dry and the slug challenge low - two factors that would have reduced the likelihood of metaldehyde reaching water. The Metaldehyde Stewardship Group (MSG) and water companies have been busy over the last couple of years making sure that users of metaldehdye are aware of the issues and doing all they can to prevent this pesticide getting into rivers.

Dr Paul Fogg, spokesperson for the MSG, warns growers to stick to the metaldehyde application guidelines introduced in response to pesticide exceedances in water supplies.

“Above average rainfall during April caused slug populations to increase and then provided ideal conditions for breeding,” explains Dr Fogg. “The continuing wet conditions has led to an explosion in slug populations and standing cereal and oilseed crops are besieged by them.”

Many potato crops have already received multiple early applications of slug pellets as growers try to protect crops from damage. Dr Fogg reminds growers that from August 1 to 31 December, the guidelines are for a maximum total dose of 210g metaldehyde a.s./ha – with the option to reduce to 160g/ha upon the advice of a BASIS adviser.

“Applications should be targeted to make best use of the metaldehyde allowance, particularly bearing in mind potential drainage and run off losses during the unsettled weather we are experiencing,” advises Dr Fogg.

AIC’s Head of Crop Protection and Agronomy, Hazel Doonan, agrees that agronomists and growers need to plan ahead in order to keep metaldehyde applications within the guidelines.

"It is important to remember the annual cap on metaldehyde applications, particularly when slug pellets are being applied to stubbles or potatoes and then again later in the autumn to following crops,” warns Ms Doonan. “A planned approach to pellet applications is essential to avoid applying too much metaldehyde, remembering the maximum total dose is based over a calendar year and not on the crop in the ground, so applications to a previous crop must be taken into account.”

Early indications are that slug pellets are being ordered on to farm earlier than normal. “Growers should remember to make sure slug pellets are being stored appropriately at a time when storage space may be at a premium, to avoid the possibility of point source contamination incidents.”