The grey field slug, Deroceras sp., is the most widespread and damaging slug pest in arable crops. Feeding can seriously damage plants, particularly young seedlings in which slug feeding interferes with crop establishment. Activity, survival and reproduction are dependent on moisture. Slug damage is much greater after previously cropping leafy crops such as oilseed rape. Slugs are more abundant in heavy soils with high clay or silt content. Crop residues or applications of manure, especially in the autumn, as well as weeds and volunteers, provide slugs with a source of food and shelter. Consequently, direct drilling, as well as delayed drilling, increases the risk of slug damage.
Monitor oilseed rape and cereal seedlings for slug damage. Slug traps can assist with this; they consist of a cover about 25 cm across, with a small heap (2 heaped spoonfuls) of bait (chicken layers’ mash poultry feed). A catch of 4 or more slugs per trap per night indicates a risk if soil and weather conditions favour slug activity.
Ploughing is a good way of reducing slug populations but even minimum tillage gives considerable reduction in slug damage compared to direct drilling. Shallow cultivation to incorporate crop residues reduces slug numbers. A fine, consolidated seedbed is important and will protect seeds and prevent slugs accessing seedlings before emergence. Rolling can assist in providing a fine tilth, free of clods that attract slugs. Drill at 3cm depth to deny slugs access to the seed and increase sowing depth to 4–5 cm if the seedbed is cloddy. Sow deeper and roll after sowing. Weeds should also be removed where they are sustaining slug and snail populations prior to drilling.
Parasitic nematode (‘Nemaslug’, Phasmarhabditis hermaphrodita) can be applied for biological control. Nematodes are best applied in dull weather, in the evening and before rain. They can be applied in advance of expected damage, at sowing or any time during the crop’s lifetime, however, success is dependent on wet conditions after application.
The only chemical option available for slug control is ferric phosphate. The use of metaldehyde was banned from 1st April 2022 due to environmental concerns particularly around water courses. Any remaining slug pellets must be disposed of through a licensed waste contractor.