1. Know your species – There are about 46 species of slug in the UK, but just three of them are a concern in arable crops. These include the grey field slug (Deroceras reticulatum), round back slugs (Arion spp.) and keeled slugs (Milax/Tandonia spp.). Lifecycles are variable, with anywhere between two and four each year. Grey field slugs have a maximum lifespan of 9-12 months and is the most important species in cereals and oilseed rape.
2. Know when crops are susceptible – In cereals, slugs cause seed hollowing and one slug can kill up to 50 seeds in the first week post-drilling. Shredding of shoots and leaves is also a problem and crops are susceptible until GS21. Oilseed rape is very susceptible to early damage, too, with slugs potentially nipping off the growing point as it comes out of the ground. OSR is susceptible until the four-leaf stage, so requires protection early. For potatoes, the most significant damage is caused at early tuber bulking, when slugs eat into tubers and leave unsightly cavities.
3. Know what factors increase risk – Moisture and temperature are the two biggest factors that influence slug risk. Cool and wet conditions favour slugs, but even in a dry season slugs can still quickly repopulate soils and cause damage when rain eventually arrives. Clay and silt soils pose the greatest risk, while reduced tillage, cover crops, poor drainage and poor harvest residue management can all increase risk further. Previous crop also has an influence, with oilseed rape, in particular, facilitating population growth.
4. It is impossible to eradicate slugs – Slugs causing visible damage to crops are just the tip of the iceberg. A large proportion of the population is distributed through the soil profile out of sight, so it is impossible to completely eliminate the pest in any location. This makes summer slug pellet applications to reduce autumn damage a waste of time, as numbers quickly build when new crops are planted.
5. Use cultural methods as first defence – Rotation is a key consideration. Do not plant susceptible crops such as salads and leafy vegetables after oilseed rape. Late-drilled cereals can also be at greater risk, as it takes crops longer to grow away from the susceptible growth stage. Cultivations play a role in reducing slug damage and growers should aim for fine and firm seed-beds to minimise pest movement. Also ensure that crop residue is evenly distributed to avoid creating slug hotspots.
6. Monitor populations to establish need for treatment – Slug pellets are most effective when applied early and timed to coincide with slug activity. Use traps ahead of planting and until the crop is past the susceptible stage. Traps should ideally consist of a plastic cover about 25cm across, baited with a grain-based bait such as layers mash, to establish numbers. Use about 9-13 traps in a “W” pattern across known hotspots and leave overnight. For cereals and oilseed rape, 4 or more per trap indicates risk and the need for treatment. For potatoes or field vegetables, 1 per trap is the threshold.
7. Choose a quality slug pellet formulation – When choosing a slug pellet, key requirements are palatability, durability and spreadability. A premium brand such as ferric phosphate-based pellet Sluxx HP offers all these attributes. Made from pasta dough and containing a food grade anti-mould agent, Sluxx pellets are present and palatable for longer. Size is also more uniform, so spread well to 24m and the product provides more baiting points at field rates than its competitors.
8. Attractants don’t work – Behavioural monitoring has shown slugs to be random feeders. No evidence exists that they are attracted to a specific food source. Instead, once they stumble across a food source, they test feed and if it’s tasty will continue feeding until their crops are full. Therefore, palatability is far more important for delivering a lethal dose of molluscicide when baiting than “attractants”.
9. Calibrate application machinery – It is important to calibrate applicators when switching between different brands of pellet. Each may have different size and ballistic properties, so incorrect applicator setup may lead to uneven application and inconsistent control.
For more technical detail and information on all aspects of slug ecology and control, visit the Slug Force webpage