Slugs are a major pest within UK agriculture with species such as the Common Keeled Slug (Tandonia budapestensis), the Garden Slug (Arion hortensis/Arion distinctus) and the Grey Field Slug (Deroceras reticulatum) amongst those found on UK land.
Why Are Slugs Such A Problem?
Slugs are hermaphrodites and can reproduce asexually when a mate is not present, resulting in batches of around 10-50 eggs being laid at any given time, multiple times across the season (AHDB).
One slug can often lay between 100 and 500 eggs in its lifetime which spans between 6 to 18 months. It is this rapid breeding that leads slugs to be such a problem in the autumn.
Eggs are laid close to the soil surface in areas that are dark and damp: places such as holes and crevices created by cultivation. In favourable conditions, the juvenile slugs begin to hatch and start to feed, thereby causing significant damage to crops: it is estimated that a single slug can kill up to 50 wheat seeds within one week of sowing and decimate oilseed rape crops where seedlings are emerging.
If the eggs are laid in the spring, egg hatch is rapid and the juveniles become adults during the summer. If the process occurs in the autumn, the eggs take longer to develop due to the colder weather, so the juveniles do not become adults until the following spring. These adults are then able to reproduce in around 8 weeks, thus starting the cycle again.
As slugs require moisture to survive, the mild and wet autumns in recent years have provided favourable conditions for slug populations to proliferate, thereby causing increased crop damage. This, combined with cropping practices which provide suitable conditions for breeding and overwintering, means the problem is becoming ever more prevalent.
The focus going forwards should be on the use of Integrated Pest Management (IPM) to help reduce slug numbers prior to the need for reliance on Ferric Phosphate or Metaldehyde as our only control for measures.