2018 - Winning the war against slugs

Part 1: Assessing the scale of the problem 

Slugs are a major pest within UK agriculture, particularly in arable farming where a single slug can kill up to 50 wheat seeds within one week of sowing.  We have therefore put together a two-part guide to enable you to get a better understanding of how to deal effectively, efficiently and responsibly with their ever-present threat.

This week we’ll look at why slugs are such a problem, particularly in emerging crops and some of the measures you can take to reduce their impact.  In next week’s knowledge hub we’ll then go on to discuss how to use slug pellets effectively, precisely and responsibly.  The key message throughout is that effective control is reliant on a combination of factors, with slug mapping, cultivation techniques, chemical control measures and stewardship all playing their part in an integrated approach to slug management.

What is the problem with slugs?

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) commonly found throughout the UK, with the latter being the most common, widespread and troublesome in UK arable and horticultural systems.

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 at key crop timings: for example in the autumn when both oilseed rape and wheat are at particular risk from germination through to establishment.

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. 

Effective slug control through Integrated Pest Managment

Effective slug control focuses on the use of Integrated Pest Management (IPM) to control slug numbers and to reduce reliance on chemical control measures, such as slug bait products based on either ferric phosphate or metaldehyde.

An IPM approach to slug control is more effective than relying solely on slug pellets and can also help to ensure maximum protection to the environment.

In terms of controlling slug populations, IPM involves the following steps:

• Identification and analysis of the potential risk factors associated with slug damage
• Consideration of the most suitable cultural control techniques that can be used to help reduce slug habitats and overall pressure
• Trapping and understanding thresholds to ensure treatment decisions are justified
• Monitoring of crops while they are most vulnerable and assessing if further applications are required
• Record keeping and forward planning to improve IPM programmes for the next year.

How to be #SlugAware

A key step to combat slug populations effectively as part of an IPM approach is to understand where, when and to what extent slugs are causing a problem.

Slug trapping and regular crop walking are the most obvious methods for monitoring slug populations.  Adama’s #SlugAware tool (part of the WaterAware smartphone app) can also be used to predict when slugs are likely to be active.

The #SlugAware app is designed to protect the longevity of metaldehyde-based slug pellets such as Gusto 3 by ensuring pellets are only applied when absolutely necessary.

By considering factors such as soil type, soil moisture, temperature, wind speed, cultivation type, and current and previous cropping, #SlugAware gives growers a low, medium or high threat of slug activity warning based on their land’s specific conditions in a given 24 to 72 hour period.

With this information to hand, growers can make informed crop protection decisions, thereby ensuring key active ingredients are only ever applied at the right time and thus reducing the risk of these chemicals being lost from the crop protection armoury due to regulatory pressures.

The WaterAware app featuring /#SlugAware is completely FREE to download and use

Winning the war on slugs: Part 2

Tune in next week to read part two of our guide on how to win the war against slugs.  We’ll discuss the importance of using a quality slug pellet and look at why it’s important to apply slug pellets accurately.