Lisa Harlow, product manager at Doff Portland, part of the Pelsis Group

Over the last two years, arable farmers have faced extensive slug pressures. Oilseed rape and winter wheat have been particularly vulnerable to attack by slugs, with farmers having to treat quickly to protect yields.

Slug infestations were also a key factor behind the yield loss amongst pumpkins in 2024, which was highly publicised in the run up to Halloween.

Earlier in the spring, the Royal Horticultural Society advised gardeners that in 2025 we might see fewer slugs compared to previous years as numbers decline through factors such as predation.

However, 2025 is expected to be another year of continued slug pressures. Setting up our spring slug trials and talking to farmers and agronomists, we would estimate that numbers are 20-30 per cent above a normal year.

This is something growers need to be aware of now and ensure they are prepared to react accordingly. This applies not only now as they prepare to drill spring crops, but also to protect potato tubers from damage in the summer and then new season drillings of oilseed rape and winter wheat.  

Understanding increased slug pressures

As with many pests, weather is a significant influence.  This applies not only now, as spring crops are drilled, but for potato crops in the summer and most importantly autumn drilled oilseed rape and winter cereals between August and November. The very high slug pressure that we’ve seen over the last couple of years is due to increasingly wet summers and autumns, which seem to becoming more unpredictable and intense with climate change.

Prolonged periods of milder temperatures, often above 13 degrees, and wetter weather have created the optimal conditions for slugs. This leads to an accelerated lifecycle, faster reproduction, with a single slug capable of laying up to 500 eggs in a season, hatching and ultimately more slugs feeding on susceptible crops at their vulnerable growth stages.  

In the winter of 2024/25, the absence of a sustained cold/frosty period has failed to kill a large number of both slugs and eggs, leaving a high number of viable slugs and eggs coming into the spring season.

Although a prolonged, dry summer with high temperatures will help reduce the impact of slugs, this cannot be guaranteed, and it would need to be a sustained and intense period of heat.

Another factor behind the increasing slug numbers in arable crops is the more widely used practice of cover crops. These provide an ideal environment for slugs as they favour the dark and damp conditions that they offer.

Optimising slug management

To help farmers stay on top of another year of potentially high slug pressure, there are several measures they should undertake to assess what will be the likely pressure, when should they apply slug pellets, and which pellet they should choose.

When to apply

The first step in navigating effective slug management is to assess the potential size of slug populations in the fields farmers about to drill by slug trapping.

Slug trapping at the pre-drilling crop stage will help to give an indication of the pressure and whether there is a requirement to treat. We recommend that the following thresholds are used: If four slugs are found in traps in cereal crops; just one slug for oilseed rape, then farmers should apply a suitable slug pellet immediately post-drilling.

There are other factors which also increase slug activity, apart from wet weather. These are the previous crop (e.g. wheat following oilseed rape), cover crops, cloddy seed beds, heavy soils, minimal cultivation, previous field history and slow emergence. These should all be taken into account when calculating the potential risk of slug damage.

It is recommended that pellets are applied as soon as possible after drilling. Often, the damage is done as the seed chits and before it emerges.

Firescale is a unique slug pellet formulation in that it contains a resin, which improves its resistance to rain and was authorised as ‘Rainproof’ by Health and Safety Executives. However, in very wet conditions crops should be reassessed after seven days to see if reapplication is required.

It is recommended that Firescale is applied at the label rate of 7kgs per hectare and that applications are repeated if necessary. Up to four applications can be applied to a crop in a growing year.

Considering pellet ballistics

Pellet ballistics and how they spread are just as important in protecting the crop as the efficacy of the pellet. A pellet needs to be able to spread to 12m to fit with tramlines, and give a uniform pattern over the field. We have carried out independent work with SCS Ltd, which show Firescale has excellent ballistic properties, spreading to 12m.

The number of baiting points should also be taken into consideration and it should fall within the range of 40-50 per square meter to ensure that slugs have the best chance of coming into contact with a pellet. Firescale provides 44 pellets per square meter.

In order to achieve the best results, farmers should ensure that their spreader is calibrated correctly for the pellet which they are using.

Acting on risks

The year ahead will present another challenging growing season for farmers when it comes to slug pressures.

Using the previous two years’ experience of high pressure and assessing the risk potential for the coming season, farmers will be able to protect yields of susceptible crops during their vulnerable growth stages.

Alongside considering the impact of weather patterns, farmers should monitor crops closely, using thresholds where necessary and choosing a pellet which is both efficacious and shows good ballistic properties. This should ensure that farmers successfully establish crops like oilseed rape and winter wheat.

When slug pellets ae used in a timely manner and applied as recommended, farmers can ensure slug issues do not remain a persistent challenge.