Tips on killing slugs with ferric phosphate pellets

A Shropshire farmer has successfully switched from metaldehyde to ferric phosphate slug pellets without compromising slug control, as he looks to cut the risk of water pollution. 

Doug McCowan farms 456ha of arable land at Woodlands Farm on a mix of soils, ranging from very sandy to medium to heavy loam.

More importantly from a water aspect, Back Brooks flows through part of the farm which eventually feeds into the Aqualate Mere nature reserve, the largest natural lake in the West Midlands.

See also: Video: Ultimate guide to good slug pellet application

He was, therefore, already interested in the environment and attended a group meeting at the nature reserve aimed at stopping the mere silting up.

While at the meeting, Mr McCowan heard from another farmer taking part in the Severn Trent Farm to Tap scheme and this convinced him to join in.

It wasn’t until the first winter in the scheme that he realised the risk to water from metaldehyde slug pellets.

Woodlands Farm, Shifnal

  • 456ha of all arable land
  • Milling and feed wheat, oilseed rape, feed barley, seed beans for Wynnstay and potatoes for McCain.
  • Applies sludge cake in rotation to replace phosphate and apply potash variably.

“I used a mixture of ferric phosphate and metaldehyde and there were two spikes in metaldehyde levels in water.”

The first spike occurred in October after heavy rain and the second was in December. “This was long after when you would expect to see the chemical in water,” he recalls.

“I was horrified to see how see how easy it was for metaldehyde to get in water. If we want to keep them, then we need to look after them and do what we can to reduce the risk of them reaching water.”

In the second year, he used just ferric phosphate and there were no spikes seen, resulting in him receiving a bonus (see below).

Making the switch has also simplified slug pellet applications, with just one product being used. Ferric phosphate was already being applied to the metaldehyde-free buffer zones 10m from the field boundary.

When comparing performance of metaldehyde and ferric phosphate – he has seen no difference.

Doug McCowan with Ben Young of Severn Trent Water

Integrated approach

Mr McCowan takes an integrated approach, using cultural controls and only using pellets on his wheat, rape and potato crops when needed.

The cultural measures include cultivating early to help encourage slug eggs to dry out and good straw management. For example, he chops and spreads rape straw to minimise areas harbouring slugs.

He also rolls fields after drilling, as slugs don’t like firm seed-beds.

Top tips for getting the most from ferric phosphate

Geoffrey Bastard, Certis’ regional technical specialist, outlines his top six tips for those looking to maximise their ferric phosphate applications.

1 Field history

Start by thinking about the field history, the previous crop, soil type and weather conditions.

These all need considering on a field-by-field basis before doing anything else.

For example, this year’s dry and warm conditions mean that on very light ground slug populations may be non-existent, but on heavier land that’s had rainfall, slug populations will be active.

Be aware that slugs can quickly repopulate and thrive at the first onset of rainfall.

Slug with slug pellet

Taking a total field perspective will help to develop a holistic approach and maximise slug control.

2 Assess slug pressure

Ferric phosphate should always be used as part of an integrated pest management approach and monitoring for slug pressure before application is vital.

To make sure you get the most out of applications and apply at the right time, monitor slug numbers using a slug mat or a simple piece of plastic with layers mash underneath. Place traps overnight and check early in the morning when slugs are usually active.

For oilseed rape crops, the treatment threshold is four or more slugs to justify slug pellet applications.

3 Pellet choice

It’s important to choose a high-quality ferric phosphate pellet that spreads well and is durable.

The four main characteristics that come together to form a good pellet include size, which should be between 2mm and 3mm, uniform shape, crush strength over 3kg and a density over 0.7kg/litre.

The aim is to have a pellet that is uniform, durable, rainfast and has anti-moulding properties. This all means the pellet will spread well and survive in the field without leaching, even after rainfall.

4 Calibration

Ensure that pelleters are calibrated for ferric phosphate pellets with a maximum width of 24m to ensure good coverage.

If using both ferric phosphate and metaldehyde on-farm, ensure that both the setting for spread pattern and rate are correctly adjusted between the two products.

Callibrating a slug pelleter

To achieve this, carry out a calibration test on both products and ensure that the operator is trained in the different spread patterns, dose rates and how to adjust settings accordingly.

Finally ensure that baiting points and pellet dose rate are relevant to the slug pressure in each individual field.

5 Application

Application of ferric phosphate should only occur once thresholds have been reached.

The active can be used on all arable crops and should be applied with a maximum dose of 7kg/ha. In high-pressure cases, up to four applications of can be made as long as the maximum total dose does not exceed 28kg/ha/crop.

6 Be aware of the mode of action

Although both ferric phosphate and metaldehyde essentially do the same thing, kill slugs, their mode of action differs.

With metaldehyde, growers are used to seeing dead slugs and slime trails on the surface, but with ferric phosphate slugs migrate underground to die.

Therefore, when assessing treatment efficacy of ferric phosphate, monitor the crop for damage rather than looking for dead slugs.

How the Severn Trent Farm to Tap scheme works

Farmers in certain catchments are eligible to join the scheme, which offers farmers payments to reduce metaldehyde levels in water by switching to ferric phosphate.

In the scheme, farmers can earn up to £8/ha hectare and there is a further bonus if water levels are less than 0.1ppb, with water tested fortnightly from September to early December.

Doug McCowan is about to go into his third autumn in the scheme and last year, his water levels were below 0.1ppb, triggering the bonus.

 “All in all, it was just over £1,000, which covered the cost of 1.5 applications,” he says.