How to Ensure Slug Pellets are Applied Accurately:
Best Practice Calibration Guide

Here’s how to get calibration right to apply the product evenly, at the correct rate, and only where needed
August 1, 2025 Sarah Ferrie 06 Comments

How to Ensure Slug Pellets are Applied Accurately:
Best Practice Calibration Guide

Effective slug control is about more than just choosing the right pellet—it’s about applying the product evenly, at the correct rate, and only where needed. Poorly calibrated spreading equipment can lead to under-dosing (leaving crops vulnerable) or over-dosing (wasting money).

Here’s how to get calibration right, based on guidance from the National Sprayer Testing Scheme (NSTS), the Voluntary Initiative, and industry experts.

Download the De Sangosse Spreading Calibration Guide Here

Spreading Calibration Guide

1 Start with Slug Monitoring
– Treat Only When Necessary

Before thinking about spreading, check whether slug pressure justifies treatment.

  • Bait point method: Place chicken layers’ mash under an upturned pot or saucer, check after 24–48 hours.
  • Treatment thresholds:
    • Winter cereals: ~4 slugs per trap
    • Oilseed rape & vegetables: as few as 1 slug per trap
      Applying pellets only where thresholds are reached supports Integrated Pest Management (IPM) and reduces unnecessary product use.

2 Calibrate Regularly
– and With the Pellets You’ll Use

Calibration isn’t a one-off job. It should be done:

  • At the start of the season
  • Before each application
  • Any time you change pellet brand or batch

Always calibrate using the actual pellets you intend to apply—size, density, and durability vary between products and affect spread.

The tray test  is the gold standard:

  • Place collection trays at 1 m intervals across the working width
  • Operate the spreader at normal field speed
  • Count pellets in each tray to assess pattern and evenness

3 Know and Follow NSTS Requirements

Under the Plant Protection Products (Sustainable Use) Regulations 2012, slug pellet applicators must be NSTS-tested:

  • First test: before the equipment is 5 years old
  • Re-tests: every 6 years thereafter

NSTS testing includes:

  • Mechanical inspection of the applicator
  • Tray test to verify spread pattern and width
  • Issuing a certificate for compliance

4 The Calibration Process
– Step by Step

From the Voluntary Initiative’s guidance:
  1. Prime the system
    Load pellets and run at low rate for 2–3 minutes at working speed to settle the feed mechanism.
  2. Static calibration
    Fill with 1 kg of pellets. Time how long it takes to empty at chosen settings (either stationary into a bucket or moving with a chute).
  3. Build a rate table
    Repeat for different settings and speeds to create a chart showing output in kg/ha.
  4. Pattern testing
    Use spreader trays to confirm evenness across the full width. Adjust settings if distribution is uneven.

5 Field Setup & Operating Best Practice

  • Spreader height: Maintain manufacturer-recommended height (often ~110 cm for quad-mounted units)
  • Speed: Keep forward speed steady—around 12 km/h is typical for accuracy
  • Overlap: Ensure passes overlap evenly to avoid stripes or missed areas
  • Headlands: Start and stop well clear of headlands to prevent pellet throw into margins
  • Clean-up: Collect any spilled pellets, preferably on a sheet; never leave spills in the field
  • PPE: Wear gloves, coveralls, and eye protection when handling pellets

6 Protect Watercourses and Margins

Even with ferric phosphate products—which don’t usually require buffer zones—it’s good practice to avoid applying near ditches, streams, or field margins.

7 Keep Records and Review Performance

  • Record calibration settings, tray test results, and NSTS certificates
  • After application, monitor slug damage to assess effectiveness
  • With ferric phosphate, slugs die below the surface—don’t expect to see carcasses

8 The Golden Rules for Accurate
Slug Pellet Application

  • Monitor slug activity and treat only when thresholds are met
  • Calibrate at the start of the season, before each application, and after changing pellets
  • Use tray tests to confirm evenness of spread
  • Comply with NSTS legal requirements
  • Protect watercourses and non-target areas
  • Keep accurate records for traceability
DeSangosse News Article Image

Bottom line:

Accurate slug pellet application isn’t just about better pest control — it’s about efficiency, compliance, and protecting the environment. A well-calibrated machine ensures you hit the pest hard, safeguard beneficial species, and keep every gram of product working where it should.

Engineered for UK conditions, De Sangosse ferric phosphate is the pellet that’s “just right” — with the ideal balance of integrity, palatability, and persistence to protect crops in any weather.

  • Patented Colzactive® attractant – slugs find it faster and from further away
  • Fast efficient kill - with just 0.5 of a pellet, compared to at least 2-3 pellets for competitor products
  • Market-leading rainfastness – stays active during peak slug pressure
  • Superior spreadability – consistent 24m+ coverage with minimal breakage
  • Highest efficacy rates – lowest crop damage and highest slug mortality in trials

Want to know more?

Want to know more about De Sangosse Ferric Phosphate? Visit our Ferric Focus Hub to download our product guide.

You can download our calibration guide here.

Learn more!