27 July 2001

Pellet formulation key to slug slaying success

By Charles Abel

growers in the UK are missing the point when it comes to choosing between slug pellet products, says French manufacturer De Sangosse.

Product performance, driven by formulation more than active ingredient, is the key to success, it says.

Over 40% of UK growers use lowest-cost products, mostly mini-pellets, says Eric Gussin, UK manager for metaldehyde-based Metarex pellet supplier De Sangosse.

That is in stark contrast to France – the worlds biggest slug pellet user – where Metarex has won a dominant market share on the back of superior technical performance, better environmental profile and lower cost, he says.

Finding a formulation that achieves the right balance between palatability and water resistance is the key, says technical manager Antoine Livran. "Slugs can recover from a sub-lethal dose of all products, so palatability to ensure they get a lethal dose is essential."

With 30 years experience, De Sangosse thinks it has the formulation cracked and French market share figures seem to confirm that. Over the past seven years, Metarex has grown to a 47% market share, despite Bayer recently introducing its own wet process pellet.

De Sangosse is keen to promote the technical benefits to UK growers. Mr Gussin says that 42% of growers still choose minor band products, mostly mini-pellets, showing the level of ignorance about what they are using and why.

Formulation is so important that even if the metaldehyde active ingredient were swapped for a carbamate alternative, such as methiocarb (Decoy, Draza) or thiodicarb (Genesis, Judge), slug kill would be largely unaffected, says Mr Livran.

To ensure superior palatability, De Sangosse uses food-grade pasta flour, rather than bran and wheat flour. It also avoids glues and additives, which other pellets need to aid their structure and processing. "Adding glue can improve water resistance, but it has a bigger negative effect on palatability," says Mr Livran.

Wet mixing, power pressing and a five-stage drying process over 10 hours produces a pellet that is more palatable than dry-process pellets, including mini-pellets or competitor wet process pellets, such as new Draza, which still includes additive, he says.

French field trials support that view. In one study conducted by an independent trials, firm carbamate-based dry process pellets gave a 30% lower slug kill than Metarex.

Another trial, on three sites in 2000, showed total kill dropped from 80% with Metarex to 30% with carbamate-based wet process pellets. Mr Livran says the main reason for this was that slugs failed to consume a lethal dose.

Water resistance is not as great as for pellets containing additives, he admits. But a 12-15 day pellet life in wet conditions covers the key treatment period. "Control after 20-25 days is too late."

Metarex pellets are also denser, so spread to 24m more accurately than competitors, according to official French tests.

&#8226 French growers use Magisem, a mini-pellet version of Metarex, to protect oilseed rape from slug damage at drilling. However, Mr Livran is reluctant for mini-pellets to be broadcast because rain splash can coat the small pellets in soil, concealing them from slugs. &#42

SLUGRISK2001

&#8226 Treat before damage seen.

&#8226 Prioritise fields by risk.

&#8226 Monitor prior crops.

&#8226 Extra set-aside, extra risk.

&#8226 Ex-OSR highest risk.

&#8226 Threat remains, even if weather turns dry.

&#8226 Trap, but as guide only.

&#8226 Visual checks at night?

&#8226 Speedy sowing means poorer seed-beds?

&#8226 PELLETPOINTERS

&#8226 Formulation key.

&#8226 Active ingredient less significant.

&#8226 Wet process pellets best.

&#8226 Palatability more important than water resistance.

&#8226 UK second largest pellet market in world – typically 10,000t for 1m ha, costing £10m.

&#8226 Aim for more than 40 pellets/sq m.

PELLETPOINTERS

&#8226 Formulation key.

&#8226 Active ingredient less significant.

&#8226 Wet process pellets best.

&#8226 Palatability more important than water resistance.

&#8226 UK second largest pellet market in world – typically 10,000t for 1m ha, costing £10m.

&#8226 Aim for more than 40 pellets/sq m.

METALDEHYDEMYTHS

&#8226 Slugs recover in the wet – not true. Metaldehyde causes irreversible membrane damage. Desiccation is a secondary effect. Impossible for rain to rehydrate poisoned slugs. Lab trials show slug kill same whether slugs kept wet or not.

&#8226 Wet weather impairs metaldehyde efficacy – not true. Field trials show metaldehyde affected no more than other molluscicides.