Trapping and using decision trees are fine in theory.

But knowing what drives slug populations and activity, and choosing and applying pellets carefully are more important when protecting winter oilseed rape and cereals.

That was the conclusion from a discussion on the pests last week organised on behalf of metaldehyde manufacturer Lonza.

When, seven years ago, Adrian Howes took over as manager of the 1040ha (2570 acres) of arable crops at Sennowe Park, Fakenham, he abandoned sheep, dropped roots, vining peas and ploughing and switched to a simpler rotation of wheat, oilseed rape and beans based on non-inversion tillage.

“We wanted a low risk strategy,” he explained.

“We used to have seven full-time staff.

Now there are only two.”

perennial problems

But the changes meant slugs became a perennial problem even though the land was relatively light.

“Before we grew rape we used to get patches [of damage] in the wheat.

Now slugs just love our trashy seed-beds.”

So pellets had become a routine input.

“They are an insurance because of the rape.”

His other main defence had been to up wheat seed rates by 10-20% after the oilseed rape.

Dealing with slugs was largely a matter of anticipating problems, according to Hutchinsons’ Dick Neale, who, via agronomist Giles Field-Rayner, provided strategic advice on the farm.

The key plus in Mr Howes’ cultivations shift, using a Gregoire Besson Discordon tillage train, was that the pests remained near the surface, he said.

With ploughing, especially on heavier land, dry weather could drive them deep underground.

“It’s then very difficult to know what they are doing and you can get an ‘explosion’ later on.

“We do use trapping, especially on heavy land. But on Adrian’s farm we tend to know where the problems are likely to occur. Slugs don’t get rampant, but there’s always a constant population.”

For oilseed rape, which was particularly vulnerable, it was vital to apply pellets as soon as the crop reached the cotyledon stage, said Mr Neale.

“You’ve got to protect it as it emerges.

One nip and it’s gone.”

Grain hollowing in wheat was a sign that seed-beds needed more attention.

“Getting a perfect seed-bed on heavy land is a big ask, but that’s where the effort should be put in rather than ordering an extra tonne of pellets.”

Justifying mixing

Mixing pellets with seed was only really justified where the drill slot could not be closed.

New seed treatment Deter (clothianidin) helped prevent hollowing, but did not kill slugs, Mr Neale pointed out.

He believed more growers could usefully exploit rotational opportunities for control, for example by assessing populations in standing crops during damp weather ahead of autumn sowing.

If large numbers, say 10/sq m, were found feeding on wheat flag leaves before ear emergence it might pay to apply pellets to help reduce pressure on the next crop.

However, it was hard to persuade growers to spend money on something not directly benefiting from it, he acknowledged.
Both men agreed that ultra-cheap pellets were false economy.

“Our average pellet spend is £2000-£2500 a year, said Mr Howes.

“We bought some minis last year through a buying group.

They were very cheap, but were poor quality with a lot of dust, degraded very quickly, and just didn’t work.

So I had to spend another 800 on some better quality Luxan ones.”

To be effective, a pellet, whatever its ingredients, should be uniform throughout so that feeding slugs were guaranteed to ingest a lethal dose, explained Lonza’s technical manager Markus Bieri.

Too much bran in the mix of base and active ingredient encouraged pellet breakdown.

“We don’t sell cheap minis,” stressed Mr Neale, who employed a simple “soak test” to any products he was offered for marketing.

The ideal was a pellet that softened but remained intact, he explained.

“Some were like semolina within half an hour.”

The ballistic quality of pellets was becoming increasingly important as growers needed to cover large areas quickly, he added.

The firm was planning fertiliser spreader-style tray tests on seven products at full and half doses.

andrew.blake@rbi.co.uk