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Wetter summer could encourage slugs in winter plantings

Last year dry, hot weather persisted throughout the summer, suppressing slug levels in winter crops. This August was quite a contrast, with warmer wetter conditions dampening soil and potentially increasing slug populations.

Farmers should therefore be carefully monitoring slug numbers with trapping and be ready to apply a molluscicide as soon as levels reach threshold, according to Deben Agronomy’s James Klug.

Winter rape is particularly susceptible to slug damage when the growing point is exposed, up to the four-leaf stage, and it is expected that downpours in late summer will lead to higher slug numbers, when compared with 2018.

Mr Klug is working with one oilseed rape grower on a mixture of very light sands to clay loams and has about half of a 100ha area drilled to date.

“We’re monitoring with traps. At the moment we’re not finding many as it’s been relatively dry – but we are expecting it, and as soon as we start seeing activity, we will be applying some control products.

“We have in the past couple of weeks had some heavy rain showers, and given the soil types we’re growing on, and the fact that rape is susceptible to slug damage, we are expecting relatively high pressure.”

Trapping has taken place in stubble preceding oilseed rape crops being drilled, and generally one or more slug per trap would indicate a possible risk.

This year Mr Klug has used Sluxx HP, which is a pellet bait formulation containing 29.7% ferric phosphate.

Its mode of action causes slugs to stop feeding immediately upon ingestion of the pellet, after which they will retreat underground and die.

Farmers will see that pellets have been eaten, but there will be fewer dead slugs on the surface of the soil when compared with metaldehyde-based pellets. It is therefore more effective to monitor reductions in crop damage as an indicator of efficacy.

“We don’t see a difference [in control] between ferric phosphate and metaldehyde products,” explains Mr Klug, and furthermore, with a ban on metaldehyde increasingly likely, stocks are dwindling.

“It’s had a reprieve, but it’s still under threat and looking likely we won’t have it going forward – there isn’t a huge amount of product out there available.”

But aside from that, ferric phosphate has a better environmental profile, adds Mr Klug.

“When it comes to buffer zones around water courses, and things like that, the issues aren’t there. It’s easier in terms of enivironmental stewardship.”

Earlier this year, on Capel St Andrews Farm, also in Suffolk, Mr Klug says Sluxx had seemed to suppress slug populations across its 475ha of potato plantings.

“The perception was that we were under higher pressure so we used it in places where we thought we might have a problem and it seems to be doing a good job.”

“We’re very confident in it as a product.”

Key points:

  • Last autumn was very dry, so slug activity was low.
  • Recent weeks have seen a return to wet weather, which will dampen soil and increase slug activity.
  • OSR crops are being drilled and are susceptible up to the four-leaf stage, so need protection to prevent seedling losses.
  • Download the Certis SlugWatch app to help monitor slug pressure in your area
  • It is important to calibrate your applicator when changing brand and type of pellet