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Getting to grips with the new metaldehyde stewardship guidelines

Following recent MSG guidelines and ongoing pressure to limit the presence of the active in watercourses, Abby Kellett reviews best practice slug control ahead of autumn drilling.

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Getting to grips with the new metaldehyde stewardship guidelines #slugs #clubhectare

In order to achieve effective slug control, while reducing reliance on metaldehyde based products, the Metaldehyde Stewardship Group (MSG) advises growers to adopt an integrated pest management approach this autumn.

 

This follows new guidelines issued by the MSG, which state metaldehyde slug pellets must not be allowed to fall within 10 metres of any field boundary or watercourse.

 

The buffer was previously 6m and only applied alongside watercourses. However, slug control products containing metaldehyde are currently undergoing re-registration and the regulatory risk assessment which forms part of this process has revealed a requirement for increased protection of birds and small mammals.

Metaldehyde Stewardship Group guidelines

  • Ensure no pellets fall within a minimum of 10 metres of any field boundary or watercourse
  • Use minimum rates of active per hectare to avoid drainage and run-off losses
  • Do not apply when heavy rain is forecast
  • If drains are flowing, do not apply metaldehyde based slug pellets
  • Ensure the maximum dose rate of 700g/ha/year is not exceeded
  • Do not apply more than 210g/ha from August 1 to December 31

Before growers resort to slug pellet application, Hutchinsons technical development director, Dr David Ellerton recommends assessing the risk.

 

He says: “When adopting an integrated pest management approach, it is important, firstly, to be aware of how many slugs are likely to be around, so growers should put traps out between harvest and cultivation to monitor numbers – aim for nine to 13 traps per field depending on its size.

David Ellerton pic

"Where traps contain more than four slugs before oilseed rape or a winter cereal, or more than one before potatoes or in cereal stubble, a slug pellet application can be justified.”

How to trap slugs

  • Traps should consist of a cover, about 25cm across, such as a plant pot saucer
  • Place chicken layers’ mash or a cereal grain-based food under the trap (slug pellets should never be used)
  • Place nine traps in each field in a ‘W’ formation. For fields larger than 20ha, use 13 traps
  • Leave traps overnight and examine early the following morning while the soil surface is still moist
  • Count the number of slugs present and note any slime trails

Effective establishment

A number of cultural control methods can be adopted to minimise the risk of slug damage, including effective cultivation.

 

“Try to avoid direct drilling if you think you are in a high-risk situation, because direct drilling makes it very easy for the slugs to get to the seed. Some form of cultivation, either ploughing or minimum tillage, is very important for slug control.”

 

Crop residue provides an ideal feed source for slugs, so in a direct drilling situation, the risk of slugs is likely to be high. Equally, cover crops and weeds can promote slug populations and should be taken into account when assessing the need for slug pellets post-drilling.

 

See also: 'Slug it out’ farmers achieve 93 per cent reduction in metaldehyde levels

 

“If you do some form of tillage, consolidate the seedbed by rolling it. If you have got a fine seedbed, free of clods, which is well-consolidated, it is harder for slugs to get down to the seed. If you think the field is high risk and seedbeds are cloddy, drill seed a bit deeper – maybe 4-5cm.”

 

By opting for earlier drilling, he says growers give crops the best chance to grow away from pest pressure, providing there is adequate moisture in the ground for seed to germinate.

 

Ensuring fields are well drained, free from compaction and fertile will also help plants grow away from the slug threat. The inclusion of, for example, beetle banks within a field builds populations of natural predators.

 

Although insecticidal seed dressings do not directly control slugs, many do deter them from feeding on the seed, so an effective seed dressing can prevent seed hollowing.

Assess slug pressure

Assess slug pressure

Although insecticidal seed dressings do not directly control slugs, many do deter them from feeding on the seed, so an effective seed dressing can prevent seed hollowing.

 

As well as slug trapping and monitoring, look for damage on the crop itself, whether that be hollowing of the seed or shredding of emerging leaves. However, where slug numbers exceed the relevant thresholds, Dr Ellerton advises slug pellet application immediately after drilling to prevent crop damage.

 

“Assess the risk before drilling and apply slug pellets accordingly. Once you have seen the damage, it is often too late. Where slug numbers do not exceed the threshold, keep an eye on leaf shredding in cereals up to the emergence of leaf four. Once the plant starts tillering it tends to cope with slugs.”

 

Oilseed rape is most vulnerable to leaf shredding up until leaf four has emerged, says Dr Ellerton. “With rape, if it nips off the growing point at the surface as it comes through, that plant can never recover. If you think it’s a high-risk season, you need to be applying pellets before emergence.”

Product selection

When it comes to product selection, there are two chemical options; metaldehyde and ferric phosphate, both of which have very similar efficacy, according to Dr Ellerton.

 

“Some metaldehyde pellets can be a bit cheaper, but good quality pellets of both products are often very similarly priced and have similar efficacy.”

 

Both actives work slightly differently. “Metaldehyde dries the slugs out , so they produce a lot of slime trails which can be seen on the soil surface along with dead slugs. Ferric phosphate stops the slugs from feeding immediately, but the slugs actually go underground to die so you don’t see slime or dead slugs on the surface.

 

“So although farmers won’t see those signs as they would with metaldehyde, the slugs are still dying and will not damage the crop.”

 

While both actives are interchangeable as far as efficacy is concerned, with the introduction of the 10m buffer zone around all field boundaries, ferric phosphate would be the only option in those areas. Similarly, where there is potential risk to water or where the maximum threshold of 700g of metaldehyde per hectare per year or 210g per hectare between August 1 and December 31 has been reached, Dr Ellerton recommends ferric phosphate.

 

See also: New 10 metre buffer zone for metaldehyde slug pellets

 

For best control, pellets should be applied as soon as possible after drilling, or as soon as significant crop damage has been identified.

 

“I do not usually advocate putting seed and pellets together. If you have a fine consolidated seedbed the slugs would not be able to get to the seed and pellets anyway.

 

“Pellets are best utilised across the surface. But whatever method growers choose, accurate application is important, especially near field boundaries and watercourses.”

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