Record slug populations make control crucial

Record slug populations this autumn will make control even more crucial as growers look to get delayed drilled rape crops off to a good start.

Some areas of the country have seen slug populations double as they have thrived in the wet conditions. Growers of oilseed rape and wheat, particularly on lighter soil, are being warned to be extra vigilant this year to avoid being caught out.

Independent slug specialist David Glen stresses that knowing what you are dealing with is the key starting point. “Assessing the level of slug activity in stubble and in cultivated fields through trapping will give a good idea of what precautions need to be taken.

“The threshold for wheat crops is four slugs per trap in stubble, while only one per trap in an OSR field is enough to take precautions.”

Mr Glen stressed the importance of a good solid seed-bed and rolling as soon as possible after drilling. “This is critical in preventing the slugs from reaching the seed in the early stages of growth.”

Place nine traps in a W pattern (13 if more than 20ha) across field
Note where traps have been laid. Coloured electric fencing stakes make useful markers
Place two or three tablespoons of layer’s mash under a 250mm wide inverted plastic saucer. Check traps the next morning
Target areas where there is a known history of slug damage
Concentrate on areas where seed-bed is cloddy

Tony John, technical director at Procam agrees. “Trapping is important in establishing the size of the problem. Growers should look to cultural control methods first and then turn to chemical control. So produce a fine, firm seed-bed much the same as you would for applying residual herbicides and consolidation is key.”

When using metaldehyde, growers need to apply responsibly according to Metaldehyde Stewardship Guidelines (MSG) and avoid treatments where they aren’t necessary. Autumn guidelines are a maximum application rate of 210g/ha of the active ingredient between 31 August and 31 December and no more than 700g of active ingredient in any calendar year.

Peter Stacey of Bayer Crop Science’s urges growers to target critical periods when applying slug pellets. “Once drilling is completed, pellets should go on as soon as possible for maximum effect.

“Metaldehyde slug pellets are available with different levels of active ingredient,” says Dr John. “For instance, they are available with 1.5, 2, 3, 4 and 5% metaldehyde. So, if you apply a 4% product at 5kg/ha, you will be applying 200g/ha of active ingredient.

“However, you could use a higher rate of pellets per ha at lower concentrations. This would give you more baiting points, but would still ensure that you stay within the guidelines. So you could apply 7kg/ha of 1.5% active ingredient giving you total use of 105g of active product per ha and repeat this application and still be within the limit of 210g/ha of active ingredient,” says Dr John.

Growers are also reminded not to apply metaldehyde within 6m of a watercourse to reduce the potential for pollution. “If you are applying slug pellets around watercourses, consider using 3% ferric sulphate pellets instead which have no buffer zone restrictions.

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