Recent wet weather has increased the risk of slug damage to newly emerging oilseed rape crops in some fields, but caution is needed to avoid raised metaldehyde levels in water.

Industry consultant and slug expert David Glen, of Styloma Research, believes it will be crucial for growers to get a clear idea of the threat they face from slugs this autumn, on account of the variable weather making it hard to predict overall levels.

He says that while the South and East were very dry in the spring, which is likely to have reduced slug numbers, since then it’s been a relatively wet summer for most regions, providing an ideal environment in which slugs will breed.

“Traps should be put out when the soil surface is moist, and taking advantage of rain is important as soils in late summer and early autumn can dry out quickly.

He recommends a minimum of nine traps in a typical field, but any field of more than 20ha will need a minimum of 13 traps in a “W” pattern. They should be baited with non-toxic material and left overnight before being examined, he adds.

When treating crops, Farmacy agronomist Bill Halliwell recommends using low active ingredient metaldehyde pellets, particularly high-quality wet process 1.5% products, as they allows a more efficient use of metaldehyde while achieving high levels of slug control.

“While the August to 31 December application limit is now 210g/ha of metaldehyde, we need to be aiming for a lower recommended rate of 160g/ha,” he stresses.

Low-dose products are crucial where growers wish to apply more than one application of slug pellets on the ground this autumn. “It means that a 3kg/ha dose of a 1.5% pellet can be made up to three times in the autumn, while still remaining under the 160g/ha recommended limit, or two applications if applied at 5kg/ha,” he says.

However, he adds that growers should also be using other actives in their slug control strategy. “Growers should have a plan that also combines the use of ferric phosphate and/or methiocarb-based products to reduce the environmental impact.”

Metaldehyde tips

• Use minimum active/ha

• No pellets within 6m of a watercourse/ditch

• Do not apply when heavy rain is forecast

• If drains are flowing, do not apply