Growers forced to redrill oilseed rape are being warned to ensure that they do not exceed maximum metaldehyde application limits this autumn.

There are reports of some early-drilled oilseed rape crops failing, particularly in the north east. Some are due to slug damage while in others it is a combination of pest damage and poor seed-beds.

Where the original crop was treated with metaldehyde, growers need to take this into account when making decisions about slug control in the resown crop, said Peter Stacey of Bayer CropScience. From this season there is a maximum total dose of 210g between the key dates of 1 August to 31 December when the issue of metaldehyde reaching watercourses is at its peak.

“We urge growers to follow the Metaldehyde Support Group guidelines to make sure that they will continue to have access to this active ingredient in the future,” said Mr Stacey.

Recent and current weather patterns are bringing heavy rain to most areas and growers should not apply metaldehyde when heavy rain is forecast or drains are running. After the dry summer many soils also have deep subsurface cracks that can facilitate movement of metaldehyde to water. The aim this autumn must be to prevent metaldehyde getting into watercourses.

“Our recommendation would be to use methiocarb in these situations, because it binds well to soil particles and is not easily leached.

“Like all inputs, growers should take an integrated pest control management approach and combine slug pellets with other measures such as cultivations to produce a good firm seedbed to inhibit slug movement,” suggests Mr Stacey.

“In rape the critical control point for slugs is between germination and the two true leaves stage of the crop.”