OILSEED RAPE growers are being urged not to apply residual herbicides too early this autumn, despite crop growing quickly.

Many crops in the south and Midlands are already at the 5-6 leaf stage, but applying residual products now to control grassweeds could get poor results, as soils are still relatively warm, said Makhteshim Agan’s Elizabeth Spence.

“Carbetamex [carbetamide], for example, is quickly broken down by soil microbes in warm soil,” she said.

The most effective control from carbetamide products normally comes from applications in mid-November to mid-December, according to company trials.

“While a cold snap will help, remember, soil temperatures will be slower to fall than air temperatures. As a result, residual products will still be quick to loose their efficacy, until we get a consistently cold spell.”

Miss Spence advises growers to split their spray decisions by controlling volunteers early-on and then use a residual herbicide later to control blackgrass.

“The rape crop offers a really good chance to clear up any blackgrass in the rotation, as it provides the opportunity to use actives with different modes of action to those used in cereal crops,” she noted.