Slow establishment and patchy growth has put much of the UK's expanded oilseed rape crop at risk from the larvae of the cabbage stem flea beetle – which are due to hatch from mid-October onwards.
This is the warning from BASF entomologist John Young, following reports that many crops are still struggling in dry conditions, especially in the eastern counties.
"The adult beetles that were active on the emerging crop last month will have laid eggs on the soil near the stems of the young oilseed rape plants. When the larvae emerge, they will burrow into the petioles and stems. Damage can occur to well-established crops, but patchy or backward crops are at particular risk," Mr Young says.
The normal threshold to trigger a cypermethrin spray treatment such as Contest is five larvae per plant, but Mr Young advises growers to spray at a lower threshold in thin, patchy or backward crops.
Mr Young recommends Contest because it has been shown to give good control over an extended period - due mainly to a unique formulation that holds the active ingredient on the leaf surface, therefore exposing pests to the chemical for a longer period.
And he warns growers: "The egg hatch is driven by temperature, so it could be rapid if the weather stays mild or it could be extended if temperatures suddenly drop."
