Crop Clinic

Seed weevil: The insect pest to watch out for in the majority of crops from now on is cabbage stem weevil. crops, then treatment may be worthwhile.

Cabbage seed weevils are a cause for concern this season, as numbers approaching the treatment threshold of 2 weevils per plant throughout the crop have been seen in several crops. The recent warm spell has led to an influx of weevils from the fields where rape was grown last season. The weevils themselves don’t cause any damage; the problem is down to their grubs. The weevils lay eggs within the developing seed pods, and grubs can chew their way through several seeds during their development. Once the eggs are laid within pods, the subsequent grub is protected from any insecticide treatment. Consequently, effective management of seed weevil needs to target the adult weevils before they have a chance to mate and lay their eggs. Fortunately, the weevils need to feed for a couple of weeks before they begin to lay eggs so now is the ideal time to check crops for weevil numbers and applying an insecticide if the treatment threshold of 2 weevils per plant has been reached.
Pyrethroid insecticides should be used, of which there are many.

If these products are going to be applied to a flowering oilseed rape crop, it is essential that local beekeepers are informed of your intention to treat the crop at least 24 hours beforehand. Bees are crucial in you obtaining a good oilseed rape yield as they pollinate the flowers. So safeguard your investment in growing oilseed rape by giving beekeepers sufficient notice so that they can close their hives on the day of treatment. Try to spray the crop in the early morning or evening when bees are less likely to be foraging, as wild bees and bumblebees need protection against insecticides as well.