Oilseed Rape: Pests – Pollen beetle risk – April 2020

There is a risk from pollen beetle damage to the buds, giving rise to blind-stalks with no flowers or pods forming on them. A warm spell when temperatures reach 15°C will trigger a mass pollen beetle flight into crops.

When beetles appear in crops, note that there are updated thresholds for treatment. The plant density needs to be taken into account to estimate the threat from pollen beetles at green-yellow bud.

The table below shows the plant density and pollen battle thresholds to consider.

If crops are backward because of poor overwintering, slug problems in the autumn or pigeon damage, then their capacity to cope with pollen beetle damage is reduced, so a lower threshold should be adopted for these crops.
These thresholds have been revised to help deal with the increased threat from pyrethroid insecticide-resistant pollen beetles in UK crops by ensuring that insecticides are only applied when necessary.

Resistance in pollen beetles to pyrethroid insecticides has been found in Scotland. The advice to growers is that pyrethroid insecticide use for pollen beetle control should only be used if the treatment thresholds have been exceeded. Remember that once the crop is in flower the beetles can easily reach the pollen they desire without damaging the flower, so no flowering crops should be sprayed for pollen beetle control.

If control is really necessary, only use one pyrethroid insecticide treatment per crop which will control any pyrethroid-resistant beetles.