Sugar beet growers face high-pressure virus year

Sugar beet growers face another high-pressure year for virus yellows with aphids flying into new crops as they emerge.

Aphids will be flying two to three weeks earlier in England compared to the historical average, according to the Rothamsted Insect Survey aphid forecast for 2024, which was issued on 1 March.

First capture of peach–potato aphid at the Broom’s Barn research station in Suffolk is predicted for 10 April which is much earlier than previously forecast. This suggests a virus epidemic on the scale of 2020.

Significant risk

The British Beet Research Organisation (BBRO) expects some 40% of the crop to be drilled with untreated seed and with aphids arriving when crops are at younger, more susceptible growth stages, this poses a significant risk.

In the absence of any control measures, the BBRO forecasts an 83% incidence of virus yellows for 2024. This breaches the DEFRA threshold of 65% required to trigger the use of Cruiser SB (thiamethoxam) on seed.

Patience has been key for crop establishment this spring. With wet weather and sodden soils holding back drilling, the BBRO has been advising growers to wait for warmth before getting the crop in the ground.

Waiting for warmer conditions – and for soil temperatures to rise from 5°C to 8°C – would have a big effect on germination and prepare the way for rapidly and evenly established crops. These often perform better and suffer less virus content.

Careful monitoring

Even so, crops drilled with untreated seed will still need careful monitoring for aphids from early April onwards. Choice of product for the first spray should take into consideration aphid abundance and crop growth stage.

The two available foliar insecticides – acetamiprid and flonicamid – are subtly different. InSyst (acetamiprid) is a knockdown product with faster activity than Teppeki or Afinto, which are both based on flonicamid.  

Crops drilled with Cruiser SB seed treatment should be protected for up to 10 weeks from drilling, so depending on aphid numbers in June, they may require further protection from a foliar insecticide then.

Consecutive applications of neonicotinoid products are not permitted, so the Emergency Authorisation for Cruiser SB specifies that if subsequent foliar sprays are required, the first one must be a flonicamid containing product.

If aphid thresholds are breached again this can be followed by InSyst.