How new insecticide for virus yellows will help beet growers

An emergency authorisation for foliar insecticide Biscaya (thiacloprid) use in sugar beet is expected to be published this month, bolstering virus yellows control options this summer.

Without neonicotinoid insecticide seed treatments, protecting crops from virus yellows – transmitted by the peach potato aphid (Myzus persicae) – during the crop’s susceptible stage will now rely on foliar sprays.

With resistance to pyrethroid insecticides rife in Myzus populations, the only effective insecticide with full approval is Teppeki (flonicamid), which can be applied just once.

See also: Why cultural control is key to keeping potato blight at bay

As it offers about three weeks’ protection and aphids potentially flying for 12 weeks between crop emergence and the 12-leaf stage when plants become less susceptible, growers were heading into the 2019 campaign with inadequate options.

In response, NFU Sugar, British Sugar, Bayer and the British Beet Research Organisation (BBRO) applied for an emergency authorisation for Biscaya, which is expected to be published on the HSE website on 18 April.

The product cannot be used until the official documentation is published and will be available for 120 days after publication date.

BBRO head of science Mark Stevens welcomed the positive news and hopes up to two applications of Biscaya, alongside Teppeki, will give growers a fighting chance of managing virus spread.

“The exact conditions of use are not yet confirmed, but the BBRO will publish all the technical details once available,” added Dr Stevens.

Key points – virus yellows in sugar beet

  • 120-day emergency authorisation for Biscaya expected to be published mid-April
  • Offers second option to combat virus-carrying myzus across 12-week risk period
  • Expected to be used alone or alongside Teppeki in sequences
  • BBRO virus yellows forecast predicts 30-53% of untreated plants affected by end August if left unchecked
  • Use AHDB and BBRO aphid trap data to track winged aphid flight progression
  • Only apply insecticides if thresholds for wingless aphids are met

Virus yellows risk

After 25 years of neonicotinoid seed treatment use, it would be easy to assume the reservoir of virus yellows inoculum across the UK beet growing area would be low.

However, Dr Stevens says that last season, crops of fodder beet and energy beet from the West Country to Scotland showed up to 50% infection where a neonicotinoid seed treatment wasn’t used.

This shows that despite the perceived low threat, there is the potential for levels of virus to escalate quickly, particularly after the recent mild winter and early spring, so growers must remain vigilant.

To help gauge risk, the BBRO released a virus yellows forecast in March, which is based on mean temperatures in January and February and historic aphid activity data from Rothamsted Research’s network of insect suction traps.

Following the relatively mild winter, which increases aphid survival between seasons, it predicts that 30-54% of sugar beet plants could be infected and going yellow by the end of August if aphids are left unchecked.

Treatment thresholds

Dr Stevens stressed the importance of using foliar insecticides only when absolutely necessary, applying established pest treatment thresholds (see box below) before any treatment is considered.

Virus yellows treatment thresholds

An insecticide spray should be applied if:

  • One green wingless aphid can be found per four plants, up to the 12-leaf stage
  • One green wingless aphid can be found per plant, between 12- and 16-leaf stage

First flight of winged myzus in eastern England is forecast to begin on 18 April and growers have a number of tools to monitor this, including the AHDB’s weekly Aphid News alerts.

BBRO has also established a network of 60 sites hosting yellow water traps and trap data will be used to warn of aphid risk on its website and via regular ebulletins through the season.

These will provide an early warning that can prompt growers and agronomists to head into crops and look for wingless nymphs, which indicate the potential for secondary virus spread and can potentially trigger spray thresholds.

With Biscaya and Teppeki having different modes of action, they should be rotated when used in sequences, as per Insecticide Resistance Action Committee (Irac) guidelines.

“Hopefully we won’t need any treatment at all, but at least we now have the tools to protect crops right the way through that risk period,” says Dr Stevens.

Tank mixes

The most effective herbicide programmes in sugar beet are applied early and targeted at small cotyledon weeds. Sticking to this principle and using appropriate doses should minimise the chances of weed and aphid control programmes overlapping.

However, where there is a temptation to mix insecticides with herbicides, Bayer’s root crop campaign manager Edward Hagues reminds growers that crop safety should be a priority and the fewer products in a tank mix, the less chance of checking plants.

“We want to get the crop to 12 true leaves as quickly as soon as possible [to reduce the impact of virus], so separate applications are advised.

“Where using Biscaya, increasing water volumes should be considered as the canopy gets larger to improve penetration and coverage,” he adds.