Infection threat for late emerging beet

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Delayed sugar beet planting could increase the risk of virus yellows infection at early crop growth stages, where emergence coincides with warmer weather and greater aphid pest activity.

Simon Jackson, Syngenta technical manager, warned that young plants with soft leaf tissue are particularly susceptible to the transmission of the complex of viruses responsible for virus yellows, principally from the feeding of peach potato aphid (Myzus persicae).

Simon Jackson

He said: “Growers will need to be highly alert to the threat of early aphid activity, especially in crops not protected with a thiamethoxam (Cruiser) seed treatment, under emergency authorisation, before planting.”

Early virus infection leads to significantly greater yield losses over the season, as well as increased risk from other foliar diseases.

BBRO has highlighted how the temperatures in January and February were the most reliable prediction of virus yellows infection levels – and that the mild conditions then indicated a severe year that triggered the seed treatment threshold. Even the extreme cold snap in December was expected to have had only limited influence on infection levels.

Fields drilled with Cruiser treated seed should have good protection for the first six to eight weeks after planting, but where growth has been slow could require a follow-up application of Afinto to see crops through to the 12-leaf stage, where later infection has far less serious consequences.

“Field monitoring will give a better indication of when to initiate an insect control programme,” said Mr Jackson, “starting when the first wingless aphids are identified.” He urged growers and agronomists to be extra vigilant along hedgerows and around field headlands.

Crops without a seed treatment, however, are more likely to require a two-spray insecticide programme, given the specific risks of the season that could see the 12-leaf stage not reached until late June, he suggested. “In this scenario growers can still apply a neonicotinoid foliar spray in the programme, with Afinto followed by acetamiprid, for example, as a good option.”

Mr Jackson reminded growers of the need to alternate chemistry and use resistance management strategies to minimise the risk of issues developing further, particularly with Myzus persicae populations.

With virus yellows occurring from a complex of different viruses – Beet Yellows Virus (BYV), Beet Chlorosis Virus (BChV) and Beet Mild Yellowing Virus (BMYV) – insecticides such as Afinto that quickly stop feeding activity are more effective at preventing the persistent pathogens, although not so essential for semi- or non-persistent types.    

Tracking aphid populations through the Rothamsted Insect Survey or BBRO Aphid Survey can give a useful guide to regional risks for timing and insecticide strategies, suggested Mr Jackson. In 2020, for example, infection rates with virus yellows varied from over 60% of crops around the Wissington factory in King’s Lynn, to just 6% of crops surrounding the Cantley factory near Norwich.

Mr Jackson also pointed out that fodder beet and biofuel beet growers should be aware of the implication for aphid transmission of virus yellows for crop health and yields, and adopt the same strategies as sugar beet to maximise yields and crop performance.

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