A nationwide survey by Bayer CropScience and Hutchinsons has found very high levels of Turnip yellows virus (TuYV) in oilseed rape crops.
Across 75 fields sampled during March and April the mean incidence of TuYV was 60% and it ranged from 20% to 100% (see mean results by county table below). Agronomists collected the oldest viable green leaf from a minimum of 20 randomly selected plants across each field and these were sent to the NIAB TAG laboratory for ELISA testing to determine TuYV presence/absence.
Even though 2014/15 crops are the first to be grown since the EU-wide two-year restriction on neonicotinoid seed treatments came into force, Hutchinsons technical director Dr David Ellerton was surprised at the high levels of virus found. “We know TuYV is capable of hammering oilseed rape yield so this year’s crops are bound to suffer.
“The neonicotinoid seed treatments are the number one defence against TuYV and this survey shows how desperately growers need them back. Varietal resistance, such as that found in Amalie, may help in the future but right now without the seed treatments, growers’ only proven option is foliar insecticides, and the industry needs to do more work on how to get the most out of them.”
Bayer’s Neil Thompson says their insecticide Biscaya (thiacloprid) has a label approval for autumn control of aphids in OSR and will give around two weeks protection. “It’s speed of activity, which is an important factor in reducing virus transmission, should make it first choice and in seasons with protracted aphid migration a spray of pymetrozine will give further protection.”
Virologist Dr Mark Stevens, who led the body of research that our understanding of TuYV comes from, was less surprised by the survey’s findings. He says that back in spring 2007 – before the clothianidin and thiamethoxam seed treatments were introduced – levy funded sampling found TuYV levels close to 80% in commercial crops.
“The seed treatments have a vital role to play in stopping secondary spread of virus during September/October and it’s early infection that’s the most damaging. If the autumn migration window is narrow, crops grown without them may get adequate protection from foliar sprays of thiacloprid and pymetrozine. But in an open autumn, with extended migration and higher numbers – as was the case last year – these two sprays cannot cope.”
Dr Stevens maintains that for an IPM based strategy to be viable growers have equal need for the insecticidal seed treatments and foliar sprays and hopes that in the future their use can be integrated with varietal resistance, providing this does not come with a significant yield penalty in low virus pressure situations.
Bayer Cropscience & Hutchinsons TuYV Survey Spring 2015 – mean results by county
|Counties||Number of sites sampled||%TuYV|