Survey confirms high levels of infection in oilseed rape crops across UK
Oilseed rape yields could be impacted this season as levels of 'turnip yellows virus' infection are confirmed to be as high as 100% in some areas.
Turnips yellows virus (TuYV) is spread by the peach potato aphid (Myzus persicae), and can impact yields by as much as 30% in highly infected situations.
The results come from an annual survey carried out by plant breeders Limagrain UK, in collaboration with Agrii.
Random leaf samples were taken from oilseed rape varieties in all of Agrii’s trials across the UK and tested in Limagrain’s laboratories at Rothwell, Lincolnshire.
Distribution of aphids
“We know that levels of TuYV incidence are associated with the distribution of aphids in the autumn before,” said Dr Vasilis Gegas, senior oilseed rape breeder with Limagrain.
“Levels of aphids in the autumn of 2016 were at levels comparable to 2014, which was a high infection year, and this year again the link between high numbers of aphids in the autumn and corresponding levels of infections is clear.
“You would expect to see high levels of infection in the more traditional OSR growing regions - but even here levels of infection are higher than ever before - 100% of samples taken in Fincham, Kings Lynn were infected with TuYV, and 90% of samples taken from the Woolpit site in Suffolk were infected.
“Most surprising of all was that 75% of leaf samples taken from the Balbeggie site in Perth were infected, and this is the first time that we have seen such high levels of infection in Scotland.
“However, we are also seeing higher than expected levels of infection in the west country, with 50% samples infected at the Brackley site, and 45% at the Agrifocus site in Swindon.
Dr Gegas concluded: “It is clear from these results that TuYV is endemic in the UK OSR crop, irrespective of region and is directly linked to the autumn aphid migration.”
Levels of TUYV infection in 2017
Difficult to identify
The challenge with TuYV is that it is difficult to identify visually and often yield losses will be attributed to other factors, said David Leaper of Agrii.
Early symptoms of TuYV can be expressed by purpling of the leaves, interveinal yellowing and reddening of leaf margins and can easily be confused with other stress symptoms and nutritional deficiencies.
The symptoms can often go unnoticed altogether which is why the effect of the virus is underestimated.
“With the loss of neonicotinoid seed treatments and a move to earlier drilling and increasing resistance to insecticides, control of aphids has become more and more difficult and subsequently aphid-borne diseases more prevalent,” Mr Leaper said.
“There is some good activity to be had from the new foliar insecticides, Biscaya (thiaclorpid) and Plenum (pymetrozine), however both of these have very limited persistence and it’s very difficult to optimise the timing of these with when the aphids migrating.”