Turnip Yellows Virus (TuYV) incidence in OSR has reached its highest level ever this season; but yields are protected by genetic resistance.

Annual monitoring of TuYV infection in the UK’s oilseed rape crop has shown that 84 per cent of non-TuYV resistant crops were infected in early spring 2019 - the highest level ever recorded.

Sites in the south west were, unusually for the region, recorded with very high levels of infection.

TuYV is spread by the peach potato aphid (Myzus persicae), and can impact yields by as much as 30 per cent in highly infected situations, oil content by three per cent, whilst increasing levels of glucosinolates and erucic acid.

Since 2016, Limagrain UK along with industry partners; Agrii, Openfield and the AICC, have been monitoring levels of TuYV in crops across the UK. Leaf samples are taken both in the spring and autumn and tested using the Elisa standard test.

Dr Vasilis Gegas, Limagrain’s OSR European portfolio manager said: “Results from this spring's sampling confirm that almost all sites had an infection rate between 81-100 per cent.

“Many of these sites are in regions where you would expect infection levels to be high, such as in East Anglia and the south-east, however what is noticeable is that we are now seeing sites in Scotland and the south-west with these very high levels of infection.

“Three years ago we would not have seen these levels in the west, which just goes to show how TuYV is becoming increasingly widespread, and is now endemic in the UK OSR crop, irrespective of region.”

Why are levels of TuYV so high?

"The link between high numbers of aphids in the autumn and corresponding levels of infection is clear,” says Dr Vasilis Gegas. “Infection usually occurs in September to October when aphids are still flying; the earlier a crop is infected, the less seeds/pods develop, so the harsher the yield penalty.”

Early drilled crops that are more open, corresponding with mild autumnal conditions, are at the highest risk. Since the loss of the neonicotinoids in 2016, control of aphids has become more and more difficult, so numbers have increased, with a subsequent build up of TuYV inoculum in the environment.

Once an aphid is infected, it is infected for life – if an uninfected aphid feeds on an infected plant, the aphid becomes infected and so the cycle continues.

Dr Vasilis Gegas added: “Last autumn, infection rates in some areas were as high as 100 per cent which is unusual, and the impact of this is being seen in harvest results across the country.”