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Crop Establishment High risk of virus yellows


in oilseed rape this autumn • Tenfold increase in aphid numbers • Early drilled crops are at most risk • Resistant varieties remain safest bet


fewer seeds and pods.” F


armers face an increased risk of turnip yellows virus (TuYV) in oilseed rape crops this autumn due to high aphid numbers during the summer. Some 70% of peach pota- to aphids are believed to carry TuYV, according to plant breed- ers Limagrain UK. Work carried out at Brooms Barn a decade ago found a 30% yield penalty where levels of the virus were high and infection occurred early in the crop’s life.


Recent data confirms extreme- ly high aphid pressure this sum- mer. Researchers at Brooms Barn reported 4,400 aphids caught in their traps up to 21 June – al- most a tenfold increase on the long term average of just under 500 aphids.


Some crops being monitored


had 50-100 aphids per plant. It follows warm weather with aver- age air temperatures continued to exceed the long-term average. Total cereal aphid numbers were higher than normal, said Alex Greenslade of the Rothamsted Insect survey team.


Sugar beet has already shown


the consequences of this high aphid pressure with many crops exhibiting virus yellows symp- toms. Infected aphids are will move across from these crops into oilseed rape plants later. “Infection usually occurs in September to October when aphids are still flying,” says Lim- agrain oilseed rape manager Vasilis Gegas. “The earlier a crop is infected, the more severe the symptoms tend to be with harsh- er yield penalty, as the plants have


Limagrain’s top yielding varieties all carry TuYV resistance Variety type UK Gross output*


(% treated control) Oil content (%) Stem stiffness


Shortness of stem


Ambassador Aurelia Artemis Aspire RH 108


RH 108


45.3 8 6


45.2 8 6


RH 107


45.7 8 5


Conv 106


45.7 9 7


Once an aphid is infected, it is infected for life, says Vasilis Gegas (right)


Left: Crops infected earlier usually exhibit more severe symptoms


Early drilled crops that are more open, corresponding with mild autumnal conditions, are at the highest risk. As control of aphids has become increasing- ly difficult, so numbers have in- creased, with a subsequent build up of TuYV inoculum in the en- vironment.


“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. Infected plants produce fewer side branch- es, pods and seeds per pod.” TuYV often goes undetect- ed because symptoms aren’t al- ways severe. But early infection is increasingly difficult to control with the loss of neonicotinoid seed treatments – and getting timings right for sprays can be hard.


Infection levels Levels of TuYV in UK crops have been measured since 2016 by an industry partnership involving Limagrain, Agrii, Openfield and the Association of Independent Crop Consultants. Leaf samples taken in autumn and spring are assessed using a standard test. “We’ve mapped the incidence


of TuYV from the UK to Ukraine and seen it build over the years,” says Dr Gegas. “We’re getting to a situation where in some locations 100% of crops carry the virus. It’s


Important role of genetic resistance


The ban on neonicotinoids means genetic resistance is in- creasingly important in con- trolling turnip yellows virus. Limagrain launched its first resistent variety Amalie in 1995. Initially, it came with a yield penalty – but innovative breeding has overcome this and the highest yielding varieties on the AHDB Recommended List today all carry TuYV resistance. This was confirmed in 2019 trials results conducted by the Association of Independent Crop Consultants in West Wit- tering. Varieties with TuYV re- sistance had a yield advantage of 0.4-0.5t/ha over varieties with no resistance. Limagrain’s


conventional


variety Aspire yielded 6.7t/ha – significantly higher than the 6t/ha achieved by non-resistant variety Campus, says independ- ent agronomist Peter Cowl- rick, director of CCC Agrono- my, which managed the trials. Aurelia was just behind, yield- ing 6.4t/ha. In Suffolk, the trend was the


same. Aurelia managed a top yield of 6.1t/ha, well above that of Campus at just above 5.6t/ha. Ambassador yielded just below 5.9t/ha and Aspire 5.86t/ha.


now endemic across Europe, and no longer confined to hotspots.” The small-scale autumn sur- vey in October and November is followed by extensive testing car- ried out in early spring. “The last couple of seasons we have found very high levels of infection in UK crops in the autumn, which wasn’t the case before.” TuYV incidence reached its highest level ever last season, with an average of 84% of non- TuYV resistant UK crops infect- ed in early spring 2019, adds Dr Gegas. Almost all sites had an in- fection rate between 81-100%.” Infection was highest in East Anglia and south-east England but also high in south-west Eng- land. Until recently, high levels weren’t seen in the north but last year 70-75% of rape was infect- ed in Perth, with 50-54% infec- tion in Aberdeen.


SEPTEMBER 2020 • ANGLIA FARMER 25


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