Aphid numbers are also exceeding those counted in 2014, considered a ‘serious risk year’ according to Syngenta.
Myzus is considered the key vector of TuYV in oilseed rape, but Syngenta insecticide specialist Max Newbert urged growers and agronomists to be alert to the potential for Myzus movements into crops, especially where brassica crops or potatoes that may have been holding aphid populations were burnt off or harvested.
AHDB testing of Myzus populations has found that 58% were already carrying TuYV and capable of transmitting infection. In Lincolnshire, the infected population was approaching two-thirds of trapped Myzus.
Newport said: "We are increasingly aware that many weed species can act as a host for TuYV, which becomes a source for transmission by feeding aphids," he said.
"With more farmers delaying drilling and encouraging green stubbles to control black-grass, there is a higher risk of infection being spread to oilseed rape," Newbert warned.
"Mayweed, Chickweed and Groundsel are all well-proven hosts for TuYV. Volunteer oilseed rape seedlings could further increase the risk as reservoirs for virus," he added.
"The Rothamsted Insect Survey gives a good indication of migrating background populations, but in-crop monitoring with water traps is far more indicative of local numbers for better timing of treatments," Newport advised.