Numbers of Myzus persicae aphids being caught in Rothamsted monitoring is running seven times higher than this time last year, and currently ahead of the serious risk year of 2014. Myzus is considered the key vector of TuYV in oilseed rape.
Furthermore, latest AHDB testing results of Myzus populations has revealed 58% were already carrying TuYV and capable of transmitting infection. In Lincolnshire, the infected population was approaching two-thirds of trapped Myzus.
Syngenta insecticide specialist, Max Newbert, warned that early autumn transmission of infection into oilseed rape plants is likely to result in greater susceptibility to stress and more severe yield loss. Early infection also increases the chance of secondary spread through the season.
Having studied TuYV extensively at the University of Warwick over recent years, Max is uniquely placed to understand the implications of infection in the crop. “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 reported.
“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; Mayweed, Chickweed and Groudsel are all well-proven hosts for TuYV. Volunteer oilseed rape seedlings could further increase the risk as reservoirs for virus,” he added.
Max 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 are burnt off or harvested.
“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,” he advised.
The threat potential has heightened by widespread resistance to pyrethroid sprays among Myzus populations. “It’s essential that, in the first instance, growers use full rate applications of the most effective Hallmark Zeon to get the best possible control and minimise the risk of further resistance developing.
“But where growers do suspect that Myzus control from a pyrethroid application has been incomplete, they should immediately switch to Plenum,” he advocated. “Independent research has demonstrated that Plenum was the most effective in preventing the spread of TuYV in autumn oilseed rape crops.”
Yield trials at the Syngenta Innovation Centre in Hampshire in 2015, highlighted that early intervention with Plenum treatment, before Myzus populations escalated, delivered a 0.35 t/ha increase compared to untreated, and 0.25 t/ha over later treatments when aphids were endemic – attributed to greater TuYV infection.
“Growers have just one application of Plenum for aphids in the autumn, targeted at reducing TuYV transmission – which can hit yields by 15 to 30%,” added Max. “Getting the timing right is important to get the best control of aphids.”
Furthermore, Syngenta trial have shown spray technique can significantly increase the chance of hitting aphids among the OSR crop canopy. Application with angled nozzles, such as the Defy 3D Nozzle at a water volume of 100 to 200 l/ha, could prove most effective.
Top Tips for TuYV control
- Be vigilant for Myzus persicae migration
- Take note of monitoring or use in-field water traps
- Be aware of pyrethroid resistance risks
- Use Plenum at first signs of infestation
- Use Defy 3D Nozzles for coverage
- Spray at 100 – 200 l/ha water volume