With the potential for a higher risk of BYDV infection this autumn, managing the ‘green bridge’ is more important than ever, warns leading crop production specialists Hutchinsons.
The green bridge refers to the potential reservoir of aphids that have survived either on volunteer cereals or adjacent host crops which can infect the newly emerging cereal crop.
The earlier the infection occurs, the more damaging the virus can be at impacting yield to the newly emerged crop.
BYDV infection can arise from two potential sources – directly from wingless aphids walking from infected plants in the same field or adjacent areas to the current crop from volunteers harbouring aphids, or indirectly where winged aphids migrate into newly emerged crops from further afield.
“Aphid vectors especially Bird Cherry Oat aphids are being caught in suction traps now, so any green stubbles will be attractive to the aphids – increasing the risk of transfer,” said the firm’s southern technical manager, Neil Watson.
“There are several reasons for this elevated risk from the green bridge this autumn,” he said.“There is a potential reservoir of late BYDV infections in winter rather than spring cereals this season, which is the exact opposite of this time last year. Bushel weights are not as high as normal, leading to a greater potential of seed going out the back of the combine, ultimately leading to more volunteers, and the moist soil conditions are ensuring a rapid emergence of those volunteers.
“Also, as more growers move to minimal cultivations or direct drilling this will increase the risk of direct transfer. The increased use of cover crops and environmental headlands can also act as a potential reservoir. And finally the weather has a role to play; warm conditions will increase the build-up of aphids which is currently ahead of normal.”
As a result of these factors managing the green bridge is important, he said.
“It’s key there is sufficient time between killing the volunteers through desiccation or cultivations and drilling the next crop,” he added. “As the volunteers start to die back, and they turn yellow they could present a greater risk of attracting aphids than would normally be the case. If large numbers of aphids are present on volunteers or weeds which are cultivated during seedbed preparation, they can feed on new crop roots and transmit virus directly without appearing above ground level to provide a control opportunity.
“This can be a problem in grassland which has been turned over green. Warm, moist soil conditions facilitate aphid movement through soil. Therefore it is important to monitor the flight of aphids into the newly emerged crops by using sticky traps in the newly emerging crops. Place the traps downwind of the potential source of the flight into the crop, in a sheltered area, positioning them 5m in from the headland at ground level.
He noted that whilst environmental schemes and grass margins are supposed to increase the diversity of natural predators around the field margins, there is the possibility that through a lack of species diversity, they could harbour more aphids which cannot be treated until the end of the scheme.
“The increasing use of cover crops that inevitably include an element of cereals within the mixture will act as a potential reservoir. Woodland and waste ground could equally be a source of infection.”
