Grains Research and Development

Date: 15.08.2014

Warmer weather alert for BWYV spread

Author: Rebecca Barr

Beet Western Yellows Virus (BWYV) has caused unprecedented damage to canola crops in south-east Australia this season, causing the GRDC to fund emergency research to analyse the outbreak and limit potential damage in future seasons.

Key Points

  • Weather patterns earlier this year provided ideal conditions for BWYV.
  • A ‘normal’ summer will reduce aphid populations, meaning the risk next season is no higher than usual, despite this year’s outbreak.
  • Where there are symptoms across a paddock, no control measures applied now are likely to be useful
  • Where there are no symptoms, or only patches, growers should observe aphids regularly – at least weekly – to identify when they are ready to fly.
  • Insecticides should be applied as soon as the aphids take flight.

However, this year’s outbreak does not indicate a higher chance of infection in future years according to SARDI senior pulse pathologist Jenny Davidson.

“Green peach aphids (GPA), which spread the disease, require green plants to survive. This year there were ideal conditions for the development of this disease with unusual February rain, coupled with a very mild autumn providing a green-bridge” Dr Davidson said. 

When there is average spring and summer temperatures and rainfall this causes most weeds to die off, resulting in the aphids not being able to survive in any great numbers, meaning next year’s risk is the same as any year.

For growers who have severely infected crops and will suffer significant losses this year, this means no more measures can be taken to address the outbreak in those crops.

“Where crops have symptoms all the way across the paddock, there’s no point in applying insecticides now,” Dr Davidson said.

 “The aphids have already done their damage, and should die off over summer.”

However, where growers have only patches of infection, or have crops not yet affected, Dr Davidson recommends close observation of the aphids.

“Growers can use a sweep net, and look for the presence of wings, or put up sticky traps to catch flying aphids. As soon as flying aphids are observed, at-risk crops needs to be sprayed.The aphids will take flight once the weather warms up. 

This timing will depend on the region, but will generally be after a few days of around 17 degrees. This isn’t a fixed rule though, so growers should be checking the crop at least once a week, and twice a week as soon as the days start to get warmer.”

The Green Peach Aphid (GPA), which transmits BWYV

The Green Peach Aphid (pictured) spreads BWYV. Growers need to look out for winged aphids and spray insecticide as soon as they are observed.

Photo: A. Weeks (Cesar).

Once the aphids are on the wing, spraying should be performed as soon as possible to limit any further damage the aphids can cause in further spreading of the disease. 

While infection after the mid-podding stage (growth stage 5.5) is less likely to cause significant yield losses, oil quality can still be affected. Withholding periods for canola should also been considered in deciding when to spray.

Only insecticides registered for use against aphids on the crop and crop stage should be applied when spraying for aphids.

Application of unregistered use patterns of insecticides is likely to leave residues greater than Australian and overseas MRLs which will cause problems in marketing grain. Care should also be taken to ensure there is no off target damage to non-target organisms particularly bees.

Integrated pest management strategies can be used to help manage GPA populations, including management of summer weeds, to reduce potential hosts over summer, and rotation of insecticide chemical groups to reduce the risk of resistance development.

More Information: 

Jenny Davidson,
08 8303 9389,
jenny.davidson@sa.gov.au

Learn more about BWYV in the GRDC Hot Topic: Green peach aphid and beet western yellows virus

Read a related GRDC media release: Emergency funding to address canola virus.

GRDC Project Code CES00001, DAN00179, DAW00229, DAS00139, CES00002, DAS00151

Region South