ONE of the sessions at the recent Hart Winter Walk that drew a lot of growers in was run by SARDI crop experts Jenny Davidson, Greg Baker and Bill Kimber.
All three are working on the problems caused by the beet western yellows virus, spread by green peach aphids, which has resulted in thousands of hectares of canola crop being wiped out, mainly in the Mid North.
Dr Davidson says the virus is not uncommon.
"It is about most years," she said.
"This year, it has been a perfect storm for the virus - we've never seen this level of infection before."
Riverton, Tarlee and Marrabel were the regions worst affected.
Dr Davidson said 50pc yield loss was possible if the virus infected crops at an early stage of growth.
"The plant may re-shoot after infection, but it struggles to grow," she said.
"The later the infection, the less yield loss you're going to get.
"Yield loss depends on how many plants are infected. But we have seen infection across entire paddocks."
Dr Davidson says that significant research on the virus in WA shows the plant remains susceptible to mid-podding stage.
The virus affects the plant by stopping its nutrient uptake.
Farmers will not know if the virus is present unless they get samples taken.
"This year, we're suggesting people work on the premise that if aphids are in the crop, the virus is likely to be present," Dr Davidson said.
She warns that pulses are susceptible to the virus but not appear to be infected at this stage. This can change when infected aphids start flying in late winter.
* Full report in Stock Journal, August 7, 2014 issue.