WIMMERA canola growers are warned to remain vigilant after an outbreak of the beet western yellow virus in South Australia and the Mallee.
Birchip Cropping Group research agronomist Simon Craig said the virus, spread by the green peach aphid, had taken hold in the Mallee.
"In the Wimmera I'm not too sure how bad it is; for now it's just more about taking precautions against what happened in the Mallee," he said.
"Everyone I know in the Wimmera has checked their paddock and noticed some signs of the virus.
"We'll know the full magnitude of what's happened in the Wimmera in about 10 days."
Mr Craig said regular inspections were crucial for growers to avoid the spread of the disease.
"If you don't have aphids the risk is low," he said.
"But you'd want to be certain about how much you inspect to make sure you don't have the aphids present."
Mr Craig said the virus had a 97 per cent transmission rate, meaning it would infect almost every plant bitten.
"The virus persists in the stomach and is readily transferred between colonies," he said.
Once the aphid has bitten plants, it takes two weeks for the virus to get into the plant and then a further two weeks for symptoms to become apparent.
Mr Craig said people should check for aphids under the lower leaves of plants.
"The symptoms of the virus include cupping of the leaves, leaves turning purple on the outside edge and becoming starved and stems elongating," he said.
He said the virus had caused severe malnutrition in crops in South Australia.
The virus had affected an estimated 10,000 hectares of canola in South Australia.
Mr Craig said Transform was the only registered product to combat the virus.
He said Mallee farmers should be spraying, while Wimmera farmers should consult their agronomists.
Mr Craig said warm weather aided the spread of aphids and cold weather assisted the aphid's natural predators.
He said cool conditions would help arrest the spread of beet western yellow virus throughout the Wimmera.