Russian wheat aphid has been discovered in a wheat crop at Coonabarabran in north western NSW, in the latest round of bad news for cereal farmers in the eastern states.

First discovered in South Australia in 2016, the aphid has been closely monitored by farmers and scientists for the past two years.

The pest can decimate crops and reduce cereal crop yields by up to 80 per cent, as it not only strips young growth but also injects a poison into the plant.

The owners of the property with the aphids are likely to graze the paddock. ( ABC Western Plains )

Coonabarabran agronomist James Fleming said the aphid was found in a wheat crop when his clients were inspecting it, with a view to spraying it out to be used for grazing lambs.

"We had been in that field only a few weeks before, looking at the wheat, and there was no sign of any problems," he said.

Key points: Russian wheat aphid is a high-priority pest but is manageable

Russian wheat aphid is a high-priority pest but is manageable The pest was found in Australia in 2016. The first case was identified in a wheat crop in South Australia's Mid North, and infestations have stretched into Victoria, New South Wales and Tasmania.

The pest was found in Australia in 2016. The first case was identified in a wheat crop in South Australia's Mid North, and infestations have stretched into Victoria, New South Wales and Tasmania. Do not spray where pests are not present or are present in low numbers

"But, with the lack of rain, the owners had decided the yield would not warrant the cost of harvesting, so they were looking to spray and graze it.

"And that was when they found the aphids and called me to come and inspect them."

Russian wheat aphids can reduce cereal crop yields by up to 80 per cent. ( ABC Western Plains )

He said it took him a little while to work out that the damage might be caused by Russian wheat aphids.

"I had an initial look and then thought that something was not right.

"And so I packaged up some live ones and sent them off for confirmation."

This is the furthest north that the aphid has been seen in the growing region, with the previous NSW sighting at Lake Cargelligo, more than 400 kilometres south west of Coonabarabran.

Mr Fleming said an explanation why the pest had moved so far north without being discovered in other crops could be because of the lack of cereal crops sown in the NSW grain belt because of the drought.

The Australian grains industry has formulated a response to the incursion of the aphid and provides up to date information for growers on their website.

Suspected sightings can be reported to the Exotic Plant Pest Hotline on 1800 084 881 For more tips and tactics on the Russian wheat aphid visit this GRDC resource.