The first wheat crop in Australia to be hit by the Russian aphid appears to have recovered strongly after treatment.

Authorities discovered the country's first ever case of Russian wheat aphid on a farm in South Australia in May and it quickly spread into Victoria.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Listen Duration: 3 minutes 38 seconds 3 m 38 s Grains Producers Australia chairman Andrew Weidemann discusses Russian wheat aphid Download 1.7 MB

Grain Producers Australia chairman Andrew Weidemann visited the paddock with a delegation recently, 21 days after the paddock had been sprayed with insecticide to kill the aphid.

He said the paddock's rapid recovery was a welcomed surprise.

"What we observed quite clearly, and from talking to the farmer, was the impact on the particular paddock at the time [when the aphid was discovered] was quite substantial, but the regrowth over [the period] between spraying and us actually visiting the paddock was quite substantial," he said.

"There were no insects and the paddock was back and thriving again and providing food to sheep that were actually grazing on it."

Then the aphid was discovered on the paddock last month, the crop was described as "almost dead".

While the fast recovery of the crop after spraying was encouraging, Mr Weidemann said it now appeared another valuable weapon against the aphid would be natural predators.

For that reason, he said it might be best to only spray crops when the aphid was causing substantial damage, perhaps at a threshold of 20 per cent damage to the crop.

He said spraying the aphid in cases where crop damage is negligible could be counter-productive, because it would kill the aphid's natural predators.

The visiting delegation included farmers' representatives, an entomologist and a representative from Biosecurity SA.

"Clearly [after seeing the paddock] it is a manageable pest and through talking with the entomologist, we feel that a good response method for the farmers is to ensure they observe what is in the paddock," Mr Weidemann said.

"Clearly there is a threshold to how much aphid damage you would see before you would even consider spraying."

Mr Weidemann predicted the cold winter months would control the Russian aphid until spring arrived and if an increase was observed when the weather warmed up, then it might be time to consider spraying.

Meanwhile, the pest has continued its spread into Victoria after first being confirmed to have crossed the border three weeks ago.

It has now been discovered in several areas in the state, mostly in the far west, but also as far east as Dingee, 300 kilometres from the South Australian border.

Agriculture Victoria chief plant health officer Dr Gabrielle Vivian-Smith said the department wanted to receive more samples from farmers to gain a more accurate picture of where the aphid now existed.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Listen Duration: 4 minutes 26 seconds 4 m 26 s Agriculture Victoria chief plant health officer Gabrielle Vivian-Smith discusses Russian wheat aphid Download 2 MB

"There's not a huge number of samples through that central area of Victoria around that Bendigo area," Dr Vivian-Smith said.

"So until we get more samples in, more negatives and more positives, it's hard to be confident that we know the distribution of the aphid."