Time critical for checking Russian pests

SARDI entomology research officer Helen DeGraaf said this was the highest risk period for the pest. She said, as the temperature rises, numbers would also increase.

The RWA is asexual, which creates a very fast reproductive cycle. 

Ms DeGraaf said this cycle could be as long as 20 days while daily temperatures were about 10 degrees celcius, but could speed up to nine days in 20 degrees. 

“We’re starting to see more with warm weather,” she said. “And as the weather warms, we will start to see more winged aphids.” 

But she said the heavy rainfall during winter, and particularly early spring had played its part, washing away large numbers of the pest.

Yorke Peninsula agronomist Craig Wissell, Team Wiss, said the frequent rainfall had helped contain the numbers.

“The environment is helping a lot more than the insecticides,” he said. “The massive downpours haven’t given the aphids a chance to lift numbers.

“If it had been (a season) like last year, we might have been in trouble.”

Mr Wissell said, as it gets warmer, there was an increased need for vigilance.

“We’re at the critical stage for disease and aphids,” he said. “Recent warmer days are definitely ideal for multiplying and that will continue as temperatures rise.”

Mr Wissell said until the soft dough stage – a few weeks away for most wheat crops – was the time of biggest concern.

He said farmers should be inspecting crops regularly – as much as two to three times a week – and advises farmers to randomly select 50 tillers across the paddock and inspect the entire plant, not just the top.

Ms DeGraaf said it was not enough to just see signs of aphids, as many of those, such as striping on the leaf, could be present from an earlier infestation. 

She advised making sure there were live aphids, with most recommendations advising spraying should take place once the pests were at a density of more than 10 per cent of tiller affected.

Mr Wissell said he was recommending his clients to use either Pirimicarb or Chlorpyrifos, but to try and keep beneficial species in mind as well as consider the timing and a possible withholding period.

He said it was too early to gauge the impact on crops that had already been infested and sprayed.

“Visually the crops look good but we will have to wait for the yields,” he said. “I don’t think we will have yield penalties but that may change.”