Russian Wheat Aphid may behave differently this season

THEY'RE BACK: Russian wheat aphids numbers are again building.

THEY'RE BACK: Russian wheat aphids numbers are again building.

FARMERS are being warned the lessons learnt about Russian wheat aphid (RWA) last year, when aphid numbers were decimated by the record wet September, may not be applicable this year.

Paul Umina, entomologist and co-author of PestFacts, a pest monitoring service, said RWA numbers were building as daylight hours and temperatures increase.

“There are reports from around many parts of Victoria in particular that RWA numbers are building” Dr Umina said.

“RWA activity has been reported in the Victorian Mallee, Wimmera, Northern Country, as well as the NSW Riverina.”

Dr Umina said it was impossible to assess what the implication of RWA would be.

“The pest only arrived last year, so we’ve only had that season to monitor its behaviour,” he said.

“Given it was a record wet spring in many areas it is not necessarily a good indication of what to expect in the future, it may be that it behaves differently given different season conditions.”

Kaniva farmer Malcolm Eastwood said the pest was down on his watch list of potential problems for the season.

“We haven’t seen anything much of them as yet,” he said.

“It’s been a wet late winter and numbers are at very low levels so you wouldn’t expect them to breed up to problem numbers,” he said.

“The only issue may be if they come in from elsewhere.”

Dr Umina said the wet conditions not only physically displaced RWA off leaves, but also was conducive to the build-up of a type of fungi that lowers aphid numbers.

“This was a player in the sharp drop off in aphid numbers last year.”

He said growers needed to have a strategy in place for control if necessary.

“We saw last year that beneficial species such as wasps played a key role in keeping numbers down.”

“Farmers will have to weigh up whether they feel an insecticide application is necessary and if so, what kind of product they use.”

Dr Umina said farmers had two insecticide options, chlorpyrifos and pirimicarb.

He said chlorpyrifos was cheaper and had a broader efficacy in terms of time of application, so it had been popular with growers, but he said pirimicarb would be a good option as temperatures warmed up.

“Pirimicarb is more effective when temperatures get above 15 degrees.

“It also has the advantage it is less harmful to the beneficial species.”

“Prophylactically spraying broad-spectrum insecticides for managing invading or dispersing RWA should be avoided. If spraying is warranted, aim to use pirimicarb to maintain beneficial populations.”

However before making assessments on control options, Dr Umina said growers needed to monitor their paddocks.

“It’s no good relying on beneficials to do the work if you don’t have them and there’s no need to spray if you don’t have RWA in problem numbers, the key is to get out there and check.”

Dr Umina said economic thresholds for the numbers of RWA needed before considering spraying were yet to be established in Australia, but said in the US, 10 per cent infestation of tillers was recommended as a guideline.

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